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Physics Condensed Matter

cond-mat Watch Condensed Matter

Monday 8 June

Materials Science

The impact of interfacial chemistry on the band offset of GaAs/Ga$_2$O$_3$ heterostructures

Sofia Apergi, Alfredo Pasquarello, Charles Cornet et al. (+1 more)

Ga$_2$O$_3$/GaAs heterojunctions are emerging as promising candidates for next-generation power electronics, photonics, and energy devices, leveraging the high breakdown voltage and thermal stability of Ga$_2$O$_3$ alongside the mature technology, high hole mobility, and higher refractive index of GaAs. The efficiency of these devices depends strongly on the band alignment between the two materials, however both type-I and type-II alignment have been reported in the literature for these heterostructures. To address this ambiguity, we use hybrid density functional theory to systematically investigate the band alignment at GaAs/Ga$_2$O$_3$ interfaces, focusing on the role of interface chemistry. By considering Ga-O-, As-, and As-O-rich interfaces both in amorphous and crystalline Ga$_2$O$_3$ phases, we demonstrate that interface stoichiometry determines the alignment type: Ga-O-rich interfaces exhibit type-II alignment with large valence band offsets (~3.1 eV), while As-rich and As-O-rich interfaces favor type-I alignment with reduced offsets (~2.3-2.6 eV). These trends are attributed to interface dipole formation driven by bonding configuration. Our findings provide insight into the relationship between chemistry and band alignment in GaAs/Ga$_2$O$_3$ heterostructures, enabling targeted optimization for specific device applications.
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All authors Sofia Apergi, Alfredo Pasquarello, Charles Cornet, Laurent Pedesseau

Mesoscale and Nanoscale Physics

Correlation enhanced resistance hysteresis near half filling in MoS2/WSe2 heterobilayer

Yong Chen, Weikang Zhang, Meizhen Huang et al. (+11 more)

Ferroelectricity, typically arising from ionic displacements in noncentrosymmetric lattices, enabling applications in memory devices and sensors. Recent advances in two-dimensional materials and van der Waals heterostructures have revealed novel ferroelectric phenomena, including sliding ferroelectricity and correlation-driven ferroelectricity in moire superlattices. In this work, we fabricate and study a MoS2/WSe2 moire superlattice device exhibiting a high field-effect mobility of 17,650 $cm^2V^{-1}s^{-1}$. Electrical transport measurements reveal correlated insulating states accompanied by a prominent and reproducible resistance hysteresis near half filling. Temperature and displacement field dependence further confirms the correlation-enhanced nature of the hysteresis. Our analysis suggests that displacement field-induced metal-to-insulator transition at correlated insulating state coupled with interfacial dipoles enables the observed resistance hysteresis. These results establish correlation enhanced resistance hysteresis near half filling in a MoS2/WSe2 heterobilayer, offering opportunities for exploring emergent quantum phases and device functionalities.
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All authors Yong Chen, Weikang Zhang, Meizhen Huang, Shengling Xiang, Zishu Zhou, Yaqi Ma, Chenxuan Lou, Haoxi Ji, Aoqian Zhang, Yifei Jin, Liheng An, Zefei Wu, Chun Cheng, Ning Wang

Mesoscale and Nanoscale Physics

Strain-Induced Tuning of Third-Harmonic Generation in Monolayer Black Phosphorene

Yan Meng, Kainan Chang, Wei Song et al. (+3 more)

Based on the tight-binding model and the semiconductor Bloch equations, this work systematically reveals the microscopic mechanism of strain engineering in turning of third-harmonic generation (THG) in monolayer black phosphorene (BP). % The results show that under strain-free conditions, monolayer BP exhibits significant in-plane anisotropy, and its dominant susceptibility component reaches a maximum of $\chi^{(3);xxxx} = 1.8 \times 10^{-17} \, \text{m}^2/\text{V}^2$, agreeing well with the experimental results. % By applying uniaxial and biaxial strains along the armchair ($x$), zigzag ($y$), and out-of-plane ($z$) directions, we find that the THG response presents strong direction dependence and unique spectral shifting behaviors: in-plane compressive strain and out-of-plane tensile strain both significantly enhance the THG conductivity and induce a redshift, whereas in-plane tensile strain and out-of-plane compression lead to suppression and a blueshift, with the tuning efficiency following the order of $z > y > x$. The microscopic origin of these phenomena is identified as the synergistic modulation of the bandgap and Berry connection by strain. % Furthermore, the synergistic or competitive effects of biaxial strain further enrich the manipulation of THG signals. % Strain engineering can serve as an effective strategy for dynamically controlling nonlinear optical processes in two-dimensional materials, and it also lays a theoretical foundation for the development of high-performance reconfigurable infrared photonic devices.
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All authors Yan Meng, Kainan Chang, Wei Song, Yuwei Shan, Jin Luo Cheng, Luxia Wang

Soft Condensed Matter

Evaluation of nonlinear optical coefficients in uniformly aligned dioxane-based ferroelectric nematic liquid crystals using second harmonic generation

Hirokazu Kamifuji, Jigen Furukawa, Kazuma Nakajima et al. (+3 more)

Ferroelectric nematic liquid crystals (FNLCs) are promising soft platforms for nonlinear optics, but quantitative determination of their second-order nonlinear optical coefficients has been hindered by limited alignment control. Here, polarization-resolved second-harmonic generation (SHG) measurements on a uniformly aligned dioxane-based FNLC, combined with Jones-matrix simulations, enable determination of all principal tensor components. The resulting tensor is consistent with the expected $C_{\infty v}$ and Kleinman symmetries, while the measured coefficients cannot be explained by a simple sum of molecular first hyperpolarizabilities. These results provide a quantitative basis for understanding nonlinear optical responses and guiding the design of FNLC-based nonlinear optical materials and devices.
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All authors Hirokazu Kamifuji, Jigen Furukawa, Kazuma Nakajima, Hirotsugu Kikuchi, Kenjiro Fukuda, Masanori Ozaki

Strongly Correlated Electrons

Order parameters and ground-state phase diagram of the interacting topological Su-Schrieffer-Heeger model with extended-range hoppings

Tsz Hin Hui, Pedro D. Sacramento and Wing Chi Yu

Topological insulators have attracted numerous attentions recent years, where the Su-Schrieffer-Heeger (SSH) model is one of the most studied models. While the interacting version of it has been explored recently, the interplay between interactions and long-range hoppings merit further investigations. In this work, we uncover a rich phase diagram of the interacting SSH model with extended-range hoppings, in which it consists of several topological phases, two novel superconducting-like (SC-like) phases and five distinct charge-density-wave (CDW) phases. We substantiate that the SC-like and two CDW phases are direct consequences of imbalanced interactions and extended-range hoppings. We derive the order parameters (OPs) for each of the phases and verify them in large-system simulations, finding consistency with the entanglement entropy and the fidelity in capturing the phase transitions. In contrast to the non-interacting case where the favored hoppings are unidirectional in the topological phases, the derived OPs suggest non-unidirectional hoppings are possible under the influence of interactions.
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Materials Science

Metal Halide Perovskite/Chalcohalide Heterojunctions for the Photoinduced Oxidative Coupling of p-substituted Thiophenols

Anna Cabona, Stefano Toso, Alejandro Cortés-Villena et al. (+7 more)

The introduction of a semiconductor-semiconductor junction is an effective strategy to enhance the photocatalytic performance of perovskite nanocrystal-based systems. Herein, we optimized the synthesis of CsPbX3/Pb4S3X2 (X= Cl, Br, I) perovskites-chalcohalides heterostructures, whose band alignment can be tuned by halide composition. As a proof-of-concept, we evaluated the photooxidative coupling of p-substituted thiophenols at room temperature, under visible-light, air, and without sacrificial electron donor. Notably, CsPbBr3/Pb4S3Br2 achieved up to 94 % selectivity toward disulfide (p-OCH3 thiophenol with a turnover number of 14300) highlighting the crucial role of the type-II heterojunction to promote charge separation and efficient electron delocalization across the junction.
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All authors Anna Cabona, Stefano Toso, Alejandro Cortés-Villena, Ignacio Rosa-Pardo, Mirko Prato, Michele Ferri, Julia Perez-Prieto, Ilka Kriegel, Liberato Manna, Raquel E. Galian

Soft Condensed Matter

Quantitative measurement of fluid inertial effects in confined Brownian motion

Quentin Ferreira, Pablo Palacios-Alonso, Harshit Joshi et al. (+3 more)

The hydrodynamic response of Brownian particles in liquids is fundamentally altered by inertial forces arising from unsteady momentum transport in the surrounding fluid. These forces are of two distinct types: the added mass and the history effect. While both are well understood in bulk and weakly-confined geometries, under deterministic driving, their respective behaviours under strong confinement and thermal fluctuations remain scarcely addressed, unclear and often entangled together. The goal of the present study is thus to fill this fundamental gap. The confinement-induced variations of the two distinct inertial contributions are separately investigated in the vicinity of a flat, rigid wall, using a combination of broadrange thermal colloidal-probe atomic-force-microscopy experiments, advanced numerical simulations and theoretical arguments. Specifically, the separation of the added-mass and history-force contributions is achieved through their different frequency-scaling signatures within the assumed form of the generalized dissipation coefficient. Our results pave the way towards a complete picture of Brownian motion at interfaces, in the lubrication regime, with direct relevance to nanofluidics and interfacial biophysics.
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All authors Quentin Ferreira, Pablo Palacios-Alonso, Harshit Joshi, Rafael Delgado-Buscalioni, Yacine Amarouchene, Thomas Salez

Materials Science

BSE+ calculations for 2D materials: a unified description of excitons and plasmons

Amalie H. Svaneborg and and Kristian S. Thygesen

The Bethe-Salpeter equation (BSE) accurately describes low-energy optical spectra in materials with strong excitonic effects, but its high computational cost limits the number of electron-hole transitions that can be included. Neglecting high-energy transitions leads to an underestimation of the real part of the dielectric function, often producing a spurious plasmon peak in the BSE electron energy loss spectrum (EELS). The recently introduced BSE+ method addresses this by combining a four-point BSE-like equation for the irreducible polarisability with a two-point Dyson equation that includes the high-energy transitions at the Random Phase Approximation (RPA) level. Here, we present a detailed account of the method, extend it to two-dimensional materials, and apply it to a set of transition metal dichalcogenide monolayers. BSE+ preserves the excitonic features of the BSE at low energies while reproducing the plasmonic structure of the RPA at higher energies, yielding good agreement with experimental EELS data across the full energy range and strongly suppressing the spurious plasmon. BSE+ converges much faster than BSE with respect to the electron-hole basis size, at a comparable computational cost, and is implemented in the GPAW code.
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Strongly Correlated Electrons

Designing electronic magnetoelectric matter with organic quantum spin trimers

Yuko Hosokoshi, Christopher P. Aoyama, Zhuowei Zhang et al. (+17 more)

Magnetoelectric (ME) phenomena are commonly driven by spin-lattice coupling. Here we demonstrate a different route based on frustrated quantum spin trimers that intrinsically intertwine magnetic moments and electric dipoles. Using molecular design principles, we realize a weakly coupled lattice of equilateral $S=1/2$ spin trimers in the organic radical crystal TNN$\cdot$CH$_3$CN. In this material, correlated electronic fluctuations within each trimer generate electric dipoles, while geometrically frustrated intertrimer interactions organize them into collective ME states. Magnetization, thermodynamic, and dielectric measurements reveal multiple magnetic-field-induced phases, including the $1/3$-magnetization plateau marked by pronounced dielectric anomalies. Effective low-energy theories and numerical simulations show that these phenomena are driven by electronically generated trimer dipoles whose collective order is stabilized by frustration relief of the intertrimer interactions, establishing a direct connection between geometric frustration and emergent magnetoelectricity. Our results identify quantum spin trimers as multifunctional building blocks, providing a bottom-up route for designing correlated ME materials from electronically active quantum spin clusters.
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All authors Yuko Hosokoshi, Christopher P. Aoyama, Zhuowei Zhang, Toshio Ono, Kosuke Takada, Ayaka Higashiguchi, Seitaro Iisaka, Koudai Yamasaki, Hironori Yamaguchi, Shengzhi Zhang, Mohammad Irfan, Minseong Lee, Eun Sang Choi, Yasuyuki Shimura, Toshiro Sakakibara, Zhiyuan Xie, Hiroki Nakano, Yasu Takano, Cristian D. Batista, Yoshitomo Kamiya

Materials Science

Artificial Intelligence for Instability in Inorganic Perovskites: From Mechanism Discovery to Engineering Strategies

Xue Zhao, Chuan-Xin Cui, Zi-Hao Xu et al. (+3 more)

Three-dimensional all-inorganic halide perovskites, represented by CsPbX$_3$ (X = Cl, Br, I), have attracted broad interest in photovoltaics, photodetectors, and light-emitting devices because of their outstanding optoelectronic properties. Their practical deployment, however, remains limited by instability under thermal, chemical, optical, and electrical stress. Conventional studies have established important experimental and theoretical foundations, but they still struggle with multimodal data, coupled degradation pathways, protocol dependence, sparse statistics, and uncertainty quantification. Artificial intelligence (AI) offers a practical route to address these limitations. This review summarizes recent progress in AI-assisted studies of instability in 3D CsPbX$_3$ and organizes the discussion around four linked tasks, including stability discrimination and diagnosis, microscopic mechanism analysis, consequence and reliability modeling, and engineering stability enhancement. We further discuss the main limitations of current methods, especially in data quality, protocol consistency, benchmark design, interpretability, and transferability across domains. Finally, we outline future directions for the field, including standardized data infrastructures, interpretable cross-scale models, and tighter integration of AI with automated experiments and physics-based modeling. The aim of this review is to provide a coherent and practically useful framework for researchers seeking to use AI to understand, predict, and mitigate instability in inorganic perovskites.
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All authors Xue Zhao, Chuan-Xin Cui, Zi-Hao Xu, Yuan-Long Pang, Jun-Jie Li, Jin-Wu Jiang

Materials Science

Molecular dynamic simulation of multicomponent CoCrFeNiMn high-entropy alloy thin film deposition

Oleksandr I. Kushnerov, Sergey I. Ryabtsev and Valerij F. Bashev

The deposition and growth of a thin CoCrFeMnNi high-entropy alloy film on an Al(100) substrate were investigated by molecular dynamics simulation. Interatomic interactions were described using a calibrated set of Morse potentials combined with mixing rules for regular solutions. During a 100 ns simulation, 50,000 atoms with an incident energy of 10 eV were deposited, producing a film of about 6.1 nm thickness. The resulting film contains face-centred cubic (FCC), body-centred cubic (BCC), hexagonal close-packed (HCP), and amorphous regions. Analysis of the radial distribution function (RDF) was used to determine nearest-neighbour distances and estimate lattice parameters for the crystalline phases. The simulated phase composition and structural parameters are in good agreement with available experimental data.
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Materials Science

Symmetry-Breaking Induced Spin Transport and Magneto-Optical Regulation in 2D Altermagnet Ru2MoSe4

Wenpeng Wang, Hang Shi, Yuping Tian et al. (+2 more)

Two-dimensional (2D) altermagnets (AMs) offer a compelling paradigm for advanced spintronics, yet their fully compensated macroscopic spin currents inherently limit practical device integration. In this work, using first-principles calculations and theoretical analysis, we demonstrate that the 2D material Ru2MoSe4 hosts AM ground state protected by S4zT symmetry. Using uniaxial strain modulation and stacking configuration, we show that the monolayer and the AC-stacking bilayer Ru2MoSe4 host fully spin-polarized currents, piezomagnetically induced net magnetization, and the magneto-optical Kerr effect. Our findings establish Ru2MoSe4 as a tunable platform, offering a feasible mechanism to simultaneously trigger electrical spin transport signals and amplify optical readout signatures for next-generation spintronics and valleytronics.
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All authors Wenpeng Wang, Hang Shi, Yuping Tian, Wei-Jiang Gong, Xiangru Kong

Strongly Correlated Electrons

Dynamic scaling and Family-Vicsek universality in the Hubbard model at infinite temperature

Cătălin Paşcu Moca, Doru Sticlet and Balázs Dóra

We study Family-Vicsek scaling of charge, spin, and energy fluctuations in the one-dimensional Hubbard model at infinite temperature. Using a quantum generating function approach, we compute time-dependent cumulants of transferred conserved quantities and analyze how the corresponding roughness depends on subsystem size and time. We start by focusing on a single interface at half the chain and determine the transport exponents. Then we turn to fluctuations of a small finite interval and study the Family-Vicsek universality of fluctuations over an extended timescale. We find that the long-time scaling behavior is controlled by integrability. In the free limit, charge, spin, and energy all display ballistic transport. In the interacting integrable Hubbard chain, charge and spin cross over to a KPZ scaling regime, while the energy sector remains ballistic. Once integrability is broken by a next-nearest-neighbor density interaction, the long-time dynamics becomes diffusive in all sectors. In every case we also observe a short-time microscopic regime with apparently universal ballistic growth before the hydrodynamic scaling window sets in. The Family-Vicsek setup allows us to determine the growth, the saturation as well as the dynamical exponents.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Helicity-Resolved Spatiotemporal Mapping of Chiral Plexcitons in Helicoids

Jeong Hyun Han, Sankaran Ramesh, Jaeyeon Jo et al. (+10 more)

Plasmon-exciton hybrids, or plexcitons, offer deeply subwavelength light-matter interactions with versatile pathways for energy redistribution. Incorporating chirality into such systems is particularly compelling, enabling spin-sensitive optical functionality that can operate on ultrafast timescales and within ultracompact volumes. Despite recent progress in chiral plexcitonic systems, how structural chirality and plasmon-exciton coupling determine chiroptical spectra and ultrafast energy flow remains elusive. Here we realize chiral plexcitons by functionalizing intrinsically chiral gold helicoid nanoparticles with molecular J-aggregates. Within a non-Hermitian framework, we trace the microscopic origin of the helicoid chiroptical response and its coupling to the excitonic transition, revealing how the helicity of light selectively addresses distinct hybrid responses. At the spatiotemporal extreme, we find that the gap-localized response not only enhances polarization-sensitive contrast but also strengthens the local hybrid interaction, leading to accelerated ultrafast relaxation. Together, these space-, time-, and polarization-resolved measurements provide a physically grounded and experimentally benchmarked picture of chiral plexcitonic coupling, identifying chirality as a practical control parameter for selectively steering nanoscale energy pathways and dynamics.
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All authors Jeong Hyun Han, Sankaran Ramesh, Jaeyeon Jo, Pavel Chabera, Ryeong Myeong Kim, Sung Hoon Cho, In Han Ha, Amitav Sahu, Yoonsang Tak, Jiawei Lv, Miyoung Kim, Ki Tae Nam, Tönu Pullerits

Statistical Mechanics · Cross-listed from q-bio.PE

Natural Selection in the Wake of Catastrophe

Jesse Young Lin, Omer Granek, Joshua Sodicoff et al. (+3 more)

Living organisms, from bacteria to humans, are more likely to survive if their traits enhance fitness. In populations well adapted to their environmental niches, natural selection proceeds via rarely beneficial mutations. But when a catastrophe wipes out niche diversity, sudden adaptation often follows. Here, we present a data-validated theory of natural selection in the wake of catastrophe and unveil a simple law that emerges during recovery: the mean fitness relaxes inversely with time, with a prefactor proportional to the number of traits coupled to the post-catastrophe environment. We put our approach to test using experimental fitness landscapes measured following antibiotic administration to E. coli. The resulting mean trait adaptation is not described by gradient ascent on a fitness landscape, instead it follows an algorithm known as Levenberg-Marquardt optimization. Near fitness peaks, evolutionary trajectories are biased against greediness - from an optimization perspective, post-catastrophic selection is optimistic.
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All authors Jesse Young Lin, Omer Granek, Joshua Sodicoff, Seppe Kuehn, David Pincus, Vincenzo Vitelli

Materials Science

Precipitate phase selection and grain boundary morphology in Cu-Ni-Si-Mn alloys: A machine-learning interatomic potential study

Aadil Fayaz Wani, Il-Seok Jeong, Haekwan Jeon et al. (+6 more)

Alloys inevitably contain interphase boundaries, whose energetics govern nucleation processes and precipitate morphology. In Cu-Ni-Si alloys, Mn addition markedly changes grain boundary (GB) precipitation behavior. While GB precipitation of stable Ni$_2$Si in Mn-free alloys is associated with degraded mechanical properties, Mn addition instead promotes film-shaped Mn$_6$Ni$_{16}$Si$_7$ (G-phase) precipitation, which is correlated improved mechanical properties. However, the atomic origin of the contrasting GB phase selection and morphology remains unclear. Here we perform machine-learning interatomic potential (MLIP) calculations to investigate the effect of interphase-boundary atomic structure on GB precipitates in Cu-Ni-Si alloys with and without Mn. The MLIP calculations reliably reproduce DFT-level energetics for interfacial bonding and microstructural configurations, and further predict that Mn addition favors GB precipitation of Mn$_6$Ni$_{16}$Si$_7$ rather than Ni$_2$Si. Experimentally, Mn-free alloys are observed to exhibit irregularly-shaped Ni$_2$Si precipitates with open-boundary-like Cu/Ni$_2$Si interfaces, whereas Mn-added alloys exhibit film-like G-phase at GBs. Large-scale atomistic interface calculations reveal that the coherent interface structure between Cu and Ni$_2$Si favors the formation of plate-like strained Ni$_2$Si precipitates in the matrix. Upon coarsening and stress release, an out-of-phase coherent-like interface can form at GBs, generating a local repulsive region that gives rise to surface-like open-boundary structures and explains the irregular morphology of GB stable Ni$_2$Si precipitates. In contrast, Cu/Mn$_6$Ni$_{16}$Si$_7$ interfaces remain predominantly incoherent with moderate boundary energies and no pronounced repulsive regime, thereby stabilizing continuous interfacial contact and explaining film-shaped GB precipitation.
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All authors Aadil Fayaz Wani, Il-Seok Jeong, Haekwan Jeon, Jaesun Kim, SuDong Park, Eun-Ae Choi, Seung Zeon Han, Seungwu Han, Byungki Ryu

Superconductivity

Superconducting diode effect in magnetic superconductors realized by nonreciprocal domain-wall dynamics

Dong Hui Han, Suk Bum Chung and Se Kwon Kim

A superconducting diode effect is shown to arise in ferromagnetic superconductors through the nonreciprocal dynamics of magnetic domain walls. Specifically, we show that current-driven dynamics of a magnetic domain wall under a certain external field can exhibit a nonreciprocal Walker breakdown, possessing two distinct direction-dependent critical currents beyond which the domain wall precesses continuously. In ferromagnetic superconductors, the constant rotation of a domain wall is shown to give rise to phase slips, opening up dissipation channels, whereby the nonreciprocal Walker breakdown is mapped to the superconducting diode effect. For the nonreciprocal Walker breakdown of a magnetic domain wall, we analytically examine its dependence on the magnetic field and the Gilbert damping and verify the theoretical results with micromagnetic simulations. We then extend the analysis to ferromagnetic superconductors by considering additional effects from the superconductivity and identify criteria for experimental conditions to realize the predicted superconducting diode effect. Our work demonstrates that topological defects, such as domain walls, in magnetic superconductors can serve as an intrinsic nanoscale platform for nonlinear nonreciprocal superconducting functionalities within a single homogeneous material, circumventing the need for complicated engineered heterostructures and thereby enabling the miniaturization of superconducting devices down to the nanometer scale that is challenging to achieve with conventional Josephson junctions.
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Mesoscale and Nanoscale Physics

Valley-Landscape Engineering in Bilayer WSe$_2$ Gate-All-Around Transistors

Katsunori Wakabayashi, Souren Adhikary and Kazuhito Tsukagoshi

The K-$\Gamma$ valence-band splitting $\Delta_{K\Gamma}$ that governs hole transport in few-layer WSe$_2$ is not a fixed material constant. It is tuned by interlayer stacking, strain, pressure, and the dielectric and displacement-field environment. Its computed value also depends on the level of electronic-structure theory. Bilayer WSe$_2$ therefore realizes a tunable multivalley landscape rather than a single operating point. We combine first-principles inputs with an analytical two-valley device model for gate-all-around (GAA) field-effect transistors, and obtain three results. (i) The minimum subthreshold swing stays near the thermionic limit of $60$~mV~dec$^{-1}$ independently of layer number, because well below threshold the quantum capacitance remains far below the oxide capacitance. (ii) The effective mobility is set by the K-to-$\Gamma$ occupation ratio: valley redistribution is strong when $\Delta_{K\Gamma}$ is of order $k_BT$ and fades toward single-valley $K$ transport as the splitting grows. (iii) In this small-splitting regime, biaxial strain tunes the effective mobility - and hence the on-current - through the valley population while the subthreshold swing stays at the thermionic limit, decoupling mobility control from electrostatic switching in a way distinct from scattering-based strategies. A symmetric GAA gate controls carrier density at essentially fixed splitting, and because an out-of-plane field increases $\Delta_{K\Gamma}$, its midplane-symmetric potential avoids driving the channel out of the small-splitting regime. The design principle has two facets: small $\Delta_{K\Gamma}$ - set by layer number, stacking, strain, and dielectric engineering - maximizes the valley tunability of $\mu_\mathrm{eff}$, whereas larger $\Delta_{K\Gamma}$, for example through compressive strain, suppresses the heavy $\Gamma$ valley and maximizes the on-state mobility.
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Materials Science

Chemical tuning of magnetic ordering and cryogenic magnetocaloric response in zircon-type Gd1-xErxVO4

Ming Zeng, Muqing Su, Liang Ming et al. (+4 more)

Chemical substitution offers an effective route to tune magnetic ordering and magnetocaloric performance in rare-earth oxides for cryogenic refrigeration. Here we investigate the structural evo lution, magnetic properties, and magnetocaloric effect of polycrystalline zircon-type Gd1-xErxVO4 (x=0, 0.1, 0.25, 0.5, and 0.75). Powder X-ray diffraction confirms that all samples crystallize in the tetragonal zircon structure without detectable impurity phases. Substitution of Gd3+ by the smaller Er3+ ion produces a systematic lattice contraction and modifies the magnetic behavior of the rare-earth sublattice. In particular, the magnetic ordering temperature is suppressed from 3.65(2) K in GdVO4 to 2.76(2) K in Gd0.9Er0.1VO4 , accompanied by a weakening of the spin-flop-like field-induced anomaly observed in the parent compound. A low Er concentration correspondingly improves the low-temperature magnetocaloric performance, with Gd0.9Er0.1VO4 exhibiting a max imum magnetic entropy change of 45.1 J kg-1 K-1 for mu_0 Delta H=7T. These results demonstrate that weak Er substitution effectively tunes the competition among exchange interactions, dipolar coupling, and magnetic anisotropy, optimizing the balance between magnetic ordering and available spin entropy in zircon-type rare-earth vanadates, which is crucial for developing efficient cryogenic refrigeration materials.
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All authors Ming Zeng, Muqing Su, Liang Ming, Xiaolong Yang, Wang Chen, Lingwei Li, Hai-Feng Li

Materials Science

Local electronic structure and dynamics of hydrogen in $\text{CeO}_2$

A. Koda, T. U. Ito, M. Hiraishi et al. (+2 more)

The local electronic states of muon (Mu) as an isotope of hydrogen (H) in high-quality single-crystalline ceria (CeO$_2$) are investigated using muon spin rotation/relaxation ($\mu\text{SR}$) and first-principles density functional theory (DFT) calculations. Upon positive muon implantation, both paramagnetic (Mu$^0$) and diamagnetic (Mu$^*$) states are observed below $\approx$10 K. Magnetic field dependence of the Mu$^0$ signals combined with DFT results provides evidence for the formation of a polaron state, consisting of Mu bonded to a ligand oxygen and a $4f$ electron localized on a nearby Ce site. The crystal-orientation dependence of the Mu$^0$ signal suggests strong anisotropy of the $4f$ electron due to the spin-orbit coupling with lifted degeneracy. Furthermore, the Mu$^0$ state exhibits transition to the Mu$^*$ state that corresponds to another Mu$^0$ state (exhibiting a diamagnetic response due to fast spin/charge fluctuations) at temperatures above $\approx$10 K, before disappearing above $\approx$30 K. These findings suggest rapid diffusive motion of the $4f$ electrons and/or Mu (as well as H) at higher temperatures.
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All authors A. Koda, T. U. Ito, M. Hiraishi, H. Okabe, R. Kadono

Sunday 7 June

Statistical Mechanics

Computing phase diagrams using a convex hull algorithm

C. P. Dullemond and E. D. Young

We present a simple universal computational algorithm for computing compositional phase diagrams of rocks and their melts at given temperature and pressure. It makes use of the mathematical concept of the convex hull of a set of points in the space spanned by the composition and the Gibbs free energy. All the complexities of determining the stability or separation of phases, the localization and orientation of tie lines, as well as the determination of characteristic points, curves and surfaces such as the solidus, liquidus, solvus, and the eutectic/peritectic points etc, are taken care of by the algorithm that computes the convex hull, supplemented with an algorithm to physically classify the resulting simplices. For the convex hull computation, the publicly available Qhull package can be used, which is available in SciPy. This makes this method accessible and intuitive for a broad set of scientific and educational applications. Although the method is not practical for systems of a large number of components, it is remarkably stable and efficient for systems of up to four. We present our implementation of the method as a publicly available Python package.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Impact of gate-voltage noise on silicon spin-qubit variational quantum eigensolvers

Xinning Wang, Bohdan Khromets, Zachery Merino et al. (+1 more)

Quantum computers offer a route to outperform classical methods in tasks such as molecular simulation, motivating hybrid algorithms like the Variational Quantum Eigensolver (VQE) for near-term devices. Silicon spin qubits are a promising platform for scalable quantum computation, but their performance is limited by hardware imperfections – most notably charge-noise-induced potential fluctuations and static miscalibration of gate-electrode voltages – which degrade quantum gate fidelities and, ultimately, algorithmic accuracy. Here we develop a hardware-algorithm co-simulation framework for silicon quantum-dot processors that links 3D electrostatics to effective $g$-factors and exchange couplings, and propagates voltage-level noise through realistic control pulses. Using VQE for $\mathrm{H}_2$ ground-state energy estimation as a circuit-level testbed, we study both static scaling/offset errors on the gate-electrode voltages and stochastic fluctuations modeled as random-telegraph noise with tunable amplitudes and switching times. At the gate level, we show that exchange-based two-qubit gates are roughly an order of magnitude more sensitive to these types of noise than ESR-driven single-qubit rotations. Quantum process tomography and Kraus-operator analysis further distinguish coherent and incoherent contributions and quantify the fraction of error that is, in principle, correctable by a compensating unitary. Embedding these noise models into the VQE circuit, we identify regimes of miscalibration strength and noise switching time compatible with chemically accurate energy estimates, and discuss how statistical post-processing based on the full distribution of noisy energy estimates could further improve accuracy.
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All authors Xinning Wang, Bohdan Khromets, Zachery Merino, Jonathan Baugh

Mesoscale and Nanoscale Physics

Topological invariant responsible for the integer QHE and non-commutative geometry

G. Kovyrshin, A. Mekrami, J. Miller et al. (+2 more)

We consider a wide class of $2D$ tight - binding models of solid state physics. These models are, in the most general case, non - homogeneous. The topological invariant ${\cal N}_3$ responsible for the quantization of the Hall conductivity, for the specific case of the integer quantum Hall effect in $2D$, is expressed through the Wigner transformation of the two-point electron Matsubara Green function. We express this invariant as a pairing of the element of the $K^{-1}$ group (generated by the Green function) with the specific element of the cyclic cohomology group $HC^3$. According to a set of local index theorems the values of ${\cal N}_3$ can be shown to be integer for a limited class of tight - binding models. We concentrate on systems with a spectral gap, with the chemical potential inside the gap and an invertible Dirac operator $\hat Q$ throughout the Matsubara-frequency domain. The mobility-gap case is not considered here and will be addressed in forthcoming publications.
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All authors G. Kovyrshin, A. Mekrami, J. Miller, M.A. Zubkov, A. Zuevsky

Statistical Mechanics

Time Evolution of Heat Conduction in a Generalized Model of Brownian Motion

T. Koide and F. Nicacio

We investigate the properties of heat conduction in a network of harmonic oscillators interacting with heat baths, described by a generalized model of Brownian motion. This model includes noise and dissipation terms in both the momentum and position equations. This generalization is motivated by the requirement of consistency with the Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) equation. Because standard definitions of heat current based on velocity become mathematically inconsistent in this framework, we derive an analytical expression for the steady-state heat flow based on an extended framework of stochastic energetics. We confirm that Fourier's law (linear thermal response) is satisfied and that the model naturally captures microscopic thermal boundary resistance, analogous to Kapitza resistance. This demonstrates that our generalized model functions as a valid phenomenological framework for simulating non-equilibrium processes, marking a crucial step toward a unified formulation of stochastic and quantum thermodynamics. Furthermore, we analyze the time evolution of heat conduction by numerically solving the corresponding differential equations for the correlation functions. Unlike standard Brownian motion, the generalized model generates continuous and nowhere differentiable trajectories for both momentum and position (as is characteristic of overdamped dynamics). Finally, we show that the heat current exhibits characteristic transient behavior when the inter-particle interaction is switched on. Specifically, an instantaneous heat flow emerges, whose direction is strictly governed by whether the interaction is attractive or repulsive, significantly differing from the predictions of the standard model.
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Materials Science

Chiral Surface Phonons

Mike Pols and Nicola A. Spaldin

We use symmetry arguments combined with density functional theory to demonstrate that surfaces of centrosymmetric crystalline materials host surface phonons that are chiral. As model systems, we study slabs of highly symmetric AB rocksalt compounds, and find surface-localized phonons whose atomic displacements exhibit chiral motion. We further show that these chiral surface phonons generate in-plane magnetic moments at the surface. Our results indicate that chiral phonons can emerge in all crystalline materials as a result of reduced symmetry at surfaces or interfaces. These findings establish surfaces as a previously overlooked source of chiral phonons and their associated magnetic moments, which could play a role in surface-sensitive measurements.
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Disordered Systems and Neural Networks

Predictable Mean-Field Chaos in Random Recurrent Neural Networks

Alkesh Yadav, Vladimir Shaidurov and Jonathan Kadmon

Dynamical mean-field theory (DMFT) maps deterministic chaos in random recurrent neural networks to an effective Gaussian process, usually treated as an ensemble description rather than a predictor of individual trajectories. Contrary to this view, we show that the chaotic mean-field process of the Sompolinsky–Crisanti–Sommers model can be perfectly predictable at the level of a single neuron. When the nonlinearity has a Gaussian or faster Fourier decay, the exact continuous past of one realization determines its entire future: the conditional prediction error vanishes despite a positive Lyapunov exponent. We trace this result to complex-time singularities of the self-consistent covariance through the Paley–Wiener criterion. A Lanczos/Krylov representation turns the covariance into a state-space predictor and defines $\alpha$, the rate at which predictive information is transferred to higher temporal modes. For smooth odd nonlinearities in this predictable class, the Krylov rate and the largest Lyapunov exponent scale differently near the chaotic transition, demonstrating that predictive complexity and microscopic instability are distinct characteristics of the dynamics. Resolving the first $p$ Krylov modes yields a prediction horizon that grows as $\log p$ and enables finite-network forecasts from a single neuron's observed past, without knowing the connectivity and without observing the rest of the network. Thus, the mean-field power spectrum becomes a diagnostic of whether apparent variability reflects irreducible fluctuations or hidden deterministic structure encoded in the observed past.
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Statistical Mechanics

Fluctuation-stable generalized entropy probes of spectral heterogeneity

Arpita Goswami

Generalized entropy measures are widely used to characterize localization and multifractality, and the regime \(q>1\) is often empirically found to exhibit improved numerical stability and cleaner scaling behavior. Here, we develop a fluctuation-stability framework for generalized entropy diagnostics and show that weak-amplitude spectral fluctuations are amplified for \(q<1\) and suppressed for \(q>1\), thereby providing a theoretical basis for the physically robust \(q>1\) regime. A thermodynamic scaling analysis further identifies an asymptotically stable regime beyond a critical threshold. As an application, we introduce the entropy-gradient susceptibility \(\chi_q\) as a coarse-grained probe of spectral heterogeneity. Using the Aubry-André and generalized Aubry-André models, we demonstrate that \(\chi_q\) sharply distinguishes homogeneous localization transitions from mobility-edge coexistence regimes. Our results establish fluctuation stability as a guiding principle for generalized entropy diagnostics in quasiperiodic systems.
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Disordered Systems and Neural Networks · Cross-listed from quant-ph

Graph Neural Networks for Fast Operator Selection in Adaptive VQE

Javad Vahedi and Hadi H. Arefi

Adaptive variational quantum algorithms like ADAPT-VQE construct tailored ansätze by iteratively selecting operators from a pool using gradient-based criteria. While this avoids oversized parameter spaces, repeatedly scanning the full pool incurs a classical cost that scales linearly with pool size-a major bottleneck for systems with long-range interactions or large operator sets. Here, we reformulate adaptive operator selection as a graph-based decision problem and introduce a graph neural network (GNN) policy that predicts the next entangling operator directly from the interaction graph and state-dependent observables. Training data are generated from exact simulations of disordered long-range spin chains, using gradient magnitudes as supervision signals. The learned policy accurately reproduces the dominant structure of the greedy gradient-based selection rule, significantly outperforming heuristics based solely on interaction strength. Integrated into a variational quantum eigensolver (VQE) workflow, this GNN-VQE approach achieves energy errors close to standard ADAPT-VQE while drastically reducing full-pool gradient evaluations. To test transferability beyond spin models, we evaluate the policy on small active-space molecular benchmarks (LiH and BeH_$2$). We find the GNN is highly effective as a shortlist generator: exact rescoring over just a few GNN-proposed candidates recovers near-oracle rollout behavior while searching only a small fraction of the pool. These results demonstrate that adaptive circuit construction contains learnable structure that can be exploited to accelerate variational quantum algorithms.
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Soft Condensed Matter · Cross-listed from physics.geo-ph

Injection-rate effects on failure in a fluid-saturated granular fault gouge

Pritom Sarma, Stanislav Parez, Renaud Toussaint et al. (+1 more)

Fluid injection into the Earth's subsurface, performed for energy extraction, waste disposal, and resource development, is known to reactivate gouge-filled faults and induce seismicity, a key hazard in modern geotechnical operations. Nevertheless, the role of injection rate in controlling fault-gouge failure remains poorly understood. Here we present both an analytical theory and coupled fluid–granular (discrete element) numerical simulations to explain this rate dependence. Assuming a pre-stressed gouge-filled fault subject to fluid injection, we derive a pore-pressure diffusion equation with a dilative sink. Its solution predicts a rate-dependent failure criterion, arising from pressure heterogeneity within the layer: slow injection allows pressure to diffuse uniformly throughout the layer, promoting uniform weakening, whereas rapid injection produces strong gradients, leaving distal regions stronger. The numerical simulations confirm the theory and reproduce experimental observations not captured by classical, uniform-pressure effective-stress theory. The framework links grain-scale physics to fault-scale failure and provides quantitative guidance for the design of injection protocols in geotechnical operations involving granular geomaterials.
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All authors Pritom Sarma, Stanislav Parez, Renaud Toussaint, Einat Aharonov

Soft Condensed Matter

Energy Barriers for Reversible Chain Scission and Healing under Tension with Displacement Control

Mohammad A. Ansari, Kenneth M. Liechti, Dmitrii E. Makarov et al. (+1 more)

Polymer chain scission is a key mechanism for fracture of soft materials. It is well known from single-molecule force spectroscopy experiments that the critical condition for chain scission depends on the loading rate and other environmental effects (e.g., temperature and solvent). Common approaches to describing the kinetics of chain scission often assume force-controlled conditions, that is, when a polymer chain is stretched by a prescribed force. As a result of this assumption, chain scission is irreversible, excluding the possibility of healing. In many soft materials, however, self-healing has been observed after fracture, suggesting possibly reversible chain scission. Here, we show that reversible chain scission is possible under displacement-controlled conditions, that is, when a polymer chain is stretched with a prescribed end-to-end distance. We present a breakable freely-jointed chain model, assuming that a polymer chain breaks when one of its links breaks while the other links remain nearly rigid. At a prescribed end-to-end distance, the free energy of the chain has two local minima and a local maximum (the transition state), giving rise to energy barriers for chain scission and healing. As the prescribed displacement increases, the energy barrier decreases for scission but increases for healing, depending on the chain length (number of links) and the potential energy of the link. With the energy barriers, we adopt a kinetic approach to predict the statistics and kinetics of a single polymer chain under tension, first by integrating the rate equation and then by kinetic Monte Carlo simulations. Notably, the present model predicts rate-dependent chain scission, with a lower bound for the rupture force that could be several orders of magnitude lower than the upper bound (which is close to the theoretical strength of the covalent bonds).
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All authors Mohammad A. Ansari, Kenneth M. Liechti, Dmitrii E. Makarov, Rui Huang