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Physics Condensed Matter

cond-mat Watch Condensed Matter

Friday 8 May

Strongly Correlated Electrons

Probabilistic denoising for reliable signal extraction in spectroscopy

Younsik Kim and Changyoung Kim

While deep learning offers powerful capabilities for scientific research, its application is often hindered by a lack of quantitative reliability. To address this, we introduce a probabilistic denoising framework that simultaneously extracts denoised signals and element-wise predictive uncertainties from noisy data. We demonstrate this approach on three-dimensional angle-resolved photoemission spectroscopy data, showing that the model reliably recovers the spectral features of a cuprate superconductor from Poisson-distributed noise with an average count of only 0.02 electrons per voxel. Crucially, we show that these predicted uncertainties can be propagated into subsequent superconducting gap analyses, enabling quantitative parameter extraction with scientifically meaningful error bars. Furthermore, we validate the broad applicability of our approach by successfully extending it to two-dimensional X-ray diffraction data. Ultimately, this approach establishes uncertainty-aware deep learning not merely as a visualization tool, but as a rigorous framework for scientific data analysis.
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Materials Science

Ferroelectric domains in methylammonium lead iodide perovskite thin-films

Holger Röhm, Tobias Leonhard, Michael J. Hoffmann et al. (+1 more)

We explore the ferroic properties of methylammonium lead iodide perovskite solar cells by Piezoresponse Force Microscopy (PFM). In vertical and horizontal PFM imaging, we find domains of alternating polarization with a width of 90 nm which we identify as polarized ferroelectric domains. High-resolution photo-conductive atomic force micrographs under illumination also show alternating charge carrier extraction patterns which we attribute to the local vertical polarization components within the ferroelectric domains. The correlation of the sample properties with Atomic Force and Kelvin Probe Force Micrographs evidence the piezo-electric nature of the domains.
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All authors Holger Röhm, Tobias Leonhard, Michael J. Hoffmann, Alexander Colsmann

Soft Condensed Matter

Elastocapillary morphing of self-encapsulated droplets floating at the oil-air interface

D. Andrini, D. Riccobelli, L. Gazzera et al. (+3 more)

Self-encapsulated droplets floating at an oil–air interface undergo striking shape changes during evaporation, including flattening and localized loss of membrane tension leading to crumpling and wrinkling. Here we combine experiments, modeling and simulations to obtain predictive morphological maps. We perform contact-angle and evaporation experiments on water droplets coated by a hydrophobin protein film and floating in a fluorinated oil, providing reference profiles and volume-loss sequences for quantitative validation. We develop an axisymmetric mechanics framework in which equilibria follow from minimization of a total free energy combining surface energies, membrane strain energy and gravitational potential, subject to volume and contact-line constraints. A quasi-convex tension-relaxation rule accounts for compression-free states and enables coexistence of taut, wrinkled (one principal tension vanishes) and crumpled (both vanish) membrane domains. A finite element algorithm computes quasi-static morphing under volume reduction; key parameters are identified by fitting the reference contact-angle profile and then used without further tuning. The model reproduces the experimentally observed shape evolution and resolves the associated stress redistribution. Systematic parameter scans yield morphological phase diagrams governed by the Bond number, the oil–droplet surface-tension ratio and the density ratio. For buoyant droplets, crumpling relocates between exposed and submerged caps as parameters vary; for heavy droplets, a crossover to circumferential wrinkling along the immersed sidewall emerges. Wall-meniscus variations shift phase boundaries and can suppress bottom crumpling, consistent with wall-affected experiments.
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All authors D. Andrini, D. Riccobelli, L. Gazzera, S. Molteni, P. Metrangolo, P. Ciarletta

Soft Condensed Matter

Droplet Deformation and Emulsion Rheology in Two-Dimensional Odd Stokes Flow

Thomas Appleford, Hugo França and Maziyar Jalaal

We study the deformation of a two-dimensional viscous droplet in simple shear in the presence of odd viscosity. We derive an analytical solution for the droplet shape and surrounding flow field within the framework of odd Stokes flow, allowing for differences in both even and odd viscosity between the droplet and the surrounding fluid. This solution yields closed-form expressions for the macroscopic apparent even and odd viscosities of a dilute emulsion. We show that, provided all viscosity differences remain moderate, the steady-state Taylor deformation parameter satisfies $D_T^\infty = \text{Ca} + \mathcal{O}(\text{Ca}^2)$ so that the leading-order droplet deformation is unchanged from the classical (even-viscous) result. Nevertheless, pronounced effects emerges beyond leading order, where our direct numerical simulations reveal odd-viscous differences to the droplet deformation. In addition, we show that the flow is influenced only by the difference in odd viscosity between the droplet and the medium and not on their individual values. Our analysis clarifies how odd viscosity might modify the effective rheology of dilute emulsions and provides a framework for interpreting droplet-based measurements of odd-viscous response. Key words: odd viscosity $|$ droplets $|$ emulsions $|$ surface tension $|$ chiral fluids
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Statistical Mechanics · Cross-listed from quant-ph

Universal Symmetry-Breaking Dynamics at Continuous Phase Transitions: Evidence for a New Dynamical Critical Exponent

Tobias Wiener, Laurin Brunner and Markus Heyl

Uncovering and understanding universal dynamics in matter far from equilibrium remains a key challenge. In this work, we identify a so far unrecognized form of universal behavior that emerges after a sudden symmetry-breaking quench at continuous phase transitions. Our key observation is that the order-parameter fluctuations in Ising models exhibit a compelling temporal collapse across a wide range of system sizes and quench strengths, indicative of an emergent single-variable scaling form. This phenomenon can be explained by introducing a so far unknown dynamical critical exponent for the underlying continuous phase transition. We find evidence for a lower critical effective dimension of this universal regime: it is observed in the 2D quantum and 3D and 4D classical Ising models, but not in the 1D quantum or 2D classical cases. Our results suggest that our observed universal far-from-equilibrium scaling may extend beyond the Ising models studied here and could more broadly characterize systems with non-conserved order parameters, opening new avenues for exploring universal dynamics both theoretically and in current experimental platforms.
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Strongly Correlated Electrons

Beyond the conventional Emery model: crucial role of long-range hopping for cuprate superconductivity

Eric Jacob, M. O. Malcolms, Viktor Christiansson et al. (+6 more)

The Emery model is the quintessential model for cuprate superconductors. In his eponymous paper, Emery only considered the next-nearest-neighbor oxygen-copper hopping. Later, also the relevance of nearest- and next-nearest oxygen-oxygen hoppings has been pointed out. Using dynamical vertex approximation, we find a superconducting dome consistent with cuprates. However, long-range hoppings beyond the three conventional hopping parameters are necessary for the quantitatively correct phase diagram and for a proper d-wave order parameter.
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All authors Eric Jacob, M. O. Malcolms, Viktor Christiansson, Leonard M. Verhoff, Paul Worm, Liang Si, Philipp Hansmann, Thomas Schäfer, Karsten Held

Strongly Correlated Electrons · Cross-listed from hep-th

Characterizing gapped phases by smeared boundary conformal field theories: Duality in unusual ordering with spontaneously broken generalized symmetries

Yoshiki Fukusumi and Shuma Nakashiba

We study the classification of the gapped phases or massive renormalization group (RG) flows dual to the massless RG flows under changing the sign of the coupling constants. Whereas our formalism is based on combining Higgs- or Nambu-Goldstone-type arguments with Cardy's smeared boundary conformal field theories (SBCFTs), several puzzling structures arise. More specifically, the established Higgs or Nambu-Goldstone type arguments on the duality imply that the natural basis for the gapped states should be constructed from a set of smeared Ishibashi states, which are unphysical in boundary critical phenomena. Hence, the module of the gapped phases can be outside of that of boundary critical phenomena, whereas one can still calculate characterizing quantities by applying SBCFTs to the models. For example, we demonstrate that the massive RG flow dual to the massless RG flow from the tricritical Ising model to the Ising model, one of the simplest massless RG flows, has this unusual structure. This can be regarded as a quantum field-theoretic analogue of order-disorder coexistence in lattice models. More generally, the resultant gapped phases usually spontaneously break non-group-like symmetry (or noninvertible symmetry). Our work provides systematic quantum field theoretic descriptions of such unusual phases with spontaneous symmetry breaking of non-group-like (or noninvertible) symmetries.
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Materials Science

Selectivity- and Activity-Aware Catalyst Descriptors for CO$_2$ Hydrogenation on Alloy Nanocatalysts using Machine-Learned Force Fields

Prajwal Pisal, Ondřej Krejčí and Patrick Rinke

Adsorption energy distributions (AEDs) have emerged as a powerful and increasingly adopted descriptor for catalytic performance in high-entropy alloys and, more recently, in conventional metallic alloy nanocrystal catalysts. By accounting for diverse adsorption sites and crystallographic facets, AEDs more fully represent nanoparticle-based catalytic surfaces and show strong promise for accelerating rational design and discovery of heterogeneous catalysts, especially for CO$_2$ hydrogenation. However, previous high-throughput screenings have not provided simultaneous facet-level insight into catalytic activity, product selectivity, and thermodynamic stability. Here, we implement and extend the AED framework to individual crystallographic facets, combining facet-resolved adsorption fingerprints with Wulff-derived facet abundances and an interpretable latent-space analysis of C1-product selectivity. We employ universal machine-learned force fields trained on Open Catalyst Project data to compute adsorption energies across 226 experimentally observed metals, binary alloys, and previously unexplored ternary alloys, encompassing ~1.4 million adsorption configurations on >2,600 crystallographically distinct surfaces. Using distribution-based similarity analysis and principal component analysis of AED moments, we identify composition-facet combinations with adsorption landscapes associated with activity and qualitative selectivity trends toward methanol, methane, formic acid, and CO. Our framework links surface structure to adsorption-based catalytic trends, providing experimentally testable composition-facet candidates for further investigation and validation.
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Materials Science · Cross-listed from physics.optics

Active Control of Topological Exceptional Points in Non-Hermitian Metasurfaces

Parul Sharma, Sobhan Subhra Mishra, Yash Gupta et al. (+4 more)

Active control and ultrafast switching of non-Hermitian photonic systems are essential for next-generation reconfigurable optical technologies. Here, we demonstrate dynamic temporal manipulation of EPs in the terahertz (THz) regime using optically excited germanium (Ge) as an active medium. By exploiting pump-probe delay as a continuous tuning parameter, we achieve sub-picosecond eigenmode switching (~0.5 ps) and realize a complete time-resolved EP encirclement within ~2 ps, enabling direct observation of topological phase accumulation. At EP, the metasurface exhibits highly asymmetric transmission for circularly polarized light, characteristic of chiral mode response. Furthermore, we observe ultrafast eigenmode switching and topological phase evolution within ~1 ps, achieving >99% cross-polarization modulation depth. The measured results show strong agreement with theoretical modeling, with a high Petermann factor of approximately 10^3, confirming the effectiveness of the design. Our work establishes pump-probe delay time as a dynamical control parameter for EP topology, introducing a new regime of ultrafast non-Hermitian photonics for high-speed switching, enhanced sensitivity, and tunable polarization control in the THz domain.
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All authors Parul Sharma, Sobhan Subhra Mishra, Yash Gupta, Brijesh Kumar, Ranjan Singh, Abhishek Kumar, Anshuman Kumar

Materials Science

Epitaxial growth of beta-bismuthene on Sb2Te3

Giorgia Sementilli, Arslan Masood, Fabio Ronci et al. (+7 more)

Over the past decades, two-dimensional crystals have attracted considerable interest as promising materials for electronic and optoelectronic applications. Among them, graphene analogs composed of heavy atoms occupy a particularly distinctive niche due to their enhanced spin-orbit interaction. Here, we present an epitaxial heterointerface formed by beta-bismuthene on Sb2Te3, a well-known three-dimensional topological insulator. Using scanning tunneling microscopy, we systematically investigated the effects of Bi coverage and substrate temperature on nucleation processes, island morphology, and atomic structure. In addition, substrate-induced defects were identified throughout the bismuthene lattice.
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All authors Giorgia Sementilli, Arslan Masood, Fabio Ronci, Stefano Colonna, Marilena Carbone, Marco Papagno, Ziya S. Aliev, Evgueni V. Chulkov, Sergey V. Eremeev, and Roberto Flammini

Strongly Correlated Electrons

Ground states of quantum XY dipoles on the Archimedean lattices

Marcus Bintz, Ahmed Khalifa, Vincent S. Liu et al. (+4 more)

We report numerical ground states for the dipolar XY spin model, which describes extended antiferromagnetic interactions in two-dimensional arrays of polar molecules and two-level Rydberg atoms. Carrying out large-scale density matrix renormalization group (DMRG) calculations, we compute ground state properties on nine of the eleven Archimedean lattices–tilings of the plane by regular polygons. Four of these host trivial paramagnets, while another four develop collinear Neel magnetic order, as was found previously for the square lattice. For the ordered states, we calculate the hydrodynamic parameters (magnetization, susceptibility, and stiffness) and compare to linear spin wave theory. We also investigate the triangular lattice, for which we find several competing phases including coplanar magnetism, stripe density wave order, and a possible spin liquid; their relative stability is sensitive to the long-range couplings present in our dipolar model. Finally, the Archimedean classification is completed by the kagome lattice, which we argue in a companion work is likely to be a Dirac spin liquid.
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All authors Marcus Bintz, Ahmed Khalifa, Vincent S. Liu, Johannes Hauschild, Michael P. Zaletel, Shubhayu Chatterjee, Norman Y. Yao

Materials Science

Harnessing Structural Disorder: Unraveling Hydrogen Evolution in Monolayer Amorphous Carbon via First-Principles Simulations and Machine-Learned Potentials

Sreehari M S, Ashutosh Krishna Amaram and Raghavan Ranganathan

Disorder and defective coordination in the catalytic plane are crucial for enhancing the Hydrogen Evolution Reaction (HER) on two-dimensional catalysts. Amorphous materials are disordered, making them catalytically adaptive for many reactions. In this work, the HER capabilities of Monolayer Amorphous Carbon (MAC) were studied in comparison with crystalline carbon derivatives, such as pristine graphene (GE) and graphyne derivatives. MAC generated from melt-quench simulations revealed a diverse framework of predominantly sp2 and sp3 carbons with numerous 5-, 6-, and 7-membered rings. Density Functional Theory (DFT) calculations investigated free-energy variations in hydrogen adsorption for each material. According to Sabatier's principle, optimum activity is achieved when the Gibbs free energy (Delta GH) change approaches zero. Crystalline carbon materials possess limited active sites, with beta-graphyne showing the best Delta GH value of +0.34 eV. The adsorption study for MAC was conducted in 30 distinct local environments, where core structural properties were analyzed against varying radii. Calculations showed a Delta GH distribution for MAC ranging from -0.02 eV to +1.35 eV. To evaluate activity across the entire MAC surface, a MACE MLIP foundation model was finetuned, achieving optimal energy and force fitting of 1.67 meV/atom and 29.15 meV/A, respectively. The MLIP predicted Delta GH values from -0.91 eV to +1.70 eV, with approximately 15% of sites exhibiting values below +0.25 eV. Feature analysis revealed that 7-membered rings, curvature, and ripple height enhance HER activity. Our findings suggest that, with careful optimization of local features, MAC can be tuned to compete with noble metal catalysts.
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Superconductivity

Finite temperature pair density wave superconductivity in $d$-wave altermagnets

Amrutha N Madhusuthanan and Madhuparna Karmakar

We demonstrate that altermagnetism provides a field-free mechanism for stabilizing finite-momentum superconductivity in two dimensions. Using a non-perturbative static path approximation Monte Carlo approach, we show that a d-wave altermagnet supports a robust pair-density-wave (PDW) phase that persists over a finite temperature window despite strong thermal fluctuations. The underlying mechanism originates from momentum-dependent spin splitting, which effectively enhances pairing instabilities at finite center-of-mass momentum without Zeeman fields. We identify distinct thermal scales associated with phase coherence, gap closing, and pseudogap formation, and establish characteristic spectroscopic and real-space signatures of the PDW state. Our results reveal altermagnetism as a robust route to thermally stable finite-momentum superconductivity and provide experimentally testable signatures for altermagnetic materials.
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Mesoscale and Nanoscale Physics

Bias-Engineered Synthetic Antiferromagnets Hosting sub-20 nm Zero-Field Skyrmions at Room Temperature

Emily Darwin, Riccardo Tomasello, Reshma Peremadathil Pradeep et al. (+3 more)

Synthetic antiferromagnetic skyrmions (SAFsk) are nanoscale, topologically protected spin textures with strong potential for spintronic technologies because of their high stability and the absence of the skyrmion Hall effect. However, robust zero field stabilization remains a central challenge. Here, a synthetic antiferromagnetic (SAF) bias system is introduced as a novel strategy to stabilize both ferromagnetic skyrmions (FMsk) and SAFsk at zero field. Ferromagnetic (FM) and SAF multilayers are designed, fabricated and integrated with the SAF bias system to enable controlled skyrmion stabilization and polarity setting via multilayer design and a preparatory field cycle. Combining quantitative and high-sensitivity magnetic force microscopy (MFM) with micromagnetic modeling, reliable zero field skyrmion formation is demonstrated and sub 20nm SAFsk are directly observed, the smallest SAFsk reported to date. Moreover, the SAF bias system concept introduced here offers a robust and scalable route to bias future skyrmion multilayers, as its compensated nature suppresses domain formation and preserves a uniform exchange field.
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All authors Emily Darwin, Riccardo Tomasello, Reshma Peremadathil Pradeep, Mario Carpentieri, Giovanni Finocchio, Hans J. Hug

Strongly Correlated Electrons · Cross-listed from quant-ph

Entanglement-informed distributed wavefunction approach to scalable quantum many-body systems

Adriano Amaricci

We show that the entanglement structure of quantum many-body states defines a natural and optimal distributed representation for their simulation. An arbitrary entanglement cut induces a bipartite decomposition of the wavefunction, mapping its distribution onto that of the entanglement spectrum. In this representation the Hamiltonian application, the core of Krylov-subspace methods, reduces to local contractions and communication-optimal operations. Using benchmarks from different methods and models, we demonstrate near-linear scaling for sufficiently large systems and identify entanglement spectrum fragmentation as a key factor controlling computational cost. This establishes entanglement as an organizing principle and unified, method-independent, route for scaling up quantum many-body simulations.
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Statistical Mechanics · Cross-listed from quant-ph

Typical Mixing and Rare-State Bottlenecks in Open Quantum Systems

Caisheng Cheng and Ruicheng Bao

Mixing in open quantum systems is often summarized by a single worst-case time, even though that benchmark can be set by exponentially rare initial states. We show that for broad unstructured ensembles the nonlinear trace-distance relaxation curve itself concentrates around a deterministic mean. For Haar-random pure states this yields fixed-time concentration of the instantaneous trace distance to the steady state, which we term vertical concentration since typical relaxation curves bundle along the distance axis. Whenever the mean curve crosses the distance threshold with a finite slope, it converts this vertical concentration into a horizontal concentration of the mixing time, extending typicality from standard physical observables to a fundamentally non-observable dynamical quantity. This sharp concentration naturally raises the question of how the typical mixing timescale compares to the worst-case benchmark. We show that in a one-mode tail regime, this separation is controlled by the logarithmic ratio of extremal to typical initial-state overlaps for the slow left eigenoperator. This rare-state bottleneck law yields a hierarchy that is logarithmic in skin-effect settings, linear for boundary-supported many-body slow modes, and exponential in a protected-sector family where generic states mix rapidly while rare states stagnate. The framework also extends beyond Haar to exact and approximate unitary 2-designs and Hilbert-Schmidt/induced ensembles.
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Statistical Mechanics

Hydrodynamics and boundary-induced phase transitions in the $n$-species particle-exchange process

Gunter M. Schutz and Ali Zahra

The $n$-species particle-exchange process (PEP($n$)) is an exclusion process in which particles of $n$ different species exchange positions on neighbouring sites with rates chosen such that the invariant measure on the discrete torus is a product measure. We address the large-scale hydrodynamic behaviour of this process which yields a system of $n$ coupled inviscid Burgers equations. This system of conservation laws is shown to admit Riemann invariants for arbitrary $n$ from which explicit solutions of the Riemann problem in terms of shock waves and rarefaction fans are obtained. We also introduce the open PEP($n$), in which particles are exchanged with boundary reservoirs. For a distinguished manifold of boundary rates, we prove that the invariant measure is the same product measure as in the periodic system. The hydrodynamic description in terms of Riemann invariants is used to derive the stationary phase diagram explicitly in terms of microscopic boundary rates. In the generic case, the steady state exhibits $2n+1$ phases, with boundary-induced phase transitions analogous to those of the single-species asymmetric simple exclusion process.
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Strongly Correlated Electrons

Emergent Dynamic Magnetic Ground State in a Mixed 3d/5d Heavy Fermion System CaCu3Ir4O12

J. Ming, Abhisek Bandyopadhyay, G. B. G. Stenning et al. (+5 more)

Quantum-disordered magnetic ground states are challenging to identify in three-dimensional (3D) oxides, where strong exchange pathways typically favour long-range magnetic order or spin freezing. The quadruple perovskite $\mathrm{CaCu_3Ir_4O_{12}}$, crystallizing in the cubic $Im\bar{3}$ structure, provides a 3D lattice where $\mathrm{Cu^{2+}}$ $3d$ moments are coupled to an extended Ir $5d$ network, offering a rare platform for probing quantum-disordered magnetism in a mixed $3d/5d$ electron system. Here, we combine bulk probes, including DC and AC magnetic susceptibility, and heat capacity measurements (down to $50~\mathrm{mK}$), along with the local microscopic probe muon spin relaxation ($\mu$SR) (down to $40~\mathrm{mK}$), to investigate the true magnetic ground state of $\mathrm{CaCu_3Ir_4O_{12}}$. Despite strong antiferromagnetic interactions ($\theta_{\mathrm{W}} \sim -200~\mathrm{K}$, with an applied-field dependence), no signature of long-range magnetic ordering or spin freezing is detected down to the lowest measured temperatures. Furthermore, our in-depth zero-field (ZF) and longitudinal-field (LF) $\mu$SR characterizations confirm strong quantum spin fluctuations and the truly dynamic nature of the local moments down to $40~\mathrm{mK}$. These results establish $\mathrm{CaCu_3Ir_4O_{12}}$ as a promising 3D quantum-disordered magnet and a well-characterized platform for exploring fluctuation-dominated states in correlated $3d/5d$ oxides.
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All authors J. Ming, Abhisek Bandyopadhyay, G. B. G. Stenning, M. T. F. Telling, N. N. Wang, G. Wang, J.-G. Cheng, D. T. Adroja

Statistical Mechanics

Nonreciprocal McKean-Vlasov Equations: From Stationary Instabilities to Travelling Waves

Arjun R, Pratyush Prakash Patra and A. V. Anil Kumar

Nonreciprocal interactions, in which action-reaction symmetry is broken, provide a powerful route to collective dynamics that cannot be captured by equilibrium free-energy minimisation. Here, we introduce and analyse a two-species nonreciprocal McKean-Vlasov equation derived from an underlying system of interacting stochastic particles. Combining linear stability analysis, weakly nonlinear arguments, pseudo-spectral simulations, and Langevin particle dynamics, we show that the structure of nonreciprocity controls the onset and nature of collective order. For spatially uniform weak nonreciprocity, asymmetry shifts the critical diffusion threshold but produces only stationary instabilities, indicating that uniform imbalance alone is insufficient to generate sustained time-dependent motion. In contrast, spatially modulated nonreciprocity fundamentally enriches the dynamics: depending on its symmetry and coupling to the interaction potential, the homogeneous state can lose stability through Hopf bifurcations, giving rise to standing and travelling wave states. We identify both subcritical and supercritical Hopf transitions, relate the selected patterns to Landau saturation coefficients, and show that travelling waves can emerge even in the weak-nonreciprocity regime without explicit microscopic run-and-chase rules. Direct Langevin simulations confirm that these oscillatory and travelling states persist at the particle level and are not artefacts of the continuum mean-field description. Our results establish nonreciprocal McKean-Vlasov equations as a minimal framework for understanding how spatially structured asymmetric interactions generate self-organized motion, dynamical phase transitions, and nonequilibrium collective order.
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Superconductivity · Cross-listed from physics.ins-det

Optimisation of TES design for the CRESST experiment

G. Angloher, S. Banik, A. Bento et al. (+54 more)

The CRESST experiment aims at the direct detection of sub-GeV dark matter particles via elastic scattering off nuclei in different target crystals at cryogenic temperatures. The advancement in W-TES sensors allowed the CRESST detectors to reach energy thresholds of 10 eV and lower, opening the way to the exploration of dark matter masses as low as 70 MeV/c2. This work presents optimisation studies of W-TESs aimed at further improving the signal-to-noise ratio and overall detector performance. In particular, we investigate the thickness, dimensions and material composition of phonon collectors and assess their impact on detector response. The results demonstrate a significant performance enhancement and establish new benchmarks for the sensors used within CRESST.
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All authors G. Angloher, S. Banik, A. Bento, A. Bertolini, R. Breier, C. Bucci, J. Burkhart, L. Burmeister, L. Canonica, E. Cipelli, S. Di Lorenzo, J. Dohm, F. Dominsky, A. Erb, E. Fascione, F. v. Feilitzsch, S. Fichtinger, D. Fuchs, V.M. Ghete, P. Gorla, P.V. Guillaumon, S. Gupta, D. Hauff, M. Ješkovský, J. Jochum, M. Kaznacheeva, H. Kluck, H. Kraus, B. von Krosigk, A. Langenkämper, M. Mancuso, B. Mauri, V. Mokina, C. Moore, P. Murali, M. Olmi, T. Ortmann, C. Pagliarone, L. Pattavina, F. Petricca, W. Potzel, P. Povinec, F. Pröbst, F. Pucci, F. Reindl, J. Rothe, K. Schäffner, J. Schieck, S. Schönert, C. Schwertner, M. Stahlberg, L. Stodolsky, C. Strandhagen, R. Strauss, I. Usherov, M. Zanirato, V. Zema

Strongly Correlated Electrons · Cross-listed from quant-ph

svPITE: A Python package for the state-vector-based probabilistic imaginary-time evolution algorithm

Pascal Sievers and Satoshi Ejima

We present a Python package for ground-state preparation based on the probabilistic imaginary-time evolution algorithm, with particular focus on its state-vector-based implementation. A standard shot-based simulation is also supported, and results can be benchmarked against exact diagonalisation via a dedicated wrapper. The package enables efficient tuning of initial parameters, facilitating systematic exploration and optimisation of the method's performance. Starting from the prepared ground state, the strong interoperability with other packages further enables real-time evolution and the computation of spectral functions, such as the spin-spin dynamical structure factor.
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Strongly Correlated Electrons

Noncollinear antiferromagnetic structure and physical properties of CrRhAs with distorted kagome lattice

Chenglin Shang, Daye Xu, Bingxian Shi et al. (+8 more)

CrRhAs was theoretically proposed to be a kagome metal with unusual magnetic ground states; however, little is known about its magnetic structure and physical properties experimentally. Here, we present an experimental investigation of CrRhAs with ZrNiAl-type structure and a distorted Cr kagome lattice. CrRhAs is an antiferromagnet with TN = 149 K. Powder neutron diffraction analysis reveals a noncollinear antiferromagnetic structure with propagation vector k = (1/3, 1/3, 1/2), which features a ferromagnetic second nearest neighbor coupling in the kagome plane that is different from the prediction in previous density functional theory calculations. Furthermore, CrRhAs exhibits anomalous electrical transport properties which are possibly related to multiband effects and strong spin fluctuations. For the temperature-dependent longitudinal resistivity h̊o}xx, it is semiconductinglike above TN and becomes metallic below TN . The Hall coefficients exhibit two sign changes near 70 and 300 K. Combined with the results of heat capacity measurements, a large Kadowaki-Woods ratio {\alpha} = 33.9 {\mu}{\Omega} cm mol2 K2/J2 is obtained. The above results suggest CrRhAs is a strongly correlated kagome metal with multiband and noncollinear magnetic structure features.
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All authors Chenglin Shang, Daye Xu, Bingxian Shi, Xuejuan Gui, Zhongcen Sun, Juanjuan Liu, Jinchen Wang, Hongxia Zhang, Hongliang Wang, Lijie Hao, Peng Cheng

Mesoscale and Nanoscale Physics

Exciton-mediated optical control of liquid-solid friction

Timur Pryadilin, Alexey Kavokin and Baptiste Coquinot

Interfacial friction in nanofluidic systems can arise from fluctuation-induced coupling between liquid charge fluctuations and the internal excitations of the confining solid. Here, we develop a microscopic theory of exciton-mediated solid-liquid friction based on the coupling between optically generated excitons and charge fluctuations in water. We distinguish between static excitons, localized by disorder or functionalization, and dynamic excitons, which interact with water through polarization fluctuations. In both cases, we derive analytical formulas for the excitonic friction, which is experimentally tunable and can significantly reduce the slip length and thereby the hydraulic permeability of nanochannels. Applying our framework to carbon nanotubes, we quantitatively reproduce the recent measurements of Kistwal et al., showing a reduction of nanotube diffusion under optical excitation, without fitting parameters. More broadly, our results establish excitons as a mechanism to optically control nanofluidic transport and suggest that excitonic photoluminescence could provide an optical probe of flow velocity inside nanochannels.
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Statistical Mechanics · Cross-listed from quant-ph

Breaking QAOA's Fixed Target Hamiltonian Barrier: A Fully Connected Quantum Boltzmann Machine via Bilevel Optimization

Jun Liu

To overcome the limitations of classical partially connected Boltzmann machines and mainstream quantum Boltzmann machines (QBMs), this work extends the conventional circuit of the quantum approximate optimization algorithm (QAOA) to a bilevel optimization architecture and proposes a fully connected QBM. The inner-loop training simulates positive phase energy minimization based on the computational process of the conventional QAOA circuit, whereas the outer-loop training simulates negative phase contrastive divergence learning by optimizing the structural parameters of the target Hamiltonian. It is found that, first, the model exhibits superior performance using only a single layer (p=1) in the QAOA circuit, with an average probability of 0.9559 in measuring the target quantum state under noiseless conditions. Second, the model exhibits notable noise robustness. Under the typical noise level of current mainstream commercial quantum computing devices, the average probability of measuring the target quantum state reaches 0.6047; when the noise rises to a more stringent level with doubled intensity, this probability remains at 0.3859. In both scenarios, the target quantum state maintains the highest measurement probability among all detected states, with a value several times higher than that of the second-ranked state. This indicates that the model retains strong robustness even when noise meets or exceeds the upper limit of current mainstream commercial quantum computing devices. Third, under a block-by-block learning strategy with p=1 and only 10 measurement shots, the model consistently generates the target "qubit" grid image regardless of noise interference, demonstrating strong robustness in image generation.
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Materials Science

Dislocations in (011)-oriented vertical Bridgman $\beta$-Ga$_2$O$_3$ substrates

Yongzhao Yao, Daiki Katsube, Hirotaka Yamaguchi et al. (+1 more)

Dislocation in (011)-oriented $\beta$-Ga$_2$O$_3$ substrates grown by the vertical Bridgman method was investigated using X-ray topography (XRT), combined with X-ray reticulography. Transmission XRT reveals dislocations lying on the (001) plane and extending along [010], forming arrays associated with domain boundaries. Dislocations on the (011) plane were also identified but differ from those responsible for line-shaped pits on (001) epilayers. Reflection XRT shows good agreement with transmission XRT and enables classification of dislocation types based on contrast features. Reticulography confirms domain boundaries with misorientation on the order of 1E-5 rad, providing insight into defect formation relevant to epi-growth and device performance.
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All authors Yongzhao Yao, Daiki Katsube, Hirotaka Yamaguchi, Yukari Ishikawa

Materials Science

Spin-lattice coupling enables adaptive adsorption in magnetically-driven electrocatalysts

Arnold Gaje, Lulu Li, Felipe A. Garcés-Pineda et al. (+14 more)

A major challenge in electrochemistry is to decouple the reactive intermediates of a catalytic cycle to optimise their energies independently. During the oxygen evolution reaction (OER), such energy interdependence results from the need to generate multiple adsorbates at the same site and sets the minimum overpotential. Here, we show that an external stimulus, such as a magnetic field, can relax the scaling relationships between intermediates during the OER. Spectroscopic measurements and Density Functional Theory simulations in Ni-Fe oxyhydroxides reveal that applying a magnetic field alters surface chemisorption and injects structural flexibility at the interface. We interpret these observations as a consequence of stimulated changes in the spin-lattice coupling, which allow access to quasi-degenerate oxygenated intermediates that modulate the reaction energy demands. Our findings redefine the scaling limitations as state-projected rather than intrinsic and establish external stimulation as a strategy to navigate multi-state energy landscapes in electrocatalysis and sensing applications.
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All authors Arnold Gaje, Lulu Li, Felipe A. Garcés-Pineda, Camilo A. Mesa, Ghazaleh Abdolhosseini, Aditya K. Kushwaha, Dora Zalka, Elzbieta Trzop, Nicolas Godin, Raffaella Torchio, María Escudero-Escribano, Eric Collet, Sixto Giménez, Niels Keller, José Ramón Galán-Mascarós, Núria López, Ernest Pastor

Mesoscale and Nanoscale Physics

Point-gap topology of damped magnon excitations in skyrmion strings

Yusuke Koyama and Yuki Kawaguchi

We theoretically study the non-Hermitian topology of magnons with finite lifetimes due to Gilbert damping. By incorporating the spin-wave theory and perturbation theory for the Landau-Lifshitz-Gilbert equation including nonlocal damping terms, we analytically evaluate the spectral winding number for point gaps, which indicates the existence of the non-Hermitian skin effect (NHSE). We find that, in noncollinear magnetic textures, the NHSE can occur even in the absence of nonlocal damping, due to the momentum-dependent mixing of the particle and hole components of magnon eigenmodes, which is absent in collinear magnets with a single magnon band. In the presence of nonlocal damping along one direction, we show that the winding number for an energy band with a unique minimum is determined from the sign of the wave number at the band minimum. We demonstrate these results using a model that hosts a skyrmion-string lattice as a steady state. We further investigate spin-wave propagation dynamics excited by a magnetic-field pulse and show that the propagation direction changes drastically from band to band depending on the presence of local and nonlocal damping, consistent with the nontrivial winding numbers.
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Mesoscale and Nanoscale Physics

Effective Gilbert damping in the stochastic Landau-Lifshitz-Gilbert equation

Mexx. E.Y. Regout, Bertrand Dupé and Matthieu J. Verstraete

Quasi particle based (e.g. Boltzmann equation) studies of spin wave transport often assume that their scattering rates follow the simple form $\eta=\alpha \omega$, with the Gilbert damping $\alpha$ and frequency $\omega$. In this work, we examine the effective damping $\alpha_{eff,T}=\eta/\omega$ observed in atomistic spin dynamics, when temperature and spin wave interactions are introduced for a 1D spin chain. We extract the dynamical correlation functions from spin trajectories propagated using the stochastic Landau-Lifshitz-Gilbert equation, and fit the dynamical structure factor, yielding the dispersion and scattering rates for a wide range of temperatures. The resulting effective damping can be very different from the initially constant Gilbert value. It exhibits a temperature and crystal momentum scaling which we explain based on interactions with the Gilbert bath and spin wave scattering by changes in local magnetic order.
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Statistical Mechanics · Cross-listed from math-ph

Volume-Independent Spectral Stability of Energy-Truncated Effective Hamiltonians in Quantum Spin Systems

Ayumi Ukai

We prove a volume-uniform effective-Hamiltonian theorem for bounded finite-range quantum spin systems on possibly infinite lattices. For any finite target region, we construct an energy-truncated Hamiltonian and prove a volume-uniform spectral-overlap bound controlling the leakage of its low-energy spectral subspace into the high-energy spectral subspace of the original Hamiltonian. The bound may contain non-exponential spectral-window terms, but its cutoff-dependent remainder decays exponentially in the cutoff. In finite volume, this yields stability of low-lying eigenvalues, with eigenvalue errors controlled by the exponentially small cutoff-dependent remainder. In infinite volume, we prove the corresponding spectral-overlap estimate in the GNS representation of an infinite-volume ground state. Thus, for bounded finite-range interactions, we extend and strengthen the effective-Hamiltonian mechanism of Arad, Kuwahara, and Landau by replacing the finite-volume operator-norm formulation with a volume-uniform spectral-overlap formulation applicable in the thermodynamic limit.
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Materials Science

Revisiting Ferroelectricity Beyond Polar Space Groups

Yudi Yang, Changming Ke and Shi Liu

Ferroelectricity, a hallmark of spontaneous inversion-symmetry breaking, has been a central concept in condensed matter physics and functional materials research, yet recent discoveries are revealing that switchable polarization can emerge in forms far richer than allowed by the conventional symmetry-based paradigm. Fractional quantum ferroelectricity and ionic-conductor ferroelectricity challenge the long-standing association of ferroelectricity exclusively with polar space groups. In this Review, we reconcile these emerging phenomena within the Berry-phase modern theory of polarization. We emphasize that polarization in insulating periodic crystals is not a single-valued vector, but a multivalued lattice quantity defined modulo a polarization quantum. Consequently, nonpolar crystals may possess nonzero formal polarization, and adiabatic paths connecting symmetry-equivalent structures can produce quantized changes in polarization without violating symmetry principles. The symmetry of this multivalued formal polarization is governed by a generalized Neumann principle. We further show that the large polarization changes induced by long-range ion migration in both fractional quantum ferroelectrics and ionic-conductor ferroelectrics can be naturally understood through the topological definition of oxidation state, which links ionic transport to quantized charge transfer and polarization change. We discuss the physical accessibility of these unconventional polarization states, highlighting the roles of switching pathways, boundary conditions, and domain-wall dynamics, particularly in systems such as $\alpha$-In$_2$Se$_3$. Finally, we suggest that the most promising functionality of these materials may lie not in conventional bulk ferroelectric switching, but in the creation and control of charged interfaces and domain walls arising from discontinuities in formal polarization.
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