Peer Revenue Play credits. Real papers.

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Friday 20 March

Materials Science · Cross-listed from cond-mat.mes-hall

Anatomy of the modern theory of orbital magnetism from first-principles: term-by-term analysis in the gauge-covariant formalism

Hojun Lee, Insu Baek, Mirco Sastges et al. (+3 more)

We present an in-depth analysis of the orbital magnetism by means of the so-called modern theory based on the Berry phase across distinct classes of materials-d transition metals, sp metals, and transition metal dichalcogenides-highlighting the microscopic nature of band structure characteristics. We adopt a gauge-covariant formulation of the modern theory proposed in [Lopez et al. Phys. Rev. B 85, 014435 (2012)], which enables the calculation of orbital magnetism in a controlled manner in any chosen gauge of Wannier functions and gives the total contribution as a gauge-invariant measurable. This captures consistently the contributions due to the anomalous position, velocity, and orbital angular momentum of Wannier basis, as well as the contributions due to Hamiltonian such that their sum is gauge-invariant. For d transition metals, we find that the atom-centered approximation captures the majority of the total contribution given by modern theory, which we attribute to localized nature of d electrons. However, 5d metals tend to exhibit larger deviation between the two methods than 3d metals do, as 5d electrons are more delocalized than 3d electrons. On the other hand, sp metals exhibit a strong deviation between the two methods, where large kinetic energy of sp electrons is important. Finally, in 1H-MoS2, we find that the valley orbital moment far exceeds the atomic limit of d electrons due to coherent hybridization between valence and conduction bands in direct band gaps. Our work elucidates the interplay of the chemical nature of electronic orbitals and the effect of band structures in a consistent manner and highlights the role of Berry phase in orbital magnetism. The results suggest a promising direction of orbitronics beyond controlling atomic orbitals, in which the orbital magnetism can be greatly enhanced by exploiting Berry phase.
Read the full abstract

All authors Hojun Lee, Insu Baek, Mirco Sastges, Yuriy Mokrousov, Hyun-Woo Lee, Dongwook Go

Materials Science

First-principle study of the influence of hydroxyapatite on magnesium surfaces

Anthony Veit Berg, Ablai Forster, Tim Hansson et al. (+3 more)

Hydroxyapatite (HA) on a magnesium (Mg) surface is studied using density functional theory, to help understand the effect of HA coating and alloying in the surfaces of Mg-based biodegradable implants. We determine the adsorption energies and structural changes of a single layer of HA on pure Mg(0001) and on sparsely calcium (Ca) or zinc (Zn) doped Mg(0001) and find that both Zn and Ca doping improves the adsorption, except in a few positions of HA relative to the dopant position. All adsorption configurations, whether with pure or doped Mg surfaces, show deformation of the surface and HA layer. For Ca doping, we found that for a certain adsorption configuration, the dopant Ca atom moves out of the Mg surface and into the HA layer, leaving behind a Mg vacancy in the top layer of the Mg surface. Plots of electron density changes show that electrons accumulate around the Ca dopant and the neighboring Mg atoms, while in Zn doping this is less pronounced. Overall, our results demonstrate that the dopant choice and relative position of HA influence the interaction between HA and Mg-surfaces, and affect both adsorption energies and atomic and electronic structures.
Read the full abstract

All authors Anthony Veit Berg, Ablai Forster, Tim Hansson, Alexandra J. Jernstedt, Emmy Salminen, Elsebeth Schröder

Materials Science · Cross-listed from cond-mat.mes-hall

Magnon-Driven Anomalous Hall Effect in Altermagnets

Zheng Liu, Yang Gao and Qian Niu

We propose a magnon-driven anomalous Hall effect in altermagnets, arising from the coupling between coherently excited chiral magnons and chiral electronic motion. Using density-matrix perturbation theory and symmetry analysis, we show that the resulting Hall conductivity is solely determined by the chiralithy of the Néel-order precession, in sharp contrast to the anomalous Hall effect from the equilibrium Néel order. It then has distinct symmetry requirements from the latter and can exist even when the latter is forbidden by symmetry. The magnon-driven anomalous Hall effect is exemplified in a minimal lattice model with the same symmetry of the altermagnet CrSb, which hosts no static anomalous Hall effect. Our results reveal a direct interplay between chiral magnons and chiral electronic motion, paving the way of probing magnon chirality and to control electronic chirality through magnons.
Read the full abstract

Materials Science · Cross-listed from cond-mat.mes-hall

Commensurate moiré superlattices in anisotropically strained twisted bilayer graphene

Ayan Mondal, Cristina Joseph and Bheema Lingam Chittari

We investigate how anisotropic strain reorganizes commensurate moiré superlattices and electronic structure in twisted bilayer graphene (TBG) across a finite range of reference twist angles. Motivated by experiments showing robust moiré phenomenology under angular disorder and heterostrain (Kapfer et al., Science 381,677 (2023)), we construct commensurate strained supercells generated by a general anisotropic deformation of the top graphene layer of TBG. The results show that anisotropic strain does not generically destroy the electronic structure of nearby pristine moiré systems; rather, its effect depends sensitively on whether the strained commensurate geometry remains two dimensional or crosses over toward a quasi one dimensional regime. This provides a geometric perspective on the persistence of moiré electronic features over a finite window of twist angle and heterostrain. Within this framework, the allowed strained configurations naturally separate into tilted two dimensional moiré patterns and quasi one dimensional stripe like patterns. We find that several such strained two dimensional solutions occur near a given pristine twist angle, and that nearby solutions retain triangular like AA-region localization, comparable low energy bandwidths, and a low field Hofstadter spectrum close to the unstrained system. In contrast, quasi one dimensional strained configurations show stronger dimensional reduction, reduced Dirac point multiplicity, stripe like spatial localization, and stronger Hofstadter splitting.
Read the full abstract

Materials Science

Influence of oxygen ion implantation on magnetic microstructure in Pt/Co/Pt multilayers with perpendicular magnetic anisotropy

Anmol Sharma, Mukul Gupta, Prasanta Karmakar et al. (+7 more)

The interaction of oxygen with cobalt and cobalt-based alloys has been a very important topic in the field of spintronics as it leads to enhanced orbital anisotropy and interfacial Dzyaloshinskii-Moriya interaction (DMI), which are crucial in the context of applications such as magnetic tunnel junctions (MTJs) based data storage and domain wall (DW) motion. To understand the complex and interesting relationship between oxygen and ferromagnetic (FM)/heavy metal (HM) interfaces, we studied controlled oxygen ion implantation in a cobalt layer located in a Pt/Co 1.2 /Pt (nm) multilayer with a specific structure. At high implantation fluence, the perpendicular anisotropy was lost, as verified by in-plane hysteresis measurements. Under low magnetic field conditions, the DW dynamics of Co/Pt multilayers were analyzed, highlighting key parameters such as DW velocity, roughness amplitude, and roughness exponent. After O+-ion implantation, the DW velocity increased by more than 50 times, rising from 5 um/s to 300 um/s compared with the as-deposited multilayer. The fundamental cause of this improvement is the structural and magnetic changes brought by the implantation, which successfully lower the energy barriers preventing DW movements. The results show how oxygen implantation can be used to precisely tailor the ferromagnetic interfaces, leading to promised improvements in the functionality of next-generation spintronic devices.
Read the full abstract

All authors Anmol Sharma, Mukul Gupta, Prasanta Karmakar, V. Raghavendra Reddy, Vivek K. Malik, Andrei Gloskovskii, Ranjeet Kumar Brajpuriya, Ajay Gupta, Vishakha Kaushik, Sachin Pathak

Materials Science · Cross-listed from physics.optics

Mid-infrared reconfiguration of population flow in lanthanide nanocrystals

Xinyang Yu, Yin Huang, Karin Yamamura et al. (+15 more)

Converting mid-infrared (MIR) radiation to visible or near-infrared wavelengths is essential for imaging and sensing, yet achieving sensitive, low-power, and scalable detection remains challenging. Lanthanide nanocrystals provide an alternative through ratiometric luminescence but are typically constrained by Boltzmann statistics, which tie population distributions to lattice temperature and limit signal contrast. Here we show that MIR irradiation rebalances dissipative relaxation pathways, driving lanthanide emitters into a non-Boltzmann steady state that enables non-thermal control of population distributions. This allows emission behaviors inaccessible under thermal equilibrium. We exploit this regime to achieve linear MIR detection with respect to MIR power across 6.8 to 8.6 micrometers. The ratiometric response is intrinsically independent of the pump power, enabling operation at an ultralow excitation power of 10 uW, several orders of magnitude lower than conventional approaches. Using standard silicon photodetectors, we then demonstrate room-temperature MIR imaging with detection limits approaching 4 nW um-2. Our results establish lanthanide nanoparticles as an efficient platform for MIR conversion and sensing in nanophotonic systems.
Read the full abstract

All authors Xinyang Yu, Yin Huang, Karin Yamamura, Chenyi Wang, Lei Ding, Mehran Kianinia, Yang Yu, Jiyun Kim, Baolei Liu, Xiaoxue Xu, Otto Cranwell Schaeper, Yue Bian, Lan Fu, Guochen Bao, Qian Peter Su, Fan Wang, Igor Aharonovich, Chaohao Chen

Materials Science · Cross-listed from cond-mat.str-el

Magnetic anisotropy from interligand hopping in strongly correlated insulators: application to the magnon spectrum of CrI$_3$

Evgenii Barts, Paolo Barone and Maxim Mostovoy

Spin-orbit coupling (SOC) gives rise to complex magnetic states such as spin liquids, skyrmion crystals, and topological spin-wave excitations. We consider exchange interactions in multi-orbital Mott insulators where SOC is strong on ligand ions. SOC on the ligands enables electron hopping accompanied by spin flips and fluctuations in the orbital state of the ligand hole. These processes generate anisotropic exchange interactions and greatly increase the number of possible exchange paths. The number grows further with the inclusion of hopping between ligands, which mediates interactions between more distant spins. We propose an effective method to calculate exchange interactions at arbitrary separations between spins. Applying it to monolayer CrI$_3$, we obtain anisotropic interactions between nearest-neighbor and next-nearest-neighbor Cr spins, as well as single-ion anisotropy induced by long-range hopping. In this material, magnetic anisotropy stabilizes long-range ferromagnetic order and opens a magnon gap at the Dirac points, which defines a nontrivial magnon band topology. Using Hubbard model parameters from first-principles calculations, the resulting spectrum agrees well with the spin-wave dispersion observed experimentally in bulk CrI$_3$, except that the calculated Dirac gap is much smaller.
Read the full abstract

Materials Science

Realizing giant valley polarization effect based on monolayer altermagnets

Weifeng Xie, Libo Wang, Xiong Xu et al. (+4 more)

Stable and remarkable valley polarization effect is the key to utilizing valley degree of freedom in valleytronic devices. According to first-principles calculations and symmetry analysis, we reveal that valley polarization effect in monolayer V2Se2O altermagnet is correlated with the net magnetic moment between magnetic V atoms under uniaxial strain, thereby proposing two strategies for achieving giant valley polarization effect. Firstly, substituting one V atom in V2Se2O with Cr to construct a ferrimagnetic monolayer VCrSe2O enhances the net magnetic moment between magnetic atoms, thereby realizing a giant valley polarization effect. Applying uniaxial strain along either the a-axis or b-axis significantly increases the value of valley polarization, which exhibits a nearly linear relationship with the net magnetic moments between the magnetic atoms. Secondly, constructing a van der Waals heterostructure composed of V2Se2O and {\alpha}-SnO monolayers breaks mirror symmetry, thereby inducing a net magnetic moment, which in turn causes a remarkable valley polarization effect. Compressing the interlayer distance of the heterostructure can increase the net magnetic moment between V atoms, then enhancing the value of valley polarization to nearly 400 meV. This work reveals that valley polarization in monolayer altermagnet is correlated with the net magnetic moment between magnetic atoms. Finally, we propose two strategies to achieve giant valley polarization based on monolayer altermagnets, providing theoretical guidance for the potential applications of ferrimagnetic monolayers and altermagnet-based heterostructures in valleytronics.
Read the full abstract

All authors Weifeng Xie, Libo Wang, Xiong Xu, Yunliang Yue, Huayan Xia, Longhui He, Hui Wang

Thursday 19 March

Materials Science · Cross-listed from q-bio.PE

Broad presence of ferromagnetism in bees and relationship to phylogeny, natural history, and sociality

Laura Russo, Caleb Allen, Cameron S. Jorgensen et al. (+7 more)

Scientists have long been fascinated by magnetoreception, the innate capacity of many animals to sense and use the Earth's magnetic field for navigation. In eusocial insects like honey bees, magnetoreception has been linked to communication and foraging. However, little is known about magnetoreception's phylogenetic patterns and relationship to species traits and natural history. Here, we demonstrate that putative magnetoreception based on ferromagnetic particles is widespread across a diversity of bee species (72 out of 96 species tested), with no phylogenetic signal. We also detected such putative magnetoreception in non-bee outgroups, suggesting this magnetic capacity predates the evolution of the Anthophila. While magnetic signals were found across a diversity of life history traits, the strength of the magnetic signal varied within and between species, and increased with body size and social behavior.
Read the full abstract

All authors Laura Russo, Caleb Allen, Cameron S. Jorgensen, Lizabeth Quigley, C. Charlotte Buchanan, Michael Winklhofer, Seán G. Brady, Laurence Packer, Anne Murray, Dustin A. Gilbert

Materials Science

First principles characterization of spinterfaces between magnetic Cobaltocene molecule and 2D magnets (CrI$_3$, Fe$_3$GeTe$_2$)

Nikola Machacova and Biplab Sanyal

In this paper, we examine the properties of spin-polarized interfaces consisting of single-molecule magnet bis(cyclopentadienyl)cobalt(II) (cobaltocene) and two-dimensional magnetic materials, semiconducting CrI$_3$ and metallic Fe$_3$GeTe$_2$, using first-principles density functional theory based calculations. Our calculated adsorption energies indicate the stability of these hetero-interfaces with the observation of hybridization of electronic states across the interface. Magnetic exchange interaction parameters have been obtained from both total energy differences and the Liechtenstein-Katsnelson-Antropov-Gubanov (LKAG) formalism in the basis of maximally localized Wannier functions (MLWFs). Analysis of these parameters shows a strong directional anisotropy in the magnetic substrate-molecule interaction in agreement with the nature of orbital hybridization. Additionally, possible exchange mechanisms are proposed based on orbital-resolved exchange and hopping parameters. We also show that the molecular adsorption may enhance the intralayer exchange interactions, with some exchange parameters reaching up to a 3-fold increase in magnitude compared to the freestanding case. Finally, we observe a 100 % spin polarization at the Fermi level in the cobaltocene/CrI$_3$ interface, which makes it particularly promising for spin-transport applications.
Read the full abstract

Materials Science

Theoretical investigation of the photovoltaic properties of MgSnN$_{2}$ for multi-junction solar cells

Issam Mahraj, Mossab Oublal and Andrzej Ptok

The orthorhombic crystal structure of the MgSnN$_2$ compound with Pna2$_1$ symmetry has been investigated as a low-cost, non-toxic material for photovoltaic (PV) applications using density functional theory (DFT) and spectroscopic limited maximum efficiency (SLME) calculations. A detailed analysis of the electronic and optical properties was performed using the mBJ semilocal exchange functional. The bandgap of MgSnN$_2$ is found to be 2.45 eV. SLME photovoltaic analysis suggests that a thin film of MgSnN$_2$ with a thickness of 2 $\mu$m can reach an efficiency of 13.17% at room temperature. This efficiency was further improved through the simulation of a multi-junction device, where the tandem configuration increased the efficiency from 12.80% (single-junction) to 22.42%. Furthermore, introducing cation disorder can further reduce the bandgap, enhancing its suitability for solar cell applications.
Read the full abstract

Materials Science · Cross-listed from cond-mat.mes-hall

Energy renormalizations of resident carriers and excitons in transition metal dichalcogenide monolayers

Dinh Van Tuan, Junghwan Kim and Hanan Dery

Energy renormalizations of resident carriers and excitons are studied theoretically, and compared with recent experiments of electrostatically-doped WSe$_2$ monolayers. The calculated energy renormalization of resident carriers, subjected to strong out-of-plane magnetic field, reveals the importance of dynamical screening in transition metal dichalcogenides. The energy renormalization of tightly bound excitons is analyzed through the exchange interaction between the electron (or hole) component of the exciton and resident carriers that share the same spin and valley quantum numbers. Our theory explains the weak energy shift of excitonic resonances despite the strong energy renormalization of resident carriers. We identify the dependence of the energy renormalization on the envelope function of a tightly-bound exciton, showing that unlike free electron-hole pairs, this energy renormalization is not the added renormalizations of a resident electron and resident hole.
Read the full abstract

Materials Science

Auxetic Response in Two-Dimensional MXenes with Atomically Defined Perforations

Hossein Darban

Recent advances in nanoscale fabrication enable atomic-scale manipulation of two-dimensional (2D) materials by introducing engineered pores and perforations. This provides new opportunities to tailor functional properties of 2D materials for applications such as selective ion transport, desalination membranes, and molecular filtration. Despite this progress, the auxetic mechanical behavior of perforated 2D materials has received little attention. In this work, large-scale reactive molecular dynamics (MD) simulations, validated against experimental measurements and first-principles calculations, are employed to investigate the mechanical response of perforated monolayer titanium-based MXene metamaterials. Architectures containing rectangular perforations with straight ligaments and sinusoidally curved ligaments are systematically examined under uniaxial tension and compression over a range of geometric parameters and temperatures, from the onset of deformation to fracture. The results demonstrate that MXene metamaterials exhibit a tunable negative Poisson's ratio (NPR), which can be controlled through the perforation geometry and surface termination. Atomistic stress analysis reveals alternating in-plane shear stresses at the junctions that induce rotational deformation of the ligaments. This rotating-junction mechanism is coupled with out-of-plane deflections arising from the low bending rigidity of atomically thin materials, producing complex three-dimensional deformations. Comparison with graphene metamaterials indicates that the perforation geometry governs qualitative auxetic trends, whereas intrinsic material properties determine quantitative responses. These findings identify MXenes as a versatile candidate for the design of tunable 2D mechanical metamaterials and provide atomistic insight into the interplay between geometry, bending rigidity, and auxetic deformation mechanisms.
Read the full abstract

Materials Science

Tailoring Emergent Magnetic Moment in La$_{0.7}$Sr$_{0.3}$MnO$_3$-Bi$_2$Te$_3$ Heterostructures via Interfacial Reconstructions

Damian Brzozowski, Yu Liu, Øyvind Finnseth et al. (+6 more)

We report emergent magnetic behavior in heterostructures composed of (111)-oriented La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) and (00$l$)-oriented Bi$_2$Te$_3$ (BT), controlled by interfacial reconstructions. When BT is deposited directly onto LSMO, an intermediate interfacial layer forms between the two materials. Polarized Neutron Reflectometry modeling reveals that this reconstructed region stabilizes a secondary magnetically ordered phase that is coupled to the underlying ferromagnetic LSMO layer. As a consequence, the heterostructures exhibit unconventional self-crossing magnetic hysteresis loops at room temperature, characterized by a reversal of the net magnetization at low applied fields. In contrast, the introduction of a tellurium seed layer results in a sharper LSMO-BT interface, while preserving the anomalous hysteresis behavior and enhancing the saturation magnetization. Element-specific X-ray absorption spectroscopy suggests that the emergent magnetic phase originates from the chemical reconstruction of manganese species. These results demonstrate that interface engineering in magnetic oxide-topological insulator heterostructures provides a pathway to control emergent magnetic coupling and emergent magnetic states in oxide-topological insulator heterostructures.
Read the full abstract

All authors Damian Brzozowski, Yu Liu, Øyvind Finnseth, Egil Y. Tokle, Andrew J. Caruana, Christy J. Kinane, Alexander J. Grutter, Dennis G. Meier, Ingrid Hallsteinsen

Materials Science · Cross-listed from cond-mat.mes-hall

Programmable, Spontaneous Superlattice Memory in a Monolayer Topological Insulator

Jian Tang, Thomas Siyuan Ding, Shuhan Ding et al. (+24 more)

Memory is a foundational concept across disciplines, from neurobiology and electronics to artificial intelligence and quantum gravity. In materials, memory effects typically arise from ferroic orders, such as ferroelectricity and ferromagnetism, where information is stored in charge or spin degrees of freedom. Here, we report a surprising discovery of a nonvolatile superlattice memory effect in monolayer TaIrTe4, a dual quantum spin Hall insulator, where information is encoded through sharply contrasting lattice periodicities. In particular, in a pristine monolayer, we observe the spontaneous emergence of a long-period superlattice that can be programmed ON and OFF in a nonvolatile manner by electrostatic tuning of low-energy electronic states. This switching toggles the system between two structural configurations with unit cell areas differing by nearly two orders of magnitude. Mechanistically, our results reveal two independent and distinct instabilities, one in the lattice and the other in the QSH electrons, which are coupled, leading to electrostatic control of lattice configurations with nonvolatile memory. This finding is enabled by combining linear and nonlinear transport measurements, Raman spectroscopy, and scanning tunneling microscopy, which probe complementary aspects of the underlying orders. Remarkably, this nonvolatile memory effect stabilizes a spontaneous superlattice with a periodicity on the few-nanometer scale that remains robust across a wide doping range, persists over days, and survives above 70 K. Combined with the QSH topology, this stability offers a promising route to nonvolatile memory control of topological flat bands and their filling enabled quantum states. Our preliminary data indeed show the emergence of new insulating states at fractional superlattice fillings, which can be clearly switched ON and OFF together with the superlattice.
Read the full abstract

All authors Jian Tang, Thomas Siyuan Ding, Shuhan Ding, Jiangxu Li, Changjiang Yi, Tianxing Tang, Zumeng Huang, Xuehao Wu, Zhiheng Huang, Birender Singh, Tiema Qian, Vsevolod Belosevich, Mingyang Guo, Anyuan Gao, Nikolai Peshcherenko, Zhe Sun, Mohamed Shehabeldin, Kenji Watanabe, Takashi Taniguchi, Abhay N. Pasupathy, Claudia Felser, Kenneth S. Burch, Ni Ni, Yao Wang, Yang Zhang, Su-Yang Xu, Qiong Ma

Materials Science

Electrically switchable ferron upconversion in a van der Waals ferroelectric

Sujan Subedi, Wuzhang Fang, Fan Fei et al. (+7 more)

Nonlinear phononics provides a powerful ultrafast route to control lattice excitations, enabling access to hidden quantum orders, phononic computing, and quantum transduction. However, dynamic control of anharmonic phonon interactions remains limited, as these interactions are typically fixed by the equilibrium crystal lattice and lack external tunability. Emergent ferrons in ferroelectrics, which are collective oscillations of the spontaneous electric polarization, may offer a promising platform to overcome this limitation by combining intrinsic phononic nonlinearity with direct electrical control of the ferroelectric order parameter. Here we report electrically controllable nonlinear ferron upconversion in the van der Waals ferroelectric NbOI2. We show that resonant THz excitation of a 3.1 THz ferron drives coherent upconversion to a 7.0 THz optical phonon. Using two-dimensional THz spectroscopy, we directly resolve off-diagonal coupling features and establish the nonlinear upconversion pathway. Supported by first-principles calculations and analytical modeling, we identify the microscopic origin as a cubic anharmonic lattice coupling. Importantly, in situ electric-field switching enables nonvolatile control of both the ferron dynamics and the associated upconversion process. The phase reversal and hysteretic behavior across the coercive fields establish that the ferron-mediated nonlinear phononic interaction is strongly dependent on the underlying ferroelectric order parameter. These results introduce ferron upconversion as a new and universal regime of nonlinear phononics in ferroelectrics and establish an electrically programmable platform for coherent lattice control, paving the way for ferronic information processing and quantum phononic transduction.
Read the full abstract

All authors Sujan Subedi, Wuzhang Fang, Fan Fei, Zixin Zhai, Jack P. Rollins, Carter Fox, Alaina Drew, Bing Lv, Yuan Ping, Jun Xiao

Materials Science · Cross-listed from cond-mat.str-el

Interface magnetic coupling and magnetization dynamic of La$_{2/3}$Sr$_{1/3}$MnO$_3$ single layer and (La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$)$_n$ (n = 1, 5) superlattice on SrTiO$_3$(001) substrate

Ilyas Noor Bhatti, Rachna Chaurasia, Kazi Rumanna Rahman et al. (+3 more)

In this work, we investigate the structural, magnetic, and microwave magnetic dynamics of multilayered \([{\rm LSMO}/{\rm SRO}]_n\) heterostructures \((n = 1 \text{ and } 5)\) grown on SrTiO\(_3\) (001) substrates. X-ray diffraction confirms high crystallinity and atomically sharp interfaces. Magnetic measurements reveal strong interfacial magnetic coupling, with a distinct two-step magnetization switching observed in the \(n = 5\) heterostructure, while this feature is significantly suppressed in the \(n = 1\) structure. Ferromagnetic resonance (FMR) analysis shows a broad linewidth, pronounced positive magnetic anisotropy, and Gilbert damping on the order of \(10^{-2}\), with damping decreasing as the number of multilayer repetitions increases. These observations demonstrate that Ru–Mn exchange coupling at the interface critically governs the magnetic response and dynamic behavior of the system. The tunable switching and damping properties highlight such oxide heterointerfaces as promising platforms for exploring spin textures, magnetic domain behavior, and room-temperature spintronic applications.
Read the full abstract

All authors Ilyas Noor Bhatti, Rachna Chaurasia, Kazi Rumanna Rahman, Sukhendu Sadhukhan, Amantulla Mansuri, Imtiaz Noor Bhatti

Materials Science

Photoferroelectric Coupling and Polarization-Controlled Interfacial Band Modulation in van der Waal Compound CuInP2S6

Subhashree Chatterjee, Rabindra Basnet, Rajeev Nepal et al. (+1 more)

Understanding how optical excitation couples with polarization and interfacial electrostatics in van der Waals (vdW) ferroelectrics (FEs) is essential for the development of light-programmable nanoelectronic and optoelectronic devices. Here, we present direct nanoscale evidence of photoferroionic coupling in the vdW FE semiconductor CuInP2S6 (CIPS), where optical excitation jointly modulates electronic band bending, FE switching, and Cu+ ionic relaxation. The use of correlated Kelvin probe force microscopy, piezoresponse force microscopy, and conductive atomic force microscopy under above-bandgap illumination reveals illumination-induced enhancement of surface work function, persistent surface photovoltage, reduced coercive field, and positive imprint shifts. These effects arise from synergistic photocarrier redistribution and slow Cu+ migration that reshape interfacial depletion widths and internal electric fields. Illumination-assisted barrier lowering further enhances carrier injection and produces sweep-rate-dependent ferroionic transport hysteresis. Our results establish photoferroionic coupling as the governing mechanism for light-controlled band modulation and polarization stability in CIPS, providing a nanoscale framework for designing light-addressable FE memories, optoelectronic switches, and neuromorphic devices based on layered ferroionic materials.
Read the full abstract

All authors Subhashree Chatterjee, Rabindra Basnet, Rajeev Nepal, Ramesh C. Budhani

Materials Science

Ferroelectric $p$-wave magnets

Jan Priessnitz, Anna Birk Hellenes, Riccardo Comin et al. (+1 more)

Couplings between ferroelectric and magnetic orders offer promising routes toward low-dissipation electronics. However, such couplings are notably rare, largely due to the poor compatibility between insulating band structures and ferromagnetism. Here, we study a different strategy: we identify previously overlooked time-reversal-symmetric $p$- and $f$-wave spin-polarized insulating electronic states in ferroelectrics with noncollinear magnetic sublattices. We show that combining spin and magnetic group theory enables a systematic classification of the origin of polar symmetry breaking. We distinguish crystallographic, exchange-, or spin-orbit-driven mechanisms. Furthermore, we identify more than 50 candidate materials. Using first-principles calculations, we demonstrate a pristine, time-reversal-symmetric $p$-wave spin-polarized electronic structure in the well-known multiferroic $\mathrm{GdMn_2O_5}$. We further show that its $p$-wave order can be switched electrically, opening alternative paths toward spintronic and multiferroic functionalities in this class of materials.
Read the full abstract

All authors Jan Priessnitz, Anna Birk Hellenes, Riccardo Comin, Libor Šmejkal

Materials Science · Cross-listed from cond-mat.str-el

Magnetic properties of a buckled honeycomb lattice antiferromagnet

A. Yadav, U. Jena, A. Pradhan et al. (+2 more)

The intriguing interplay between competing degrees of freedom in frustrated magnets can lead to non-trivial magnetic phenomena with exotic low-energy excitations that are highly relevant for addressing some of the fundamental questions in quantum condensed matter as well as potential technological applications. Herein, we report the synthesis and thermodynamic results on a frustrated magnet Co3ZnNb2O9. The Co2+ moments constitute buckled AB-type honeycomb layers in the ab-plane. The temperature-dependent magnetic susceptibility shows a sharp anomaly at 14 K, indicating the onset of long-range magnetic ordering. The Curie-Weiss fit of the magnetic susceptibility above 100 K, yields a Curie-Weiss temperature of -70 K, suggesting strong antiferromagnetic (AFM) interactions between the Co2+ spins and an effective magnetic moment of 5.54 muB, indicating the presence of unquenched orbital angular momentum. A field-induced spin-flop-like metamagnetic transition below the ordering temperature is characterized by a critical magnetic field of 1.2 T. The specific heat shows a lambda-type anomaly at 14 K, confirming the presence of long-range magnetic ordering, due to finite interlayer interaction. Interestingly, our study of the magnetocaloric effect near the transition temperature revealed an entropy change of 2.81 J/kg.K, which is ascribed to competing interactions, underlying anisotropy, and reduced net magnetization lead to relatively small isothermal entropy changes that suggest that frustrated honeycomb magnets are promising contenders for field-induced exotic phases and magnetocaloric response.
Read the full abstract

All authors A. Yadav, U. Jena, A. Pradhan, Satish K., P. Khuntia

Materials Science

Deterministic nucleation of nanocrystal superlattices on 2D perovskites for light-funneling heterostructures

Umberto Filippi, Alexander Schleusener, Simone Lauciello et al. (+4 more)

Semiconductor heterostructures that combine components with different dimensionality provide an interesting way to manipulate the physical properties of the resulting material. Two-dimensional lead halide perovskites crystallize as flat microcrystals and have efficient in-plane exciton mobility, while perovskite nanocrystals are efficient emitters with a tunable bandgap that can self-assemble into microscopic superlattices. However, combining such intricate architectures into heterostructures has been challenging due to the mismatch in solubility properties and the challenging transfer procedures. Here we realize heterostructures where CsPbBr3 nanocrystal superlattices are deterministically grown along the faces of PEA2PbBr4 two-dimensional layered perovskite microcrystals. The growth can be limited to the lateral faces of the microcrystals and result in core-crown epitaxial heterostructures, or extended to the vertical direction leading to core-shell-like structures. The growth method is simple yet effective and versatile, and promises to be expanded to a large variety of other materials. We demonstrate that these heterostructures can be employed as efficient light-harvesting systems. In fact, energy can be transferred from the two-dimensional microcrystal domain to the superlattices, enabling switching between linear and non-linear carrier recombination regimes by tuning the excitation fluence. Moreover, by exploiting the lifetime shortening of CsPbBr3 nanocrystal emission upon sample cooling, we ensure that energy transfer occurs after the biexcitonic and single-excitonic decays of the nanocrystals, effectively extending the radiative recombination of superlattices.
Read the full abstract

All authors Umberto Filippi, Alexander Schleusener, Simone Lauciello, Roman Krahne, Dmitry Baranov, Liberato Manna, Masaru Kuno

Materials Science

Imaging short- and long-range magnetic order in a quantum anomalous Hall insulator

Andriani Vervelaki, Boris Gross, Daniel Jetter et al. (+11 more)

The quantum anomalous Hall effect has been observed in several magnetically doped topological insulators, where its robustness and macroscopic magnetization properties have been taken to suggest the presence of long-range ferromagnetic order. However, experiments in such systems have found evidence for both long- and short-range order, leaving the precise nature of the magnetism in these systems unclear. Here, we use scanning superconducting quantum interference device microscopy to study magnetic domains in V-doped (Bi,Sb)$_2$Te$_3$ exhibiting a quantum anomalous Hall effect with precise quantization. By imaging stray magnetic fields as a function of applied field, we map the formation and evolution of domains through magnetic reversal. We reconstruct the magnetization configuration underlying the measured stray field and find that magnetic domains and crystallographic grains are of similar size. Moreover, magnetic reversal is found to occur through domain expansion, typical of ferromagnets, rather than through nucleation at random sites. Our measurements thus reveal a coexistence of both local magnetic interactions within crystallographic grains and long-range ferromagnetic coupling between grains. This behavior in V-doped (Bi,Sb)$_2$Te$_3$ is markedly distinct from that previously reported for Cr-doped (Bi,Sb)$_2$Te$_3$.
Read the full abstract

All authors Andriani Vervelaki, Boris Gross, Daniel Jetter, Katharina Kress, Timur Weber, Dieter Koelle, Kajetan M. Fijalkowski, Martin Klement, Nan Liu, Karl Brunner, Charles Gould, Laurens W. Molenkamp, Martino Poggio, Floris Braakman

Materials Science

Microscopic Origin of Temperature-Dependent Anisotropic Heat Transport in Ultrawide-Bandgap Rutile GeO2

Pouria Emtenani, Marta Loletti, Felix Nippert et al. (+7 more)

Ultrawide-bandgap rutile GeO2 is emerging as a promising semiconductor for power electronics, where efficient heat dissipation is essential to suppress self-heating and ensure device reliability. However, the temperature dependence and microscopic origin of its anisotropic heat transport have remained experimentally unresolved. Here, temperature-dependent time-domain thermoreflectance measurements combined with first-principles phonon transport calculations are used to quantify the thermal conductivity of single-crystal rutile GeO2 from 80 to 350 K along [001] and [110]. At 295 K, the thermal conductivity reaches 47.5 W m^-1 K^-1 along [001] and 32.5 W m^-1 K^-1 along [110], corresponding to an anisotropy ratio of 1.46, in good agreement with theory. Rather than following a simple T^(-1) law, the thermal conductivity exhibits an approximate T^(-1.4) dependence, indicating additional scattering beyond purely three-phonon-limited transport. Mode-resolved analysis reveals that the room-temperature anisotropy originates from the combined effect of larger phonon group velocities along [001] and direction-dependent phonon lifetimes. Upon cooling, depopulation of high-frequency phonons progressively suppresses their contribution to heat transport and reduces the anisotropy. The temperature-dependent thermal boundary conductance of Al/rutile GeO2 interfaces is further resolved, and the scaled conductance indicates predominantly elastic interfacial transport. These findings establish the microscopic basis of bulk and interfacial heat transport in rutile GeO2 and position this material as a promising thermally robust platform for ultrawide-bandgap electronics.
Read the full abstract

All authors Pouria Emtenani, Marta Loletti, Felix Nippert, Eduardo Bede Barros, Zbigniew Galazka, Hans Tornatzky, Christian Thomsen, Juan Sebastian Reparaz, Riccardo Rurali, Markus R. Wagner

Materials Science

Bridging Crystal Structure and Material Properties via Bond-Centric Descriptors

Jian-Feng Zhang, Ze-Feng Gao, Xiao-Qi Han et al. (+7 more)

Although chemical bonding is the fundamental mechanistic bridge connecting atomic structure to macroscopic material properties, current data-driven materials science largely treats it as an implicit "black box". Existing machine learning (ML) models rely predominantly on geometric coordinates, forcing them to implicitly relearn complex quantum mechanics from scratch. This lack of intermediate physical features limits model interpretability and generalizability, particularly when training data is scarce. To solve this problem, we introduce MattKeyBond, a bond-centric materials database that explicitly maps the local electronic landscape and bonding interactions of materials. Building on this, we propose Bonding Attractivity (BA), a novel element-specific descriptor that quantifies the intrinsic capability of atoms to form covalent networks. By providing pre-calculated, energy-dimensional bonding descriptors, MattKeyBond transforms the implicit "black box" into physically interpretable features. This strategy relieves ML models from the burden of deducing physical laws from pure geometry, enabling accurate predictions even with limited data and seamlessly integrating electronic structure theory into modern AI workflows.
Read the full abstract

All authors Jian-Feng Zhang, Ze-Feng Gao, Xiao-Qi Han, Bo Zhan, Dingshun Lv, Miao Gao, Kai Liu, Xinguo Ren, Zhong-Yi Lu, Tao Xiang

Materials Science · Cross-listed from physics.optics

Phonon-modulated Kerr nonlinearity in ultrathin 2H-MoTe2

Shaoxiang Sheng, Yang Luo, Chenyu Wang et al. (+8 more)

Controlling nonequilibrium responses in optically driven quantum materials is essential for advancing applications in energy conversion, ultrafast electronics, and quantum computation. Nonlinear optical spectroscopy serves as a powerful tool to investigate ultrafast electron and phonon dynamics in these systems; however, conventional nonlinear approaches often require intense laser pulses (> 10 GW/cm2) and typically encounter a strong background. Here, we introduce a phase-sensitive nonlinear spectroscopic technique that operates at low laser powers (~ 10 kW/cm2, pulse energies ~ 10 pJ) and enables real-time monitoring and active control of coherent phonons in a few-layer (three to five) thick 2H-MoTe2. Upon excitation with ultrashort (~ 10 fs) pump pulses, we achieve displacive excitation of coherent phonons, which periodically modulate the Kerr nonlinearity of the material, leading to cross-phase modulation (XPM) of a delayed probe pulse. This phase modulation induces spectral broadening and oscillations in the center of mass (COM) of the probe spectrum in time, enabling the detection of subtle nonlinear optical responses in a background-free manner. The nonlinear response can be selectively amplified or attenuated by adjusting the strength of the pump pulse, which controls the distribution of photoexcited carriers in the electronic bands. By combining two-color nondegenerate pump-probe measurements and time-dependent density-functional theory (TDDFT) calculations, we directly resolve the coupled nonequilibrium electronic and phonon dynamics. A dual-pump pulse scheme enables precise control of phonon oscillations, allowing selective activation or suppression of specific phonon modes and correspondingly the modulation of the Kerr nonlinearity.
Read the full abstract

All authors Shaoxiang Sheng, Yang Luo, Chenyu Wang, Sayooj Sateesh, Yaxian Wang, Marko Burghard, Sayantan Patra, Bhumika Chauhan, Ashish Arora, Sheng Meng, Manish Garg

Materials Science

Phonon Band Center: A Robust Descriptor to Capture Anharmonicity

Madhubanti Mukherjee, Ashutosh Srivastava and Abhishek Kumar Singh

Understanding anharmonicity is crucial for designing materials with desired lattice thermal conductivity. Designing a material descriptor that effectively captures anharmonicity while being cost-effective remains a significant challenge. This work proposes a simple metric that helps explain the diversity in lattice thermal conductivity (kl) among materials by quantifying their anharmonic effects. This descriptor "phonon band center" (PBC) encapsulates the critical factors associated with the physics of phonon scattering, revealing a simple inverse relationship with the Gruneisen parameter, the response of phonons with changing volume, and strong correlation with lattice thermal conductivity. This metric has been established using the chalcopyrite class of materials and subsequently validated across various classes of materials using experimental kl. Our approach effectively differentiates materials based on PBC, thereby streamlining the identification of candidates with desirable kl.
Read the full abstract

Materials Science

Direct observation of strain and confinement shaping the hole subbands of Ge quantum wells

Enrico Della Valle, Arianna Nigro, Miki Bonacci et al. (+6 more)

Germanium-silicon-germanium (Ge/Si$_{x}$Ge$_{1-x}$) heterostructures have emerged as a promising platform for hole-spin quantum technologies and high-mobility electronics, where strain and quantum confinement strongly reshape the Ge valence bands. However, the momentum-resolved valence-band structure of buried strained Ge quantum wells has so far been inferred only indirectly. Here we use soft X-ray angle-resolved photoemission spectroscopy (SX-ARPES) to directly probe the electronic structure of strained Ge quantum wells embedded in SiGe barriers. We resolve strain-split and size-quantized valence subbands, determine their heavy-hole, light-hole and split-off composition, and measure the valence-band offset at the Ge/SiGe heterojunction. Comparison with ab initio calculations shows that an accurate description requires explicit inclusion of the confinement potential imposed by the SiGe barrier, which plays a decisive role in determining the dispersion, ordering and mixing of the hole states. Our results provide the first direct experimental picture of how strain and confinement determine the valence-band structure of Ge quantum wells, establishing a foundation for predictive modelling of hole-spin qubits and high-mobility devices based on group-IV heterostructures.
Read the full abstract

All authors Enrico Della Valle, Arianna Nigro, Miki Bonacci, Nicola Colonna, Andrea Hofmann, Michael Schüler, Nicola Marzari, Ilaria Zardo, Vladimir N. Strocov

Materials Science

A first-principles linear response theory for open quantum systems and its application to Orbach and direct magnetic relaxation in Ln-based coordination polymers

Mikolaj Żychowicz, Jakub J. Zakrzewski, Szymon Chorazy et al. (+1 more)

Single-Molecule Magnets (SMMs) exhibit slow magnetic relaxation as a result of axial magnetic anisotropy inhibiting spin-phonon transitions. In order to establish a direct link between physical observables and the microscopic theory of magnetic relaxation, we here develop and numerically implement a first-principles linear-response theory for open quantum systems that provides access to the complex a.c. magnetic susceptibility in the presence of an oscillating a.c. magnetic field. Once combined with density functional theory and multiconfigurational electronic structure simulations, this formalism is applied in a fully first-principles fashion to three cyanido-bridged Ln/Y-based coordination polymers with general formula {Ln$^{III}_x$ Y$^{III}_{1-x}$ [Co(CN)$_6$]}, where Ln = Yb (1), Tb (2), and Dy (3). The method is able to reproduce the low-temperature direct relaxation process and its field dependence, as well as the high-temperature Orbach relaxation regime for all the investigated compounds. These results demonstrate the feasibility of ab initio simulations of magnetic a.c.susceptibility in lanthanide-based SMMs and support the potential of further development of ab initio open quantum systems methods towards the completion of a magnetization dynamics theory.
Read the full abstract

All authors Mikolaj Żychowicz, Jakub J. Zakrzewski, Szymon Chorazy, Alessandro Lunghi

Materials Science

Origin of Reduced Coercive Field in ScAlN: Synergy of Structural Softening and Dynamic Atomic Correlations

Ryotaro Sahashi, Po-Yen Chen and Teruyasu Mizoguchi

Among wurtzite-type ferroelectrics, scandium-doped aluminum nitride (ScAlN) has emerged as a leading candidate for CMOS-compatible low-voltage memory, combining strong spontaneous polarization with process compatibility. A remarkable feature of this system is the pronounced reduction of the coercive field (Ec) with increasing Sc concentration; however, its microscopic origin remains poorly understood at the atomic scale, particularly under finite temperature and applied electric fields. Here, we integrate a density-functional-theory-accurate machine-learning force field with an equivariant neural-network-based Born effective charge model to perform large-scale electric-field-driven molecular dynamics simulations at near-first-principles accuracy. The framework correctly reproduces the experimentally observed qualitative trends in key experimental trends, including the decrease in the c/a ratio and the monotonic reduction of Ec with increasing Sc content. Beyond static structural softening, we uncover a dynamic mechanism underlying Ec reduction. Sc atoms exhibit larger thermal vibrations and undergo preceding displacements during switching, acting as dynamic triggers for polarization reversal. Moreover, the displacement correlation between Sc and Al atoms evolves systematically with composition, enhancing cooperative atomic rearrangements and lowering the effective switching barrier. These results demonstrate that Ec reduction in ScAlN arises from the synergy of structural softening and dynamic correlation evolution, providing a new perspective for designing hexagonal ferroelectrics.
Read the full abstract

Materials Science · Cross-listed from cond-mat.mes-hall

Time reversal reserved spin valve and spin transistor based on unconventional $p$-wave magnets

Ze-Yong Yuan, Jun-Feng Liu, Pei-Hao Fu et al. (+1 more)

The anisotropic spin splitting in unconventional magnets opens new opportunities for realizing spintronic functionalities without relying on net magnetization or relativistic spin-orbit coupling. Here, we propose a spin valve and a spin transistor based on unconventional $p$-wave magnets (UPMs). The spin valve is realized in a junction where a normal metal is sandwiched between two UPMs whose exchange-field strength vectors are oriented transverse to the junction direction. The conductance of such a device is governed by the spin alignment between two UPMs: when their strength vectors are parallel, the spin-state alignment enables efficient electron transmission, leading to a high-conductance state; in contrast, the antiparallel configuration suppresses the conductance owing to the opposite spin orientations. Furthermore, the spin-valve can be extended to a spin transistor by replacing the central normal metal with another UPM with a longitudinally oriented strength vector and a perpendicular spin polarization axis. The central UPM enables uniform spin precession with the same precession frequency for all transverse modes. Both devices can be electrically controlled by modulating the strength vectors of UPMs. These findings establish UPMs as a promising platform for developing spintronic devices without net magnetization or relativistic spin-orbit coupling.
Read the full abstract

All authors Ze-Yong Yuan, Jun-Feng Liu, Pei-Hao Fu, Jun Wang