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Physics Condensed Matter

cond-mat Watch Condensed Matter

Sunday 31 May

Materials Science

Giant enhancement in spin-to-charge conversion in Bi2Se3/NiFe heterostructure via interface engineering

Sourav Rajat Subhra Maitra, Poulami Manna, Ravi Prakash Singh et al. (+2 more)

Topological insulators provide a promising platform for spintronic applications owing to their spin-momentum-locked surface states and efficient spin-to-charge conversion. Among these, Bi2Se3 has been the subject of intensive investigation due to its large bulk bandgap and single Dirac cone band structure. However, spin-to-charge conversion strongly depends on the quality of the topological insulator/ferromagnet interface. Here, we investigate spin transport and spin-to-charge conversion in sputter-deposited Bi2Se3/Ti/NiFe heterostructures at room temperature. The topological insulator layer is deposited on a CMOS-compatible silicon substrate. Low-temperature magnetoresistance measurements are conducted to establish the existence of a surface conducting channel in the deposited topological insulator layer. Pure spin current is injected into the Bi2Se3 layer through the titanium spacer layer via spin pumping induced by the spin precession in microwave-driven ferromagnetic resonance of the ferromagnetic film. Spin pumping studies are carried out by varying the thickness of the Bi2Se3 layer. The Bi2Se3 thickness dependence of the Gilbert damping reveals a pronounced 55% enhancement at a thickness of 4 nm, consistent with the hybridization of the top and bottom surface states of the topological insulator layer. The spin Hall angle, a parameter that quantifies the spin-to-charge conversion efficiency, exhibits an approximately one-order-of-magnitude enhancement upon insertion of the Ti spacer compared with Bi2Se3/NiFe heterostructures without the spacer. The significant enhancement of the spin Hall angle is attributed to Ti, which inhibits interdiffusion between the Bi2Se3 and NiFe layers, thereby protecting the topological surface states. Our findings highlight the role of titanium spacers in topological spintronics applications.
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All authors Sourav Rajat Subhra Maitra, Poulami Manna, Ravi Prakash Singh, Chandrasekhar Murapaka, Arabinda Haldar

Mesoscale and Nanoscale Physics

Hot carrier diffusion-assisted ideal carrier multiplication in monolayer MoSe2

Joonsoo Kim, Hong-Guk Min, Sehwan Park et al. (+4 more)

Carrier multiplication (CM), the process of generating multiple charge carriers from a single photon, offers an opportunity to exceed the Shockley-Queisser limit in photovoltaic applications. Despite extensive research, no material has yet achieved ideal CM efficiency, primarily owing to significant energy losses from carrier-lattice scattering. In this study, we demonstrate that monolayer MoSe2 can attain the theoretical maximum CM efficiency permitted by energy-momentum conservation principle, using ultrafast transient absorption spectroscopy. By resolving the scatter-free ballistic transport of hot carriers and validating our findings with first-principles calculations, we identify the cornerstone of optimal CM in monolayer MoSe2: superior hot-carrier dynamics characterized by suppressed energy dissipation via minimized carrier-lattice scattering, and the availability of abundant CM pathways facilitated by 2Eg band nesting. Comparative analysis with bulk MoSe2 further emphasizes the enhanced CM efficiency in the monolayer, attributed by superior hot-carrier diffusion and access to additional CM pathways. These results position monolayer MoSe2 as a promising candidate for high-performance optoelectronic applications, providing a robust platform for next-generation energy conversion technologies.
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All authors Joonsoo Kim, Hong-Guk Min, Sehwan Park, Jin Cheol Park, Junhyeok Bang, Youngkuk Kim, Ji-Hee Kim

Quantum Gases

Ground-state phase diagram of Rydberg atoms in a triangular-prism array

Qing-Yuan Zuo, Shuo Geng, Shan-Wen Tsai et al. (+1 more)

We study the ground-state phase diagram of Rydberg atoms in a triangular-prism optical tweezer array using the density matrix renormalization group. By tuning the detuning-to-Rabi-frequency ratio and the Rydberg blockade radius, the system realizes several density-wave phases with spontaneous breaking of translational and leg-exchange symmetries. Unlike two-leg Rydberg ladders with $\mathbb{Z}_2$ leg-exchange symmetry, the triangular prism has $\mathbb{D}_3$ symmetry, leading to a richer set of ordered phases and transitions. For blockade radius moderately larger than the lattice spacing, a phase with alternating double and single Rydberg occupancy appears at large detuning. It breaks $\mathbb{Z}_2$ translational and $\mathbb{Z}_3$ rotational symmetry while preserving a rung reflection symmetry. Upon decreasing detuning, it melts through two Berezinskii-Kosterlitz-Thouless transitions with an intermediate critical phase described by a $\mathbb{Z}_6$ clock model. At larger blockade radius, a phase with one Rydberg excitation per triangle and broken $\mathbb{D}_3$ symmetry appears through a first-order transition. When double occupation of neighboring triangles is suppressed, rung-trimerized density waves develop as detuning increases from the disordered phase. Their melting follows the same structure as in Rydberg chains and two-leg ladders: the $\mathbb{Z}_2$ case has Ising critical lines, while the $\mathbb{Z}_3$ and $\mathbb{Z}_4$ cases have chiral critical lines, with Potts and Ashkin-Teller points only on the corresponding commensurate lines. Inside the $\mathbb{Z}_2$ rung-trimerized phase, an entanglement-entropy peak signals a crossover regime with enhanced period-2 density modulation before a first-order transition into a $\mathbb{Z}_2\times\mathbb{D}_3$ phase. Floating phases with incommensurate quasi-long-range order appear between trimerized states of different periods.
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All authors Qing-Yuan Zuo, Shuo Geng, Shan-Wen Tsai, Jin Zhang

Mesoscale and Nanoscale Physics · Cross-listed from cs.DC

Magnum.np.distributed: Accelerating Finite Difference Micromagnetic Simulations with Multiple GPUs

Tsz Chung Cheng, Yuichiro Kurokawa and Hiromi Yuasa

Micromagnetic simulations are essential tools in nanomagnetism and spintronics research. Although widely adopted solvers like Mumax3 and the Python-native magnum.np use GPU acceleration to improve performance, these tools are limited to single-device computation. In this work, we present the first Python-native multi-GPU micromagnetic framework by extending magnum.np with PyTorch Distributed. This leverages high-speed communication and computation across multiple GPUs while retaining the benefits of ease of installation, platform-agnostic design, and compatibility with Python. For computationally intensive demagnetisation effective-field calculations, we achieve a 7.0x speedup across 8 GPUs connected via NVLink, whereas Halo exchange required for Heisenberg exchange shows limited scaling due to kernel dispatch latency. We also demonstrated the framework's versatility by achieving a 6.8x speedup in demagnetisation field computation on CPU with NUMA pinning via the MPI backend of PyTorch Distributed. Faster turnaround times will enable researchers to explore larger, more complex systems and accelerate the design cycle for novel spintronic devices.
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Materials Science

A literature-grounded scientific reasoning framework for defect-engineered TiO$_{2}$ photocatalysts

F. J. Dominguez-Gutierrez and E. Wierzbicka

Defect-engineered TiO$_2$ photocatalysts are extensively investigated for photocatalytic hydrogen evolution; however, the highly heterogeneous nature of the literature, including inconsistent descriptors, diverse synthesis protocols, non-uniform activity metrics, and incomplete mechanistic reporting, limits the applicability of conventional machine-learning approaches based solely on statistical regression. Here, we present a literature-grounded large language model (LLM)-assisted scientific reasoning framework for defect-engineered TiO$_2$ photocatalysts integrating curated literature data, mechanistic rule extraction, and retrieval-augmented reasoning. A harmonized database was constructed from experimentally relevant publications specifically selected for hydrogen-evolution-related defect engineering in TiO$_2$, covering polymorph-dependent behavior, hydrogenation conditions, Ti$^{3+}$ defect states, oxygen vacancies, illumination conditions, and photocatalytic activity descriptors. In parallel, mechanistic evidence sentences and publications-defined scientific rules were encoded into a structured reasoning layer enabling explainable inference beyond black-box prediction. The resulting framework combines structured experimental descriptors, semantic literature retrieval, and mechanistic interpretation to generate confidence-aware recommendations for optimal defect-engineering conditions. For example, the AI agent identified a consistent optimal anatase hydrogenation window centered at ~500 $\deg$C under H$_2$-containing atmospheres for approximately 1 h, supported by mechanistic evidence linking balanced Ti$^{3+}$/oxygen-vacancy populations with enhanced photocatalytic hydrogen evolution.
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Materials Science

Topological Surface States and Anisotropic Magnetotransport in SnSb$_6$Te$_{10}$

Mohit Mudgal, Subhajit Mandal, Bishal Das et al. (+11 more)

We have investigated the electronic structure and magnetotransport properties of SnSb$_6$Te$_{10}$ single crystals using density functional theory (DFT), synchrotron-based angle-resolved photoemission spectroscopy (ARPES), and quantum transport measurements. Our DFT calculations reveal a clear spin-orbit coupling driven band inversion between the Sb-$p$ and Te-$p$ states together with a non-trivial $\mathbb{Z}_2$ topological invariant. The calculated surface-state dispersion and hexagonally warped Fermi surface contours agree well with the ARPES measurements. Temperature-dependent transport measurements indicate dominant electron-phonon scattering, while Hall measurements confirm hole-type carriers with carrier density of the order of $10^{21}$ cm$^{-3}$. Both transverse and longitudinal magnetotransport exhibit weak antilocalization behavior, while Shubnikov-de Haas oscillations observed for $H \parallel c$ yield a Berry phase close to $\pi$, consistent with Dirac-like surface states. Furthermore, angle-dependent magnetotransport measurements reveal pronounced anisotropy associated with an anisotropic Fermi surface topology and mixed bulk-surface transport behavior. Our combined theoretical and experimental results establish SnSb$_6$Te$_{10}$ as a strong topological insulator and a promising platform for investigating topological transport phenomena in layered telluride systems.
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All authors Mohit Mudgal, Subhajit Mandal, Bishal Das, Priyanka Meena, Amarjyoti Choudhury, Vishnu Kumar Tiwari, Yogendra Kumar, Vivek Kumar Malik, Tulika Maitra, Kiyohisa Tanaka, Shinichiro Ideta, Kenya Shimada, Aftab Alam, Jayita Nayak

Mesoscale and Nanoscale Physics

Wilson Holonomy and Spectral Monodromy in Spin-Orbit Rings: Effective Gauge Connections and Loop Observables

N. Bolivar

A spin-orbit Hamiltonian with an effective gauge structure carries two distinct loop objects that are routinely conflated: an energy-independent Wilson holonomy, which organizes interference and internal spin transport, and an energy-dependent monodromy, which quantizes the spectrum. We show that cleanly separating these objects supplies a precise, computable bridge between the loop/holonomy representation of gauge theories and condensed-matter spin-orbit transport. The construction maps a spin-orbit Hamiltonian to an effective $U(1)$ plus internal non-Abelian connection, reduces it to a first-order transport problem, and reads physical predictions from holonomy, monodromy, curvature, and eigenphase data. Two rings make the separation explicit. For a Dirac (graphene) ring with Rashba coupling and Aharonov-Bohm flux, the total holonomy factorizes exactly into a commuting $U(1)$ flux phase times an internal spin/pseudospin holonomy, and the spectrum follows from a holonomy-eigenvalue condition. For a Rashba-Dresselhaus ring, the internal $SU(2)$ transport is genuinely non-Abelian away from the $\alpha=\pm\beta$ pure-gauge locus, where curvature controls path ordering; spectral quantization then requires an explicit first-order reduction obtained by phase-space doubling of the second-order Schrödinger problem. A non-Abelian Stokes formulation and Magnus expansion serve as ordering diagnostics rather than spectral tools. Spin-network ideas enter only as historical geometric motivation, not as a dynamical import into spintronics.
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Materials Science · Cross-listed from cs.AI

Property Prediction of Stacked Bilayer Materials: A Multimodal Learning Approach

An Vuong, Minh-Hao Van, Chen Zhao et al. (+1 more)

AI for materials science is a critical topic within AI for science, aiming to accelerate materials discovery and produce accurate property predictions. Bilayer 2D material stacking is essential for exploring new materials with novel functions and inherent phenomena, enabling the creation of new 2D bilayers for diverse real-world applications. Research on bilayer vdWs materials has made significant progress from experimental and computational perspectives. Various bilayer materials have been successfully synthe sized experimentally and the increasing utilization of high-throughput computing technology has con structed several computational two-dimensional materials databases. However, the use of AI to model bilayer stacking and predict new properties remains underexplored, necessitating further research studies. In this work, we propose a novel multimodal learning approach to study the interfaces between dissimilar materials that jointly enable new or multiple functions, and to predict new properties arising from the vertical integration (stacking) of different functional material layers under given configurations. Comprehensive experiments demonstrate the effectiveness and efficiency of our approach compared to baseline methods. Our code is available at https://github.com/AnVuong123/bimat ml.
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All authors An Vuong, Minh-Hao Van, Chen Zhao, Xintao Wu

Mesoscale and Nanoscale Physics · Cross-listed from physics.app-ph

Surface Excitations, Energy Loss, and Decoherence in Electron Interferometry

David Kordahl

A recent pedagogical paper by Strauch concretely demonstrated how interaction-mediated entanglement can suppress fringe visibility in a one-dimensional model of the electron double-slit experiment. Here we extend that framework to model actual experimental data from electron biprism interferometry. Kerker et al. showed that the macroscopic QED model of Scheel and Buhmann successfully describes their measured results. We show that this Scheel-Buhmann model can be recovered from Strauch's simplified framework by employing a Markov approximation and including thermal effects. The resulting decoherence rate is expressed in terms of mode-resolved scattering probabilities familiar from electron energy-loss spectroscopy (EELS), directly relating EELS to decoherence. The thermal dependence is significant in its own right, as recent theoretical work suggests that visibility reduction could serve as a non-invasive thermal probe for nanoscale systems. This progression from a toy model, to a quantitative account of real data, to a measurement application offers a case study in how simplified models can be made experimentally relevant.
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Mesoscale and Nanoscale Physics

Electronic Hall viscosity: hidden indicator for antiferromagnets

Ding Li, Tao Qin and Jianhui Zhou

The antiferromagnets with negligible stray fields and ultrafast spin dynamics play a crucial role in the fields of energy-efficient spintronics and topological electronics. However, the detection and control of the underlying nontrivial Berry curvature become extremely limited by the vanishing magnetization and anomalous Hall conductivity. Here, we show the electronic Hall viscosity is closely related to the quadruple Berry curvature of Bloch bands and is bounded by the $d$-orbit factor modulated second moment of the quantum volume. Moreover, we derive the symmetry requirement for nonzero electronic Hall viscosity that could characterize antiferromagnetic ordering even when the linear anomalous Hall response gets forbidden. We further examine our key findings in two archetypal antiferromagnets: $d$-wave altermagnet $\mathrm{RuO}_{2}$, and noncollinear $\mathrm{Mn_{3}Sn}$ through direct first-principle calculations. Thus, our work reveals a new and fundamental quantum geometry quantity of generic antiferromagnets and offers a broadly applicable way to design antiferromagnetic spintronics devices via unconventional Hall viscosity.
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Soft Condensed Matter · Cross-listed from math-ph

Axisymmetric membrane shapes in the Willmore and Helfrich models: first integrals and a hyperbolic formulation

Z. C. Tu

The equilibrium shapes of fluid lipid membranes are governed by nonlinear differential equations derived from the Helfrich bending energy. In the tensionless, pressure-free, and zero-spontaneous- curvature limit, the governing equation reduces to the Willmore equation. We show that the combination of the Zheng–Liu and Langer–Singer first integrals reduces the third-order axisymmetric Willmore equation to a first-order ordinary differential equation. This formulation recovers the sphere, axisymmetric minimal surfaces, and the Clifford torus as special cases, while organizing the local solution space according to two integration constants. For nonzero spontaneous curvature, the axisymmetric Helfrich functional is reformulated as the energy of an inhomogeneous hyperbolic elastica with a preferred curvature proportional to the distance from the axis. This formulation identifies a constant-mean-curvature branch and a logarithmic branch associated with a biconcave disk profile. The resulting exact relations provide analytical constraints and benchmark solutions for configurations of axisymmetric vesicles and biomembranes.
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Saturday 30 May

Strongly Correlated Electrons

Locality-Induced Hierarchical Backflow Wavefunctions for Correlated Fermions

Yu-Tong Zhou, Zheng-Wei Zhou and Wen-Yuan Liu

We show that locality provides a natural principle to hierarchically organize backflow wavefunctions. This leads us to propose a family of variational fermionic states, termed hierarchical backflow (HB) wavefunctions. The expressive power of HB is systematically improvable, controlled by a path depth $K$ which reflects the range of backflow correlations. At half-filling, the HB with $K=1$ already achieves high energy precision, with an accuracy around $0.5\%$ for system sizes from $4\times 4$ to $10\times 10$. At hole doping $n_h=0.125$, the method scales efficiently to $12\times16$ and $16\times16$ systems, and the energy systematically achieves higher accuracy with $K$ increasing, yielding a clear stripe phase. The HB further enables a local-nonlocal decomposition, naturally bridging to neural quantum states, while featuring compact representations and efficient optimization. Our work reveals locality as a natural organizing principle of backflow wavefunctions, opening a new framework with systematic improvability and interpretability for large-scale simulations of correlated fermion systems.
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Soft Condensed Matter · Cross-listed from physics.flu-dyn

Solubility enhanced surfactant-induced flow in air-liquid-air sheets

Jun Eshima, Tristan Aurégan, Emmanuel Villermaux et al. (+2 more)

Liquid interfaces appear throughout nature and engineering and are typically contaminated by surface active agents (surfactants), which are characterized by a wide range of solubility. We demonstrate that solubility enhances by an order of magnitude surfactant-induced flow in air-liquid-air films, in contrast to previously studied geometries where solubility dampens the flow. The enhancement is described by a single parameter comparing the depletion length to the film thickness. Our experiments are well described by an asymptotic theory of the Navier-Stokes equations with surfactant kinetics.
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All authors Jun Eshima, Tristan Aurégan, Emmanuel Villermaux, Howard A. Stone, Luc Deike

Superconductivity

Structure, Composition, and High-Field Superconductivity in Metal-Rich $\mathrm{\eta}$-Carbide-Type Compounds

Manuele Balestra, KeYuan Ma, Harald O. Jeschke et al. (+1 more)

$\mathrm{\eta}$-Carbide-type compounds have recently emerged as a diverse class of materials in the study of superconductivity. These phases contribute to a growing family of metal-rich quantum materials that exhibit unusual superconducting properties emerging from complex metallic bonding. Several members of the $\mathrm{\eta}$-carbide-type phases have been found to be bulk superconductors – such as Nb$_4$Rh$_2$C$_{1-\delta}$, Ta$_4$Rh$_2$C$_{1-\delta}$, Ti$_4$Ir$_2$O$_{1-\delta}$, and Ti$_4$Co$_2$O$_{1-\delta}$ – with transition temperatures up to $T_{\rm c} \approx$ 10 K and upper critical fields as high as $\mu_0 H_{\rm c2}(0) \approx$ 30 T. Whereas the transition temperatures may fall within the range typical for intermetallic superconductors, the pronounced violation of the weak-coupling Pauli limit in many of these crystallographically high-symmetry materials is noteworthy. Here, we review recent progress on superconducting $\mathrm{\eta}$-carbide-type phases, emphasizing how crystal symmetry, synthetic challenges, transition-metal composition, and electronic structure govern their superconducting properties. Furthermore, we outline open questions and future directions, including the possible discovery of new $\mathrm{\eta}$-carbide-type materials.
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All authors Manuele Balestra, KeYuan Ma, Harald O. Jeschke, Fabian O. von Rohr

Statistical Mechanics

High Resolution Study of the 2D ANNNI Model Using a Two-replica Cluster Algorithm and Population Annealing

Shane Keiser and Jon Machta

The axial next-nearest-neighbor Ising (ANNNI) model in two dimensions is studied using population annealing combined with a two-replica cluster algorithm. We are able to fully resolve the sequence of sharp specific heat peaks that characterize the finite-size incommensurate floating phase. We also show that the two-replica cluster algorithm is much more effective in equilibrating the system than either single-replica cluster methods or the Metropolis algorithm when these are combined with population annealing. We argue that effectiveness of the new algorithm is due to its ability to move groups of defect lines between replicas combined with resampling in population annealing, which removes replicas from the population that have larger numbers of defect lines.
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Materials Science · Cross-listed from quant-ph

Topological Edge States from Molecular Chirality: A General Framework for Dimerized Dipolar Arrays

Muhammad Arsalan Ali Akbar, Mohsin Raza and Sabre Kais

We establish a general theoretical framework for realizing topological edge states in dimerized arrays of chiral dipolar molecules and demonstrate that molecular handedness provides a natural and tunable route to SSH-like topology in an interacting one-dimensional setting. Starting from an effective spin-$\tfrac{1}{2}$ model generated by Stark-dressed chiral molecules, we introduce bond dimerization and show that the chirality-induced Dzyaloshinskii–Moriya interaction amplifies the effective hopping amplitudes and enlarges the bulk topological gap relative to an achiral chain of equivalent dipole strength. Using self-consistent mean-field theory with periodic- and open-boundary calculations, we map out the trivial, critical, and topological regimes through bulk spectra, complex-plane winding, and boundary-localized probability densities. A central result is that the two in-gap boundary modes carry opposite molecular chirality: the left edge state localizes on a left-handed molecule and the right edge state on a right-handed molecule, a stereochemical labeling with no analogue in conventional SSH implementations. The two-leg ladder extension supports a richer four-band bulk structure and a rung-split edge sector whose robustness is characterized by a continuous sweep of the interchain coupling. All results are expressed in dimensionless units of the reference hopping scale $t_0$, making the framework directly applicable to any dipolar molecular platform – from bialkali polar molecules at MHz coupling scales to future arrays of ultracold chiral polyatomic species. These findings establish dimerized chiral molecular arrays as a controllable and chirality-addressable platform for quasi-one-dimensional topological quantum matter.
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Quantum Gases

Three- and four-boson systems expanded around the unitarity limit: Application to $^4$He molecules

Feng Wu, Xincheng Lin, Ubirajara van Kolck et al. (+1 more)

The three- and four-boson systems with a large scattering length and a short effective range in the two-body sector are studied in the framework of Short-Range Effective Field Theory (SREFT). The starting point (leading order) of the EFT is taken to be the universal unitarity limit, where the two-body sector is parameter-free and only one three-body parameter enters. In this limit, physical systems manifest discrete scale invariance. Deviations from universality arising from finite scattering-length and effective-range corrections, as well as a four-body force required by renormalization, are included perturbatively at next-to-leading order. The three-body ground state and its associated four-body ground and first-excited states are studied using the Faddeev-Yakubovsky (FY) formalism and a complementary diagrammatic approach. By employing techniques to remove contributions from deep trimers in tetramer calculations, we extend our analysis to larger cutoffs than previously accessible within the FY approach to SREFT. Our results for binding energies and radii of $^4$He three- and four-atom systems converge well to results obtained with sophisticated phenomenological potentials. These successes suggest that the physics of $^4$He atomic clusters is governed by only small deviations from discrete scale invariance.
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All authors Feng Wu, Xincheng Lin, Ubirajara van Kolck, Sebastian König

Mesoscale and Nanoscale Physics

Ultrafast formation of a large dynamic magnetic soliton

Ondřej Wojewoda, Sina Mayr, Miela J. Gross et al. (+17 more)

Nonlinear magnetization dynamics offers a rich variety of phenomena ranging from bistability to chaos. Here, we report the ultrafast formation of a dynamic magnetic soliton in thin ferrimagnetic garnet films with perpendicular magnetic anisotropy, driven by the microwave magnetic field of a microstrip antenna. Using time-resolved Brillouin light scattering microscopy and scanning transmission X-ray microscopy, we directly track the build-up of the large-angle precession state. The observed soliton is distinct from other nonlinear magnetic excitations in two key aspects: (i) it forms inside the linear spin-wave frequency band, and (ii) it is exceptionally large, reaching tens of microns beyond the antenna. We explain the soliton formation by the self-limiting mechanism upon a positive nonlinear frequency shift and the spatial extent of the near-field of the antenna. At large distances from the drive, the soliton collapses and emits short-wavelength spin waves via almost instantaneous spatial wavenumber conversion. Time-resolved measurements further reveal a small finite delay during soliton formation, while coherent long-range oscillations appear essentially simultaneously over distances up to 40 micrometers. These results establish microwave-driven solitons as a robust nonlinear phenomenon in thin-film garnets and suggest opportunities for fast, nonlocal manipulation of magnetic states and for applications in novel computational schemes.
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All authors Ondřej Wojewoda, Sina Mayr, Miela J. Gross, Jan Klíma, Jaganandha Panda, Jakub Krčma, Jakub Holobrádek, Kristýna Davídková, Andrii V. Chumak, Igor Gerasimchuk, Roman Verba, Philipp Pirro, Markus Weigand, Simone Finizio, Morris Lindner, Carsten Dubs, Qi Wang, Sebastian Wintz, Caroline A. Ross, Michal Urbánek

Mesoscale and Nanoscale Physics

Quantum control of spin qubits using SOT-driven nanomagnets

Aniruddha Chakraborty, Kanishk Modi, Dhritiman Bhattacharya et al. (+3 more)

Spin rotation (SR) is an essential capability for realization of single and two-qubit gates in spin quantum computing (SQC) architectures. To perform SR, resonant AC magnetic fields are either generated by microwave current pulses fed to an antenna, or voltage pulses applied to a gate, in presence of an inhomogeneous Zeeman field. While the former approach is limited by gate-speed and site-selectivity of SR, the latter adds to the decoherence of the spin qubits. Here, we propose an alternative technique for driving high-speed SR without compromising the qubit coherence, by employing spin-orbit-torque (SOT)-driven nanomagnets to produce oscillating magnetic fields, locally at the qubit site. The proposed scheme is highly energy-efficient, scalable, and compatible with the CMOS fabrication technology.
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All authors Aniruddha Chakraborty, Kanishk Modi, Dhritiman Bhattacharya, Uditendu Mukhopadhyay, Suddhasatta Mahapatra, Jayasimha Atulasimha

Materials Science

Benchmark Dataset for Catalysis on 2D MXenes

Pavlo Melnyk, Anmar Karmush, Mårten Wadenbäck et al. (+4 more)

Merging first-principles calculations with machine learning (ML), we aim to accelerate the exploration of catalytic behaviour in novel materials. We focus on two-dimensional (2D) Ti$_2$CT$_y$ MXenes, whose versatile surface chemistry makes them particularly compelling candidates for catalysis. Resolving their composition and structure under realistic conditions exceeds the reach of standard density functional theory (DFT) due to computational cost. To address this challenge, we generate a comprehensive dataset of 50,000 DFT calculations for training and 10,000 for testing, encompassing both Ti$_2$CT$_y$ MXene configurations and molecular systems, along with an additional test dataset with 1000 genuinely new, larger systems to investigate how well models generalise. We train and validate widely used and competitive machine learning interatomic potential (MLIP) models, including EquiformerV2, MACE, MatRIS, and UPET, that accurately predict atomic forces and formation energies – quantities that DFT must repeatedly compute for structural and catalytic investigations – for these 2D materials. This combined DFT-ML framework achieves computational acceleration on the order of approximately $1-4 \cdot 10^3$ (on a CPU) while maintaining desired-level accuracy (approximately +/- $10$ meV/A for forces and approximately +/- $1$ meV for per-atom energies), paving the way for more efficient investigations of MXene catalytic behaviour. Moreover, we perform an extensive qualitative evaluation of the trained models, showcasing the importance of comprehensive simulation-based comparison beyond benchmark metrics. The dataset and the trained models with the code are available at https://huggingface.co/datasets/CatalystAnonymous/catalyst_mxenes.
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All authors Pavlo Melnyk, Anmar Karmush, Mårten Wadenbäck, Ania Beatriz Rodríguez-Barrera, Johanna Rosen, Michael Felsberg, Jonas Björk

Statistical Mechanics

Pre-failure response spectra predict finite-amplitude fragility

Surachate Limkumnerd

Failure theories often identify a single leading route to failure: the most unstable mode, weakest link, minimum-action escape path, or optimal perturbation. Yet finite-amplitude susceptibility depends not only on the nearest route but on how much of perturbation space lies near dangerous directions. We cast this distinction as a fragility problem: for each perturbation direction, the failure distance is the smallest amplitude that crosses a prescribed boundary, and the fragility curve is the fraction of directions that fail below a given amplitude. Measuring this curve directly requires nonlinear trials over many directions; instead, we show that it is predicted, before any failure occurs, by the tail of a single pre-failure quantity: the boundary-normalized fragility gain computed from the linearized response. The breadth of the associated response spectrum sets how many near-dangerous pathways coexist beyond the strongest direction. We demonstrate the mechanism in a high-dimensional nonlinear non-normal network with the strongest directional gain held fixed: the system with broader response-channel breadth has a larger nonlinear fragility curve, isolating breadth from the worst direction. An independent scalar test in deterministic traffic breakdown confirms the predicted sign: response breadth lowers calibrated jam thresholds once the strongest response is matched, with residual margins screening but never reversing the effect. Response-spectrum breadth thus emerges as a pre-failure coordinate for finite-amplitude fragility beyond the strongest path.
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Materials Science

Catalytic precursor dissociation in Hot-Wire CVD and comparing a-Si:H growth under continuous and pulsed silane flow conditions

Swati Goyal, Karam Veer Singh, Rajiv O. Dusane et al. (+1 more)

Hot-wire Chemical vapor deposition (HWCVD) of hydrogenated amorphous silicon (a-Si:H) thin films utilizes the dissociation of silane (SiH4) precursor over heated tungsten or tantalum filaments (\geq 1600 {\deg}C). In this work, assuming catalytic dissociation mechanism, we present kinetic model for SiH4 dissociation and the resulting a-Si:H film growth. Our model calculations showed that for an identical dose of the introduced SiH4 precursor, a-Si:H thickness was considerably higher for the pulsed SiH4 flow as compared to the continuous SiH4 flow. The pulsed SiH4 flow is represented by time intervals t_ON and t_OFF, where the SiH4 flow rate (F_(SiH_4)) is at the set-point and zero, respectively. In agreement with our model calculations for an introduced 75 cm^3 (STP) SiH4 dose, the resulting a-Si:H film thickness was 175 \pm 5 nm under continuous precursor flow, whereas it considerably increased to 425 \pm 8 nm when this SiH4 dose was split into 15 shorter pulses (t_ON =15s ; t_OFF = 60s). Moreover, these a-Si:H films deposited using pulsed SiH4 flow exhibited improved electrical properties, with a dark conductivity ({\sigma_d}) of 1.1 \times 10^-11 S/cm and a photoconductivity ({\sigma_ph}) of \sim 5.8 \times 10^-5 S/cm, compared to films deposited under continuous SiH4 flow ({\sigma}_d \sim 2.5 \times 10^-10 S/cm and {\sigma}_ph \sim 3.5 \times 10^-6 S/cm).
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All authors Swati Goyal, Karam Veer Singh, Rajiv O. Dusane, Triratna P. Muneshwar

Materials Science

Compressibility and High-Pressure Structure of CaMg$_2$Bi$_2$ and YbMg$_2$Bi$_2$

Mario Calderón-Cueva, Allison Pease, Cheng Peng et al. (+5 more)

Compounds with the formula $AM_2X_2$ in the CaAl$_2$Si$_2$ structure type have garnered increasing interest across various solid-state research domains, such as quantum topological and thermoelectric materials. Prior studies have identified high-pressure phase transitions in several compounds, including Mg$_3$Sb$_2$, Mg$_3$Bi$_2$, CaMn$_2$Bi$_2$, and SrAl$_2$Si$_2$. In this study, we investigate the structural behavior of CaMg$_2$Bi$_2$ and YbMg$_2$Bi$_2$ under varying pressure conditions. We synthesized crystals using the molten metal flux method and examined them through single-crystal synchrotron X-ray diffraction, employing diamond anvil cells to exert pressures up to 20 GPa. Our analysis reveals insights into the anisotropic compressibility of these materials, highlighting the more compressible and flexible octahedral $A$-Bi bonds as the primary contributors to this anisotropy. Moreover, we observed a phase transition in both CaMg$_2$Bi$_2$ and YbMg$_2$Bi$_2$ at pressures above 9.6 GPa and 8.7 GPa, respectively. The newly identified high-pressure phase exhibits a distortion of the original CaAl$_2$Si$_2$ structure with space group $C2/m$. This high-pressure structure is distinct from that of related compounds (e.g., CaMn$_2$Bi$_2$, MgMg$_2$Bi$_2$), the latter exhibiting a square pyramidal coordination for the $M$ site.
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All authors Mario Calderón-Cueva, Allison Pease, Cheng Peng, Wanyue Peng, Megan Rylko, Weiwei Xie, Susannah M. Dorfman, Alexandra Zevalkink

Materials Science

Autonomous scanning electrochemical cell microscopy enables rapid exploration of large compositionally complex material spaces

Felix Thelen, Moonjoo Kim, Geovane Arruda de Oliveira et al. (+3 more)

Alloying is a central strategy in electrocatalysis, enabling fine-tuning of electronic structure. In particular, compositionally complex solid solutions (CCSS) often called high-entropy alloys are of high interest as they allow active site design. However, the "combinatorial explosion" in the number of possible compositions poses a critical bottleneck for the discovery of active CCSS electrocatalysts. We present an autonomous scanning electrochemical cell microscopy (SECCM) system for ultrahigh-throughput and large-scale CCSS activity screening. The platform rapidly establishes composition-electrocatalytic activity relationships for large compositional spaces across multiple thin-film CCSS materials libraries via active learning and automated library exchange. Embedding analytical expressions of voltammetry in the algorithm enables the learning of whole voltammograms rather than a single selected metric. As a demonstration, we investigated hydrogen evolution reaction (HER) activities of Au-Ir-Rh, where Ir and Rh exhibit strong metal-hydrogen binding and Au exhibits relatively weak binding as derived from the HER volcano plot. The composition-activity trend was accurately predicted after measuring only 15% of all 966 measurement areas. Au30Ir20Rh50 and Au10Ir35Rh55 exhibit highest activities with standard rate constants of about 0.012 cm/s, demonstrating positive synergistic contributions from elemental mixing. The autonomous robotic SECCM platform is broadly applicable to a wide range of electrocatalytic reactions, providing a general pathway for accelerating CCSS electrocatalyst discovery and optimization.
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All authors Felix Thelen, Moonjoo Kim, Geovane Arruda de Oliveira, Jan Lukas Buergel, Wolfgang Schuhmann, Alfred Ludwig

Strongly Correlated Electrons

Low-Temperature Suppression of Intertwined Orders in La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ Thin Films

Mayia A. Vranas, Robin Glefke, Katherine Matthews et al. (+27 more)

The strong coupling between spin, charge, and lattice degrees of freedom in perovskite oxides leads to an array of exotic phenomena, giving these materials rich phase diagrams that can include coupled orders. This is exemplified by the A-site doped ferrite La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ (LSFO), which exhibits a coupled paramagnetic-antiferromagnetic and charge ordering phase transition at $\sim$190 K that has been well studied in thin films, bulk, and polycrystalline samples. However, the low temperature behavior of LSFO thin films below $\sim$100 K has not been thoroughly explored. This work uses several X-ray scattering and spectroscopy techniques to directly probe LSFO's magnetic and charge order down to low temperature. Using resonant X-ray scattering, we observe a complete suppression of LSFO's known antiferromagnetic and charge order below $\sim$25 K. Further spectroscopy and coherent scattering measurements provide insight into LSFO's electronic structure and domain dynamics in this new low temperature phase, and we propose possible explanations for the observed order suppression based on reduced dimensionality of domains in our thin films. Our findings provide insight into the effects of competing interactions in strongly correlated materials, particularly those with coupled orders.
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All authors Mayia A. Vranas, Robin Glefke, Katherine Matthews, Xiaoke Li, Tianxing Wang, Henry Navarro, I-Ching Lin, Sarmistha Das, Biswajit Sahoo, Rourav Basak, Wei He, Holden Bauer, Ella Di Liberti, Jacob Butler, Elliot Kisiel, Erik Lamb, Jun-Sik Lee, Cheng-Tai Kuo, Heemin Lee, Christie Nelson, Sophie Morley, Sujoy Roy, Christoph Klewe, Fanny Rodolakis, Jessica McChesney, Oleg Shpyrko, Yimei Zhu, Eric Fullerton, Ivan Schuller, Alex Frano

Quantum Gases

Energy spectra and cascade in the spin turbulence of a driven spinor Bose-Einstein condensate

Junghoon Lee, Jongmin Kim, Donggyu Lee et al. (+1 more)

We investigate the spin-interaction energy spectrum of spin turbulence in a driven spinor Bose-Einstein condensate. Continuous spin driving of a spin-1 condensate produces a nonequilibrium steady state with spatially fluctuating magnetization. We observe a power-law scaling consistent with the $-7/3$ exponent predicted for spin-wave turbulence, which persists across our full range of drive strengths despite substantial changes in the spectral anisotropy. After switching off the drive, we track the free-decay evolution and find evidence consistent with a direct cascade of spin-interaction energy toward higher wavenumbers. These results establish an energy-spectral hallmark of spin turbulence and enable quantitative studies of cascade dynamics in spinor superfluids.
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All authors Junghoon Lee, Jongmin Kim, Donggyu Lee, Yong-il Shin

Materials Science

Thermodynamic origin of entropy-assisted stabilization in multicomponent rock-salt oxides

Supriya Ghosal, Swapan Pati and Ashutosh Kumar

High entropy oxides are commonly associated with high configurational entropy ($\Delta S_{conf}\geq$ 1.61R) corresponding to five equimolar cations occupying a crystallographic sublattice. However, recent experimental observations indicate that medium-entropy compositions may also exhibit entropy-stabilized rock-salt phases, raising an important question regarding the minimum entropy required for phase stabilization. In this work, we employ a first-principles thermodynamic framework to investigate the stability of rock-salt oxides containing two to five principal cations components analogous to (Ni$_{0.8}$Cu$_{0.2}$)O, (Ni$_{0.6}$Cu$_{0.2}$Zn$_{0.2}$)O, (Ni$_{0.4}$Cu$_{0.2}$Zn$_{0.2}$Co$_{0.2}$)O, (Ni$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$Co$_{0.2}$Mg$_{0.2}$)O. Density functional theory, MCSQS-based structural modeling, and finite-temperature Gibbs free-energy analysis are combined to quantify the roles of enthalpy mixing ($\Delta H_{mix}$), configurational ($\Delta S_{conf}$), vibrational ($\Delta S_{vib}$), electronic and magnetic ($\Delta S_{mag}$) contributions towards ($\Delta S_{elec}$) entropy change in governing phase stability. The results show that $\Delta S_{conf}$ alone is not a universal descriptor of phase stability. While the two-cation system is enthalpy-stabilized but three-, four- and five-cation systems become thermodynamically stable at high-temperature due to entropy-driven reduction of the Gibbs free energy. These findings demonstrate that single-phase rock-salt oxides are not restricted to the conventional high-entropy limit and that medium-entropy compositions can also be stabilized under suitable thermodynamic conditions.
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Mesoscale and Nanoscale Physics

Edge Detection Framework Utilizing SOT-MTJ Bit-Cell Arrays

Kushagra Singh and Debasis Das

Traditional edge detection algorithms, foundational to computer vision, face significant challenges in energy efficiency and processing latency on conventional CMOS-based hardware. Existing algorithms, such as Canny, are computationally expensive, posing challenges in resource-constrained hardware where energy efficiency and low latency are critical. This study introduces a novel, hardware-efficient algorithm that leverages the intrinsic characteristics of magnetic tunnel junction (MTJ) devices. We present a detailed device-level analysis of an MTJ-based system for edge detection, outlining its operational cycles, including write, read, and reset methods. The algorithm's efficacy is evaluated against the standard Canny edge detection method. We provide a quantitative performance analysis, including metrics such as energy consumption and latency, which demonstrates that our proposed spintronics-based approach offers a promising solution for achieving low-power, high-speed image processing.
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Materials Science

Impact of Cu-Mn ratio on Structure and Defects in Layered Multiferroic Cu1-xMn1+ySiTe3

Sai Venkata Gayathri Ayyagari, Boyang Zheng, Sreekant Anil et al. (+10 more)

Multiferroic materials exhibit the coexistence of magnetic and ferroelectric order, enabling control of magnetism through electric fields and vice versa. These properties make them attractive for spintronic and memory device applications. Recent studies on Cu1-xMn1+ySiTe3 (0.04 \leq x \leq 0.26; 0.03 \leq y \leq 0.15) have revealed strong magnetoelectric coupling, with variations in Mn-to-Cu concentration leading to variations in optical, electronic, and magnetic responses. Despite these findings, the influence of nanoscale structure and defects on the observed properties remains poorly understood. In this study, we investigate the structure and nanoscale defects in Cu-deficient Cu1-xMn1+ySiTe3 (Cu:Mn ratio <1, i.e., with 0.04 \leq x \leq 0.26 and 0.03 \leq y \leq 0.15) and Cu-rich Cu1+xMn1-ySiTe3 (Cu:Mn ratio >1, i.e., with 0.04 \leq x \leq 0.3 and 0.13 \leq y \leq 0.31) crystals using scanning/transmission electron microscopy and single-crystal X-ray diffraction. Cu-deficient crystals exhibit extensive stacking faults correlated with chemical inhomogeneity between Mn and Cu, along with variations in Te stacking. In contrast, Cu-rich crystals show fewer stacking faults but contain other local structural variations, such as needle-shaped precipitates and loop-like features. These distinct local structural features between Cu-rich and Cu-deficient crystals can be correlated to variations in their observed properties. Complementary density functional theory calculations confirm that the Cu-rich structure is more polar than the Cu-deficient structure. Overall, this study provides a comprehensive understanding of how subtle changes in chemistry influence the nanoscale structure, defect distribution, and functional properties in Cu1-xMn1+ySiTe3, offering guidance for designing multiferroic materials with tailored performance.
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All authors Sai Venkata Gayathri Ayyagari, Boyang Zheng, Sreekant Anil, Subrata Ghosh, Yuxi Zhang, Yu Liu, Chandan De, Ke Wang, Jeffrey Shallenberger, Weiwei Xie, Vincent H. Crespi, Zhiqiang Mao, Nasim Alem

Mesoscale and Nanoscale Physics

Optically programmable and erasable cryogenic flash memory on an undoped Si/SiGe heterostructure

S Rastogi, S Samanta, V Jangir et al. (+6 more)

Scalable cryogenic memory is a critical yet unresolved requirement for large-scale quantum computing architectures, particularly for computing-in-memory schemes. We exploit the interplay between optical excitation and gate bias in an undoped Si/SiGe heterojunction field-effect transistor (HFET) to realize non-volatile memory functionality. The device exploits a high interface trap density ($D_{it} > 1.6 \times 10^{12}$~eV$^{-1}$cm$^{-2}$), which, in conjunction with the oxide thickness and dielectric constant, enables effective "locking" of the threshold voltage to the applied gate bias over a wide voltage range. Two of these states can be selected for binary operation, while the availability of multiple stable states within the same device enables multibit data storage. Robust cycling endurance ($>~10^3$ cycles) and long-term state retention ($>~10^4$~s) of the memory states at 1.5 K confirm the suitability of this approach for integration into Si/SiGe-based quantum computing architectures.
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All authors S Rastogi, S Samanta, V Jangir, L Patra, K Modi, A Jain, G Scappucci, U Mukhopadhyay, S Mahapatra