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Physics Condensed Matter

cond-mat Watch Condensed Matter

Tuesday 21 April

Mesoscale and Nanoscale Physics

Ultrafast Light-Induced Magnetoelectric Effect in van der Waals Magnetic Semiconductor Heterostructures

Wenyi Zhou, Ravi Kumar Bandapelli, Hari Paudyal et al. (+8 more)

Atomic-scale heterostructures of van der Waals (vdW) magnets and semiconductors provide a unique environment for exploring magnetic dynamics. In contrast to typical photothermal excitation of precessional magnetization dynamics by a pump laser pulse, we find that ultrafast optical excitation of a WS$_2$/CrGeTe$_3$ (CGT) bilayer produces an opposite sign of magnetic torque compared to an isolated CGT film. Experimental observations by time-resolved magneto-optic Kerr effect (TR-MOKE) and theoretical analysis by density functional theory (DFT) and Landau-Lifshitz-Gilbert (LLG) simulations support a mechanism in which charge transfer of photoexcited carriers across the interface alters the perpendicular magnetic anisotropy, which in turn generates a torque on the magnetic layer to trigger precessional magnetization dynamics. These results provide new avenues for ultrafast manipulation of magnetization in vdW heterostructures with type-II band alignments. Lastly, we show that optically-generated spin currents from WS$_2$ into CGT can also trigger precessional dynamics via angular momentum transfer.
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All authors Wenyi Zhou, Ravi Kumar Bandapelli, Hari Paudyal, Bangzheng Han, I-Hsuan Kao, Ziling Li, Yuqing Zhu, Durga Paudyal, Jyoti Katoch, Simranjeet Singh, Roland K. Kawakami

Strongly Correlated Electrons

Re-examination of electronic structure of dilute Kondo transition-metal ions substituted into a Heavy Fermion compound

Kou Takubo, Shintaro Suzuki, Kohei Yamamoto et al. (+9 more)

Correlations between the localized and conductive spins/charges have been the central issue of various fascinating quantum phenomena found on itinerant electron systems. Here, the obvious multiplet structures are presented on the Mn 2$p$ to 3$d$ x-ray absorption for a heavy fermion $\alpha$-(Yb,Lu)(Al$_{1-x}$Mn$_x$)B$_4$, indicating that the unoccupied electronic structure of the Mn site is described as the correlated high-spin 2+, even though magnetic measurements show the Mn sites to be nonmagnetic. This apparently paradoxical result demonstrates that a ligand field can effectively appear between localized Mn 3$d$ and surrounding B 2$p$ orbitals, which has been anticipated as a manifestation of a Kondo effect but not been clearly confirmed for most itinerant metals in spectroscopy. By contrast, the Mn 2$p$ photoemission indicates that the occupied Mn$^{2+}$ 3$d$ electrons still exhibit itinerant and nonlocally screened nature also owing to the Kondo-like correlation with the conductive B 2$p$, and heavier Yb 4$f$ and 5$d$ bands below the Fermi energy. The asymmetry on the particle-hole stimulates a reconsideration of the correlation and screening effects in the core-level spectroscopies.
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All authors Kou Takubo, Shintaro Suzuki, Kohei Yamamoto, Kohei Yamagami, Masafumi Horio, Toshiaki Ina, Kiyohumi Nitta, Masaichiro Mizumaki, Eiji Ikenaga, Yosuke Matsumoto, Hiroki Wadati, Satoru Nakatsuji

Strongly Correlated Electrons

Seniority Eigenstate Configuration Interaction

Thomas M Henderson, Guo P. Chen and Gustavo E. Scuseria

Zero-seniority methods have shown great promise for the description of strongly-correlated electronic systems. Other seniority sectors have been much less explored, and in particular the maximal seniority sector and zero seniority have the same underlying algebraic structure. We introduce a seniority eigenstate configuration interaction in which the wave function is constrained to have good fixed local seniority for each paired orbital, by which we mean we partition orbitals into a pairing set with seniority zero, and a spin set with seniority one. We show how to build the effective Hamiltonian for this ansatz, and demonstrate that high-seniority wave functions have unexpectedly excellent accuracy for strongly-correlated fermionic systems, with accuracy competitive with or better than seniority zero for the Hubbard model and for the dissociation of the nitrogen molecule.
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Strongly Correlated Electrons

Stealthy hyperuniform disorder: A new route to controlling electric states and magnetic phase transition in correlated systems

Akihisa Koga and Takanori Sugimoto

We investigate the effects of stealthy hyperuniform bond distributions on the electronic and magnetic properties of the Hubbard model on the honeycomb lattice. Hyperuniform structures, distinct from random and quasiperiodic ones, have recently attracted considerable interest due to their anomalous suppression of density fluctuations. By diagonalizing the noninteracting Hamiltonian, we show that a linear density of states (DOS) robustly emerges, while the stealth property of the bond distribution changes the wave functions in the higher-energy region extended and significantly modifies the DOS near the band edge. To clarify the impact on magnetism, we apply the real-space Hartree approximation to the Hubbard model. We find that, the phase transition always occurs between semimetallic and antiferromagnetically ordered states and its critical interaction strength is sensitive to the stealth property. A comparison with the quasiperiodic honeycomb tiling further highlights the role of structural correlations. These results demonstrate that stealthy hyperuniform disorder provides a novel route to controlling electronic states and magnetic phase transitions in correlated systems.
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Strongly Correlated Electrons

Energy relaxation due to two-phonon scattering of electrons: Breakdown of the energy diffusion model

Joshua Covey and Dmitrii L. Maslov

Recent THz spectroscopy of the quantum paraelectric SrTiO$_3$ (arXiv:2501.15771) and a high-$T_c$ cuprate (arXiv:2503.15646) has renewed interest in energy relaxation in correlated electron systems. We consider a situation in which single-phonon scattering is forbidden by symmetry or momentum conservation, while two-phonon scattering is allowed. Solving the Boltzmann equation, we show that above the Bloch-Grüneisen temperature the energy relaxation rate from two soft transverse optical phonons exceeds the single-phonon one: while the latter scales as $1/T$, the former is linear in $T$. This dominance of two-phonon scattering invalidates the usual picture of energy diffusion due to frequent scattering by subthermal phonons; instead, energy relaxes via rare scattering events involving thermal phonons. Below the Bloch-Grüneisen temperature, the energy relaxation rate scales as the single-particle rate, namely as $T^3$ for soft phonons. For anisotropic electron bands, an intermediate regime appears between two Bloch-Grüneisen temperatures, in which both allowed single-phonon and two-phonon processes scale as $T^2$.
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Soft Condensed Matter

Geometric quantification for nonlinear deformation in knitted fabrics

Jiani Fang, Xiaoxiao Ding and Gary P. T. Choi

Knitted fabrics exemplify a broad class of architected materials capable of large deformations, enabling shape morphing, mechanical biocompatibility, and embedded multifunctionality without material damage. Although geometric nonlinearity has been intuitively utilized in their design, a quantitative description of stitch-resolved deformation and its temporal evolution remains lacking. Here, we introduce a geometric quantification framework that reconstructs smooth yarn centerlines and fabric surfaces from sparse yarn-level representations and extracts interpretable descriptors across dimensions. Applied to representative knitted structures, this framework resolves how global deformation is distributed among stitch reorientation, loop bending, surface bending, and dilation. Moreover, it reveals how regions of large geometric variation emerge, persist, and redistribute over time. Rather than directly measuring stress, these geometric descriptors define a unified geometric state space for comparing knitted structures and identifying candidate regions of mechanical localization. The framework provides a quantitative language for nonlinear deformation in knits and establishes a geometry-based representation that can be coupled to constitutive models, experimental measurements, and graph-based inverse-design workflows.
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Disordered Systems and Neural Networks · Cross-listed from quant-ph

Asymptotic Metrological Scaling and Concentration in Chaotic Floquet Dynamics

Astrid J. M. Bergman, Yunxiang Liao and Jing Yang

We study quantum sensing with Floquet chaotic dynamics generated by Haar random unitary gates. The metrological resources consist of three ingredients: A given initial state, a set number of Haar random unitary gates and the sensing gates. There are two natural ways of organizing the resources: the first one is the "control" protocol, where the random unitary gates act as random controls and intertwine with the deterministic sensing gates and the second one is the "state-preparation" protocol, where random unitary gates play the role of preparing the metrological useful states. In each protocol, we consider both global Haar random unitary gates and a set of local two-site Haar random unitary gates that forms a Floquet random quantum circuit (RQC) respectively. We find linear, shot-noise scaling of the metrological precision, quantified by the quantum Fisher information (QFI), in the asymptotic limit when the Hilbert space dimension becomes large, and quantum advantages beyond linear scaling in the non-asymptotic regimes. We also bound the fluctuation of the QFI using concentration inequalities. Our analytical findings are corroborated by numerical simulations. Finally, along the way of analyzing the precision limit, we prove an empirical conjecture of RQC: In the asymptotic limit of large local Hilbert space dimension, the Floquet operator of a Floquet RQC essentially behaves like a global unitary operator.
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Quantum Gases · Cross-listed from hep-ph

Vortex structures in electron-positron pair production by two-colored fields

Adiljan Sawut, Ying-Jun Li, Hong-Hao Fan et al. (+1 more)

We investigate the spin resolved vortex properties of electron positron pairs created from vacuum in time delayed, two color electromagnetic fields. By treating the temporal delay G as a continuous tuning parameter, we reveal a dynamic transition from interference-dominated domain patterns at G=0 to the nucleation of quantized vortex lattices at G=0.5. These topological structures exhibit a staggered arrangement analogous to von Karman vortex streets in fluid dynamics. We demonstrate that the momentum-space morphology is strictly governed by spin orbit selection rules, i.e., parallel spin configurations enforce a dipole-like connectivity, while anti-parallel configurations resolve into distinct quadrupole structures. This difference originates from the conservation of total angular momentum Jz, where the spin projection determines the required orbital angular momentum Lz of the created pairs. At large delays (G greater than 1), macroscopic vortex coherence dissolves into a chaotic phase landscope due to multi-channel interference, yet the spin-dependent nodal geometries remain robust. Our findings suggest that these topological signatures provide a high-fidelity diagnostic for the quantum dynamics of vacuum excitations in strong field QED.
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All authors Adiljan Sawut, Ying-Jun Li, Hong-Hao Fan, Bai-Song Xie

Strongly Correlated Electrons

Room-temperature multistage metastability in a moiré superstructure

B. Q. Lv, Yifan Su, Alfred Zong et al. (+16 more)

Metastability is fundamental not only to phase ordering and transitions, but also to a broad range of modern technologies, from memory devices to metallic glasses. In condensed-matter physics, charge density waves (CDWs) offer versatile platforms for accessing metastable states due to their sensitivity to external stimuli. However, most metastable CDW states are stabilized only at low temperatures, limiting their practical utility. In this study, we report the observation of electrically driven, room-temperature, nonvolatile metastable states in the bulk form of EuTe$_4$, a recently discovered compound that hosts an innate moiré superlattice characterized by the stacking of incommensurate monolayer and bilayer CDWs. Systematic transport measurements reveal discrete resistivity plateaus and strong electric-field sensitivity, with a large number of metastable states readily induced across a wide temperature window within a giant hysteresis loop, making them well-suited for high-temperature, multi-bit memory applications. By integrating photoemission spectroscopy, diffraction, and in-situ transport measurements, we uncover that these metastable states do not stem from conventional mechanisms such as the emergence of new ordered phases or changes in incommensurate periodicity. Instead, they are characterized by a suppression of the original CDW amplitude and a reduction in correlation length, pointing to a unique electric-field-induced switching of out-of-plane CDW phases in the moiré superstructure. Our findings not only provide critical insights into metastable phenomena in moiré systems with stacked electronic orders but also establish EuTe$_4$ as a promising platform for developing room-temperature, multi-bit memory devices.
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All authors B. Q. Lv, Yifan Su, Alfred Zong, Karna Morey, Bryan T. Fichera, Qiaomei Liu, Dong Wu, Yongchang Ma, Dupeng Zhang, Faran Zhou, Makoto Hashimoto, Dong-Hui Lu, Donald A. Walko, Haidan Wen, Jiarui Li, Suchismita Sarker, Jacob P. C. Ruff, N. L. Wang, Nuh Gedik

Strongly Correlated Electrons · Cross-listed from quant-ph

Quantum Decoherence of the Surface Code: A Generalized Caldeira-Leggett Approach

E. Novais and A. H. Castro-Neto

Standard quantum error correction (QEC) models typically assume discrete, Markovian noise, obscuring the continuous quantum nature of physical environments. In this manuscript, we investigate the fundamental limits of an actively corrected surface code coupled to a continuous, un-reset quantum environment at zero and finite temperature. Using the generalized Caldeira-Leggett framework, we map the long-time evolution of the logical qubit to a boundary conformal field theory, establishing an exact equivalence to the anisotropic Kondo model. We evaluate computational times for a finite code distance $L$ for all spatial and temporal correlations. Our analysis reveals that a true thermodynamic threshold exists strictly for short-range environments ($z>1/(s+1)$). In critical or long-range regimes, the macroscopic footprint of the code weaponizes the continuous bath, hindering the topological protection.
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Superconductivity

AngstromPro: A software platform for STM data management, visualization and analysis

Huiyu Zhao, Jiahao Yan, Catherine Dawson et al. (+2 more)

Modern scanning tunneling microscopy (STM) experiments increasingly generate multidimensional datasets that require coordinated data management, visualization, and analysis. We present AngstromPro, an open-source Python-based software platform designed to support these activities within a common interactive environment. Its application architecture organizes inapplication data through independent module instances, each combining a Workspace with a common structure and module-specific visualization and interaction. Scientific processing methods are registered independently of individual modules and operate on explicitly selected inputs through common execution services. A unified I/O subsystem maps heterogeneous ondisk formats to supported in-application data types. The plugin subsystem can add new modules, processing methods, I/O handlers, and in-application data types without modifying the core package. Representative workflows demonstrate the integration of established methods. In the registration example, the normalized cross-correlation maximum increases from 0.855 to 0.966. AngstromPro therefore provides an integrated software architecture for organizing, visualizing, processing, and extending STM data-analysis workflows.
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All authors Huiyu Zhao, Jiahao Yan, Catherine Dawson, Haitao Yang, Hong-Jun Gao

Materials Science

Magnetic Polarons Enable Exceptional Magnetocaloric Response

Joshua Ancheta, Caeli Benyacko, Fanghao Zhang et al. (+2 more)

Magnetocaloric materials are typically limited by a trade-off between magnetic entropy and field responsiveness. Here we show that magnetic polarons provide an intermediate regime that mitigates this constraint and enables an exceptional magnetocaloric response. Using EuB$_6$ as a model system, we combine thermodynamic and magnetic measurements to demonstrate that nanoscale ferromagnetic clusters emerging near the Curie temperature strongly enhance the field-induced entropy collapse. These clusters possess large effective moments that respond efficiently to applied fields while retaining substantial entropy due to their small size and dynamic fluctuations. As a result, EuB$_6$ exhibits a giant cryogenic magnetocaloric response, with both large isothermal entropy change and adiabatic temperature change in the technologically important 10-40 K range. Our results identify magnetic polarons as an underexplored route for optimizing magnetocaloric performance and establish an intermediate magnetic length scale as a design principle for high-performance cryogenic cooling materials.
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All authors Joshua Ancheta, Caeli Benyacko, Fanghao Zhang, Stephen D. Wilson, Bolin Liao

Materials Science

Proximity Magnetism in Mn(Bi,Sb)2Te4-(Bi,Sb)2Te3/MnTe Natural Heterostructures

Owen A. Vail, Shu-Wei Wang, Yasen Hou et al. (+13 more)

Magnetic topological insulators and their heterostructures provide great opportunities in coupling band topology with nontrivial spin configuration for enhanced spintronic device performance as well as designing totally new magnetoelectric systems and functionalities. We find that Mn interdiffusion from MnTe when interfaced with (Bi,Sb)2Te3 stabilizes as self-organized Mn(Bi,Sb)2Te4 septuple lamellae amongst alternating (Bi,Sb)2Te3 quintuple layers, as observed using scanning transmission electron microscopy and depth-sensitive polarized neutron reflectometry. We further demonstrate a valuable combination of magnetic and topological orders in these naturally formed Mn(Bi,Sb)2Te4-(Bi,Sb)2Te3 heterostructures that are exchange coupled with MnTe. Magnetotransport experiments and quantum magnetism simulations reveal that, above its own Neel temperature TN of 20 K, Mn(Bi,Sb)2Te4 mediates the exchange field leading to an anomalous Hall effect at the (Bi,Sb)2Te3/MnTe interface, with an enhanced interfacial TN exceeding 200 K. This novel magnetic interface in turn allows a robust and deterministic spin-orbit torque switching without an external magnetic field at a low critical current density of 300 kA cm-2. The antiferromagnetically coupled architecture of Mn(Bi,Sb)2Te4-(Bi,Sb)2Te3/MnTe, featuring unique magnetic and topological proximity effects across a chalcogenide backbone, is rich in fundamental interface physics and holds potential for practical applications in spintronics.
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All authors Owen A. Vail, Shu-Wei Wang, Yasen Hou, Dinura Hettiarachchi, Jean-Felix Milette, Tim B. Eldred, Wenpei Gao, Wendy Sarney, Haile Ambaye, Jong Keum, Valeria Lauter, George J. de Coster, Matthew J. Gilbert, Don Heiman, Jagadeesh S. Moodera, Hang Chi

Monday 20 April

Statistical Mechanics · Cross-listed from physics.flu-dyn

Functional Renormalization for Elastic Burgulence

Johannes Conrad and Martin Oberlack

We formulate elastic and elasto-inertial turbulence in the Martin-Siggia-Rose path-integral formalism and develop a systematic source-extended symmetry algorithm to derive Ward identities directly from the Euler-Lagrange equations. These identities provide nonperturbative constraints and a principled foundation for constructing closure schemes. As a dimensionally reduced model for elastic turbulence, we propose an extended Burgers equation that preserves the characteristic coupling between the extra stress and velocity gradient, while remaining simple enough for first controlled calculations. In particular, we obtain an extended set of Ward identities that strongly constrains admissible closures and provides insight into the scaling behaviour near the fixed point.
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Statistical Mechanics

Coordination-number dependent universality in Mixed Wet Percolation

Jnana Ranjan Das, Santanu Sinha, Alex Hansen et al. (+1 more)

Mixed-wet percolation was introduced recently in the context of two-phase flow in porous media. In this model, the sites of the primal lattice are occupied with a certain probability $p$, and bonds are placed on the dual lattice between two adjacent occupied and unoccupied sites of the primal lattice. The occupied bonds on the dual lattice form perimeter clusters. In this paper, we investigate the scaling properties of the geometric quantities associated with the perimeter clusters of mixed-wet percolation on the dual triangular and dual honeycomb lattices. Although mixed-wet percolation on the dual triangular lattice with a higher coordination number ($z=6$) exhibits ordinary site percolation, the model on the dual honeycomb lattice with a lower coordination number ($z=3$) exhibits the properties of the hull of ordinary site percolation clusters. Such a $z$ dependent breakdown of universality in mixed-wet percolation is rare in the percolation literature. The perimeter clusters in the triangular lattice represent the boundary of the site clusters in the primal lattice, whereas the perimeters in the honeycomb lattice represent their hulls. Because of the low $z$ of the honeycomb lattice, the external and internal perimeters remain isolated. However, the combined external and internal perimeters form cluster boundaries of the site clusters that belong to the site percolation universality class.
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All authors Jnana Ranjan Das, Santanu Sinha, Alex Hansen, Sitangshu Bikas Santra

Statistical Mechanics

Energy landscape of the kagome antiferromagnet: Characterization of multiple energy scales

Brandon B. Le, Seung-Hun Lee and Gia-Wei Chern

We investigate the energy landscape of the kagome Heisenberg antiferromagnet within its coplanar ground-state manifold. Although coplanar states are degenerate at harmonic order, transitions between them require collective weathervane-loop rotations whose barriers grow strongly with loop size. To characterize this structure, we construct disconnectivity graphs using two complementary approaches: exact enumeration and minimax-barrier calculations for small lattices, and a statistical construction for large lattices based on random walks through configuration space, with loop length used as a proxy for barrier height. The exact landscape reveals a dominant low-barrier scale associated with elementary six-spin loops and a broader higher-barrier sector from longer rearrangements. For large systems, the statistical analysis exposes a hierarchy of barrier scales, including a pronounced six-spin-loop peak and an intermediate scale-free regime of loop lengths. This hierarchy provides a natural basis for multiple dynamical time scales: six-spin loops govern the fastest local relaxation, while slower collective dynamics arise from activation of longer loops. These results show that the coplanar manifold is dynamically rugged, with its low-energy dynamics governed by a hierarchy of loop-mediated barriers.
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Quantum Gases

Stabilization of bulk quantum orders in finite Rydberg atom arrays

Yash M. Lokare and Matthew J. Coley-O'Rourke

Arrays of ultracold neutral atoms, also known as Rydberg atom arrays, are rapidly developing into a powerful and versatile platform for quantum simulation. However, theoretical predictions about the bulk quantum phases of matter present in these systems have often diverged from experimental realizations on finite-sized arrays due to the strong effects of the boundaries. Here we propose a general, experimentally straightforward strategy to mitigate the effects of the boundaries and thus enable finite-sized arrays to stabilize bulk-like quantum order. Our scheme makes use of the properties of the ubiquitous disordered phase in Rydberg systems, driving the boundaries into an unbiased set of configurations that depend on the bulk physics. We numerically demonstrate the efficacy of this protocol in one- and two-dimensional systems on both ordered and critical phases.
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Mesoscale and Nanoscale Physics

Landau levels and magneto-optics in 30$^\circ$ quasi-periodic twisted bilayer graphene

Masaru Hitomi, Takuto Kawakami and Mikito Koshino

We develop a theoretical framework for Landau levels in quasi-periodic twisted bilayer graphene at a $30^\circ$ twist angle, a system without translational symmetry but possessing 12-fold rotational symmetry. Using a quasi-band formalism, we incorporate the magnetic field through a conventional momentum substitution in the zero-field Hamiltonian. This approach provides a transparent physical interpretation by directly relating the Landau levels to the quasi-band structure, allowing them to be understood as quantized orbits of quasi-band pockets. By using this method, we reveal distinctive spectral features, including nearly flat bands with weak magnetic-field dependence and highly degenerate levels arising from twelve off-center pockets. The resulting Landau levels are classified by two quantum numbers: the Landau-level index and the angular momentum associated with the underlying quasicrystalline symmetry. We also compute the magneto-optical conductivity and show that optical transitions follow angular-momentum selection rules enforced by the 12-fold symmetry. Our approach provides a symmetry-based and computationally efficient framework for bulk quantum magneto-optics in quasicrystalline van der Waals systems, predicting spectroscopic signatures accessible in high-field infrared and THz experiments.
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Superconductivity

Stripping Symmetry: Electrochemical Oxidation to a Superconducting Polar Metal in Au2Pb0.914P2

Scott B. Lee, Stephanie R. Dulovic, Joseph W. Stiles et al. (+11 more)

Polar metals and noncentrosymmetric superconductors are exceptionally rare, yet their broken inversion symmetry can give rise to emergent electronic phenomena including mixed singlet-triplet superconducting pairing. As only a few such materials have been found among known compounds, accessing new examples requires synthetic strategies that go beyond conventional crystal growth. Here, we use electrochemical topotactic deintercalation to remove Pb from the centrosymmetric parent compound Au$_2$PbP$_2$, producing the polar metal Au$_2$Pb$_{0.914}$P$_2$. Unlike conventional chemical doping, this transformation actively drives structural symmetry-breaking: the partial removal of Pb triggers a cooperative electronic and geometric rearrangement, mediated by a second-order Jahn-Teller effect and stereochemically active lone pairs, that locks the product into a polar, noncentrosymmetric superspace group Ama2(01g)ss0. We solve the complete (3+1)D modulated structure by synchrotron single-crystal X-ray diffraction and confirm the polar assignment through nonlinear electronic transport. Below T$_c$ = 1.52 K, Au$_2$Pb$_{0.914}$P$_2$ becomes a type-II superconductor whose heat capacity and AC susceptibility both exhibit power-law behavior, suggestive of a gap structure governed by the broken inversion symmetry of the host lattice. This work establishes electrochemical oxidation as a rational route to metastable noncentrosymmetric superconductors through chemically directed symmetry-breaking.
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All authors Scott B. Lee, Stephanie R. Dulovic, Joseph W. Stiles, Xin Zhang, Fatmagül Katmer, Sudipta Chatterjee, Jaime Moya, Allana G. Iwanicki, Abby N. Neill, Chris Lygouras, Tieyan Chang, Tyrel M. McQueen, Yu-Sheng Chen, Leslie M. Schoop

Materials Science · Cross-listed from cs.AI

AI scientists produce results without reasoning scientifically

Martiño Ríos-García, Nawaf Alampara, Chandan Gupta et al. (+5 more)

Large language model (LLM)-based systems are increasingly deployed to conduct scientific research autonomously, yet whether their reasoning adheres to the epistemic norms that make scientific inquiry self-correcting is poorly understood. Here, we evaluate LLM-based scientific agents across eight domains, spanning workflow execution to hypothesis-driven inquiry, through more than 25,000 agent runs and two complementary lenses: (i) a systematic performance analysis that decomposes the contributions of the base model and the agent scaffold, and (ii) a behavioral analysis of the epistemological structure of agent reasoning. We observe that the base model is the primary determinant of both performance and behavior, accounting for 41.4% of explained variance versus 1.5% for the scaffold. Across all configurations, evidence is ignored in 68% of traces, refutation-driven belief revision occurs in 26%, and convergent multi-test evidence is rare. The same reasoning pattern appears whether the agent executes a computational workflow or conducts hypothesis-driven inquiry. They persist even when agents receive near-complete successful reasoning trajectories as context, and the resulting unreliability compounds across repeated trials in epistemically demanding domains. Thus, current LLM-based agents execute scientific workflows but do not exhibit the epistemic patterns that characterize scientific reasoning. Outcome-based evaluation cannot detect these failures, and scaffold engineering alone cannot repair them. Until reasoning itself becomes a training target, the scientific knowledge produced by such agents cannot be justified by the process that generated it.
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All authors Martiño Ríos-García, Nawaf Alampara, Chandan Gupta, Indrajeet Mandal, Sajid Mannan, Ali Asghar Aghajani, N. M. Anoop Krishnan, Kevin Maik Jablonka

Soft Condensed Matter

Tunable turbulence in driven microscale emulsions

Majid Bahraminasr and Anand Yethiraj

We present a tunable, non-equilibrium oil-in-oil emulsion that serves as a model system for investigating the transition from controlled droplet deformation to multiscale flows reminiscent of turbulence. By utilizing a miscible mixture of silicone and motor oils as the continuous phase and the immiscible castor oil as the droplet phase, we isolate electrical conductivity as a single experimental control parameter, varying it by over two orders of magnitude while keeping viscosity and permittivity nearly constant. This high degree of control allows us to systematically traverse the electrohydrodynamic (EHD) phase diagram with dielectric constant and conductivity as control parameters. We validate small-deformation theory at low fields before driving the system into a regime of multiscale, unsteady flows at high fields. We employ three complementary approaches on the same system (particle image velocimetry (PIV), used to map velocity fields, and rheometry and differential dynamic microscopy (DDM), two techniques used to probe viscosity and diffusion) to quantify the emergence of scale invariance in the energy spectra with increasing field strength. Above a threshold field, we find that the spatio-temporal energy spectra obtained by PIV analysis of droplet dynamics display power-law scaling, $E(k) \sim k^{-\alpha_k}$, where $\alpha_k$ approaches the inertial turbulence exponent of $5/3$ at high fields. Energy spectra from rheometry also yield a power law, $S(\nu) \sim \nu^{-\alpha_\nu}$, with $\alpha_\nu = 5/3$ at high fields. Mean square displacement (MSD) analyses on the same datasets reveal super-diffusive behavior, $\mathrm{MSD} \sim t^{\gamma}$, with $\gamma = 3/2$. These observations provide strong evidence of a conductivity-tunable transition to EHD-driven turbulence in a microscale emulsion.
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Quantum Gases · Cross-listed from hep-th

Thermal Phase Structure of the Attractive Fermi Hubbard Model with Imaginary Chemical Potential

Evangelos G. Filothodoros

We study the BCS–BEC crossover of the large $N$ attractive Fermi-Hubbard model on a one-dimensional lattice using the mean field approximation in the presence of an imaginary chemical potential. We show that the crossover is governed by three parameters. The imaginary chemical potential $i\theta$, the temperature via a thermal kernel $g(\beta E_k,\beta\theta)$ and the parameter $\delta_u$ whose sign controls the weak and strong coupling regimes. At the unitarity point ($U=U_c$), we find a thermal window $\phi=\beta\theta=2\pi/3,4\pi/3$ where the gap vanishes while the fermion number $N_f$, which quantifies the balance between particle-like and hole-like excitations, has a local maximum/minimum. Inside this thermal window BCS and BEC physics are await changes in the coupling to be selected as the dominant regime. We expect that our results will unveil a better understanding of pairing correlations in lattice many-body physics.
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Strongly Correlated Electrons

Dynamical magnetism in the disordered cubic lattice material $\gamma$-${\rm Ba}_{3}{\rm CoNb}_{2}{\rm O}_{9}$

Fanjun Xu, Ralf Feyerherm, Cecilie Glittum et al. (+12 more)

$\gamma$-${\rm Ba}_{3}{\rm CoNb}_{2}{\rm O}_{9}$ realizes a disordered simple-cubic spin-$1/2$ lattice in which Co$^{2+}$ ions randomly occupy one third of the sites, placing the system close to the site-percolation threshold for magnetic order. Specific-heat, susceptibility, neutron spin-echo, and muon spin-rotation measurements reveal a broad thermodynamic crossover, short-range magnetic correlations, and persistent fast spin dynamics down to at least 0.1~K, with no evidence for static order or conventional spin-glass freezing. Monte Carlo simulations yield a broad distribution of orphan spins, finite clusters, and an infinite network. The calculated orphan-spin fraction ($\approx 8.8\%$) agrees well with the weakly correlated spin fraction inferred from magnetization ($\approx 8.2\%$). Exact diagonalization of a diluted $S = 1/2$ Heisenberg model captures the broad magnetic specific-heat anomaly and supports the coexistence of weakly and strongly correlated spin environments. These results support a picture in which spin-$1/2$ quantum fluctuations, together with dilution and proximity to the percolation threshold, can support a disorder-driven dynamical state with short-range correlations in three dimensions, distinct from both classical spin glasses and geometrically frustrated quantum spin liquids.
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All authors Fanjun Xu, Ralf Feyerherm, Cecilie Glittum, Thomas J. Hicken, Hubertus Luetkens, Jonas A. Krieger, Cintli Aguilar-Maldonado, Sven Luther, Lucy K. Saunders, Clemens Ritter, Peter Fouquet, Margarita Russina, Karel Prokes, A.T.M. Nazmul Islam, Bella Lake

Superconductivity

Competition and coexistence of superconductivity and nematic order in a two-dimensional electron gas with quadrupolar interactions

Nei Lopes, Guilherme da Silva do Vale and Daniel G. Barci

We investigate the interplay between superconductivity and nematic order in a two-dimensional electron gas with competing pairing and quadrupolar forward-scattering interactions. The model includes both $s$-wave and $d$-wave superconducting channels. We compute the mean-field free energy density and determine the phase diagrams as functions of interaction strengths and temperature by solving a set of coupled self-consistent equations. At zero-temperature, we find that the nematic order competes strongly with $d$-wave superconductivity, leading to a direct first-order phase transition, while its interplay with $s$-wave pairing allows for a coexistence phase characterized by an anisotropic Fermi surface with a uniform superconducting gap. At finite-temperatures, quadrupolar interactions promote the emergence of additional superconducting components, giving rise to regimes where $s$-wave, $d$-wave, and nematic orders coexist. Our results highlight the role of symmetry and interaction strength in shaping the phase structure and provide a minimal framework to describe intertwined nematic and superconducting phases in correlated electron systems.
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Mesoscale and Nanoscale Physics

Proximitized Topological Insulator Charge Island Fabricated via In Situ Multi-Angle Stencil Lithography

Benedikt Frohn, Tobias Schmitt, Vanessa Serrano et al. (+7 more)

Hybrid superconductor-topological insulator (TI) nanostructures constitute a promising material platform for exploring proximity-induced superconductivity in systems with topologically protected surface states. A key obstacle has been the realization of clean and well-controlled superconductor-TI interfaces, as TI surfaces rapidly degrade under ambient conditions. Here, we introduce a fully in situ, multi-angle stencil lithography technique that enables the fabrication of proximitized charge islands in TIs. The approach combines selective area growth of (Bi,Sb)$_2$Te$_3$ nanoribbons with angle-controlled deposition of diffusion barriers, superconducting Al, and ultrathin oxide tunnel barriers, allowing scalable fabrication of hybrid nanostructures without post-growth processing. Low-temperature transport measurements reveal robust Coulomb blockade and a pronounced suppression of low-energy conductance, which vanishes with a magnetic field, consistent with proximity-induced superconductivity in the island. These results establish a versatile nanofabrication platform that enables access to previously unexplored TI-based hybrid quantum devices and opens new routes for investigating superconductivity in topological nanostructures.
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All authors Benedikt Frohn, Tobias Schmitt, Vanessa Serrano, Anne Schmidt, Michael Schleenvoigt, Albert Hertel, Benjamin Bennemann, Abdur Rehman Jalil, Detlev Grützmacher, Peter Schüffelgen

Strongly Correlated Electrons · Cross-listed from hep-th

Gauging in superconductors and other electronic systems

Marcus Berg, Andrea Cappelli and Riccardo Villa

Ordinary, s-wave superconductors have been recognized as being topological phases of matter, in which the dynamical gauge field implies less understood global features. Using the tools of topological field theories and generalized symmetries, we provide an updated description of these systems. At very low energies, the Higgs model reduces to the BF theory, which exhibits topological order. Furthermore, the gauge field must be a spin$_c$ connection, to describe the spin of fermions forming Cooper pairs. Gauging implies that superconductors are inherently bosonic systems, yet they are endowed with a gravito-magnetic anomaly that is the remnant of their fermionic origin. We recognize that this anomaly is related to the Gaiotto-Kapustin-Thorngren bosonization, achieved via gauging fermion parity $(-1)^F$, now included in the gauge dynamics. This anomaly characterizes gauged electronic matter in great generality in three and four spacetime dimensions, forbidding trivial massive phases at low energy. It holds beyond the validity of the Higgs model, nd in other kinds of superconductors as well. It also appears in the nontrivial massless phase of three-dimensional electrodynamics, recently understood.
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Mesoscale and Nanoscale Physics

Large Scale Optimization of Disordered Hubbard Models through Tensor and Neural Networks

Jacob R. Taylor and Sankar Das Sarma

We theoretically demonstrate a practical method for tuning randomly disordered 2D quantum-dot grids underlying spin qubit platforms using vision-based neural networks trained on tensor-network generated charge-stability data. We show that a simulatable local $3\times 3$ window already contains sufficient information to tune the central dot within a much larger array, thereby validating a sliding-window approach in which one tunes a local region and then translates that window across the lattice to calibrate a larger device. This avoids the computationally intractable necessity for obtaining the ground states for large systems with exponentially large Hilbert space. For the experimentally relevant case where only the on-site disorder is unknown, the neural network predicts the relevant parameters with very high fidelity in the $3\times 3$ setting [$R^2 >0.99$], and after fine tuning on only a small number of larger-device samples, it retains high accuracy for the central dot of a $5\times 5$ plaquette [$R^2\approx 0.98$]. When all the dots parameters are treated as unknown, prediction of the on-site disorder remains robust [$R^2>0.9$ for both $3\times 3$ and $5\times 5$], although the remaining parameters are substantially more difficult to infer from the same charge-stability data. This shows that the most practically important disorder parameter for tuning can still be inferred reliably even in the fully disordered setting for the computationally difficult 5x5 arrays.
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Disordered Systems and Neural Networks

Charge Transport Capacity as a Probe of Resonances in Models of Many-Body Localization

Jessica Kaijia Jiang, Federica Maria Surace and Olexei I. Motrunich

The fate of Many-Body Localization (MBL) in the thermodynamic limit remains elusive, partly because numerical studies suffer from unexplained finite-size effects. We introduce and numerically study the charge transport capacity (CTC) – a quantity that upper bounds the number of particles that can ever be transported across a central cut of a 1D lattice. For ergodic systems, the CTC is linear with the system size $L$, while we expect it to be $O(1)$ for localized models. Surprisingly, in the interacting Anderson model for numerically accessible $L$, the disorder-averaged CTC is small, but grows with $L$ at an increasing rate. Moreover, this growth rate appears to be independent of the disorder strength $W$ at very large $W$. We find that, for these system sizes, this growth occurs because, as $L$ increases, many-body resonances that transport more charge across the cut become more likely. Using a perturbative model for the weakly interacting regime, we provide an understanding of the microscopic origins of the growth of these charge transport resonances (CTRs). We find that the CTRs are sensitive to charge configurations over a spatial region whose size is set by the range of the resonance, not by $W$, and that numerics cannot access system sizes where their behavior will converge. However, this effective model is consistent with a regime of strong disorder where, for large $L$, resonances are exponentially suppressed in their size. Finally, we study measures of average charge transport and suggest that for strong enough disorder, average product states can only transfer $O(1)$ charge. Our work suggests that the unsettled growth of short-ranged many-body resonances with $L$ contributes to the numerical drift towards thermalization at numerically accessible system sizes, and provides an understanding of how they can remain controlled or eventually destabilize the MBL phase.
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Soft Condensed Matter

Equation of state for the edge flow of chiral colloidal fluids

Jessica Metzger, Cory Hargus, Julien Tailleur et al. (+1 more)

We explore the edge flows that emerge at boundaries in nonequilibrium passive and active chiral colloidal fluids. We show that these complex interface currents obey an equation of state that relates their fluxes to bulk observables. For confined fluids, the edge flux is given by the average odd stress in the fluid. In phase-separated systems, the flux along the interface is given by the jump of the odd stress across the interface. We then use the equation of state to reveal, and contrast, the microscopic origins of the edge currents in passive and active systems.
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All authors Jessica Metzger, Cory Hargus, Julien Tailleur, Frédéric van Wijland

Statistical Mechanics · Cross-listed from quant-ph

Synchronization in a dissipative quantum many-body system

B. Çakmak, K. Sümer, S. Campbell et al. (+1 more)

We study synchronization in the XX qubit chain subject to local or multi-local amplitude-damping noise. Analyzing the decoherence-free subspace (DFS) structure of the model, we show that it is completely determined by a simple number-theoretic function involving the noise sites and the chain length. We derive a closed-form expression for local qubit observables restricted to the DFS and prove that stable synchronization of the edge qubits for arbitrary initial states occurs if and only if the DFS supports exactly one single-excitation eigenstate. We further show that this same condition also guarantees constant asymptotic entanglement between the edge qubits, so that generic stable synchronization and constant asymptotic entanglement necessarily coexist. By contrast, when the DFS supports multiple single-excitation eigenstates, synchronization becomes initial state dependent and may be entirely absent, even though stable oscillatory entanglement can persist indefinitely.
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All authors B. Çakmak, K. Sümer, S. Campbell, G. Karpat