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Physics Condensed Matter

cond-mat Watch Condensed Matter

Wednesday 5 November

Mesoscale and Nanoscale Physics

Giant field-tunable nonlinear Hall effect by Lorentz skew scattering in a graphene moire superlattice

Pan He, Min Zhang, Yue-Xin Huang et al. (+13 more)

The nonlinear Hall effect (NHE) can enable rectification and energy harvesting, and its control by external fields, including gate, strain and magnetic field, has been pursued intensively. However, existing tuning pathways rely predominantly on fully quantum mechanical effects and are typically inefficient, resulting in weak NHE signals that limit further progress. In this work, we report the discovery of a distinct type of NHE in a graphene-hBN moire superlattice, which arises from a classical-quantum cooperative effect called Lorentz skew scattering (LSK), induced by a perpendicular magnetic field. This field-driven NHE exhibits a linear dependence on magnetic field and a pronounced unidirectional angular dependence. Remarkably, its magnitude reaches up to 32% of the linear Hall signal. We show that this giant, field-tunable NHE originating from LSK follows a unique quartic scaling law and produces a record-high nonlinear Hall conductivity (36000 {\mu}mV-1{\Omega}-1) near van Hove singularities of moire minibands, which is over an order of magnitude larger than all previously reported NHEs. Our findings establish an efficient, magnetic-field-driven route to giant Hall rectification in high-mobility materials, offering a broadly applicable paradigm for modulating the NHE beyond electrostatic gating.
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All authors Pan He, Min Zhang, Yue-Xin Huang, Jingru Li, Ruibo Wang, Shiwen Zhao, Chaoyu Pan, Yuxiao Gao, Takashi Taniguchi, Kenji Watanabe, Junxiong Hu, Yinyan Zhu, Cong Xiao, X. C. Xie, Shengyuan A. Yang, Jian Shen

Strongly Correlated Electrons

Free Majorana Fermions with Superconducting Quantum Wires and a Magnetic Impurity

Karyn Le Hur

Through the two-channel Kondo model, I address a magnetic spin-1/2 impurity interacting with a bound state of spin origin at the edge in a Luther-Emery liquid showing a spin gap in the bulk. The system presents two zero-energy Majorana fermions of magnetic origin, one on the impurity site and one at the edge. I derive the wavefunction at the edge for the produced zero-energy Majorana fermion bound state within the same formalism as topological interfaces. I present alternative versions of the quantum field theory revealing the specific pairing of the Majorana fermions in the bulk. I address local physical responses. I develop the idea that this model can be realized with a magnetic impurity bridging the gap between two s-wave superconducting wires. I show the protection of the zero-energy Majorana fermions that will be referred to as free Majorana fermions.
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Materials Science

Enhancing composition-based materials property prediction by cross-modal knowledge transfer

Ivan Rubtsov, Ivan Dudakov, Yuri Kuratov et al. (+1 more)

Crystal graph neural networks are widely applicable in modeling experimentally synthesized compounds and hypothetical materials with unknown synthesizability. In contrast, structure-agnostic predictive algorithms allow exploring previously inaccessible domains of chemical space. Here we present a universal approach for enhancing composition-based materials property prediction by means of cross-modal knowledge transfer. Two formulations are proposed: implicit transfer involves pretraining chemical language models on multimodal embeddings, whereas explicit transfer suggests generating crystal structures and implementing structure-aware predictors. The proposed approaches were benchmarked on LLM4Mat-Bench and MatBench tasks, achieving state-of-the-art performance in 25 out of 32 cases. In addition, we demonstrated how another modeling aspect of chemical language models - interpretability - benefits from applying a game-theoretic approach, which is able to incorporate high-order feature interactions.
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All authors Ivan Rubtsov, Ivan Dudakov, Yuri Kuratov, Vadim Korolev

Materials Science

Core-Shell Confinement Blocks Hydride Formation: The Impact of Surface Oxides on Hydrogen Sorption in Nanoporous FeTi

Lukas Schweiger, Florian Spieckermann, Michael Burtscher et al. (+10 more)

Metal hydrides remain an intriguing alternative to conventional gaseous and liquid hydrogen storage methods, offering high volumetric storage density and enhanced hydrogen storage safety at ambient conditions. In this regard, the intermetallic compound FeTi is one of the most promising storage materials. However, its widespread industrial application remains challenging due to the need for activation, slow initial kinetics, large hysteresis, and high material costs. In this study, we aim to overcome these limitations by devising an alternative synthesis pathway to prepare nanoporous and ultra-fine porous FeTi with controlled grain and ligament sizes, allowing us to study the obtained well-defined microstructures in detail. In particular, we observe the confinement of the FeTi phase by surface oxides, which can be correlated with the hydrogen sorption properties of the respective material. These experimental results are further supported by an analytical model allowing the calculation of the absorption pressure as a function of microstructure-dependent elastic stresses. Additionally, we show that such stresses also influence the absorption-desorption hysteresis. This study lays the groundwork for the controlled and systematic study of the processing-structure-properties relations in metal hydrides and FeTi in particular, thereby paving the way to cost-effective and efficient hydrogen storage solutions based on metal hydrides.
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All authors Lukas Schweiger, Florian Spieckermann, Michael Burtscher, Stefan Wurster, Sebastian Stock, Nikolaos Kostoglou, Oskar Paris, Alexander Schökel, Fahim Karimi, Gökhan Gizer, Claudio Pistidda, Daniel Kiener, Jürgen Eckert

Materials Science

Axial phono-magnetic effects

Natalia Shabala, Finja Tietjen and R. Matthias Geilhufe

Axial or circularly polarized phonons are collective lattice vibrations with angular momentum. Over the past decade they have emerged as a promising mechanism for the manipulation of magnetism, in parallel to well established optical protocols. In particular, coherent axial phonons were shown to induce magnetization in materials without spin-ordering, making them a viable tool for ultrafast magnetic switching. The experimental evidence suggests that the size of this magnetization is significant, opening a new research area on the phono-magnetic effect. Remarkably, the coupling of axial phonons to magnetism has been observed a broad class of materials, pointing to a universal nature of the underlying mechanisms. In this review article, we present the recent progress in the field. We give an introduction to the phenomenological perspective and an overview of the experimental evidence for the magnetization emerging from axial phonons, which includes discussing the observations of phonon Zeeman effect, the magneto-optical Kerr effect and the proximity-induced magnetization switching. We present recently proposed microscopic theories for the phono-magnetic effects, based on perturbation theory, adiabatic motion and Floquet theory as well as the emergence of the phonon magnetic moment due to artificial gauge fields or inertial effects. This summary allows us to see correspondences between the seemingly different theoretical approaches, facilitating a more complete perspective of the effect.
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Strongly Correlated Electrons

Moiré modulated quantum spin liquid candidate 1T-TaSe$_2$

Ziying Wang, Adolfo O. Fumega, Ana Vera Montoto et al. (+7 more)

Quantum spin liquids are quantum phases of matter featuring collectively entangled states and emergent fractional many-body excitations. While methods exist to probe three-dimensional quantum spin liquids experimentally, these techniques lack the sensitivity to probe two-dimensional quantum spin liquids. This seriously hampers the study of potential monolayer quantum spin liquid candidates such as $\alpha$-RuCl$_3$ and 1T-TaSe$_2$. Scanning tunneling microscopy (STM) and spectroscopy (STS) have recently been suggested as promising probes of the quantum spin liquid state, as they can access the spinon spectrum through inelastic tunneling spectroscopy (IETS). In this work, we employ this approach on the quantum spin liquid candidate material 1T-TaSe$_2$ and directly measure its low-energy inelastic excitations. We observe the emergence of a $\sqrt{3}\times\sqrt{3}$ reconstruction driven by the substrate, equivalent spectroscopy across all spin sites and coexistence of zero and finite energy excitations. We show that these observations are consistent with a modulated $\sqrt{3}\times\sqrt{3}$ spin liquid ground state. Our results demonstrate that IETS provides a powerful route to obtain atomic-scale insight into the magnetic excitations of two-dimensional materials, allowing to explore the effects of moiré modulations on potential quantum liquid phases.
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All authors Ziying Wang, Adolfo O. Fumega, Ana Vera Montoto, Mohammad Amini, Büşra Gamze Arslan, Aleš Cahlík, Yuxiao Ding, Jose L. Lado, Robert Drost, Peter Liljeroth

Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Graphene-enabled coherent (sub-)terahertz wave detection and thickness determination

Ronny de la Bastida, Enzo Rongione, Karuppasamy Pandian Soundarapandian et al. (+9 more)

Phase-sensitive terahertz (THz) detection enables applications ranging from astronomy to non-destructive testing. However, current THz detectors lack phase sensitivity, unless they are combined with external interferometers, or through photomixing. This implies a large footprint and sensitive dependence on alignment. Here, we demonstrate a graphene-enabled, on-chip, integrated (sub-)THz detector-interferometer with optical cavity and antenna, exhibiting high sensitivity to the phase of incident THz light. We exploit this by determining the thickness of thin films placed in front of the detector-interferometer, obtaining a deep sub-wavelength thickness accuracy of a few micrometer, while we predict that an improved accuracy is within reach. This is relevant for a range of industrial application domains, including automotive, construction, and health. We furthermore achieve a record-high external responsivity - considering bias-free graphene-based (sub-)THz detectors - of 172 mA/W and a noise-equivalent power of 26 pW$~\rm{Hz}^{-1/2}$. This performance is due to enhanced absorption at the resonant cavity mode around 89 GHz, in agreement with multi-physics simulations. These results pave the way to exploiting coherent wave detection in the (sub-)THz regime with utility in spectroscopy, next-generation wireless communication, and beyond.
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All authors Ronny de la Bastida, Enzo Rongione, Karuppasamy Pandian Soundarapandian, Ioannis Vangelidis, Anand Nivedan, David Saleta Reig, Kenji Watanabe, Takashi Taniguchi, Elefterios Lidorikis, Frank H. L. Koppens, Sebastián Castilla, Klaas-Jan Tielrooij

Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Incorporating QM/MM molecular dynamics into the few-mode quantization approach for light-matter interactions in nanophotonic structures

Ruth H. Tichauer, Maksim Lednev, Gerrit Groenhof et al. (+1 more)

In the context of light-matter interactions between organic chromophores and confined photons of (plasmonic) nano-resonators, we introduce a general framework that couples ab initio QM/MM molecular dynamics with few-mode field quantization to simulate light-matter interactions of molecular emitters at the nanoscale. Arbitrary, lossy, and spatially inhomogeneous photonic environments are represented by a minimal set of interacting modes fitted to their spectral density, while geometry-dependent molecular properties are computed on the fly. Applications to few-molecule strong coupling show that strong coupling persists when molecular degrees of freedom and disorder are included for the chosen system consisting of a nanoparticle dimer coupled to multiple emitters. At the same time, symmetry-protected degeneracies of two-level models are lifted. The framework further reveals how spatial field inhomogeneity and molecular disorder shape cavity-mediated energy transfer, illustrated for an HBQ-Methylene Blue donor-acceptor combination in a five-emitter system.
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All authors Ruth H. Tichauer, Maksim Lednev, Gerrit Groenhof, Johannes Feist

Strongly Correlated Electrons

The nexus between negative charge-transfer and reduced on-site Coulomb energy in a correlated topological metal CoTe$_2$

A. R. Shelke, C.-W. Chuang, S. Hamamoto et al. (+7 more)

The layered $3d$ transition metal dichalcogenide (TMD) CoTe$_2$ is a topological Dirac Type-II metal. However, the Co $3d$-bands in CoTe$_2$ do not exhibit the expected correlation-induced band narrowing seen in CoO. We address this conundrum by studying the electronic structure of CoTe$_2$ using hard x-ray photoemission spectroscopy (HAXPES), x-ray absorption spectroscopy (XAS) and Resonant-PES. We quantify the on-site Coulomb energy $U_{dd}$ via single-particle partial density of states and the two-hole correlation satellite using valence band Resonant-PES), and obtain $U_{dd}$ = 3.0 eV for CoTe$_2$. Charge-transfer (CT) cluster model simulations of the measured core-level Co $2p$ PES and $L$-edge XAS spectra of CoTe\textsubscript{2} and CoO validate their contrasting electronic parameters:$U_{dd}$ and CT energy $\Delta$ are (3.0 eV, -2.0 eV) for CoTe\textsubscript{2}, and (5.0 eV, 4.0 eV) for CoO, respectively. The $d$-$p$ hybridization strength $T_{eg}$ for CoTe$_2$$<$CoO, and indicates that the reduced $U_{dd}$ in CoTe\textsubscript{2} is not due to $T_{eg}$. The increase in $d^n$-count$\sim$1 by CT from ligand to Co site in CoTe$_2$ is due to a negative-$\Delta$ and reduced $U_{dd}$. Yet, only because $U_{dd}$$>$$\big|\Delta\big|$, CoTe$_{2}$ becomes a topological metal with $p$$\rightarrow$$p$ type lowest energy excitations. The study reveals the nexus between negative-$\Delta$ and reduced $U_{dd}$ required for setting up the electronic structure framework for achieving topological behavior via band inversion in the correlated metal CoTe$_2$.
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All authors A. R. Shelke, C.-W. Chuang, S. Hamamoto, M. Oura, M. Yoshimura, N. Hiraoka, C.-N. Kuo, C.-S. Lue, A. Fujimori, A. Chainani

Mesoscale and Nanoscale Physics

Lorentz Skew Scattering Nonreciprocal Magneto-Transport

Xiu Fang Lu, Xue-Jin Zhang, Naizhou Wang et al. (+9 more)

In materials with broken inversion symmetry, nonreciprocal magneto-transport (NRMT) manifests as a bilinear dependence of charge conductivity on applied electric (E) and magnetic (B) fields. This phenomenon is deeply rooted in symmetry and electronic quantum geometry, holding promise for novel rectification and detector technologies. Existing experimental studies generally attribute NRMT to Zeeman-driven mechanisms and exhibit quadratic scaling with conductivity. Here, we report a previously unknown NRMT microscopic mechanism - Lorentz skew scattering (LSK) - revealed through the discovery of an unprecedented quartic scaling law of NRMT as well as quantitative agreement between theory and experiment in BiTeBr. LSK emerges from the interplay of Lorentz force and skew scattering, bridging classical field effect to quantum scattering effect on the Fermi surface. We demonstrate that the LSK dominates NRMT in BiTeBr, and elucidate that this dominance over other possible contributions stems from high mobility and strong Rashba splitting. The finding of LSK mechanism is of unique importance because it unveils the leading NRMT effect in high-mobility systems and suggests a universal principle towards strong NRMT by enhancing electronic relaxation time in topological materials, rendering a new designing idea for low-dissipation rectifiers and high-performance quantum electronics.
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All authors Xiu Fang Lu, Xue-Jin Zhang, Naizhou Wang, Jin Cao, Dan Zhao, Hui Wang, Tao Wu, Xian Hui Chen, Shen Lai, Cong Xiao, Shengyuan A. Yang, Weibo Gao

Materials Science

Tunable Multistage Refrigeration via Geometrically Frustrated Triangular Lattice Antiferromagnet for Space Cooling

Jianqiao Wang, Chushu Fang, Zhibin Qiu et al. (+8 more)

Low-temperature refrigeration technology constitutes a crucial component in space exploration. The small-scale, low-vibration Stirling-type pulse tube refrigerators hold significant application potential for space cooling. However, the efficient operation of current Stirling-type pulse tube cryocoolers in space cooling applications remains challenging due to the rapid decay of the heat capacity of regenerative materials below 10 K. This study adopts a novel material strategy: using a novel high-spin S = 7/2 magnetic regenerative material, Gd2O2Se, we construct a multistage tunable regenerative material structure to achieve an efficient cooling approach to the liquid helium temperature range. Under substantial geometric frustration from a double-layered triangular lattice, it exhibits two-step specific heat transition peaks at 6.22 K and 2.11 K, respectively. Its ultrahigh specific heat and broad two-step transition temperature range effectively bridge the gap between commercially used high-heat-capacity materials. Experimental verification shows that when Gd2O2Se is combined with Er3Ni and HoCu2 in the Stirling-type pulse tube cryocooler, the cooling efficiency of the pulse tube increases by 66.5 % at 7 K, and the minimum achievable temperature reaches 5.85 K. These results indicate that Gd2O2Se is an ideal magnetic regenerative material for space cooling
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All authors Jianqiao Wang, Chushu Fang, Zhibin Qiu, Yang Zhao, Quan Xiao, Xiying Sun, Zhaoyi Li, Laifeng Li, Yuan Zhou, Changzhao Pan, Shu Guo

Materials Science

Mysterious Role of Cap Configuration in Single-Walled Carbon Nanotube Catalytic Growth

Tianliang Feng and Ziwei Xu

Understanding the role of cap structure during the nucleation and growth of single-walled carbon nanotubes (SWCNTs) is essential for achieving chirality-controlled synthesis. In this work, we propose a novel and intuitive algorithm to determine the chirality of nascent carbon caps by tracking the relative shifts of six pentagons within a topological coordinate system. Based on this algorithm, we propose three routes of pentagon shifts for the chirality mutations from armchair (AC) to near-AC caps, namely the transverse shift (n,n) to (n+1,n-1), inward shift (n,n) to (n-1), and outward shift (n,n) to (n+1,n), can occur according to the energy profiles calculated based on the density function theory (DFT), providing a new perspective to explain the experimental abundance of near-AC SWCNTs. After that, we construct 24 representative short caps and long SWCNTs with different chiralities and symmetries, and perform DFT calculations to evaluate their thermodynamic stability and deformation behaviors on flat Ni(111) surfaces and curved Ni55 particle, respectively. The results reveal that cap topology and catalyst curvature together induce dual deformations that significantly influence the formation and interface energies. Notably, AC and near-AC caps exhibit superior flexibility and robust energetic advantages, especially the (6,6) cap with C6v symmetry. A linear correlation between cap-induced deformation and formation energy is established through a defined shape factor, highlighting the interaction between cap structure and catalyst interface as a key driver of chirality selection. This study theoretically reveals the cap evolution mechanism and lays the foundation for the rational design of SWCNT growth strategies.
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Quantum Gases

Bistability and Exact Reflectionless States in Nonlinear Scattering of a Bose–Einstein Condensate

Feilong Wang, Jinlin Fan, Ruolin Chai et al. (+2 more)

We investigate the mean-field scattering dynamics of a quasi-one-dimensional Bose–Einstein condensate interacting with a Rosen–Morse potential. For specific potential and nonlinearity parameters, we derive analytically exact, degenerate scattering states (doubly or triply degenerate) exhibiting perfect transmission. Using the Bogoliubov–de Gennes approach, we analyze the stability of these reflectionless degenerate states, demonstrating that only one solution within each degenerate manifold is dynamically stable. Furthermore, we study a configuration with spatially localized nonlinearity, identifying an exact reflectionless state under specific conditions. Numerical analysis shows that this state marks the system's transition from monostability to bistability as the incident wave amplitude increases. Our work establishes an analytic framework for these multistable transmission phenomena, directly relevant to coherent matter-wave transport in ultracold atomic systems and optical propagation in engineered photonic lattices.
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All authors Feilong Wang, Jinlin Fan, Ruolin Chai, Zhibin Zhao, Qiongtao Xie

Quantum Gases

Finding the stable mechanism of ring solitons in two-dimensional Fermi superfluids

Hao-Xuan Sun, Liu-Yang Cheng, Shi-Guo Peng et al. (+2 more)

We theoretically investigate the stable mechanism of a ring soliton in two-dimensional Fermi superfluids by solving the Bogoliubov-de Gennes equations and their time-dependent counterparts. In the uniform situation, we discover that the ring soliton is always driven away from its initial location, and moves towards the edge due to a curvature-induced effective potential. The ring soliton is impossible to remain static at any location in the uniform system. To balance the density difference between the ring soliton's two sides, a harmonic trap is introduced, which can exert an effect to counterbalances the curvature-induced effective potential. This enables the ring dark soliton to become a stable state at a particular equilibrium position r_s, where the free energy of the ring dark soliton just reaches the maximum value. Once ring soliton is slightly deviated from r_s, some stable periodic oscillations of ring soliton around r_s will turn out. Some dissipation will possibly occur to ring soliton once its minimum radius is comparable to the healing length of soliton's Friedel oscillation. This dissipation will increase the oscillation amplitude and finally make the ring soliton decay into sound ripples. Our research lays the groundwork for a more in-depth understanding of the stable mechanism of a ring dark soliton in the future.
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All authors Hao-Xuan Sun, Liu-Yang Cheng, Shi-Guo Peng, Yan-Qiang Li, Peng Zou

Mesoscale and Nanoscale Physics

Extrinsic anomalous Hall effect in altermagnets

A. Osin, A. Levchenko and M. Khodas

We find the extrinsic anomalous Hall conductivity (AHC) to be comparable to the intrinsic one in roughly half of the altermagnetic spin Laue groups in the limit of large exchange splitting. In materials with a finite Dzyaloshinskii-Moriya type interaction, the extrinsic contribution is essential even in the clean limit. In other altermagnets it is mostly negligible. This peculiar behavior is linked to the nonanalytic dependence of the intrinsic AHC on spin-orbit coupling. Both originate from the lifting of the spin degeneracy along the nodal planes as the weak spin-orbit coupling breaks the nonrelativistic spin symmetry.
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Materials Science

Commutative Algebra Modeling in Materials Science – A Case Study on Metal-Organic Frameworks (MOFs)

Caleb Simiyu Khaemba, Hongsong Feng, Dong Chen et al. (+2 more)

Metal-organic frameworks (MOFs) are a class of important crystalline and highly porous materials whose hierarchical geometry and chemistry hinder interpretable predictions in materials properties. Commutative algebra is a branch of abstract algebra that has been rarely applied in data and material sciences. We introduce the first ever commutative algebra modeling and prediction in materials science. Specifically, category-specific commutative algebra (CSCA) is proposed as a new framework for MOF representation and learning. It integrates element-based categorization with multiscale algebraic invariants to encode both local coordination motifs and global network organization of MOFs. These algebraically consistent, chemically aware representations enable compact, interpretable, and data efficient modeling of MOF properties such as Henry's constants and uptake capacities for common gases. Compared to traditional geometric and graph-based approaches, CSCA achieves comparable or superior predictive accuracy while substantially improving interpretability and stability across data sets. By aligning commutative algebra with the chemical hierarchy, the CSCA establishes a rigorous and generalizable paradigm for understanding structure and property relationships in porous materials and provides a nonlinear algebra-based framework for data-driven material discovery.
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All authors Caleb Simiyu Khaemba, Hongsong Feng, Dong Chen, Chun-Long Chen, Guo-Wei Wei

Soft Condensed Matter

Surface wakes on ultra-soft solids

Aditi Chakrabarti, Divya Jaganathan, Robert Haussman et al. (+1 more)

We explore the dynamical response of the free surface of an ultra-soft solid driven by a localized moving pressure disturbance. Experiments reveal a steady V-shaped wake analogous to a surface Mach wedge. A simple geometric argument provides a qualitative explanation consistent with observations. A theoretical framework combining elastodynamic, capillary, and gravitational effects yields a generalized dispersion relation that smoothly interpolates between Kelvin's theory of liquid interface wakes and Rayleigh's theory of elastic surface waves. Together, our experiments and theory reveal the existence of a soft wake regime that bridges fluid and solid surface wave physics, offering new routes for probing the dynamics of soft surfaces.
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All authors Aditi Chakrabarti, Divya Jaganathan, Robert Haussman, L. Mahadevan

Materials Science

EGMOF: Efficient Generation of Metal-Organic Frameworks Using a Hybrid Diffusion-Transformer Architecture

Seunghee Han, Yeonghun Kang, Taeun Bae et al. (+5 more)

Designing materials with targeted properties remains challenging due to the vastness of chemical space and the scarcity of property-labeled data. While recent advances in generative models offer a promising way for inverse design, most approaches require large datasets and must be retrained for every new target property. Here, we introduce the EGMOF (Efficient Generation of MOFs), a hybrid diffusion-transformer framework that overcomes these limitations through a modular, descriptor-mediated workflow. EGMOF decomposes inverse design into two steps: (1) a one-dimensional diffusion model (Prop2Desc) that maps desired properties to chemically meaningful descriptors followed by (2) a transformer model (Desc2MOF) that generates structures from these descriptors. This modular hybrid design enables minimal retraining and maintains high accuracy even under small-data conditions. On a hydrogen uptake dataset, EGMOF achieved over 94% validity and 91% hit rate, representing significant improvements of up to 39% in validity and 29% in hit rate compared to existing methods, while remaining effective with only 1,000 training samples. Moreover, our model successfully performed conditional generation across 29 diverse property datasets, including CoREMOF, QMOF, and text-mined experimental datasets, whereas previous models have not. This work presents a data-efficient, generalizable approach to the inverse design of diverse MOFs and highlights the potential of modular inverse design workflows for broader materials discovery.
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All authors Seunghee Han, Yeonghun Kang, Taeun Bae, Junho Kim, Younghun Kim, Varinia Bernales, Alan Aspuru-Guzik, Jihan Kim

Tuesday 4 November

Materials Science · Cross-listed from cs.LG

Fine-Tuning Vision-Language Models for Multimodal Polymer Property Prediction

An Vuong, Minh-Hao Van, Prateek Verma et al. (+2 more)

Vision-Language Models (VLMs) have shown strong performance in tasks like visual question answering and multimodal text generation, but their effectiveness in scientific domains such as materials science remains limited. While some machine learning methods have addressed specific challenges in this field, there is still a lack of foundation models designed for broad tasks like polymer property prediction using multimodal data. In this work, we present a multimodal polymer dataset to fine-tune VLMs through instruction-tuning pairs and assess the impact of multimodality on prediction performance. Our fine-tuned models, using LoRA, outperform unimodal and baseline approaches, demonstrating the benefits of multimodal learning. Additionally, this approach reduces the need to train separate models for different properties, lowering deployment and maintenance costs.
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All authors An Vuong, Minh-Hao Van, Prateek Verma, Chen Zhao, Xintao Wu

Disordered Systems and Neural Networks · Cross-listed from stat.ML

Precise asymptotic analysis of Sobolev training for random feature models

Katharine E Fisher, Matthew TC Li, Youssef Marzouk et al. (+1 more)

Gradient information is widely useful and available in applications, and is therefore natural to include in the training of neural networks. Yet little is known theoretically about the impact of Sobolev training – regression with both function and gradient data – on the generalization error of highly overparameterized predictive models in high dimensions. In this paper, we obtain a precise characterization of this training modality for random feature (RF) models in the limit where the number of trainable parameters, input dimensions, and training data tend proportionally to infinity. Our model for Sobolev training reflects practical implementations by sketching gradient data onto finite dimensional subspaces. By combining the replica method from statistical physics with linearizations in operator-valued free probability theory, we derive a closed-form description for the generalization errors of the trained RF models. For target functions described by single-index models, we demonstrate that supplementing function data with additional gradient data does not universally improve predictive performance. Rather, the degree of overparameterization should inform the choice of training method. More broadly, our results identify settings where models perform optimally by interpolating noisy function and gradient data.
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All authors Katharine E Fisher, Matthew TC Li, Youssef Marzouk, Timo Schorlepp

Materials Science

A Normalized Descriptor for Unbiased Screening of Second-Order Nonlinear Optical Materials

Aubrey G. J. Nyiri, Michael J. Waters and James M. Rondinelli

Second-order nonlinear optical materials enable frequency doubling of light (second-harmonic generation, SHG), which is essential for optoelectronic applications ranging from materials characterization to quantum technologies. However, comparing SHG performance across materials remains challenging as the second-order nonlinear susceptibility $\chi^{(2)}$ spans several orders of magnitude and strongly depends on the band gap $E_g$. To address this, we empirically validate a theoretical upper bound on $\chi^{(2)}$ using new databases of ab initio-computed nonlinear optical (NLO) properties. We then formulate a normalized descriptor, $\hat{d}$, which expresses the NLO response of a material relative to the band gap-dependent physical limit. We show that $\hat{d}$ exhibits a similar distribution across a wide range of band gap energies. This universality supports the use of $\hat{d}$ as a robust, generalizable descriptor for data-driven and chemistry-informed machine learning models of NLO response, enabling accelerated materials discovery and optimization across broad application frequencies.
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Materials Science

Critical Disconnect Between Structural and Electronic Recovery in Amorphous GaAs during Recrystallization

Ellis Rae Kennedy, Adric Jones, Yongqiang Wang et al. (+6 more)

Understanding the evolution of structure and functionality through amorphous to crystalline phase transitions is critical for predicting and designing devices for application in extreme conditions. Here, we consider both aspects of recrystallization of irradiated GaAs. We find that structural evolution occurs in two stages, a low temperature regime characterized by slow, epitaxial front propagation and a high-temperature regime above dominated by rapid growth and formation of dense nanotwin networks. We link aspects of this structural evolution to local ordering, or paracrystallinity, within the amorphous phase. Critically, the electronic recovery of the materials is not commensurate with this structural evolution. The electronic properties of the recrystallized material deviate further from the pristine material than do those of the amorphous phase, highlighting the incongruence between structural and electronic recovery and the contrasting impact of loss of long range order versus localized defects on the functionality of semiconducting materials.
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All authors Ellis Rae Kennedy, Adric Jones, Yongqiang Wang, Miguel Pena, Hyosim Kim, Chengyu Song, Farida Selim, Blas P. Uberuaga, Samuel Greer

Materials Science

Dirac semimetal strontium iridate thin films with strong spin-orbit interaction for magnetic heterostructures

Gennady A. Ovsyannikov, Nikita V. Dubitskiy, Georgi D. Ulev et al. (+6 more)

The structural crystal features, electron transport and magnetotransport of the epitaxial strontium iridate (SrIrO$_3$) and iridate/manganite SrIrO$_3$/La$_{0.7}$Sr$_{0.3}$MnO$_3$ heterostructure have been investigated. The influence of epitaxial strain relaxation caused by the lattice mismatch between SrIrO$_3$ films and five substrates: SrTiO$_3$, NdGaO$_3$, (LaAlO$_3$)$_{0.3}$(Sr$_2$TaAlO$_6$)$_{0.7}$, LaAlO$_3$, and Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$-PbTiO$_3$ on electron and magnetic transport has been observed. A pronounced impact of strong spin-orbit interaction on characteristics of SrIrO$_3$ films has been revealed by means of X-ray photoelectron spectroscopy, magnetoresistance and Hall-resistance measurements at temperatures T = 2-300 K. These findings highlight the tunability of spin-orbit-driven transport phenomena in strain-controlled SrIrO$_3$-based epitaxial systems, relevant for future spintronic oxide heterostructures. The contribution of Kondo scattering on temperature dependence of SrIrO$_3$ films resistance was observed.
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All authors Gennady A. Ovsyannikov, Nikita V. Dubitskiy, Georgi D. Ulev, Karen Y. Constantinian, Ivan E. Moskal, Victoria A. Baydikova, Andrei M. Petrzhik, Anton V. Shadrin, Alexei V. Mashirov

Soft Condensed Matter

Randium: A minimal model of universal viscous liquid dynamics

Ulf R. Pedersen

When liquids are cooled and crystallization is avoided, their dynamics slow dramatically and the material eventually solidifies into an amorphous glass. Experiments show that chemically distinct glass forming liquids share universal features in both the spectral shape and the temperature dependence of the primary structural relaxation. We introduce Randium, a generic, energetically coarse-grained minimal model of viscous liquids. The model, inspired by results from atomistic molecular-dynamics simulations, is implemented on a two-dimensional lattice with Gaussian-distributed nearest-neighbor interactions. Temperature is the only control parameter, and at low temperatures, dynamic facilitation and dynamical heterogeneity emerge from simple nearest-neighbor rearrangements. The relaxation spectra obey time-temperature superposition, and they reproduce shapes observed experimentally for chemically distinct systems. The temperature dependence of the structural-relaxation time follows parabolic scaling, and the relaxation time grows exponentially with the heterogeneity length scale. The mean-squared displacement collapses onto the universal master curve of the random barrier model. The absence of elasticity-induced facilitation in Randium shows that this is not required for universal viscous-liquid dynamics. Other explanations for universal relaxation are discussed in light of Randium.
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Materials Science

An Atomistically Informed Device Engineering (AIDE) Method Realized: A case study in GaAs

Leopoldo Diaz, Harold P. Hjalmarson, Jesse J. Lutz et al. (+1 more)

Radiation-induced defects can have a significant impact on the longevity and performance of semiconductor devices. We present an Atomistically Informed Device Engineering (AIDE) method that integrates first-principles defect properties and experimentally measured parameters into a device model to dynamically simulate the defect chemistry in semiconductors. For a silicon-doped gallium arsenide (GaAs) material, we showcase three capabilities: (i) Fermi level $E_F$ movement including its component electron and hole Fermi levels, (ii) dynamical charge equilibration with the arsenic vacancy serving as an example, and a (iii) diffusion-driven reaction between Coulomb attracted gallium interstitial ($Ga_i$) and arsenic vacancy ($v_{As}$). Governed by charge carrier reactions, the electron and hole Fermi levels remained dissimilar until equilibrium was achieved at $E_F\approx1.32$ eV. The equilibrium Fermi level was verified by successfully identifying $v_{As}^{3-}$ as the most populated charge state within the arsenic vacancy defect. Lastly, a Coulomb attraction, created by the shifted Fermi level and the charge equilibration process, between $Ga_i^{1+}$ and $v_{As}^{3-}$ resulted in the formation of a doubly negative gallium antisite ($Ga_{As}^{2-}$). The AIDE method can access experimentally inaccessible short-time and low-concentration regimes, is generalizable to other more complex systems (e.g., indium gallium arsenide), and, after solving open problems in GaAs, will serve as a virtual experiment to bound estimates for difficult-to-measure physical quantities.
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All authors Leopoldo Diaz, Harold P. Hjalmarson, Jesse J. Lutz, Peter A. Schultz

Soft Condensed Matter

Taming polymorphism of tubule self-assembly using templated growth

Sirui Liu, Thomas E. Videbæk and W. Benjamin Rogers

Self-closing assembly is prone to polymorphism due to thermally-excited bending fluctuations, which permit the formation of off-target assemblies at the point of self-closure. One way to overcome this source of polymorphism is to use templated growth, a process in which assembly initiates from a precisely-defined seed rather than by spontaneous nucleation. We explore this approach to quelling polymorphism in the self-closing assembly of cylindrical tubules assembled from DNA-origami subunits with user-specified inter-subunit binding angles and specific interactions. We develop two strategies to create seeds with precisely-defined diameters and helicity: 1) using multicomponent assembly; and 2) purifying a specific seed-type from a polymorphic mixture using gel electrophoresis and gel extraction. By tuning the seed and monomer concentrations, and adjusting the assembly temperature, we determine the conditions under which tubules grow from the seed while avoiding spontaneous nucleation. We observe that templated tubules tend to follow the guidance of the seed, thereby increasing the selectivity of the target geometry. Also, we find that by tuning the diameter of the seed, one can template the growth of monodisperse tubules over a range of target diameters, even while using a single monomer type with a single preferred local curvature. Our results demonstrate that employing precisely defined seeds to guide assembly can significantly decrease polymorphism in self-closing assembly in a controllable and economical way.
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Superconductivity

Analog-to-Digital Converter Based on Voltage-controlled Superconducting Device

Md Mazharul Islam, Connor A. Good, Diego Ferrer et al. (+5 more)

The increasing demand for cryogenic electronics in superconducting and quantum computing systems calls for ultra energy efficient data conversion architectures that remain functional at deep cryogenic temperatures.In this work, we present the first design of a voltage-controlled superconducting flash analog-to-digital converter (ADC) based on a novel quantum enhanced Josephson junction field effect transistor (JJFET).Exploiting its strong gate tunability and transistor-like behavior, the JJFET offers a scalable alternative to conventional current controlled superconducting devices while aligning naturally with CMOS style design methodologies.Building on our previously developed Verilog A compact model calibrated to experimental data, we design and simulate a three bit JJFET based flash ADC.The core comparator block is realized through careful bias current selection and augmented with a three terminal nanocryotron to precisely define reference voltages.Cascaded JJFET comparators ensure robust voltage gain, cascadability, and logic level restoration across stages.Simulation results demonstrate accurate quantization behavior with ultra-low power dissipation, underscoring the feasibility of voltage driven superconducting mixed signal circuits.This work establishes a critical step toward unifying superconducting logic and data conversion, paving the way for scalable cryogenic architectures in quantum classical co-processors, low-power AI accelerators, and next generation energy constrained computing platforms.
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All authors Md Mazharul Islam, Connor A. Good, Diego Ferrer, Juan P. Mendez, Denis Mamaluy, Wei Pan, Kathleen E Hamilton, Ahmedullah Aziz

Superconductivity

Theory of ballistic SNS junctions revisited

Edouard Sonin

The recently suggested theory of planar ballistic SNS junctions demonstrated that in junctions without normal scattering (the case of equal Fermi velocities and effective masses in all layers) phase gradients in superconducting leads cannot be ignored. The revision of the previous theory ignoring them essentially changes the current-phase relation (CPR) of short junctions at $T=0$. It transforms it from forward-skewed to backward-skewed. The CPR at temperatures exceeding the energy spacing between Andreev levels but less than the critical temperature was also calculated. The current at these temperatures is temperature independent and decreases with growing $L$ as $1/L^4$. The previous theory predicted the current exponentially decreasing with growing $T$ and $L$. The SNS junctions with normal scattering (non-equal Fermi velocities in leads and inside the junction) were also analyzed. At strong mismatch of Fermi velocities the planar ballistic SNS junction becomes a common Josephson junction, which is a weak link and satisfies the Ambegaokar–Baratoff relation. Implications of the analysis for non-planar junctions (narrow normal bridge between two bulk superconductors) are also discussed. A qualitative explanation of experimental observation of backward-skewed CPR in short InAs nanowire bridge junctions was suggested.
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Materials Science

Electron and hole $g$ factors in semiconductors and nanostructures (Review)

A.V. Rodina, M.A. Semina and E.L. Ivchenko

We present a review of experimental and theoretical studies of the spin response of charge carriers to an external magnetic field in bulk semiconductors and semiconductor nanostructures. The linear response is quantitatively characterized by the magnitude of the electron or hole g factor. Various experimental methods for measuring the electron g factor are considered, beginning with historical works and including modern research. A detailed analysis of theoretical methods for calculating the electron and hole g factors in bulk semiconductors and nanostructures of various shapes also includes fundamental work from previous years and the present time.
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Superconductivity

Niobium's intrinsic coherence length and penetration depth revisited using low-energy muon spin spectroscopy and secondary-ion mass spectrometry

Ryan M. L. McFadden, Jonathan W. Angle, Eric M. Lechner et al. (+7 more)

We report direct, simultaneous measurements of the London penetration depth ($\lambda_L$) and Bardeen-Cooper-Schrieffer (BCS) coherence length ($\xi_0$) in oxygen-doped niobium, with impurity concentrations spanning the "clean" to "dirty" limits. Two depth-resolved techniques - low-energy muon spin spectroscopy (LE-$\mu$SR) and secondary-ion mass spectrometry (SIMS) - were used to quantify the element's Meissner screening profiles, analyzed within a framework that accounts for nonlocal electrodynamics. The analysis indicates intrinsic length scales of $\lambda_L = 29.1(10)$ nm and $\xi_0 = 39.9(25)$ nm, corresponding to a Ginzburg-Landau (GL) parameter of $\kappa = 0.70(5)$. The obtained $\lambda_L$ and $\kappa$ values, accurately quantified at the nanoscale, are smaller than values commonly used in applications and modeling, and indicate that clean niobium lies at the boundary between type-I and type-II superconductivity, supporting the contemporary view that its intrinsic state may be type-I.
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All authors Ryan M. L. McFadden, Jonathan W. Angle, Eric M. Lechner, Michael J. Kelley, Charles E. Reece, Matthew A. Coble, Thomas Prokscha, Zaher Salman, Andreas Suter, Tobias Junginger