Materials Science · Cross-listed from cond-mat.supr-con
Tunneling spectra of $\mathrm{TaO}_x$ junctions for van der Waals superconductors
Yixuan Niu, Jun Cheng, Shiji Ding et al. (+5 more)
Tunneling spectroscopy and its
evolution are crucial for elucidating the intricate electronic structure and emergent phenomena in
quantum materials.Nevertheless, high-quality measurements – specifically those tracking
evolution across temperature and external fields – remain a formidable challenge. We have fabricated a high-quality $\mathrm{TaO}_x$-based planar tunneling junction by using magnetron sputtering for van der Waals (vdW)
superconductors. Using the vdW
superconductor $\mathrm{Bi}_2\mathrm{Sr}_2\mathrm{CaCu}_2\mathrm{O}_{8+\delta}$ (Bi2212) as a
benchmark, this platform yields high-quality tunneling spectra, reproducing the electronic signatures obtained from scanning tunneling spectra acquired from atomically clean surfaces under ultra-high
vacuum conditions. This architecture enables high-precision spectroscopy across extensive temperature and
magnetic field ranges, offering a universal strategy for probing the electronic structures of diverse two-dimensional systems and facilitating future explorations of material properties.
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All authors Yixuan Niu, Jun Cheng, Shiji Ding, Zhongxin Guo, Shang Wang, Chenglong Li, Meining Zhang, Peng Cai
Materials Science
Quantifying the coupling between strain and cation valence in high entropy oxide thin films using electron microscopy
Sai Venkata Gayathri Ayyagari, Saeed SI Almishal, Debangshu Mukherjee et al. (+3 more)
High
entropy oxides (HEOs) are a class of materials with vast compositional space and tunable properties, making them attractive for applications in thermoelectrics, magnetism, ionic conduction, and beyond. However, their metastable nature makes the local structure, and consequently their properties, highly sensitive to growth conditions. It is therefore essential to probe the local modulations in atomic, chemical, and electronic structure as a function of growth conditions. Here, advanced S/TEM techniques, including 4D-STEM combined with electron energy loss spectroscopy and energy-dispersive X-ray spectroscopy are used to investigate the effect of substrate temperature on structure and strain at the nanoscale regime in HEO thin films. We quantify how nanoscale strain variations correlate with Co valence and subtle chemical differences in the films with the same nominal composition but different growth temperatures. Our results demonstrate that identical HEO compositions can accommodate distinct strain and defect states in thin film form and highlight how synthesis conditions can be leveraged to manipulate strain and Co valence. These findings establish a framework to tailor functional properties via strain and valence control in high
entropy oxide thin films.
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All authors Sai Venkata Gayathri Ayyagari, Saeed SI Almishal, Debangshu Mukherjee, Kevin M. Roccapriore, Jon-Paul Maria, Nasim Alem
Materials Science
Hybrid Improper Ferroelectricity and Moiré Superlattices-induced Exciton Quantization in Layered 2D Halide Perovskite
Sanika S. Padelkar, Sharidya Rahman, Mattia Belotti et al. (+10 more)
2D Ruddlesden-Popper perovskites are compelling platforms for
quantum-confined optoelectronics. However, polar order in iodide composition remains rare under ambient conditions, and the mechanistic origin of anomalous photoluminescence in this class of perovskite is still speculative. Here, we demonstrate that solution-grown $(PA)_2FAPb_2I_7$ single
crystals develop an inadvertent moiré superlattice through pseudo-merohedral twinning, driven by hybrid improper ferroelectricity in which trilinear mode coupling between two primary zone-boundary modes ($X_2^+$ and $X_3^-$) and a secondary $\Gamma_4^-$ polar displacement simultaneously breaks inversion
symmetry and imposes a ca. 5.17{\deg} rotational misalignment between adjacent layers. This
symmetry breaking activates one of the highest piezoelectric coefficients $d_{33}$ (ca. 20 pm/V) reported among 2D perovskites. This misalignment generates a moiré superlattice that undergoes a thermally driven commensurate-incommensurate transition, switching between a periodic confinement potential that quantizes
excitons into an equidistant photoluminescence ladder at 123 K and a disordered incommensurate phase with broadened emission at 298 K. These emissions are attributed to moiré-confined
excitons, resolving a longstanding debate on anomalous secondary photoluminescence in layered 2D perovskites and opening pathways to twistronics, photoferroelectrics and piezo-optoelectronic devices.
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All authors Sanika S. Padelkar, Sharidya Rahman, Mattia Belotti, Naufan Nurrosyid, Craig Forsyth, Alasdair Mckay, Tam Nguyen, Thi Vu Mung, Lan Nguyen, Naeimeh Mozaffari, Alexandr N. Simonov, Aftab Alam, Jacek J. Jasieniak
Materials Science
Phonon Interactions in Metal Halide Perovskites elucidated by Raman Scattering
Alejandro R. Goñi
There is a growing consensus that the exceptional optoelectronic properties of metal halide perovskites (MHPs) are largely due to the peculiar interplay between the inorganic cage
lattice, composed of a labile network of corner-sharing metal halide octahedra, and the A-site cationic sublattice. This interaction significantly affects the vibrational spectrum of MHPs (
phonon frequencies, linewidths, and lifetimes), resulting from the effects of
lattice potential anharmonicity and/or static/dynamic disorder. Raman scattering is a suitable technique to probe
phonon interactions in solids, allowing for the in-situ characterization of chemical environments, revealing the nature of
lattice vibrations. In this perspective, the available experimental evidence of the aforementioned interplay will be reviewed with special emphasis on understanding Raman signatures depending on whether the coupling is principally mediated by hydrogen bonding or steric hindrance. The controversy about the origin of a strong Raman background, steeply rising towards zero Raman shift and called central peak, will be specifically addressed. This background signal, which is typically observed in the temperature range of stability of cubic and tetragonal phases when the A-site cation dynamics unfold, will be shown to be mostly due to disorder-induced second-order acoustic-
phonon Raman scattering. This interpretation receives support from other
semiconductor systems with nanoscale structural disorder, where the central Raman peak arises either from the vertical misalignment of Ge
quantum dots in multi-stack
heterostructures or from the interface roughness exhibited by short-period GaAs/AlAs superlattices. In this way, a unifying picture of
phonon interactions in MHPs and how they impact different Raman processes is provided, which is key to interpreting their Raman spectra.
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Materials Science · Cross-listed from cond-mat.mes-hall
Huge ultrafast spin Seebeck effect mediated by laser-excited superdiffusive magnon currents
Luca Mikadze, Peter M. Oppeneer and Markus Weißenhofer
Subpicosecond
laser excitation of
ferromagnetic metals induces strongly nonequilibrium dynamics involving scattering and transport of electrons,
phonons, and
magnons. Widely used theoretical approaches, such as the three-temperature model and
diffusion equations, are ill-suited to capture these processes on ultrafast timescales. Here, we present an ab initio-parameterized microscopic framework that incorporates nonthermal
magnon scattering and transport via the
quantum Boltzmann equation. We apply this approach to simulate ultrafast
laser-induced demagnetization in bcc Fe films. The model predicts an ultrafast
spin Seebeck effect, characterized by a strong burst of fast-moving magnonic
spin current reaching technologically relevant amplitudes. Furthermore, we identify a superdiffusive transport regime: a crossover from initially ballistic
magnon transport to a diffusive regime at later times. To connect our theoretical predictions to experimentally accessible observables, we calculate the magneto-optical Kerr angles resulting from the predicted depth-resolved magnetization profiles. Our framework provides a route to describe ultrafast nonthermal
magnon transport beyond diffusive models and will aid in the design and interpretation of time-resolved
spin-transport experiments.
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Materials Science
Pulse-Driven Reconfiguration of Fractional Polar Topology in Zr-Substituted Barium Titanate
Florian Mayer
Polar topological textures in ferroelectrics can host internal structure beyond a single integer topological charge. Here, effective-
Hamiltonian molecular-dynamics simulations are used to examine whether such internal fractional
topology can be reconfigured by local electric excitation in ordered 12.5% Zr-substituted barium titanate. Chemical doubling along the polar axis stabilizes a coupled nanodomain texture consisting of alternating Q = -2 antiskyrmionic and Q = +4 skyrmionic slices, in which the local topological charge fragments into six -1/3 and six +2/3 localized contributions, denoted here as topological
quarks, separated by Bloch-point-like singular conversion regions. Picosecond local electric-field pulses applied to selected
vortex-core columns drive reconfiguration of the internal dipolar texture of a 2.6 nm nanodomain. Under a binary pulse-mask protocol addressing the six
vortex cores, all 64 masks lead, within the chosen low-temperature simulation protocol, to distinct relaxed metastable configurations. The switching calculations are performed in a cryogenic regime, and the programmed states remain stable over at least 1 ns of field-free
evolution on the simulation timescale. The resulting configurations are distinguishable both by sector-resolved topological fingerprints and by their real-space polarization fields. These results provide a computational proof of concept that fractional polar
topology in a ferroelectric nanodomain can be locally reconfigured by ultrafast electric excitation and used as a multistate configurational degree of freedom in an idealized low-temperature setting.
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Materials Science
Ultra-Confinement of Polaritons in Single Atomic Layer Ag Photonic Quantum Dots
Xinyi Li, Tetyana Ignatova, Chengye Dong et al. (+8 more)
Light scattering by two-dimensional (2D) van der Waals
heterostructures (vdWHs) is immense, especially given their infinitesimal volume, thus enabling strong light-matter interactions. Surface 2D polariton waves manifest through large concentration of electromagnetic field in vertical direction, normal to their propagation. By confining vdWH materials into 2D photonic shapes, one can manipulate and compress light in lateral directions. Scattering-type scanning near-field optical microscopy is a perfect tool for direct imaging of the propagating polaritons and studying the properties of confined polaritons in nanostructures. Though, thus far the quantitative analysis, such the wavelength extraction, has been challenged for confined polaritons by incapability of mapping of the wave period on sub-wavelength scale and difficulty of identifying an adequate substrate's "background" to subtract. Here, an analytical approach is developed to reveal the local propagation constant of confined polaritons under abovementioned constraints and map it with the sub-wavelength resolution. Applied to analysis of the SiC/2D-Ag/EG (epitaxial
graphene) photonic nanostructures, the technique uncovered that the polaritons are highly confined in both vertical ($\sim\lambda$/50) and lateral directions ($\sim\lambda$/40) by 2D metal.
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All authors Xinyi Li, Tetyana Ignatova, Chengye Dong, Krishnan Mekkanamkulam Ananthanarayanan, Rinu Abraham Maniyara, Arpit Jain, Furkan Turker, Vinay Kammarchedu, Aida Ebrahimi, Joshua A. Robinson, Slava V. Rotkin
Materials Science
Occupation Dynamics of Floquet-Volkov States and Spectral Sum Rule
Xuanxi Cai, Changhua Bao, Benshu Fan et al. (+9 more)
Time-periodic light fields can dress electronic states in
quantum materials, forming Floquet states whose dynamic occupation determines transient material properties. Here by using time- and angle-resolved photoemission spectroscopy (TrARPES), we reveal the transient occupation of Floquet-Volkov states in two
semiconductors, black phosphorus and MoSe$_2$. While the occupation of the light-induced sidebands, directly reflected by TrARPES spectral weight, strongly depends on the driving field, we find that the total spectral weight obtained by summing up all sidebands is conserved upon below-gap driving. Our work provides critical insights into the Floquet population dynamics, which are essential for light-field tailoring of transient material properties.
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All authors Xuanxi Cai, Changhua Bao, Benshu Fan, Haoyuan Zhong, Fei Wang, Shaohua Zhou, Tianyun Lin, Hongyun Zhang, Pu Yu, Peizhe Tang, Wenhui Duan, Shuyun Zhou
Materials Science
Unconventional Magnetism: Symmetry Classification, Hybrid-parity and Unconstrained-parity Classes
Xun-Jiang Luo, Dan Li, Rui-Chun Xiao et al. (+4 more)
Unconventional magnetism has emerged as a transformative frontier in condensed matter physics. Such phases are characterized by substantial non-relativistic
spin splitting (NSS) in
symmetry-compensated magnets. They have been classified by the parity of their
spin textures under momentum inversion, leading to the paradigms of altermagnets (even-parity) and odd-parity magnets. However, the full
symmetry landscape remains largely unexplored. In this Letter, we present a systematic classification framework for unconventional magnetism based on the representation theory of the
spin textures and the associated parity properties. Within this framework, we predict two previously unidentified classes beyond the established pure-parity categories: hybrid-parity magnets (HPMs) and unconstrained-parity magnets (UPMs), where the
spin textures exhibit contrasting parities among their Cartesian components and the parity of the
spin textures is ill-defined, respectively. We derive universal
symmetry criteria that categorize HPMs into three distinct types. Importantly, by combining the
spin splitting characteristics of altermagnets and odd-parity magnets, HPMs can enable the coexistence of the
spin current and Edelstein effects. Taking FePO4 as an example, we perform first-principles calculations to demonstrate this coexistence. Finally, we discuss the potential applications of HPMs in spintronic devices. Our work provides a comprehensive
symmetry classification of unconventional magnetism and establishes HPMs as a promising platform for multi-functional spintronics.
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All authors Xun-Jiang Luo, Dan Li, Rui-Chun Xiao, Ding-Fu Shao, Lei Li, Mingliang Tian, Yugui Yao
Materials Science
Ferroelectric KNbO3 nanoplatelets for thermally driven pyrocatalytic hydrogen evolution and dye degradation
Salma Touili, Bouchra Asbani, Youness Hadouch et al. (+9 more)
Day- and night-induced thermal cycling offers a promising route for harvesting ambient thermal energy to drive sustainable hydrogen production and pollutant degradation. Pyroelectric materials enable this process by converting temperature fluctuations into surface charges capable of promoting catalytic water splitting and advanced oxidation reactions. In this work, we demonstrate efficient pyrocatalytic hydrogen
evolution and Rhodamine B (RhB) degradation using orthorhombic ferroelectric Potassium niobate (KNbO$_3$) nanoplatelets (KN-np). Under thermal cycling between 20 and 50 $^\circ$C, KN-np achieved a hydrogen yield of 680 $\mu$mol g$^{-1}$ after 30 thermal cycles, corresponding to an average hydrogen production rate of 22.67 $\mu$mol g$^{-1}$ per cycle. In addition, KN-np exhibited excellent pyrocatalytic activity toward RhB degradation, reaching 84% removal after only 16 thermal cycles with an apparent kinetic rate constant of 0.11 cycle$^{-1}$. The remarkable catalytic performance is attributed to the strong spontaneous polarization and excellent pyroelectric properties of the KNbO$_3$ nanoplatelets, which promote efficient charge generation and interfacial redox reactions. These findings highlight the potential of KNbO$_3$ nanostructures as efficient pyrocatalysts for clean hydrogen production and environmental remediation.
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All authors Salma Touili, Bouchra Asbani, Youness Hadouch, Mbarek Amjoud, Daoud Mezzane, Nejc Suban, Hana Ursic, Nitul S. Rajput, Zdravko Kutnjak, Brigita Rozic, Mustapha Jouiad, Mimoun El Marssi
Materials Science · Cross-listed from cond-mat.mes-hall
Designing Magnetic Topological Insulator Trilayers for Highly-Efficient Spin-Orbit Torque Switching
Ling-Jie Zhou, Deyi Zhuo, Han Tay et al. (+5 more)
Spin-orbit torque (SOT) enables efficient electrical control of magnetization, offering a pathway towards low-power spintronic devices.
Magnetic topological
insulators (TIs), with
spin-momentum-locked surface states and intrinsic ferromagnetism, provide a unique platform for realizing SOT switching of edge current chirality in
quantum anomalous
Hall (QAH)
insulators. In this work, we employ molecular beam epitaxy to synthesize a series of
magnetic TI trilayers with controlled layer thicknesses on heat-treated SrTiO3(111) substrates. Electrical transport measurements reveal that SOT-driven magnetization reversal and the associated switching of edge current chirality are governed by the SrTiO3(111) substrate-induced charging effect, which generates an asymmetric chemical-potential
alignment between the top and bottom
magnetic TI layers. Furthermore, we demonstrate that the switching polarity and efficiency can be tuned through
heterostructure design, gate voltage, and in-plane
magnetic field, consistent with SOT
symmetry. These findings identify chemical potential asymmetry as the origin of the large SOT switching ratio in
magnetic TI trilayers and establish a route for electrical control of edge current chirality in QAH
insulators. This work advances the understanding of SOT switching mechanism in
magnetic topological materials and paves the way for next-generation, energy-efficient QAH-based logic and
memory devices.
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All authors Ling-Jie Zhou, Deyi Zhuo, Han Tay, Zi-Jie Yan, Pu Xiao, Xiaoda Liu, Bomin Zhang, Cui-Zu Chang
Materials Science · Cross-listed from cond-mat.mes-hall
Deyi Zhuo, Han Tay and Cui-Zu Chang
Magnetic topological
insulators (TIs) provide a highly tunable platform for engineering
quantum states that emerge from the interplay between
topology and magnetism. In this review article, we summarize experimental progress over the past decade in designing
magnetic TI multilayers by molecular beam epitaxy (MBE). By treating magnetically doped and undoped TI layers as topological Legos, we discuss how layer thickness,
magnetic doping,
heterostructure architecture, and stacking sequence can be used to control
magnetic exchange gaps, interlayer coupling, and the Chern number C with atomic-layer precision. We first briefly review the realization of the C = 1
quantum anomalous
Hall (QAH) effect in uniformly Cr-doped (Bi,Sb)2Te3 films in 2013 and uniformly V-doped (Bi,Sb)2Te3 films in 2015. We then discuss how Cr-doped and undoped (Bi,Sb)2Te3 layers can be combined to realize the C = 1 QAH effect in magnetically modulation-doped trilayers, including its extension into the three-dimensional (3D) regime. Next, we review the development of high-C QAH states, engineered plateau phase transitions, mesoscopic QAH devices, and electrical switching of
chiral edge-current chirality. Finally, we discuss the realizations of
axion insulator and C = 1/2 parity anomaly states in asymmetric
magnetic TI trilayers. These advances establish
magnetic TI multilayers as a versatile materials platform for creating new designer
quantum states, including synthetic Weyl semimetal and QAH metal phases, and for probing the topological magnetoelectric effect in thick
axion insulators and 3D QAH
insulators.
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Materials Science
Role of Bi3+ ion substitution on the piezocatalytic degradation performance of lead-free BaTi0.89Sn0.11O3 at low vibrational energy
Salma Touili, Sara Ghazi, Mbarek Amjoud et al. (+5 more)
Harnessing low ultrasonic vibration energy to drive piezocatalytic reactions has attracted increasing
attention in response to current environmental and energy challenges. In this study, we investigate the effect of heterovalent bismuth doping on the piezocatalytic degradation of Rhodamine B (RhB) under low-power ultrasonic excitation. Bismuth ions (Bi$^{3+}$) were substituted into the lead-free ferroelectric BaTi${0.89}$Sn${0.11}$O$_3$, yielding BTSn11-xBi with x = 0, 0.02, and 0.04. The powders were synthesized by the sol-gel method as submicron cubes. The structural, morphological, optical, and piezocatalytic properties were strongly influenced by the Bi content. Compared with pristine BTSn11 and BTSn11-0.04Bi, the BTSn11-0.02Bi sample exhibited the lowest band gap (3.22 eV), the smallest particle size (283 nm), the highest piezoelectric current (approximately 8 microA cm$^{-2}$), and the lowest coercive field required to obtain piezoresponse force microscopy hysteresis loops. As a result, BTSn11-0.02Bi showed the highest RhB degradation efficiency and the largest apparent kinetic rate constant, confirming its superior piezocatalytic performance. Total organic carbon measurements revealed significant mineralization of RhB. In addition, BTSn11-0.02Bi demonstrated good reusability and stability, maintaining high degradation efficiency over three consecutive cycles. These results highlight the potential of Bi-doped BTSn11 ferroelectric materials, particularly BTSn11-0.02Bi, as efficient piezocatalysts for environmental remediation.
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All authors Salma Touili, Sara Ghazi, Mbarek Amjoud, Daoud Mezzane Hana Ursic, Zdravko Kutnjak, Bouchra Asbani, Mustapha Jouiad, And Mimoun El Marssi
Materials Science
Ligand-mediated Origin of Altermagnetic Spin-Splitting
Luigi Camerano, Federico Bisti and Gianni Profeta
Altermagnets host
spin-split electronic bands despite zero net magnetization, opening new routes for spintronics beyond conventional ferromagnets. Going beyond
symmetry-based classifications, which specify allowed terms but not their hierarchy, here we use first-principles calculations and Wannier
Hamiltonian engineering to uncover the microscopic bonding contributions of altermagnetic
spin splitting in the $g$-wave altermagnet Co$_{1/4}$NbSe$_2$. We show that the splitting is captured by a short-range tight-binding model, establishing its local origin. By selectively controlling hopping channels, we demonstrate that the dominant contribution arises not from direct
magnetic-ion hopping, but from ligand-mediated hybridization that transfers anisotropy to itinerant states. This identifies ligand-assisted coupling as the key mechanism of altermagnetic
spin splitting and provides a microscopic bridge between minimal models and
symmetry guided first-principles material searches, enabling real-space design of altermagnetic functionality.
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Materials Science
Shear-Mode Raman Imaging of Ferroelectric Switching in Multilayer 3$R$-MoS$_2$
Yulu Liu, Kenji Watanabe, Takashi Taniguchi et al. (+1 more)
We use shear-mode Raman imaging to track ferroelectric switching in multilayer 3$R$-MoS$_2$. Within a single flake, mechanically segmented regions respond independently and follow distinct pathways. Partially polarized end states indicate that domain walls can reside between selected layer pairs, producing partial stacking transformations. The dwell time of intermediate states varies widely, indicating that pinning sites strongly influence the dynamics. Second-harmonic generation measurements further reveal three characteristic sample-boundary and domain-wall orientations, including a prevalent
chiral direction near the zigzag-armchair bisector. These results provide a direct, noninvasive view of domain-wall-mediated switching in a prototypical sliding ferroelectric and identify pinning and exfoliation-created boundaries as key factors governing its dynamics.
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All authors Yulu Liu, Kenji Watanabe, Takashi Taniguchi, Xiaoxiang Xi
Materials Science
Oxygen-Pressure-Limited Recovery of the Hematite {\alpha}-Fe$_2$O$_3$(0001) Surface from a Reduced Fe$_3$O$_4$(111)-Like Layer
Nishant Kumar, Matthias Blatnik and Jan Čechal
The oxidation kinetics of hematite {\alpha}-Fe$_2$O$_3$(0001) surfaces are vital for its applications in catalysis, environmental remediation, and industrial processes. Despite prior studies, the roles of temperature, oxygen partial pressure, and oxygen chemical potential in controlling nucleation and growth kinetics are not fully understood. Using real-time Low Energy Electron Microscopy/Diffraction (LEEM/LEED), we systematically investigate the oxidation of a reduced Fe$_3$O$_4$(111)-like surface layer to hematite under controlled conditions. We show that complete recovery of the hematite surface termination is closely linked to the nucleation and lateral growth of a two-dimensional honeycomb (H) phase. While higher temperatures accelerate nucleation, they slow lateral growth at constant oxygen pressure, indicating that oxygen supply limits the oxidation rate. Below an oxygen partial pressure threshold (~2$\times$10$^{-6}$ mbar), growth dramatically slows, underscoring the critical role of oxygen availability. Below a certain oxygen pressure threshold, the growth time rapidly increases. Our study elucidates the interplay between thermodynamics and kinetics in hematite surface oxidation, informing strategies to optimize surface properties for catalytic and industrial processes.
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Materials Science
Observation of spin-free interatomic orbital angular momentum in a chiral crystal
Dongjin Oh, Sungsoo Hahn, Chiara Pacella et al. (+4 more)
The inherent
spin-orbit interaction of electrons inevitably couples
spin to the orbital angular momentum (OAM), posing a fundamental challenge to
spin-free orbital transport. Here, we propose a novel strategy to achieve
spin-decoupled OAM states in crystalline solids. Using angle-resolved photoemission spectroscopy (ARPES), we resolve well-isolated s-orbital bands in a
chiral Te
crystal, clearly separated from the p-orbital
manifold. Combined circular dichroism ARPES and first-principles calculations reveal that these bands host OAM arising exclusively from interatomic hopping, with no intra-atomic contribution.
Spin-resolved ARPES further confirms the absence of
spin angular momentum (SAM), providing decisive evidence of
spin-free OAM states. These findings establish the existence of OAM without
spin polarization in crystalline solids and highlight the essential role of inter-atomic OAM. This work provides a general framework for designing spinless OAM states, opening an opportunity toward pure orbital currents for orbitronics.
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All authors Dongjin Oh, Sungsoo Hahn, Chiara Pacella, Junseo Yoo, Angel Rubio, Domenico Di Sante, Changyoung Kim
Materials Science · Cross-listed from cond-mat.str-el
Magnetism of single crystalline breathing pyrochlore spinel AgInCr4S8
Andrew F. May, Christopher M. Pasco, V. O. Garlea et al. (+5 more)
Single
crystals of \ce{AgInCr4S8} were grown by chemical vapor transport and crystallographic ordering of Ag/In that results in a breathing pyrochlore motif of Cr$^{3+}$ was verified by x-ray and
neutron diffraction. Long-range
antiferromagnetic order is observed below a Néel temperature of $T_{\mathrm N}$ $\approx$ 9.6 K. The
magnetic properties are characterized using ac and dc magnetization, specific heat capacity, and single
crystal neutron diffraction measurements. The specific heat data are characterized by a small lambda anomaly near 9.5 K and the estimated
magnetic entropy reaches $\approx$ $\frac{1}{3}$ of the expected value by 3$T_{\mathrm N}$, suggesting significant short-range order in the paramagnetic phase. Single
crystal neutron diffraction evidences an incommensurate
spin structure with propagation vector $\textbf{\textit{k}}$ = (0,0,$\delta$) and $\delta$ = 0.343 at 5 K. The minimal model that accounts for the data consists of
ferromagnetic layers of Cr atoms, with
magnetic moments lying in the plane of the layers and modulating in the perpendicular direction to form a helical structure propagating along $\textbf{\textit{k}}$. This study represents a rare investigation of single
crystals within the family of breathing pyrochlore materials.
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All authors Andrew F. May, Christopher M. Pasco, V. O. Garlea, Karolina Gornicka, Matthias D. Frontzek, Xiaoping Wang, Pyeongjae Park, Andrew D. Christianson
Materials Science · Cross-listed from quant-ph
Towards transistor-based quantum computing
Y.-D. Liu, X. Xu, Q.-R. Wang et al. (+1 more)
In this work, we propose and study in depth a universal
quantum computing architecture based on a
quantum construction of transistors. Our teleportation-based
quantum transistors, called “telesistors”, are ground states of systems with
symmetry-protected topological order, hence suppress certain noises and provide high-fidelity Clifford gates without the need for active error correction. This physical protection, quantified by the string order parameters, serves as a low-overhead foundation upon which conventional fault-tolerant encoding (e.g., with stabilizer codes) can be built to achieve universal
quantum computation. This architecture shows rich connections with current known architectures, and some desirable merits especially compared with the
qubit-based
circuits regarding modularity, integration, and program storage. Our study shows that it is plausible to realize it with current technology in the near future.
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All authors Y.-D. Liu, X. Xu, Q.-R. Wang, D.-S. Wang
Materials Science
Efficient purely organic phosphorescent emitters for programmable luminescent tags: from building blocks to donor-acceptor-donor structures
Uliana Tsiko, Sebastian Kaiser, Jannis Fidelius et al. (+4 more)
Purely organic room-temperature phosphorescence (RTP) emitters are key components of programmable luminescent tags (PLTs), photonic devices for rewritable information storage and UV dosimetry. In this work, we systematically explore the design space of donor-acceptor and donor-acceptor-donor organic phosphorescent emitters in symmetric and asymmetric architectures. Phenoxathiine (PX) is introduced as an alternative donor to thianthrene (TA), combined with benzophenone (BP) or pyridine (Py) as acceptors. Through photophysical characterization,
quantum chemical simulations, and PLT device testing, we identify structure-property relationships and, in particular, investigate the impact of the individual moieties on the emission properties and stability. The RTP emission wavelength is primarily tunable through the donor moiety: PX-based emitters emit sky-blue ({\lambda}_P = 480 nm), while TA-based emitters emit in the green ({\lambda}_P = 520 nm) due to an increased Stokes shift. The acceptor unit strongly influences the phosphorescence
quantum yield, with Py-based emitters systematically outperforming BP-based ones. All newly synthesized PX-containing emitters show sufficient performance in PLT devices, though with reduced photostability compared to TA-based counterparts. Together, these results demonstrate that systematic donor-acceptor design enables predictable control over RTP emission properties, advancing the rational development of high-performance RTP-based photonic devices.
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All authors Uliana Tsiko, Sebastian Kaiser, Jannis Fidelius, Tim Achenbach, Jan J. Weigand, Sebastian Reineke, Karl Sebastian Schellhammer
Materials Science · Cross-listed from physics.optics
A Universal Magnetoelectric Limit for Chiral and Tellegen Bi-Isotropic Scatterers
Jorge Olmos-Trigo
We reveal the existence of a universal upper bound on the magnetoelectric coupling of any bi-isotropic nanoparticle. The bound arises solely from energy conservation, making it independent of the specific material properties of the nanoparticle and illumination conditions. Moreover, the bound does not rely on reciprocity, being identical for reciprocal (
chiral) and non-reciprocal (Tellegen) nanoparticles. We further show that the
chiral Mie coefficient of spherical particles of arbitrary optical size obeys the same bound across all multipolar scattering channels. Our results introduce a universal metric on the magnetoelectric coupling of bi-isotropic objects, setting identical limits on
chiral and Tellegen light-matter interactions at the single particle level.
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Materials Science
Attached Split Ring Resonator Cavity for Magnon Photon Coupling
Aram Akoi, Liubov Ivzhenko and Maciej Krawczyk
We present a chip scale planar cavity platform based on an attached split ring resonator (ASRR) integrated with yttrium iron garnet (YIG) structures to achieve strong
magnon photon coupling in a compact hybrid system. The ASRR geometry was numerically optimized by tuning inter ring spacing, gap width, substrate thickness, and permittivity, resulting in a quality factor of Q = 190 at 5.48 GHz, enabling strong microwave
magnetic field confinement and reduced radiative losses. The optimized cavity was coupled to YIG elements of three geometries: full ring, half ring, and disk. Full electromagnetic simulations show that the full ring geometry exhibits balanced performance with coupling strength 115 MHz and cooperativity 13.10, while the half ring shows a comparable coupling strength of 108 MHz and slightly higher cooperativity 13.50, despite edge induced demagnetizing effects. In contrast, the disk geometry couples at lower bias
magnetic fields and achieves the strongest interaction (135 MHz, 25.30), enabled by improved microwave
magnetic field overlap. These results demonstrate that geometry, rather than
magnetic volume alone, is a key design parameter for tailoring
magnon photon coupling, providing a practical framework for lithography compatible, on chip hybrid magnonic and
quantum devices.
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Materials Science
Multiferroic Properties of Electrospun CFO-BCTSn Nanocomposites for Magnetoelectric and Magnetic Field Sensing Applications
Youness Hadouch, Nayad Abdallah, Daoud Mezzane et al. (+11 more)
Multiferroic CFO-BCTSn composite nanofibers were synthesized using a sol-gel electrospinning method. Electron microscopy revealed well-defined fibers with diameters of 120-150 nm. Structural analyses using X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy confirmed the coexistence of the spinel CFO phase and the perovskite BCTSn phase without detectable secondary phases.
Magnetic hysteresis measurements demonstrated the
magnetic behavior of the nanofibers, while piezoresponse force microscopy confirmed their piezoelectric properties. Magnetoelectric coupling was evidenced by differences between the
magnetic hysteresis loops of electrically poled and unpoled samples. These lead-free composite nanofibers show potential for nanoscale magnetoelectric devices and
magnetic field sensing applications.
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All authors Youness Hadouch, Nayad Abdallah, Daoud Mezzane, Mbarek Amjoud, Voicu Dolocan, Khalid Hoummada, Nikola Novak, Anna Razumnaya, Brigita Rozic, Val Fisinger, Hana Ursic, Valentin Laguta, Zdravko Kutnjak, Mimoun El Marssi
Materials Science · Cross-listed from cond-mat.str-el
Hubbard-$U$-corrected electron-phonon interactions in strongly correlated materials via the finite-displacement method
Jiale Chen, Youyou Tu, Chengliang Xia et al. (+2 more)
Although the density functional theory plus Hubbard $U$ correction method (DFT+$U$) is broadly used to study electronic structure of strongly correlated materials, the extension of this method to electron-
phonon $g$
matrices has received limited
attention. Here, we implement an
algorithm that integrates DFT+$U$ method with the finite-displacement method for the calculations of
phonons and electron-
phonon $g$
matrices. The Hubbard $U$ corrections are applied not only to electronic and
phonon structures, but, more importantly, also to electron-
phonon $g$
matrices. We demonstrate our
algorithm in two prototypical correlated materials: infinite-layer nickelates LaNiO$_2$ and ruthenium dioxide RuO$_2$. We find that: i) While the Hubbard $U$ corrections weakly increase the electron-
phonon interaction of 20% hole-doped LaNiO$_2$, its total electron-
phonon coupling remains small and is insufficient to account for the observed superconducting transition temperature of about 10-30 K. Our results contrast with the recent work showing that the full GW corrections yield an elevated electron-
phonon coupling of 20% hole-doped LaNiO$_2$ five times larger than its DFT value. We attribute this discrepancy to the differences in the
Fermi surface
topology between DFT+$U$ and GW methods. ii) The inclusion of Hubbard $U$ corrections eliminates the imaginary
phonon modes of RuO$_2$ under strain on the TiO$_2$ substrate and substantially reduces the electron-
phonon coupling. Our results alleviate the discrepancy between the reported large theoretical electron-
phonon coupling and the low superconducting transition temperature observed experimentally. Our work provides an
algorithm that fully includes the Hubbard $U$ corrections on electron-
phonon properties of correlated materials, and highlights the importance of
Fermi surface shape and correlation effects on
phonon spectrum and electron-
phonon $g$
matrices.
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All authors Jiale Chen, Youyou Tu, Chengliang Xia, Jin Zhao, Hanghui Chen
Materials Science
In-Plane Ferromagnetism and Critical Dynamics in Alkali-Deficient K$_{1-x}$CrTe$_2$ (with $x \approx$ 0.3) Single Crystals
Catherine Witteveen, Felix Eder, Sara A. López-Paz et al. (+6 more)
Layered chromium tellurides are model systems for studying low-dimensional magnetism in van der Waals materials. We report the synthesis and characterization of K$_{1-x}$CrTe$_2$ single
crystals ($x \approx 0.3$), which crystallize in the $Cm$ space group with trigonal prismatic K$^+$ coordination, unlike the octahedral environments of more stoichiometric ACrX$_2$ compounds. Magnetization measurements show a sharp
ferromagnetic transition at $T_{\rm C}=117$ K and in-plane
magnetic anisotropy, supported by density functional theory.
Neutron diffraction reveals
ferromagnetic alignment of Cr
spins within and between layers. This contrasts with the out-of-plane A-type antiferromagnetism in LiCrTe$_2$ and NaCrTe$_2$, but resembles CrTe$_2$. These differences likely arise from changes in interlayer spacing, Cr oxidation state, or stacking. AC susceptibility and $\mu$SR indicate short-range order above $T_{\rm C}$ and dynamic behavior below. Overall, K$_{1-x}$CrTe$_2$ provides a tunable platform for studying
spin orientation and dimensionality in two-dimensional magnets.
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All authors Catherine Witteveen, Felix Eder, Sara A. López-Paz, Vladimir Pomjakushin, Jonas A. Krieger, Zurab Guguchia, Harald O. Jeschke, Martin Månsson, Fabian O. von Rohr
Materials Science
High-performance linear-scaling electronic structure method via chromatic superposition states
Zhikang Jiang, Zhizhi Xiao, Mingfa Tang et al. (+4 more)
We introduce a high-performance linear-scaling electronic structure method that employs chromatic superposition states (CSS) as a low-dimensional, high-fidelity representation, which can be orders of magnitude smaller than the full
Hilbert space. Grounded in the system's finite correlation length, the CSS representation aggregates the uncorrelated orbitals into a single basis via a graph-coloring scheme, and is independent of the system size yet accurately preserves all sparse operators in solving the Kohn-Sham equations. The projection onto CSSs is efficiently computed by employing the block-Lanczos Krylov method which features high hardware efficiency and linear-scaling cost, enabling fast calculation of large-scale Kohn-Sham density
matrix. We show that this method already outperforms previous linear-scaling density
matrix purification method by more than one order of magnitude in computational speed at even small scale, while preserving high accuracy. The practical utility of the CSS method is demonstrated through molecular dynamics simulation of a 10000 $H_2O$, and self-consistent calculation of a 1-million $H_2O$ with modest resources.
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All authors Zhikang Jiang, Zhizhi Xiao, Mingfa Tang, Weiyu Li, Zhaoru Sun, Ke Xia, Youqi Ke
Materials Science
Topological phononics
Zeguo Chen, Tiantian Zhang, Xulong Wang et al. (+12 more)
Topological phononics extends the foundational concepts of topological condensed matter physics to the realm of
lattice vibrations and classical mechanical waves, unlocking robust, defect-immune states and phenomena beyond the reach of conventional phononic engineering. This review provides a unified, systematic framework for understanding topological
phonons across natural and artificial systems, spanning solid-state materials, acoustic/mechanical metamaterials, and non-Hermitian platforms. We cover the core theoretical principles – from Berry
curvature and
symmetry-protected topological invariants to bulk-boundary correspondence – alongside experimental advances in probing topological
phonon states via inelastic scattering and momentum-resolved techniques for solid-state
phonons as well as pump-probe measurements in acoustic/mechanical metamaterials. Key topics include Weyl/Dirac/nodal-line
phonons in crystalline solids,
symmetry-engineered topological phases in metamaterials, non-Hermitian effects (exceptional points, skin effect), and emergent directions such as Floquet engineering, synthetic dimensions, and real-space topological textures (skyrmions, merons). We also highlight technological applications in robust waveguides, on-chip surface-acoustic-wave devices, and acoustofluidics, while outlining future challenges and opportunities in
quantum phononics, nonlinear topological phenomena, and interdisciplinary integration with photonics and electronics. This review serves as a comprehensive guide across physics, materials science, and engineering, bridging fundamental theory with cutting-edge experiments and innovations in topological phononics.
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All authors Zeguo Chen, Tiantian Zhang, Xulong Wang, Jiangxu Li, Zhi-Kang Lin, Feng Gao, Li-Wei Wang, Yizhou Liu, Qi Wang, Xiujuan Zhang, Guancong Ma, Xingqiu Chen, Minghui Lu, Yanfeng Chen, Jian-Hua Jiang
Materials Science
Transferable 3D Convolutional Neural Networks for Elastic Constants Prediction in Nanoporous Metals
Sergei Zorkaltsev, Rafał Topolnicki, Tal-El Carmon et al. (+4 more)
The
topology of nanoporous metals is crucial for determining their mechanical response. In this work, we generated 6,000 gold and 422 silver nanoporous structures and calculated three components of elastic modulus with Molecular Dynamics simulations, resulting in 19,263 data points. This study compared two distinct approaches of predicting elastic modulus: a Fully-Connected neural network trained on precomputed topological descriptors, and several 3D Convolutional neural network architectures adapted from computer
vision. The 3D CNNs outperformed the descriptor-based baseline model ($R^2 = 0.704$), with to-performing DenseNet-201 architecture achieving $R^2 = 0.955$. Additionally, the effects of training grid resolution,
dataset size, and descriptor integration into a model were investigated. We further demonstrated model robustness through Transfer learning: a pretrained model was fine-tuned on a much smaller
dataset of denser gold structures and the
dataset of denser silver structures. Finally, the trained model was employed to evaluate the mechanical properties of 100,000
stochastic nanoporous gold structures and identify the Pareto optimal designs.
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All authors Sergei Zorkaltsev, Rafał Topolnicki, Tal-El Carmon, Santhosh Mathesan, Paweł Dłotko, Dan Mordehai, Maciej Harańczyk
Materials Science · Cross-listed from math.OC
Polynomial diagrams for microstructure modelling
David P. Bourne, Maciej Buze, Thomas Gallouët et al. (+1 more)
We formulate a framework of
polynomial diagrams, which are a generalisation of power diagrams (PDs) and anisotropic power diagrams (APDs) allowing for boundaries between
cells to be algebraic curves of a prescribed degree. We show that they arise naturally from rephrasing PDs (APDs) as first-degree (second-degree) instances of linear parametrised minimisation diagrams. We also develop an efficient GPU-accelerated framework for fitting
polynomial diagrams to image data using Legendre
polynomials and by maximising a regularised concave objective function adapted from classical logistic regression literature. A largely self-contained analysis of the optimisation
algorithm is also provided, including identification of scale and gauge invariances and the limiting objective function as the regularisation parameter vanishes. We apply the
algorithm to fit
polynomial diagrams to electron backscatter diffraction images of steel.
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All authors David P. Bourne, Maciej Buze, Thomas Gallouët, Quentin Mérigot
Materials Science
Anisotropic Crystallization Kinetics and Interfacial Dynamics of Phase-Change Material Sb$_2$S$_3$ from Machine Learning Force Field Simulations
Souvik Chakraborty, Wen-Qing Li and Yun Liu
The phase-change material antimony sulfide (Sb$_2$S$_3$) relies on rapid and reversible phase transitions between crystalline and amorphous states, which are critical for their performance in data storage and photonics applications. In this work, a machine learning force field is developed based on the moment tensor potential approach, allowing us to understand the atomistic origin of the structural
evolution and crystallization kinetics in Sb$_2$S$_3$ for the first time, by enabling large-scale molecular dynamics simulations (up to 7680 atoms for 40 ns). Sb$_2$S$_3$ shows anisotropic growth rates with the [100] facet exhibiting the fastest growth due to the strong Sb-S covalent bonding along its quasi-1D ribbon-like structure of its crystalline phase. The activation energy for
crystal growth is found to be 0.55-0.57 eV, whereas that for
diffusion is around 1.16-1.56 eV. The lower activation energy for
crystal growth indicates that its heterogeneous crystallization is interface controlled rather than
diffusion limited, unlike GST and GeTe with atomic attachment at the solid-
liquid interface being energetically favoured over long range atomic transport. These findings provide key insights into the structural, thermodynamic, and kinetic properties of Sb$_2$S$_3$, paving the way for optimizing its functionality including switching speed, reliability, and energy efficiency.
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