Materials Science
Tunable Magnetic Frustration in the Cu-Ru-based Double Perovskite La$_{2-x}$Sm$_x$CuRuO$_6$ (x = 0, 1, 2) Oxides
Soumya Ghorai, Samir Rom, Irina Shamova et al. (+7 more)
In this study, we investigate structural,
magnetic, and electronic properties of the copper-ruthenate based oxide double perovskite La$_{2-x}$Sm$_x$CuRuO$_6$ (x = 0, 1, 2), synthesized through the solid-state reaction method. X-ray diffraction analysis reveals that all compounds crystallize in a monoclinic
symmetry, with varying degree of structural distortion that increases in moving from La$^{3+}$ to smaller size cation Sm$^{3+}$. Electrical resistivity studies indicate insulating behaviour in all compounds, with variable-range-hopping domination at low temperatures, due to presence of anti-site disorder. AC susceptibility and heat capacity measurements suggest suppression of frustration in Sm-bearing compounds, affecting the
magnetic behavior. Our first-principles calculations suggest that the combined effects of
lattice distortion and Sm magnetism play a crucial role in weakening
magnetic frustration, thereby rationalizing the experimental observations. These findings shed light on the complex interplay of
crystal structure and magnetism in Cu-Ru double perovskites, and open up an avenue for tuning of
magnetic properties through rare-earth-ion substitution.
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All authors Soumya Ghorai, Samir Rom, Irina Shamova, N. K. Karn, Tamanna Kumari, A. K. Shukla, Sanjoy Kr. Mahatha, O. Volkova, Nitesh Kumar Tanusri Saha Dasgupta, Setti Thirupathaiah
Materials Science · Cross-listed from cond-mat.str-el
Raman Circular Dichroism Reveals Higher-Order Quantum Geometry of Magnons
Yong Chan Kim, Youngsu Choi, Kwang-Yong Choi et al. (+1 more)
We develop a gauge-invariant framework that relates two-
magnon Raman circular dichroism (RCD) to higher-order
magnon quantum geometry. In the
magnon band basis, the Raman operator decomposes into interband Berry connections, their covariant derivatives, and products of successive connections, generating higher-order, multi-state
geometric tensors beyond the conventional single-band
quantum metric and Berry
curvature. Applying this framework to a field-polarized Kitaev magnet, we show that higher-order
geometric tensors govern the dichroic response. Our results establish RCD as a spectroscopic probe of generalized
magnon quantum geometry.
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All authors Yong Chan Kim, Youngsu Choi, Kwang-Yong Choi, Kyusung Hwang
Materials Science
Large Jahn-Teller shifts and splittings observed in halide perovskite CsPbBr3
Maryam Sajedi, Maxim Krivenkov, Dmitry Marchenko et al. (+7 more)
Despite the fundamental role of Jahn-Teller effects of first and second order in shaping structural and electronic properties, there is hardly any observation in angle-resolved photoemission of solids. In oxide and halide perovskites, band structure replicas have occasionally been reported as fingerprints of Jahn-Teller effects, but no accompanying energy shifts or splittings that would allow a conclusion about their origin. In CsPbBr3, we uncover both key signatures: Upon cooling, orthorhombic replica bands emerge which had eluded earlier studies. This includes an extra valence band maximum at {\Gamma} which can even be distinguished at room temperature. Most importantly, band narrowing along {\Gamma}-M, a splitting at {\Gamma}, and the lifting of degeneracy between nonequivalent M points, all of several 100 meV, become apparent. Temperature-dependent x-ray diffraction, used as input for band structure calculations, links these effects directly to tilts and rotations of the PbBr6 octahedra. Our results uncover a strong electron-
lattice interaction which is at the heart of so-far unresolved questions concerning polaronic transport, dynamic disorder, and
exciton trapping in halide perovskites.
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All authors Maryam Sajedi, Maxim Krivenkov, Dmitry Marchenko, Saleem Ayaz Khan, Andrei Varykhalov, Jaime Sánchez-Barriga, Daniel M. Többens, Thomas Unold, Ján Minár, Oliver Rader
Materials Science
Emergent Noncollinearity and Near-Degenerate Magnetic Superlattices in AT6X6 Kagome Metals
Weiyi Xia, Wei-Shen Tee, Peter Minch et al. (+3 more)
Ferromagnetic AT6X6 Kagome compounds are a popular class of systems in which
quantum magnetism with topological features has been observed. These systems allow easy chemical substitution, creating an opportunity to fine-tune their properties. In this paper, we present electronic-structure and
magnetic ground-state studies of several AT6X6 compounds with relatively low
magnetic-ground-state stability. We find unusual
magnetic orderings, including complex
spin-spiral states and the formation of
magnetic long-range superstructures. While LiFe6Ga6 and TiMn6Ge6 retain collinear AFM ground states with low-energy FM/AFM layer sequences, competing
spin-spiral and long-period antiferromagnetic structures in MgFe6Ga6 and a double-
spin-spiral ground state in TiFe6Ga6 were determined. Magnetism in all these systems appears local, with adiabatic energy profiles suggesting non-Heisenberg long-range interactions, including a strong biquadratic term. In TiMn6Ge6, we found the conditions for
magnetic tunneling. Our results show that, in addition to traditional
magnetic topological features in such FM Kagome systems, near-degenerate
magnetic superstructures suitable for spintronic switching applications can form naturally. Overall, these systems represent a potentially rich playground for
neutron diffraction and spintronics experimental studies.
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All authors Weiyi Xia, Wei-Shen Tee, Peter Minch, Feng Zhang, Cai-Zhuang Wang, Vladimir Antropov
Materials Science · Cross-listed from cond-mat.soft
One micron length scale controls kinetic stability of low energy glasses
Kenneth L. Kearns, M. D. Ediger, Heiko Huth et al. (+1 more)
AC nanocalorimetry was used to measure the reversing heat capacity Cp of low energy indomethacin glasses as they isothermally transform into the supercooled
liquid. As the film thickness increases from 75 to 600 nm, the transformation time increases by more than an order of magnitude, consistent with a surface-initiated transformation mechanism. Eventually, the transformation time becomes constant for films between 1.4 and 30 microns indicating a distinct bulk transformation pathway. The observation of size-dependent transformation kinetics for glass samples approaching 1 micron is unprecedented. We interpret the crossover in thickness dependence at 1 micron to signify the average distance between transformation initiation sites in the bulk low energy glass.
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All authors Kenneth L. Kearns, M. D. Ediger, Heiko Huth, Christoph Schick
Materials Science · Cross-listed from cond-mat.soft
Highly Stable Glasses of cis-Decalin and cis/trans-Decalin Mixtures
Katherine R. Whitaker, Daniel J. Scifo, M. D. Ediger et al. (+2 more)
In situ AC nanocalorimetry was used to measure the reversing heat capacity of vapor-deposited glasses of decahydronaphthalene (decalin). Glasses with low heat capacity and high kinetic stability, as compared to the corresponding
liquid-cooled glass, were prepared from cis-decalin and from several cis/trans-decalin mixtures. This is the first report of highly stable glass formation for molecular mixtures. The 50/50 cis/trans-decalin mixture is the highest fragility material reported to produce an ultrastable glass. The 50/50 mixture exhibited high kinetic stability, with an ~500 nm film deposited at 116 K (0.86 Tg,) displaying a transformation time equivalent to 104.4 times the structural relaxation time of the supercooled
liquid at the annealing temperature. Cis-decalin and the decalin mixture formed stable glasses that had heat capacities as much as 4.5% lower than the
liquid-cooled glass.
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All authors Katherine R. Whitaker, Daniel J. Scifo, M. D. Ediger, Mathias Ahrenberg, Christoph Schick
Materials Science
Defect-Mediated Nucleation and Dynamics across the Phase Transition in the Excitonic Insulator Candidate Ta2NiSe5
Guilherme Rodrigues-Fontenele, Gabriel Fontenele, Ângelo Malachias et al. (+1 more)
Ta2NiSe5 is a quasi-one-dimensional material that exhibits a structural and electronic phase transition from a low-temperature monoclinic (
semiconductor) to a high-temperature orthorhombic (semimetal) phase at approximately TC = 326 K. Here, we used variable-temperature scanning tunneling microscopy and spectroscopy to resolve the phase transition spatially, identifying the distinct spectroscopic signatures of the monoclinic and orthorhombic phases in pristine regions and near isolated point-defects and step edges. Although the phase transition of Ta2NiSe5 is generally regarded as second-order, it has previously been described as exhibiting martensitic-like characteristics. This implies that the transformation may proceed via spatial phase coexistence and domain boundaries rather than through a continuous
evolution. Our surface-sensitive measurements confirm this scenario, retrieving the coexistence and
evolution of monoclinic and orthorhombic domains in real space. Upon heating through TC, we find that the two phases coexist as spatially segregated regions over extended timescales, separated by well-defined boundaries that evolve via localized nucleation and growth, rather than a spatially uniform transformation. In pristine regions, the orthorhombic phase nucleates anisotropically, perpendicular to the Ta-Ni-Ta chains, whereas point-defects and step edges act as local nucleation centers that promote the transition and suppress this intrinsic anisotropy. These results provide direct real-space visualization of how surface-specific structural and electronic variations, together with local disorder, modify the martensitic-like phase transition in Ta2NiSe5.
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All authors Guilherme Rodrigues-Fontenele, Gabriel Fontenele, Ângelo Malachias, Rogério Magalhães-Paniago
Materials Science · Cross-listed from cond-mat.soft
Comparison of mechanical and molecular measures of mobility during constant strain rate deformation of a PMMA glass
Benjamin Bending and M.D. Ediger
We performed constant strain rate deformation and stress relaxation on a poly(methyl methacrylate) glass at Tg - 19 K, utilizing three strain rates and initiating the stress relaxation over a large range of strain values. Following previous workers, we interpret the initial rate of decay of the stress during the relaxation experiment as a purely mechanical measure of mobility for the system. In our experiments, the mechanical mobility obtained in this manner changes by less than a factor of 3 prior to yield. During these mechanical experiments, we also performed an optical measurement of segmental mobility based upon the reorientation of a molecular probe; we observe that the probe mobility increases up to a factor of 100 prior to yield. In the post-yield regime, in contrast, the mobilities determined mechanically and by probe reorientation are quite similar and show a similar dependence upon the strain rate. Dynamic heterogeneity is found to initially decrease during constant strain rate deformation and then remain constant in the post-yield regime. These combined observations of mechanical mobility, probe mobility, and dynamic heterogeneity present a challenge for theoretical modeling of
polymer glass deformation.
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Materials Science
Resistive Switching and Neuromorphic Computing in Metal/Nb:SrTiO$_3$: Mechanisms, Interface Physics, and Charge Transport
Christopher Broyles, Elizabeth Krenkel, Frank Barrows et al. (+2 more)
Resistive switching (RS) in Nb-doped SrTiO$_3$ (Nb:STO) based memristive devices has attracted sustained interest in information processing and novel computing because of its forming-free operation, large on/off ratio, and gradual conductance modulation. Metal/Nb:STO Schottky junctions have emerged as a prototypical system for understanding RS mechanisms. Despite more than two decades of research, the physical origin of RS remains controversial, with proposed mechanisms including charge trapping and detrapping, oxygen vacancy migration, tunneling, interfacial redox reactions, and conductive filament formation. In this review, we examine these seemingly competing mechanisms and show that many experimental observations can be understood within a unified framework centered on the formation and
evolution of an extrinsic interfacial layer at the metal/Nb:STO interface. We discuss how interface quality and defect-mediated processes, including
proton incorporation, oxygen vacancy dynamics, and tunneling, govern Schottky barrier modulation and RS behavior. We further summarize how fabrication conditions, measurement protocols, and aging influence the interface formation and switching characteristics. This review establishes an integrated picture of M/Nb:STO heterojunctions and provides design principles for reliable oxide memristive devices through interface and defect engineering in M/Nb:STO and M/oxide/Nb:STO systems.
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All authors Christopher Broyles, Elizabeth Krenkel, Frank Barrows, Sundar Kunwar, Aiping Chen
Materials Science
Mapping metallic d-wave altermagnetism across the TiNiSi structural family
Zhen Zhang, Subhadip Pradhan, Kirill D. Belashchenko et al. (+1 more)
The prospect of using altermagnets as switchable sources of perpendicularly polarized
spin currents has intensified the search for candidate materials, yet metallic d-wave systems with sizable
spin-splitter responses remain scarce. Here, we identify an empirical
magnetic motif that supports metallic d-wave altermagnetism in the TiNiSi structural family: ferromagnetically ordered zigzag chains with antiferromagnetic interchain coupling in a relatively low-
symmetry crystal environment. The TiNiSi structure type combines this motif with broad chemical flexibility and competing
magnetic ground states. By combining first-principles screening of thermodynamic stability and
magnetic ground states across 280 ternary systems, we identify 16 metallic d-wave altermagnets. This set recovers four experimentally known members—WFeB, NbMnP, TaMnP, and NbMnAs—and yields 12 new predictions, of which ScMnP, TaMnAs, ScMnAs, MoMnAs, MoMnSi, and WMnSi are the most promising. Noncollinear calculations indicate that the collinear altermagnetic configuration is the ground state across them. Each of the six leading new candidates has a nonzero
spin-splitter angle and a finite anomalous Hall conductivity. Notably, ScMnP and TaMnAs exhibit strong
spin-splitter responses despite modest altermagnetic band splitting. These results establish TiNiSi-type metallic d-wave altermagnets as a chemically versatile platform for efficient charge-to-
spin conversion and provide an empirical
magnetic-motif-guided route to identifying further candidates.
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All authors Zhen Zhang, Subhadip Pradhan, Kirill D. Belashchenko, Vladimir Antropov
Materials Science
The principle of detailed balance between electrons and phonons in presence of excitonic effects
Alberto Guandalini, Giovanni Caldarelli, Francesco Mauri et al. (+1 more)
Based on a many-body formulation, we derive an electron-
phonon coupling including excitonic effects that preserves thermodynamic detailed balance between electronic and phononic scattering processes. We start from the microscopic electron-
nucleus Hamiltonian, expand around the Born-Oppenheimer
equilibrium geometry, and construct an effective action for the electronic and phononic propagators. From the same effective action, we derive both electronic and phononic self-energies in terms of a nonlocal vertex $\mathcal G^{\textrm{s}}$ including excitonic effects, which generalizes the usual local interaction vertex $g^{\textrm{s}}$. When electrons and
phonons are well-defined quasiparticles in the screened-exchange approximation and $\mathcal G^{\textrm{s}}$ is taken in its static limit, both self-energies reduce to Fermi-golden-rule expressions containing the same $\mathcal G^{\textrm{s}}$, thereby ensuring detailed balance. As an application, we compute electronic and phononic linewidths in
graphene and illustrate this common-vertex construction. We analyze the competition between the reduced scattering phase space induced by the screened-exchange band structure and the enhancement of the electron-
phonon vertex due to excitonic effects, finding that the vertex enhancement can compensate for and overcome the phase-space reduction in both electronic and phononic linewidths.
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All authors Alberto Guandalini, Giovanni Caldarelli, Francesco Mauri, Francesco Macheda
Materials Science
FUCrIMODo: structure recovery from atomistic descriptors via multi-stage genetic algorithms
Louis Boehm, Martin Kuban and Claudia Draxl
Data-driven approaches to materials discovery rely on numerical representations of atomic structures as input for machine learning models. Inverting these descriptors - recovering atomic structures from their representations - is essential for most generative material design pipelines, yet it remains challenging, particularly for periodic systems. Existing inversion methods are either tailored to specific invertible descriptors or require candidate structures with similar atomic arrangements and compositions, limiting the exploration of novel regions in chemical and configurational space. Here, we propose a generalizable, similarity-driven sampling approach, powered by a novel stage-wise optimization strategy, to recover atom types, atomic positions, and unit
cell shapes directly from a descriptor. Our approach requires only descriptor features and parameters as input without any prior structural knowledge. The capability of our method is demonstrated by the averaged Smooth Overlap of Atomic Positions (SOAP) descriptor.
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Materials Science
Giant Surface-driven Nonlinear Hall Effect in BiTeCl at Room Temperature
Zhihua Liu, Ziheng Wang, Yongbo Lv et al. (+9 more)
The nonlinear Hall effect (NLHE) provides a pathway to generate a Hall response in time-reversal-symmetric yet inversion-
symmetry-broken systems. NLHE can rectify an alternating current into a transverse direct voltage, making it attractive for
radio-frequency rectification, energy harvesting, and terahertz detection, applications for which device miniaturization remains a central pursuit. In this context, the inherent inversion
symmetry breaking at surfaces is particularly appealing: because
symmetry is necessarily broken at the surface of any
crystal, irrespective of whether its bulk is centrosymmetric, surface-driven nonlinear responses lift the stringent constraint on bulk
symmetry and open a route toward compact device architectures. Here we report the observation of a giant, surface-driven second-order nonlinear Hall effect in the Rashba-type polar
semiconductor BiTeCl at room temperature. The determined second-order nonlinear Hall susceptibility at 300 K reaches 1.68 $\mu$mV$^{-1}$, which is 80 times larger than that of the best previously reported surface-dominated systems. We attribute this giant response to the synergistic interplay between BiTeCl's polar
crystal structure and its rich surface states: the polar stacking renders the top and bottom surfaces inequivalent, so that the nonlinear response originates from a single surface without compensation from the other.
Symmetry and scaling analyses suggest that both skew-scattering and side-jump mechanisms contribute to the observed effect. Our findings not only identify BiTeCl as a promising platform for future applications utilizing the NLHE, but also establish the asymmetry between the opposite surfaces of a polar
crystal as a general design principle for discovering surface-driven materials with larger nonlinear Hall responses.
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All authors Zhihua Liu, Ziheng Wang, Yongbo Lv, Hanru Feng, Zhiwei Zhang, Bo Zhang, Feng Liu, Guohua Wang, Shengwei Jiang, Hao Chu, Hui Li, Dong Qian
Materials Science
Determination of the ferrimagnetic structure of monoclinic TbFe$_{2}$D$_{4.2}$ deuteride and its evolution versus temperature and high magnetic field
Valerie Paul-Boncour and Olivier Isnard
The
magnetic properties of monoclinic TbFe$_{2}$D$_{4.2}$ have been investigated by combining different
magnetic measurements, including those involving a high pulsed
magnetic field, with
neutron diffraction experiments versus temperature and applied field. TbFe$_{2}$D$_{4.2}$ displays a ferrimagnetic ground state with M$_{Tb}$ = 8.2(2) $\mu$$_{B}$ and M$_{Fe}$ = 2.1(2) $\mu$$_{B}$. At 4.2 K a large
magnetic anisotropy related to the Tb moments is observed, as saturation is not reached at 50 T. In addition, two metamagnetic transitions are observed for fields of 3 and 29 T. Upon heating, the Tb moment decreases progressively whereas the Fe moment remains constant up to 150 K. At 160 K both Tb and Fe moments sharply decrease, and a 0.38% contraction of the
cell volume is observed due to an itinerant electron metamagnetic behavior of the Fe sublattice. This transition temperature is 76 K higher than that of YFe$_{2}$D$_{4.2}$ due to an increase in
cell volume, as well as exchange interactions between the Fe and Tb moments. The deuteride becomes paramagnetic above 220 K.
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Materials Science
Absence of lateral domain wall mobility in Zn1-xMgxO thin films
Jack Eckstein, Kyle P. Kelley, William Prudnick et al. (+4 more)
Polarization reversal in ferroelectrics arises from the coupled processes of domain nucleation and subsequent growth, yet the governing mechanisms differ fundamentally between classical perovskite oxides and emerging wurtzite ferroelectrics. While switching in perovskites is typically governed by mobile domain walls whose field-driven propagation dominates macroscopic kinetics, here we show that polarization reversal in wurtzite Zn1-xMgxO proceeds through a qualitatively different pathway. Using scanning oscillator microscopy, in combination with point pulse-imaging methods, we directly map local switching events and domain wall responses, revealing that domain walls in Zn1-xMgxO exhibit negligible lateral mobility (sub 10nm) and that polarization reversal proceeds predominantly through the nucleation of vertically extended columnar filaments with a lateral size on the order of the grains. This nucleation-controlled switching contrasts sharply with the growth-mediated dynamics characteristic of perovskite ferroelectrics and explains the abrupt, spatially localized switching behavior observed in wurtzite systems. These results establish nucleation-dominated filamentary reversal as a defining switching mechanism in Zn1-xMgxO and point towards the need for further studies to understand correlation lengths and nucleation processes across a range of grain sizes.
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All authors Jack Eckstein, Kyle P. Kelley, William Prudnick, Jon-Paul Maria, Stephen Jesse, Neus Domingo, Rama K. Vasudevan
Materials Science · Cross-listed from cond-mat.mes-hall
Quantum Geometry Driven Optical Responses in 1T-MX$_2$ Monolayers: A Symmetry-Constrained Slater-Koster Tight-Binding Approach
Bikram Baruah, Snehasish Nandy and Subhasis Panda
Centrosymmetric 1T-MX$_2$ monolayers(MLs) have attracted considerable
attention owing to their intriguing transport properties and potential technological applications arising from the interplay among
quantum geometry, electronic band structure, and band-gap characteristics. Despite this rich physics, a comprehensive microscopic tight-binding(TB) description that simultaneously captures these properties remains insufficiently established, while first-principles approaches can be computationally demanding for systematic investigations across different materials and perturbations. Here, we develop a transferable eleven-band Slater-Koster TB description of ML 1T-MX$_2$ TMDs and use it to establish a connection among their microscopic electronic structure,
quantum geometry, and optical response. The model is constructed in an orthogonal orbital basis from the
crystal geometry and
symmetry-constrained SK parameters, with material-specific parametrizations obtained from DFT calculations for ML ZrS$_2$ and HfS$_2$. The resulting geometry-based
Hamiltonian accurately describes the low-energy electronic structures and provides a natural framework for extending the analysis to the broader isostructural 1T-MX$_2$ family. We find that the pristine MLs possess a finite
quantum metric, with the dominant contribution concentrated in the two highest occupied bands owing to the small near-gap energy separation and strong metal-chalcogen $p$-$d$ hybridization. Furthermore, we verify the interband $f$-sum rule, which directly relates the integrated optical spectral weight to the Brillouin-zone-averaged
quantum metric. Our results establish optical spectral weight as an experimentally accessible probe of the
quantum geometry of occupied Bloch states and provide a unified microscopic framework for connecting electronic structure,
quantum geometry, and measurable optical responses across the 1T-MX$_2$ family.
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Materials Science
FDTBX - Computational Tools for Simulation of X-ray Fiber Diffraction Patterns from Atomic Coordinates
Pawel Sikorski
Fiber diffraction is one of the few experimental techniques capable of resolving molecular structure in partially ordered, non-crystalline systems such as fibrous
proteins, biopolymers and synthetic
polymers. Because fiber diffraction patterns are complex, exhibiting paracrystalline order, packing defects and broad, overlapping reflections, their interpretation relies on model-based refinement, in which theoretical patterns simulated from candidate atomic models are iteratively compared with experiment. We present fdtbx, a modern, open and extensible Python toolbox for simulating X-ray fiber diffraction patterns directly from atomic coordinates. Built on the crystallographic library cctbx and designed for readability and multicore execution, fdtbx computes structure factors from a PDB model and constructs realistic reciprocal-space reflection profiles that incorporate the principal physical broadening mechanisms of fiber diffraction: finite crystallite size, orientational disorder (with Gaussian, Lorentzian and Voigt angular peak shapes) and paracrystalline (second-kind)
lattice disorder in Hosemann's formulation. A per-reflection shell-quadrature scheme evaluates the required convolutions at arbitrary query points rather than on a fixed grid, giving direct control over the trade-off between accuracy and speed, and an analytic Ewald-projection routine maps each sampled reflection, with an appropriate Lorentz correction, onto a flat detector to produce a simulated pattern for direct comparison with measured images. We illustrate the toolbox on $\alpha$-chitin, cellulose~I$\alpha$ and I$\beta$, cellulose triacetate and A-form DNA, and outline a practical simulation workflow. By providing a transparent, well-documented and parallelizable implementation of the specialized
algorithms of fiber diffraction, fdtbx lowers the barrier to reproducible model-based analysis.
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Materials Science
Predicted High $n$-Type $zT$ and Ultralow Lattice Thermal Conductivity in A$_2$AgIrCl$_6$ (A = Cs, Rb)
Neeraj Kulhari, Krishna Swaroop Sharma, Sung Gu Kang et al. (+1 more)
A useful thermoelectric device must impede heat flow without impeding charge transport. Here, we examine how closely cubic Cs$_2$AgIrCl$_6$ and Rb$_2$AgIrCl$_6$ approach this balance using first-principles calculations of structural stability, chemical bonding, elastic response,
lattice dynamics, and scattering-resolved carrier transport. Both materials satisfy the cubic elastic-stability criteria, and neither harmonic
phonon spectrum contains an imaginary mode. Replacing Cs with Rb mainly exerts chemical pressure: the
lattice contracts by 1.34% and the Ag–Cl and Ir–Cl bonds strengthen, whereas the band-edge
topology changes little. HSE06 calculations including
spin–orbit coupling yield direct X-point gaps of 1.597 and $1.637\,\mathrm{eV}$ for Cs$_2$AgIrCl$_6$ and Rb$_2$AgIrCl$_6$, respectively. The three
symmetry-equivalent X valleys have light electron masses of $0.43$–$0.57\,m_0$, whereas the hole masses span $2.10$–$4.68\,m_0$. For Cs$_2$AgIrCl$_6$ and Rb$_2$AgIrCl$_6$, respectively, the modified Debye–Callaway model gives
lattice thermal conductivities of 0.346 and $0.428\,\mathrm{W\,m^{-1}\,K^{-1}}$ at 300 K, decreasing to 0.118 and $0.150\,\mathrm{W\,m^{-1}\,K^{-1}}$ at 800 K. Treating acoustic-deformation-potential, ionized-impurity, and polar-optical-
phonon scattering with AMSET gives peak $n$-type $zT$ values of 2.81 and 2.36 at 800 K near $6\times10^{19}\,\mathrm{cm^{-3}}$. This response arises from the convergence of light, valley-degenerate electrons, intermediate doping, and weak
lattice heat transport rather than from a single exceptional coefficient. The predicted values are experimentally testable targets, contingent on retaining the cubic phases and controlled electron doping at elevated temperatures.
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All authors Neeraj Kulhari, Krishna Swaroop Sharma, Sung Gu Kang, K. C. Bhamu
Materials Science
The Achilles tendon enthesis rebuilds its mineralization front on reloading but retains a nanoscale imprint of unloading
M.L. Stammer, C. Camy, M. Frewein et al. (+16 more)
The enthesis is a graded fibrocartilaginous interface that transfers load between tendon and bone, yet the nanoscale mechanisms stabilizing its mineralization front remain unclear. Here, we combine
multimodal 2D/3D X-ray imaging with nonlinear optical microscopy to map structural, crystalline and extracellular
matrix organization across the murine Achilles tendon enthesis under unloading and reloading. Unloading reduces the tidemark-associated two-
photon fluorescence (2PF) peak and is accompanied by diffuse mineralization into previously unmineralized fibrocartilage. This unloading-associated mineral exhibits increased apparent crystallite size, an enlarged c-axis
lattice parameter, reduced crystalline texture and a diminished collagen order gradient, consistent with an altered mineralization environment. Upon reloading, the 2PF peak recovers, but a new tidemark forms ~20 um from the original boundary, creating a zone with a persistent nanoscale imprint in the mineral tessellation. These findings establish the enthesis as a mechanically governed graded interface in which
matrix-mediated boundary control constrains mineral formation and in which a record of mechanical history is imprinted into the nanostructure.
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All authors M.L. Stammer, C. Camy, M. Frewein, I. Silva Barreto, C. Genovesio, M. Eckermann, A. Karimbana, K. Iliopoulos, R. Ranjan, N. Wittig, T. Fovet, T. Brioche, A. Chopard, M. Burghammer, S. Brasselet, H. Birkedal, M. Pithioux, S. Roffino, T.A. Grünewald
Materials Science
First-Principles Spin-Lattice Coupling from Downfolded Electron-Phonon Interaction
Xu He, Álvaro Adrián Carrasco Álvarez, Gian-Marco Rignanese et al. (+3 more)
We present a method to calculate
spin-
phonon coupling parameters from first-principles perturbation theory by downfolding the electron-
phonon coupling (EPC). We exploit the localized nature of
magnetic moments and atomic displacements by working in the Wannier representation of the electronic
Hamiltonian and the EPC
matrix. The
spin system is mapped to a classical Heisenberg
Hamiltonian, whose parameters are obtained by treating local
spin rotations as a perturbation within a Green's-function formalism. The
spin and
phonon perturbations are connected through the EPC parameters, which enter as
lattice-induced perturbations to the tight-binding
Hamiltonian. By combining these
lattice perturbations with local
spin rotations, we obtain real-space derivatives of
magnetic exchange parameters without performing displaced
magnetic supercell calculations. We illustrate the method on SrMnO$_3$ and show that it can be integrated directly into standard workflows.
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All authors Xu He, Álvaro Adrián Carrasco Álvarez, Gian-Marco Rignanese, Eric Bousquet, Samuel Poncé, Matthieu J. Verstraete
Materials Science
Impact of Carbon Contamination on the Low-Temperature Electric Conduction of the Spark-Plasma Sintered Barium Titanate Ceramics
Oleksandr S. Pylypchuk, Taisiia O. Kuzmenko, Denis O. Stetsenko et al. (+6 more)
The dielectric and electric conduction properties of BaTiO3 samples fabricated by the spark
plasma sintering with additional contamination by different content of carbon have been investigated in the temperature range from 77 through 408 K in small non-heating electric fields and in the range of 77 - 200K under strong electric fields up to 20 kV/cm. The effective dielectric permittivity of the samples with additional carbon achieves colossal values at low frequency, up to several units per 106 at 393 K. In the low temperature range, it remains very high magnitude, 10^4 -10^5 at low frequency and is strongly dependent on the carbon content. The electric conduction in the range of 77 - 200 K bears the hopping conduction and obeys the Mott law. We also studied electric conduction and effective dielectric permittivity vs electric field strength in the range of 77 - 200 K. The results are explained within the frames of hopping conduction theory and suggestion on different constituents in polarization processes and electric conduction.
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All authors Oleksandr S. Pylypchuk, Taisiia O. Kuzmenko, Denis O. Stetsenko, Oleksyi V. Bereznykov, Serhii E. Ivanchenko, Ihor M. Danylenko, Anna N. Morozovska, Vladimir N. Poroshin, Victor V. Vainberg
Materials Science
Multiscale Quasiparticle Electronic Structure and Excitonic Properties of CdSe Nanoclusters
Surender Kumar, Martin Thümmler, Alexander Croy et al. (+2 more)
Quantum confinement in stoichiometric $\mathrm{Cd}_n\mathrm{Se}_n$ nanoclusters dramatically attenuates electronic screening, driving a delicate, size-dependent competition between quasiparticle self-energy corrections ($\Delta_{\mathrm{QP}}$) and
exciton binding energies ($E_b$). Here, we present a $GW$/BSE study across a representative size series ($n = 3, 6, 13, 33$) and leverage it to validate a scalable atomistic tight-binding (TB) framework derived from first principles. Our results demonstrate that 1-2 eV spectral blueshifts previously reported in the literature arise from single-particle $GW$ convergence artifacts rather than deficiencies in the electron–hole kernels. We show that the near-perfect cancellation between $\Delta_{\mathrm{QP}}$ and $E_b$ breaks down as cluster volume increases, driven by the rapid onset of dielectric screening attenuating $E_b$ faster than $\Delta_{\mathrm{QP}}$ and leading to a pronounced divergence from mean-field predictions. Spatial inverse participation ratio analysis of the electronic structure reveals that optical suppression of fundamental pre-peaks stems from a severe spatial mismatch between localized valence orbitals and delocalized conduction states. Finally, we demonstrate that the confinement-induced scaling of the quasiparticle gap and the optical onset is accurately reproduced by a scissor-corrected, DFT-parameterized TB model. As such, this work provides a quantitative multiscale roadmap for
embedding effective many-body effects kernels into computationally efficient models, enabling reliable optical predictions for realistic semiconducting nanostructures containing up to thousands of atoms.
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All authors Surender Kumar, Martin Thümmler, Alexander Croy, Stefanie Gräfe, Caterina Cocchi
Materials Science
Probing the transport properties of Cantor-Wu alloys by means of femtosecond and nanosecond laser ablation
David Redka, Maximilian Spellauge, Rosemary Babu et al. (+5 more)
Single-pulse
laser ablation thresholds of selected equiatomic Cantor-Wu
alloys - FeNi, CoNi, CrFeNi, CrCoNi, and CrMnFeCoNi - are measured for femtosecond and nanosecond pulse durations and interpreted through first-principles calculations of the electronic structure, the electron-
phonon coupling, and the electronic thermal conductivity.
Alloy synthesis, ablation experiments, and theory are performed consistently on the same set of samples. The absorbed femtosecond thresholds decrease systematically by up to 36 % from FeNi to the Cr-containing
alloys, a trend that reflectance variations cannot explain. Two-temperature-model scaling of the thresholds with the electronic thermal conductivity and the electron-
phonon coupling, with all parameters taken from the
spin-disordered phase, reproduces the measured hierarchy. The nanosecond thresholds instead probe the thermal
equilibrium conductivity averaged along the heating path. The apparent outlier of CoNi, whose room-temperature transport over-predicts its thresholds by up to a factor of two for both pulse durations, is resolved quantitatively by the collapse of its conductivity upon loss of ferromagnetic order. Single-pulse ablation thresholds thereby emerge as sensitive, contact-free probes of electronic transport and of its
magnetic-phase dependence in compositionally complex
alloys.
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All authors David Redka, Maximilian Spellauge, Rosemary Babu, Christopher D. Woodgate, Hubert Ebert, Ján Minár, Daniel J. Förster, Heinz P. Huber
Materials Science
Z1 oscillations and charge state in electronic stopping power from first principles
Noor Ul Ain and Emilio Artacho
The energy transfer rate from a projectile
nucleus to the electrons of the matter it traverses depends on the charge of that projectile, Q= e Z1. At low projectile velocities the friction coefficient is known to oscillate with atomic number Z1, since core electrons travel with the projectile screening its charge. The effective charge increases with velocity and oscillations disappear. That effect is studied here calculating electronic stopping power from first principles for O and Mg projectiles shooting through bulk Al, using real-time time-dependent density-functional theory. Both projectiles represent maximum and minimum of the first Z1 oscillation, respectively. The oscillation is found to be very sensitive to the direction of propagation, in spite of Al being quite an ideal metal for many purposes. The critical velocity for the oscillation disappearance ranges between below 0.1 a.u. and beyond 1 a.u. for the explored trajectories. The charge state is independently quantified with Hirshfeld and Voronoi analyses, offering remarkably consistent results in spite of their very different partition methods, as well as with an effective definition based on the stopping power itself. They display a gradual undressing of the projectile's core electrons with increasing velocity in qualitative accordance with expectations. However, electron density plots in real space present a richer picture in which the undressing is partly due to the electrons trailing behind the projectile, suggesting possible phenomenological descriptions correcting for the deformation of the density in terms of multipoles beyond the net charge. The plots also offer insights into dissipation by core electrons.
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Materials Science · Cross-listed from cond-mat.supr-con
Three-dimensional Ising superconductors designed via inversion-symmetry breaking in intercalated NbSe$_2$ and NbTe$_2$
Wenqian Tu, Run Lv, Xiaoying Li et al. (+4 more)
Ising
superconductors exhibit in-plane upper critical fields far exceeding the Pauli paramagnetic limit, a hallmark first established in two-dimensional (2D) monolayer transition-metal dichalcogenides (TMDs). This field resilience requires the coexistence of strong
spin-orbit coupling (SOC) and broken inversion
symmetry, yet three-dimensional (3D) bulk realizations remain scarce because
equilibrium stacking typically restores inversion
symmetry. Here we demonstrate that intercalation provides a practical route to break this
symmetry, systematically designing 16 NbSe$_2$- and NbTe$_2$-based compounds from four intercalants (In, Sn, Pb, Bi) across two polytypes: non-centrosymmetric $P\bar{6}m2$ and centrosymmetric $P6_3/mmc$. Four compounds in the $P\bar{6}m2$ phase, InNbSe$_2$, SnNbSe$_2$, PbNbSe$_2$, and PbNbTe$_2$, emerge as promising 3D Ising
superconductors. They exhibit SOC splittings of 80-100 meV near the Fermi level, dominant out-of-plane
spin polarization, and anisotropic superconductivity with $T_c=2.6$-$5.4$ K. Notably,
spin-texture analysis reveals that the efficiency of Ising protection is governed not by the magnitude of SOC splitting alone but by the out-of-plane
spin purity on the Fermi surface. Bogoliubov-de Gennes (BdG) calculations predict in-plane upper critical fields reaching 4-7 times the Pauli limit. These findings establish intercalation as a promising
symmetry-engineering strategy for realizing 3D Ising
superconductors in TMDs.
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All authors Wenqian Tu, Run Lv, Xiaoying Li, Li'e Liu, Dingfu Shao, Yuping Sun, Wenjian Lu
Materials Science
X-ray driven displacive excitation of coherent phonons
Oleg Dogadov, Remi Claude, Christoph Emeis et al. (+29 more)
Modulating electron-
phonon coupling offers a route to control structural displacements and tune material functionality. Valence-to-conduction band transitions, however, provide limited leverage over the driving force. Here, we demonstrate coherent
lattice dynamics in trigonal tellurium using free-electron
laser pulses tuned to the Te N4,5-edge. Over a broad fluence range, the oscillation amplitude obeys the displacive excitation of coherent
phonons framework, extended to core resonance with twice the driving efficiency of a visible pump. Ab initio calculations decompose the force into competing multiband contributions, inaccessible to optical excitation, whose balance shifts as carriers relax. Tunable extreme-ultraviolet and X-ray pulses thus open a regime in which the displacive response is set by band-dependent coupling to the
lattice, not by the number and temperature of the photocarriers alone.
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All authors Oleg Dogadov, Remi Claude, Christoph Emeis, Giovanni Batignani, Giuseppe Fumero, Roberto Costantini, Agata Azzolin, Sabine Rockenstein, Paolo Cattaneo, Rebeca Gomez Castillo, Matteo Manzi, Angelo Giglia, Dario De Angelis, Ettore Paltanin, Zeinab Ebrahimpour, Marija Krstulovic, Gabor Kurdi, Miltcho Danailov, Luca Giannessi, Riccardo Mincigrucci, Emiliano Principi, Alberto Crepaldi, Giulio Cerullo, Giovanni De Ninno, Claudio Masciovecchio, Laura Foglia, Tullio Scopigno, Fabrizio Carbone, Francesca Calegari, Fabio Caruso, Michele Puppin, Oliviero Cannelli
Materials Science
Displacement-field-driven reconstruction of low energy transport in few-layer PtSe2
Xiao Liu, Yaroslav Zhumagulov, Yuang Jie et al. (+9 more)
In layered
semiconductors, a perpendicular displacement field generates an interlayer potential difference that competes with interlayer hybridization, modifying both the band gap and the finite-density electronic states that carry current. Resolving this interplay requires a material lying close to the
semiconductor-to-semimetal transition, where moderate electric fields can strongly reshape the low-energy electronic structure. Here, we investigate displacement-field-driven transport in dual-gated semiconducting PtSe2, whose pronounced thickness-dependent electronic structure provides access to this low-band-gap regime. Unlike thinner layers, the displacement-field response is strong in six-layer PtSe2, which lies at the verge of the
semiconductor-to-semimetal crossover with only a small residual transport gap. Even weak displacement fields rapidly suppress this residual gap near charge neutrality, driving the system toward a band-overlap regime. At the same time, the conductivity decreases in the heavily hole-doped regime, demonstrating that the displacement field modifies not only the gap but also the conducting valence-band states. Fixed-relaxation-time Wannier transport calculations reproduce both responses, showing that they originate from field-induced band overlap together with reconstruction of the valence-band dispersion. These results establish finite-density transport as a sensitive probe of displacement-field-driven electronic structure reconstruction and extend electrical control beyond conventional band-gap engineering.
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All authors Xiao Liu, Yaroslav Zhumagulov, Yuang Jie, Ahmet Enes Bozcali, Johan Felisaz, Qi Zhang, Oldvrich Cicvarek, Kenji Watanabe, Takashi Taniguchi, Zdeněk Sofer, Oleg V. Yazyev, Ahmet Avsar
Materials Science
Discovery of New Zintl Films and Nanowires Grown by Topotaxy Conversion of III-V Semiconductors
Man Suk Song, Lothar Houben, Jean Souza et al. (+8 more)
Zintl phases draw broad interest for their diverse structural,
magnetic, thermoelectric, topological and optical properties. Recently, Zintl Eu$_3$In$_2$As$_4$ and Eu$_5$In$_2$As$_6$ nanowires with
axion magneto-
topology have been synthesized by molecular beam epitaxy via topotactic conversion of InAs wurtzite and zincblende nanowires. Here we extend this methodology, demonstrating that topotaxial mutual-exchange growth applies not only to a broader set of III-V
semiconductors beyond InAs but also to three-dimensional substrates whose surfaces are converted into Zintl thin films, as well as to nanowires. We report the growth of two new compounds: Eu$_5$Ga$_2$As$_6$ thin films converted from GaAs substrates, and Eu$_5$Al$_2$As$_6$ thin films from AlAs films. We also convert GaAs nanowires of both wurtzite and zincblende structures into Eu$_5$Ga$_2$As$_6$ nanowires. Though the stoichiometry is the same as in the previously reported Eu$_5$In$_2$As$_6$ case, microscopy and diffraction reveal a single-phase Pnma
symmetry group rather than Pbam, highlighting
symmetry-guided topotactic pathways to new Zintl frameworks. The compounds host an intricate
magnetic phase diagram with three
magnetic transitions, including two distinct antiferromagnetic orders and a canted antiferromagnetic phase that evolves into another antiferromagnetic phase under applied field through a
spin-flop transition. Ab initio calculations predict that both Zintls are
semiconductors with gaps of 0.79 eV in Eu$_5$Ga$_2$As$_6$ and 0.90 eV in Eu$_5$Al$_2$As$_6$. The lower
symmetry and increased structural complexity suggest suppressed
lattice thermal conductivity, pointing to thermoelectric potential alongside prospects in spintronics and detector technologies. These results give an epitaxy-compatible route for discovering and integrating
magnetic Zintl thin films and nanowires directly from relevant III-V
semiconductors.
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All authors Man Suk Song, Lothar Houben, Jean Souza, Edanel Fishbein, Moshe Haim, Ambikesh Gupta, Yufei Zhao, Anna-Eden Kossoy, Binghai Yan, Haim Beidenkopf, Hadas Shtrikman
Materials Science · Cross-listed from physics.optics
Self-consistent modelling of all-optical switching and magneto-optic readout in an integrated Si$_3$N$_4$/GdFeCo waveguide
Muhammad Arief Mulyana, Budi Adiperdana and Ayi Bahtiar
What a guided beam carries after passing through an all-optically switched
magnetic film has not been computed, although such switching has been demonstrated on a silicon nitride waveguide with electrical readout. We close the chain for an integrated Si$_3$N$_4$/GdFeCo element, an 8 nm film on a 60 $\mu$m waveguide, coupling a three-dimensional dispersive finite-difference time-domain solver to absorbed optical work, a four-temperature model, and
stochastic two-sublattice Landau-Lifshitz-Bloch dynamics with a fluctuation-dissipation-consistent Langevin field, the magnetization feeding back into the gyrotropic permittivity that a second guided shot reads. Transmission, reflection and absorption are magnetization-blind, closing to 0.974-0.975 and shifting by at most 0.02 between saturated, demagnetized and multidomain films, because magnetization enters the dielectric tensor only through an antisymmetric element on which absorbed power depends at second order; the odd-in-magnetization polarimetry separates them by an order of magnitude in Faraday rotation and two in Kerr. The guided geometry levies a cost free-space measurement does not: a $-11.77^\circ$
geometric pedestal on the reflected channel, exceeding the $8.24^\circ$ rotation it hides. Referencing against a demagnetized film returns it to $0.063^\circ$. The transmitted mode carries a second signature in its lobe balance, needing no polarimetry. Calibrated pulses toggle 0.859 of the film from either saturated state across a $2.4\times$ fluence window, and the shortfall from unity is photonic rather than
magnetic: the switched fraction is the complementary cumulative distribution of the guided-mode absorption map at the single-
cell threshold, holding to $8\times10^{-4}$ at five full-wave anchors. From exactly zero magnetization, branch selection passes to the Langevin field alone, at occupancy $0.502 \pm 0.004$ over 16 seeds.
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Materials Science · Cross-listed from physics.chem-ph
Generalizing Abell-Tersoff bond-order potential with explicit high-order many-body correlations for robust extrapolation of potential energy surfaces
Ikuma Kohata
Machine-learning interatomic potentials enable accurate and efficient atomistic simulations, yet their reliability for out-of-distribution configurations far beyond the training domain remains a significant challenge. Here, we introduce a semiparametric interatomic potential based on a generalization of the Abell–Tersoff bond-order potential, incorporating a chemically informed functional form and explicit high-order many-body correlations to address this challenge. The model is trained and evaluated on various
datasets of silicon, carbon, water, and small molecules, achieving interpolation accuracy comparable to existing MLIP models while exhibiting improved extrapolation to unseen configurations, including those at high pressures and temperatures. These results provide insights into the design of specific inductive biases for reliable extrapolation in interatomic potentials. inductive biases that can be used to control extrapolation in machine-learning interatomic potentials.
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