Materials Science
Thermal tuning of dynamic response in Ag-based nanowire networks
J.I. Diaz Schneider, C. Gomez, C. Acha et al. (+3 more)
Self-assembled networks of metallic nanowires (NWs) are being intensively explored as test benches for neuromorphic proposals. In this work, we study the electric transport properties of dense self-assembled networks of Ag-based NWs (AgNWNs) coated with a thin insulating layer, using DC and AC stimuli. The building blocks of this network are the metallic NWs and the NW-NW junctions, either metallic or memristive. In the pristine state, frequency independence of the impedance reveals an over-percolated purely resistive network. A combination of low-temperature annealing and AC stimulus is shown to drastically affect the resistivity of the sample (interpreted as a depopulation of purely metallic junctions), unveiling a rich dynamic response. This procedure triggers the achievement of a capacitive response, which is successfully rationalized using a previously introduced 'two junction model'. Thermal treatment appears to be an indirect strategy to effectively modify the humidity content at the NW-NW intersections and, consequently, enable multiple switching schemes suitable for
brain-like processing alternatives.
Read the full abstract ▾
All authors J.I. Diaz Schneider, C. Gomez, C. Acha, P.E. Levy, E.D. Martínez, C.P. Quinteros
Materials Science · Cross-listed from cs.CE
A Synthesizability-Guided Pipeline for Materials Discovery
Thorben Prein, Willis O'Leary, Aikaterini Flessa Savvidou et al. (+2 more)
Computational materials discovery relies on the generation of plausible
crystal structures. The plausibility is typically judged through density functional theory methods which, while typically accurate at zero Kelvin, often favor low-energy structures that are not experimentally accessible. We develop a combined compositional and structural synthesizability score which provides an accurate way of predicting which compounds can actually be synthesized in a laboratory. We use it to evaluate non-synthesized structures from the Materials Project, GNoME, and Alexandria, and identified several hundred highly synthesizable candidates. We then predict synthesis pathways, conduct corresponding experiments, and characterize the products across 16 targets, successfully synthesizing 7 of 16. The entire experimental process was completed in only three days. Our results highlight omissions in lists of known synthesized structures, deliver insights into the practical utility of current materials databases, and showcase the central role synthesizability prediction can play in materials discovery.
Read the full abstract ▾
All authors Thorben Prein, Willis O'Leary, Aikaterini Flessa Savvidou, Elchaïma Bourneix, Joonatan E. M. Laulainen
Materials Science
Excitons in moiré superlattices with disordered electrons
Junghwan Kim, Dinh Van Tuan and Hanan Dery
Moiré superlattices in transition metal dichalcogenides (TMDs) heterobilayers exhibit various correlated insulating states driven by long-range Coulomb interactions, and these states crucially alter
exciton resonances, particularly at fractional fillings. We revisit a theoretical framework to investigate the doping dependence of
exciton spectra by extending hydrogenic
exciton wavefunctions, systematically analyzing how the 1$s$, 2$s$, and 3$s$ Rydberg states respond to moiré-induced mixing of $s$- and $p$-type orbitals. Notably, while the 1$s$ state remains relatively robust against doping, higher Rydberg
excitons show strong
redshifts and oscillator-strength quenching near specific fractional fillings. We incorporate both defect-induced quasi-ordering and thermal fluctuations to capture realistic device conditions, employing a large supercell approach. By selectively randomizing a subset of electrons or utilizing classical Monte Carlo simulations, we present direct calculations of
exciton spectra under varying defect densities and temperatures. Our results emphasize how even moderate disorder or finite temperature can partially or completely suppress characteristic moiré
exciton physics. Especially, we show how the 2$s$
exciton states respond to the phase transition in correlated electron states. This comprehensive picture not only clarifies recent experimental observations but also provides a framework to guide the design of moiré-based optoelectronic devices.
Read the full abstract ▾
Materials Science
Comparison between first-principles supercell calculations of polarons and the ab initio polaron equations
Zhenbang Dai, Donghwan Kim, Jon Lafuente-Bartolome et al. (+1 more)
Polarons are composite quasiparticles formed by excess charges and the accompanying
lattice distortions in solids, and play a critical role in transport, optical, and catalytic properties of
semiconductors and
insulators. The standard approach for calculating polarons from first principles relies on density functional theory and periodic supercells. An alternative approach consists of recasting the calculation of polaron wavefunction,
lattice distortion, and energy as a coupled nonlinear
eigenvalue problem, using the band structure,
phonon dispersions, and the electron-
phonon matrix elements as obtained from density functional perturbation theory. Here, we revisit the formal connection between these two approaches, with an emphasis on the handling of self-interaction correction, and we establish a compact formal link between them. We perform a quantitative comparison of these methods for the case of small polarons in the prototypical
insulators TiO2, MgO, and LiF. We find that the polaron wavefunctions and
lattice distortions obtained from these methods are nearly indistinguishable in all cases, and the formation energies are in good (TiO2) to fair (MgO) agreement. We show that the residual deviations can be ascribed to the neglect of higher-order electron-
phonon couplings in the density functional perturbation theory approach.
Read the full abstract ▾
All authors Zhenbang Dai, Donghwan Kim, Jon Lafuente-Bartolome, Feliciano Giustino
Materials Science
Charge disproportionation driven polar magnetic metallic double-layered perovskite Sr$_3$Co$_2$O$_7$
Hong-Fei Huang, Houssam Sabri, Jiadong Zang et al. (+1 more)
Strong coupling among spontaneous structural symmetric breaking, magnetism and
metallicity in an intrinsic polar
magnetic metal can give rise to novel physical phenomena and holds great promise for applications in spintronics. Here, we elucidate the mechanism of metallic ferroelectricity in the recently discovered polar metal Sr$_3$Co$_2$O$_7$. Our first-principles calculations reveal that both the spontaneous ferroelectric displacements and the
metallicity originate from charge disproportionation of Co ions. This is characterized by an inverted ligand-field splitting of the Co $t_2g$ orbitals at one site, while the metallic behavior is preserved by the t$_2g$ orbitals at both sites. The charge disproportionation stabilizes the asymmetric phase Within the framework of the on-site Hubbard U interaction. We thus propose that in related transition metal
oxides, charge disproportionation within specific orbitals can concurrently drive
metallicity and ferroelectricity, enabling strong coupling between these properties. More remarkably, this mechanism allows for the coexistence of magnetism, as evidenced in Sr$_3$Co$_2$O$_7$. Our findings highlight a promising avenue for realizing polar
magnetic metals and provide a new design principle for exploring multifunctional materials.
Read the full abstract ▾
All authors Hong-Fei Huang, Houssam Sabri, Jiadong Zang, Jie-Xiang Yu
Materials Science
Intrinsic Nonlinear Planar Thermal Hall Effect
Chanchal K. Barman
We introduce the intrinsic nonlinear planar thermal
Hall effect (NPTHE)– a dissipationless thermal response proportional to $(\nabla T)^2B$, which arises when the temperature gradient $\nabla T$ and
magnetic field $\mathbf{B}$ lie within the same plane. The effect originates from a thermal gradient induced correction to the Berry
curvature, characterized by the thermal Berry connection polarizability (TBCP) tensor, leading to a nonlinear transverse heat current independent of scattering time. A
symmetry analysis shows that the intrinsic NPTHE is permitted only in noncentrosymmetric
crystal point groups lacking horizontal mirror
symmetry. Using a tilted Dirac model, we demonstrate that its characteristic angular dependence provides an effective means to control the nonlinear thermal response. Our results establish a new class of
quantum geometry driven intrinsic nonlinear thermal transport, offering both a sensitive probe of band geometry and a pathway toward nonlinear thermal functionalities in
quantum materials.
Read the full abstract ▾
Materials Science · Cross-listed from cond-mat.mes-hall
Unconventional relativistic spin polarization of electronic bands in an altermagnet
A. Dal Din, D.A. Usanov, L. Šmejkal et al. (+22 more)
Altermagnetism is a recently identified phase with a d, g or i-wave
spin symmetry of
magnetic ordering. Its discovery opens new research fronts at intersections of magnetism and spintronics with fields ranging from superconductivity to topological and relativistic
quantum physics. Here we demonstrate an unconventional relativistic
spin polarization in an altermagnet by
spin and angle resolved photoemission spectroscopy of electronic bands in single-domain MnTe. The relativistic
spin-orbit coupling origin is revealed by observing that the alternating momentum-dependent
spin polarization is orthogonal to the
magnetic-ordering vector. The collinearity, even-parity and time-reversal-odd nature of the demonstrated relativistic
spin polarization in the altermagnet is unparalleled in conventional forms of the relativistic
spin polarization. Our experimental results and methodology are supported by non-relativistic
spin-
symmetry and relativistic
magnetic-
symmetry analyses, and microscopic ab initio ground-state and photoemission theory.
Read the full abstract ▾
All authors A. Dal Din, D.A. Usanov, L. Šmejkal, S. W. D'Souza, F. Guo, O. J. Amin, E. M. Dawa, R. P. Campion, K. W. Edmonds, B. Kiraly, A. W. Rushforth, C. Polley, M. Leandersson, E. Golias, Y. Niu, S. Telkamp, F. Krizek, A. Birk Hellenes, J. Priessnitz, W. H. Campos, J. Krempaský, J. Minár, T. Jungwirth, J. H. Dil, P. Wadley
Materials Science · Cross-listed from cond-mat.mes-hall
Observation of Long-Lifetime Magnon Pairs by Fano Resonance of Photons
Qian-Nan Huang, Zhiping Xue and Tao Yu
Mode fluctuations with a long lifetime are essential for
quantum information and logic operations in magnonic devices. We probe the broadband nonlinear magnetization dynamics of a high-quality ferromagnet under a strong microwave drive using microwave spectroscopy. We observe an unexpected Fano resonance in the microwave transmission when the driven amplitude of the magnetization is large and the drive frequency $\omega_d$ is close to but not at the
ferromagnetic resonance. We interpret this Fano resonance by a scattering theory of
photons considering the three-
magnon interaction between the Kittel
magnon and
magnon pairs with opposite wave vectors of frequency $\omega_d/2$. The theoretical model suggests that the microwave spectroscopy measures the dynamics of the fluctuation $\delta \hat{\alpha}$ of the Kittel
magnon and $\delta\hat{\beta}_{\pm k}$ of the
magnon pairs over the driven steady states, which are coupled coherently by the steady-state amplitudes. With the damping of $\delta\hat{\beta}_{\pm k}$ much smaller than that of $\delta \hat{\alpha}$, the theoretical calculation well reproduces the observed Fano resonance, indicating the
magnon pairs hold a recorded long lifetime.
Read the full abstract ▾
Materials Science · Cross-listed from cond-mat.str-el
Is ruthenium dioxide altermagnet?
Alexander A. Tsirlin, Ece Uykur and Oleg Janson
Ruthenium dioxide was named as one of the first and most promising altermagnetic candidates with $d$-wave
symmetry. We summarize key findings for this material and critically discuss prospects of making it altermagnetic.
Materials Science · Cross-listed from physics.app-ph
Md. Anamul Hoque, Zoltán Kovács-Krausz, Bing Zhao et al. (+5 more)
Graphene is a promising platform for
spin-based non-volatile
memory, logic, and neuromorphic computing by combining long-distance
spin transport with electrical tunability at room temperature. However, advancing beyond passive
spin channels requires devices capable of generating large
spin signals with efficient rectification capabilities, which are essential for active spintronic components. Here, we demonstrate a folded-
bilayer graphene spin-valve device with
giant non-local
spin signals in the several mV range with pronounced
spin-rectification effects. Efficient
spin injection creates a significant
spin accumulation of 20 meV and generates a
spin diode effect with an asymmetry of over an order of magnitude between forward and reverse bias conditions. This
spin-diode effect is expected to arise from nonlinear
spin-charge interactions in the folded-
bilayer graphene channel. These observed large
spin signals and
spin-diode effects in
graphene systems offer a promising platform for developing active two-dimensional spintronic devices.
Read the full abstract ▾
All authors Md. Anamul Hoque, Zoltán Kovács-Krausz, Bing Zhao, Prasanna Rout, Ivan Vera Marun, Szabolcs Csonka, Péter Makk, Saroj P. Dash
Materials Science · Cross-listed from cond-mat.mes-hall
High-temperature superconducting Majorana fermions platforms in the layered Kitaev Materials: Case study of $Li_2IrO_3$
Elnaz Rostampour and Badie Ghavami
Recent advances in Kitaev materials have highlighted their potential to host Majorana
fermions without or high-temperature of superconductivity. In this research, we propose $Li_2IrO_3$ as a promising High-temperature superconducting platform supporting Majorana edge modes due to its strong
spin-orbit coupling, honeycomb
lattice structure, and proximity to a
quantum spin liquid (QSL) phase. A theoretical and numerical framework based on the Kitaev-Heisenberg
Hamiltonian is developed to model
spin interactions in $Li_2IrO_3$. Here, the existence of topological zero-energy states is demonstrated, and their signatures in the edge-localized spectral weight are identified. A device concept based on this material is also proposed with potential industrial applications in spintronics,
magnetic field sensing, and topological
quantum memory.
Read the full abstract ▾
Materials Science
Predictive quantum vibrational spectra through active learning 4G-NNPs
Md Omar Faruque, Dil K. Limbu, Nathan London et al. (+1 more)
Predictive simulation of vibrational spectra of complex condensed-phase and interface systems with thousands of degrees of freedom has long been a challenging task of modern condensed matter theory. In this work, fourth-generation high-dimensional committee neural network potentials (4G-HDCNNPs) are developed using active learning and query-by-committee, and introduced to the essential
nuclear quantum effects (NQEs) as well as conformational
entropy and anharmonicities from path integral (PI) molecular dynamics simulations. Using representative bulk water and air-water interface test cases, we demonstrate the accuracy of the developed framework in infrared spectral simulations. Specifically, by seamlessly integrating non-local charge transfer effects from 4G-HDCNNPs with the NQEs from PI methods, our introduced methodology yields accurate infrared spectra using predicted charges from the 4G-HDCNNP architecture without explicit training of dipole moments. The framework introduced in this work is simple and general, offering a practical paradigm for predictive spectral simulations of complex condensed phases and interfaces, free from empirical parameterizations and ad hoc fitting.
Read the full abstract ▾
All authors Md Omar Faruque, Dil K. Limbu, Nathan London, Mohammad R. Momeni
Materials Science · Cross-listed from cond-mat.stat-mech
Explosive connectivity and mechanical rigidity in cubic lattice structures
Trenton Lau and Gary P. T. Choi
We study explosive connectivity and mechanical
rigidity in three-dimensional cubic
lattice structures under Achlioptas-type product-rule dynamics. Our work combines extensive numerical simulation with a theoretical framework based on rigorous finite-size scaling. Using massive-scale simulations up to $L=192$ ($N \approx 7 \times 10^6$) with 20,000 independent realizations, we demonstrate that for $k \ge 8$, the peak susceptibility scales with an exponent of $\gamma = 1.000$, and the maximum single-step jump stabilizes at a macroscopic fraction. This confirms that while the transition is continuous in the infinite thermodynamic limit, it exhibits the exact finite-size scaling signatures of a first-order discontinuity in finite physical systems. For
rigidity, we discover numerically that for richly-connected hosts, increasing the number of choices $k$ optimally enhances the efficiency of rigidification. To explain this phenomenon, we propose a theoretical model centered on a conditional progress function that links an edge's local product-rule score to its global mechanical utility. We show that while local rigidification efficiency monotonically increases, the global
rigidity gap exhibits a “Goldilocks” minimum at intermediate $k$ due to the emergence of maximally floppy, tree-like components at large $k$. Altogether, our work provides new insights into the relationship between local dynamics and global connectivity and
rigidity in cubic
lattice structures via both theory and computation.
Read the full abstract ▾
Materials Science
Automated Workflow for Non-Empirical Wannier-Localized Optimal Tuning of Range-Separated Hybrid Functionals
Stephen E. Gant, Francesco Ricci, Guy Ohad et al. (+3 more)
We introduce an automated workflow for generating non-empirical Wannier-localized optimally-tuned screened range-separated hybrid (WOT-SRSH) functionals. WOT-SRSH functionals have been shown to yield highly accurate fundamental band gaps, band structures, and optical spectra for bulk and 2D
semiconductors and
insulators. Our workflow automatically and efficiently determines the WOT-SRSH functional parameters for a given
crystal structure and composition, approximately enforcing the correct screened long-range Coulomb interaction and an ionization potential ansatz. In contrast to previous manual tuning approaches, our tuning procedure relies on a new search
algorithm that only requires a few hybrid functional calculations with minimal user input. We demonstrate our workflow on 23 previously studied
semiconductors and
insulators, reporting the same high level of accuracy. By automating the tuning process and improving its computational efficiency, the approach outlined here enables applications of the WOT-SRSH functional to compute spectroscopic and optoelectronic properties for a wide range of materials.
Read the full abstract ▾
All authors Stephen E. Gant, Francesco Ricci, Guy Ohad, Ashwin Ramasubramaniam, Leeor Kronik, Jeffrey B. Neaton
Materials Science
Pd/Cu single atom alloys for catalysis: from single crystalline to nanostructured model systems for highly selective butanol dehydrogenation
Philipp Haugg, Jan Smyczek, Carsten Schröder et al. (+5 more)
Heterogeneous catalysts based on Single Atom
Alloys (SAA) play a significant role in numerous technical processes. The fundamental working principles of these systems, however, remain poorly understood, especially the aspects related to the nanoscopic nature of bimetallic particles and the associated structure-reactivity relationships. In this study, we developed for the first time well-defined SAA catalysts consisting of Pd atomically dispersed in Cu nanoparticles prepared under ultra-high
vacuum (UHV) conditions on model Al2O3/NiAl(110) support. Employing a unique combination of surface sensitive techniques - scanning tunneling microscopy (STM), infrared reflection absorption spectroscopy (IRAS), molecular beams - and density functional theory (DFT) calculations, we performed detailed structural characterization of these systems at the microscopic level. We demonstrate that Pd disperses atomically in Cu nanoparticles and becomes partly negatively charged. Importantly, these Pd/Cu nanostructured systems show an outstanding catalytic performance in selective dehydrogenation of butanol and exhibit 100 % selectivity toward butanal over a broad range of Pd loadings - the property that cannot be reproduced employing simplified single crystalline Pd/Cu(111) counterparts. The developed approach for preparation and characterization of these nanostructured SAA-catalysts lays a foundation for further fundamental-level catalytic studies on this important class of materials and their rational design for practical applications.
Read the full abstract ▾
All authors Philipp Haugg, Jan Smyczek, Carsten Schröder, Paul Fröhlich, Paul Kohlmorgen, Stephan Appelfeller, Konstantin Neyman, Swetlana Schauermann
Materials Science
Raman Spectroscopy Insights into the Reorientational Dynamics of Polyanions in Solid Electrolytes
Jianghai Chen, Yu Yang, Ya Tang et al. (+2 more)
The interaction between cation
diffusion and polyanion rotational dynamics has garnered significant
attention, yet characterizing the rotational dynamics of polyanions remains challenging. Previous studies have primarily relied on complex techniques such as
Nuclear Magnetic Resonance and Quasi-Elastic
Neutron Scattering. In this work, we use ab initio molecular dynamics (AIMD) simulations and temperature-dependent Raman spectroscopy to investigate the reorientational dynamics of the NO2- polyanion in Na3ONO2 and NaNO2. Our findings reveal distinct reorientational behaviors and establish a clear correlation between molecular reorientation and Raman spectral features in polyanion-based solid electrolytes. AIMD simulations show that NO2- rotates easily in Na3ONO2, while its rotational dynamics are hindered in NaNO2. Raman spectroscopy confirms these results, with temperature-dependent shifts in the internal vibrational modes of the polyanion. In Na3ONO2, the full width at half maximum (FWHM) of these modes increases with temperature, while NaNO2 exhibits a constant FWHM until a significant jump at the ordered-disordered phase transition. These insights enhance our understanding of polyanion reorientation and offer a framework for characterizing similar dynamics in other solid electrolytes.
Read the full abstract ▾
All authors Jianghai Chen, Yu Yang, Ya Tang, Hong Zhu, Wenqian Chen
Materials Science
Low-field magnetization processes of hexagonal easy-plane altermagnet $\alpha$-MnTe
Sahana Rößler, Victoria Ginga, Marcus Schmidt et al. (+5 more)
Single
crystals of $\alpha$-MnTe were synthesized by chemical vapor transport using iodine as the transport reagent. Structural characterization by powder x-ray diffraction confirmed the hexagonal structure (space group P6$_{3}$/mmc). Magnetization $M(T)$ and specific heat $C_p(T)$ measurements revealed an
antiferromagnetic phase transition at $T_N \approx307$ K. The
magnetic entropy derived from the $C_p(T)$ data is consistent with the $S = 5/2$
spin state of Mn$^{2+}$ ions. Angle- and field-dependent magnetization measurements indicate complex
magnetic responses associated with domains, and show an anomaly around 1 T. These features are analyzed using a phenomenological micromagnetic model that includes higher-order anisotropic exchange interactions coupling the weak
ferromagnetic component and the
antiferromagnetic order parameter. The model captures the generic behavior of
magnetic states and demonstrates that the observed uniaxial and unidirectional anisotropies arise from metastable domain configurations and irreversible magnetization processes.
Read the full abstract ▾
All authors Sahana Rößler, Victoria Ginga, Marcus Schmidt, Yurii Prots, Helge Rosner, Ulrich Burkhardt, Ulrich K. Rößler, Alexander A. Tsirlin
Materials Science
Intertwined Hyperferroelectricity, Tunable Multiple Topological Phases and Giant Rashba Effect in Wurtzite LiZnAs
Saurav Patel, Paras Patel, Shaohui Qiu et al. (+1 more)
Composite
quantum compounds offer a fertile ground for uncovering the complex interrelations between seemingly distinct phenomena in condensed matter physics for advanced nonvolatile and spintronics applications. Beyond topological
superconductors and
axion insulators, the idea of intertwined Hyperferroelectricity (HyFE), multiple topological phases and Rashba
spin-splitting with reversible
spin textures represents the local, global and
symmetry-driven characteristics of
quantum materials, respectively, offering unique pathways for enhanced functionalities. We unveiled a unified framework to achieve this synergy through the presence of crystalline
symmetries and
spin-orbit coupling in LiZnAs compound using first-principles calculations. HyFE exhibits ability to maintain spontaneous polarization under open-
circuit boundary conditions, even with existence of depolarization field while Rashba effect exhibits paradigmatic
spin texture in momentum space with tangential vector field. The presence of unstable $A_{2u}(LO)$ mode leads to free energy minimum with significant well depth and polarization of -66 meV and $P_{HyFE} = 0.282~C/m^2$, respectively indicating stable HyFE. The robust HyFE stem from mode-specific effective charges and larger high-frequency dielectric constants. This study also addresses the subtle question of whether critical point of topological phase transition shifts in response to drastically different Rashba
spin-splitting values obtained from VASP and WIEN2k. Moreover, biaxial strain (BAS) induced Weyl semimetal (at 3.4% BAS) and topological insulating phase (after 3.4% BAS) is observed with
giant Rashba coefficient of 5.91 eV Å and 2.42 eV Å, respectively. Furthermore, switching of bulk polarization leads to
spin texture reversal, providing a robust mechanism to leverage
spin degrees of freedom in these Hyperferroelectric Rashba topological materials.
Read the full abstract ▾
All authors Saurav Patel, Paras Patel, Shaohui Qiu, Prafulla K. Jha
Materials Science · Cross-listed from cond-mat.mes-hall
Robust structural superlubricity of twisted graphene bilayer and domain walls between commensurate moiré pattern domains from first-principles calculations
Irina V. Lebedeva, Andrey M. Popov, Yulia G. Polynskaya et al. (+3 more)
Twisted
graphene layers exhibit extremely low friction for relative sliding. Nevertheless, previous studies suggest that the area contribution to friction for commensurate moiré systems is finite and might restrict macroscopic superlubricity for large layer overlaps. In this paper, we investigate the potential energy surface (PES) for relative displacement of the layers forming moiré patterns (2,1) and (3,1) by accurate density functional theory calculations using the vdW-DF3 functional. The amplitudes of PES corrugations on the order of 0.4 and 0.03 $\mu$eV per atom of one layer, respectively, are obtained. The account of structural relaxation doubles this value for the (2,1) pattern, while causing only minimal changes for the (3,1) pattern. We show that different from aligned
graphene layers, for moiré patterns, PES minima and maxima can switch their positions upon changing the interlayer distance. The PES shape is closely described by the first spatial
Fourier harmonics both with and without account of structural relaxation. A barrier for relative rotation of the layers to an incommensurate state that can make superlubricity robust is estimated based on the approximated PES. We also derive a set of measurable physical properties related to interlayer interaction including shear mode frequency, shear modulus and static friction force. Furthermore, we predict that it should be possible to observe domain walls separating commensurate domains, each comprising a large number of moiré pattern unit
cells, and provide estimates of their characteristics.
Read the full abstract ▾
All authors Irina V. Lebedeva, Andrey M. Popov, Yulia G. Polynskaya, Andrey A. Knizhnik, Sergey A. Vyrko, Nikolai A. Poklonski
Materials Science
Switchable Polarization in an A-site Deficient Perovskite through Vacancy and Cation Engineering
Suguru Yoshida, Olivier Hernandez, Jinsuke Miyake et al. (+7 more)
While defects are unavoidable in
crystals and often detrimental to material performance, they can be a key ingredient for inducing functionalities when tailored. Here, we demonstrate that an A-site-deficient perovskite Y$_{1/3}$TaO$_3$ exhibits room-temperature ferroelectricity in a $Pb2_1m$ phase, enabled by ordered vacancies coupled with TaO$_6$ octahedral rotations. Defect-ordered perovskites are frequently trapped in centrosymmetric incommensurate states due to competing structural instabilities; we circumvent this by favoring rotational over polar instability through compositional selection. Unlike canonical improper ferroelectrics that are ferrielectric, the vanishing dipoles on vacancy layers in Y$_{1/3}$TaO$_3$ allow for a net ferroelectric
alignment of local dipoles, resulting in enhanced polarization. Upon heating, Y$_{1/3}$TaO$_3$ transforms to a paraelectric incommensurate phase at $\simeq$750 K, whose atomic arrangement mirrors the domain
topology observed in hybrid improper ferroelectrics. Superspace analysis of the modulated phase reveals a route to improve room-temperature polarization, achieved through epitaxial strain, as confirmed by our
lattice-dynamics calculations. This defect-ordering strategy should be generalizable to other improper ferroelectrics, including magnetoelectric multiferroics, providing a pathway to amplify otherwise limited macroscopic polarization.
Read the full abstract ▾
All authors Suguru Yoshida, Olivier Hernandez, Jinsuke Miyake, Kei Nakayama, Ryo Ishikawa, Hajime Hojo, Yuichi Ikuhara, Venkatraman Gopalan, Katsuhisa Tanaka, Koji Fujita
Materials Science
Orbital magnetization in the Nb-substituted Kagome metal CsV$_3$Sb$_5$
H.J. Elmers, O. Tkach, Y. Lytvynenko et al. (+12 more)
This study uses angle-resolved photoemission spectroscopy to examine the low-temperature electronic structure of Cs(V$_{0.95}$Nb$_{0.05}$)$_3$Sb$_5$, demonstrating that partially substituting V atoms with isoelectronic Nb atoms results in \blue{an increase of the band width} and enhanced gap opening at the Dirac-like crossings due to the resulting chemical pressure. This increases the
magnetic circular dichroism signal in the angular distribution (MCDAD) compared to CsV$_3$Sb$_5$, enabling detailed analysis of
magnetic circular dichroism in several bands near the
Fermi level. These results \blue{substantiate} the predicted coupling of orbital
magnetic moments to three van Hove singularities near the
Fermi level at M points. Previous studies have observed that Nb doping \blue{lowers the charge density transition temperature} and increases the critical temperature for superconductivity. This article demonstrates that Nb doping concomitantly increases the
magnetic circular dichroism signal attributed to orbital moments.
Read the full abstract ▾
All authors H.J. Elmers, O. Tkach, Y. Lytvynenko, H. Agarwal, D. Biswas, J. Liu, A.-A. Haghighirad, M. Merz, S. Pakhira, G. Garbarino, T.-L. Lee, J. Demsar, G. Schonhense, M. Le Tacon, O. Fedchenko
Materials Science
Haidong Liang, Ganesh Ji Omar, Kun Han et al. (+3 more)
The interfacial electronic properties of complex
oxides are governed by a delicate balance between charge transfer,
lattice distortions, and electronic correlations, posing a key challenge for controlled tunability in materials research. Here, we demonstrate that
proton implantation serves as a precise tool for modulating interfacial transport in SrTiO3-based
heterostructures. By introducing
protons into the SrTiO3 substrate beneath an amorphous (La,Sr)(Al,Ta)O3 capping layer, we uncover a competition between disorder and charge doping induced by implantation. At low implantation fluences below 1x1015
protons/cm2 (1E15), charge doping dominates, leading to an increase in carrier density and mobility, analogous to electrostatic gating effect. This enables the emergence of
quantum transport oscillations at low temperature. Conversely, at higher fluences (above 1E15), disorder scattering prevails, suppressing carrier mobility and inducing an insulating state. The nonmonotonic
evolution of transport with implantation fluence underscores the critical interplay between electronic correlations and disorder, offering a new paradigm for the controlled engineering of interfacial
quantum states in SrTiO3-based
oxide heterostructures.
Read the full abstract ▾
All authors Haidong Liang, Ganesh Ji Omar, Kun Han, Andrew A. Bettiol, Zhen Huang, A. Ariando
Materials Science
Strong coupling between coherent ferrons and cavity acoustic phonons
Yujie Zhu, Jiaxuan Wu, Anna N. Morozovska et al. (+7 more)
Coherent ferrons, the quanta of polarization waves, can potentially be hybridized with many other quasiparticles for achieving novel control modalities in
quantum communication, computing, and sensing. Here, we theoretically demonstrate a new hybridized state resulting from the strong coupling between fundamental-mode (wavenumber is zero) coherent ferrons and cavity bulk acoustic
phonons. Using a van der Waals ferroelectric CuInP2S6 membrane as an example, we predict an ultra-strong ferron-
phonon coupling at room temperature, where the coupling strength g_c reaches over 10% of the resonant frequency {\omega}_0. We also predict an in-situ bistable electric-field control of mode-specific ferron-
phonon hybridization via ferroelectric switching. We further show that CuInP2S6 allows for reaching the fundamentally intriguing but challenging deep strong coupling regime (i.e., g_c/{\omega}_0>1) near the ferroelectric-to-paraelectric phase transition. Our findings establish the theoretical basis for exploiting coherent ferron as a new contender for hybrid
quantum system with strong and highly tunable coherent coupling
Read the full abstract ▾
All authors Yujie Zhu, Jiaxuan Wu, Anna N. Morozovska, Eugene A. Eliseev, Yulian M. Vysochanskii, Venkatraman Gopalan, Long-Qing Chen, Xufeng Zhang, Wei Zhang, Jia-Mian Hu
Materials Science
Outstanding figure of merit at high temperature for DFT-based predicted double perovskite oxides, Ba2GaXO6 (X = V, Nb, Ta)
S. S. Saif, M. M. Hossain and M. A. Ali
Thermoelectric materials with a high figure of merit (ZT) are highly demanded for a sustainable solution to the energy crisis. In this study, we have predicted three new double perovskite
oxides (DPOs), Ba2GaXO6 (X = V, Nb, Ta), with high ZT values using density functional theory (DFT) calculations and investigated their structural, electronic, thermoelectric, and mechanical properties. The electronic properties, such as electronic band structure, density of states (DOS), and charge density mapping, are used to disclose the conductive nature, chemical bonding within these compounds, which exhibit direct band gaps of 0.924, 2.354, and 3.279 eV for Ba2GaVO6, Ba2GaNbO6, and Ba2GaTaO6, respectively, as calculated using the TB mBJ potential. The thermoelectric performance of the new DPOs, Ba2GaXO6 (X = V, Nb, Ta), was assessed using the BoltzTrap2 code, which yielded outstanding ZT values of 2.36, 1.78, and 1.91 at 1500 K for Ba2GaVO6, Ba2GaNbO6, and Ba2GaTaO6, respectively, indicating their potential for waste heat management. The high ZT values are attributed to an ultra low
lattice thermal conductivity, arising from strong scattering of acoustic and optical
phonon modes. The changes in thermoelectric parameters with temperature were analyzed and explained.
Read the full abstract ▾