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Physics Condensed Matter

cond-mat Watch Condensed Matter

Wednesday 8 April

Statistical Mechanics

Balancing Power, Efficiency, and Constancy under Broken Time-Reversal Symmetry

Ousi Pan, Zhiqiang Fan, Shunjie Zhang et al. (+3 more)

We derive general trade-off relations among the power, efficiency, and constancy for two-terminal thermoelectric systems in the linear response regime. Constancy, which quantifies the steadiness of the heat engine, is measured by its fluctuations. The bounds of the efficiency, power and fluctuations are valid even when time-reversal symmetry is broken, revealing how such a symmetry breaking alters the fundamental constraints on steady-state energy conversion. Our results extend and refine previously established universal trade-offs, offering deeper insight into the performance limits in nonequilibrium thermodynamics. Guided by this bound, heat engines with broken time-reversal symmetry can be operated at near-Carnot efficiency while maintaining finite power output and fluctuations, enabling them to outperform their traditional counterparts.
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All authors Ousi Pan, Zhiqiang Fan, Shunjie Zhang, Liwei Chen, Jincan Chen, Shanhe Su

Soft Condensed Matter

Phase coherence and disorder-induced wave propagation in micromotor arrays

Romane Braun, Alexis Poncet, Alexandre Morin et al. (+1 more)

Machines are designed, assembled, and programmed to convert power into predetermined dynamics and functions. In contrast, living systems such as interacting cells and animal groups self-organize, synchronize, and perform complex tasks without predefined patterns. Inspired by these decentralized architectures, experiments have shown that small assemblies of elastically coupled self-propelled robots can achieve two fundamental functionalities observed in nature: collective motion and oscillatory deformations. However, biological inspiration has steered research toward translational self-propulsion, while active rotation remains an underexplored route to designing broader animate materials. Here, we study the self-organization of microscopic metamachines composed of thousands of 3D-printed rotary motors. We first demonstrate and explain how motors precessing in unspecified directions collectively arrange their dynamics into a pristine antiferromagnetic phase. Next, we elucidate the emergence of spatiotemporal order in the form of phase coherence in the rotors' precession. Finally, we show how quenched disorder initiates the free propagation of phase waves across self-organized regions with mismatched rotation speeds. Our results suggest that spinner-based metamachines could illuminate metachronal-wave formation in living systems, and signal propagation in synthetic animate materials.
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All authors Romane Braun, Alexis Poncet, Alexandre Morin, Denis Bartolo

Materials Science

Unveiling Mechanisms of SEI Formation and Sodium Loss in Sodium Batteries via Interface Reactor Sampling

Zhoulin Liu, Ziliang Wang, Zherui Chen et al. (+4 more)

The solid electrolyte interphase SEI critically dictates the cyclability and Coulombic efficiency of sodium-metal batteries, yet its dynamic formation mechanisms and atomic-scale evolution during electrochemical cycling remain elusive due to the spatiotemporal limitations of existing techniques. Here, an "Interface Reactor" sampling strategy is proposed to construct a charge-aware neuroevolution potential (qNEP). This approach overcomes the instability bottlenecks of conventional machine learning potentials, enabling stable, first-principles-accurate molecular dynamics simulations of complex electrode-electrolyte interfaces on the hundred-nanosecond scale. Fundamentally distinct SEI formation mechanisms are revealed during the early stage: carbonate-based electrolytes form heterogeneous organic-inorganic matrices via "mixed co-formation," whereas ether-based electrolytes generate dense, self-limiting inorganic barriers through "surface-energy-controlled" NaF crystallization. Metadynamics simulations further elucidate that these compositional disparities govern sodium-ion storage dynamics: NaF-rich SEIs facilitate efficient metallic deposition, while carbonate-dominated interphases induce irreversible sodium trapping and continuous electrolyte decomposition. These findings establish a comprehensive atomic-scale framework linking solvation structure, interfacial reaction networks, and electrochemical performance, providing mechanistic guidelines for rational SEI engineering in next-generation alkali-metal batteries. Crucially, a general and robust computational framework is established for simulating complex interfacial reactions in electrochemical systems.
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All authors Zhoulin Liu, Ziliang Wang, Zherui Chen, Jianchun Sha, Fengzijun Pan, Pingyang Zhang, Yinghe Zhang

Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Complete coherent control of spin qubits in self-assembled InAs quantum dots under oblique magnetic fields

I. Samaras, K. Barr, C. Schneider et al. (+2 more)

We demonstrate complete coherent control of a single spin qubit confined in a self-assembled InAs negatively charged quantum dot subjected to an Oblique magnetic field, and directly compare this regime with the conventional Voigt geometry. In the Oblique-field configuration, the groundstate spin eigenstates are found to be unequal superpositions of the bare electron spin, with their composition tunable via the orientation of the applied field. This tunable spin mixing provides an additional degree of freedom to engineer the spin basis and associated optical couplings in the charged quantum dot system. Although this geometry has a distinct structure with important implications, it provides a regime in which we can fully and coherently control the tailored spin qubit. We observe Rabi oscillations and Ramsey fringes, and demonstrate arbitrary single-qubit rotations, enabling a direct comparison with the Voigt case. Our results establish that spin-qubit control does not necessarily require a pure Voigt geometry and can instead be achieved under Oblique magnetic fields. This relaxes constraints on device and field alignment and offers a versatile route to design and optimize quantum information processing architectures in semiconductor quantum dots.
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All authors I. Samaras, K. Barr, C. Schneider, S. Höfling, K.G. Lagoudakis

Materials Science

Topological Defects in Amorphous Solids

Matteo Baggioli, Michael L. Falk and Walter Kob

Topological defects (TDs) are crucial for understanding important physical properties of crystalline materials including mechanical failure, ion transport, and two-dimensional melting. This concept has not translated to disordered materials like glasses because these solids have no obvious reference structure that can be used to define TDs. As a result, key properties related to those listed above have typically been modeled using purely phenomenological approaches. Recent studies have demonstrated that certain observables commonly associated with TDs can also be identified in disordered solids indicating that topological concepts may be as crucial in amorphous solids as in crystals. This hints that TDs may offer a first-principles framework for understanding their mechanical response and complex spatiotemporal dynamics. In this Perspective, we review recent theoretical, numerical, and experimental studies that have exploited topological concepts to rationalize mechanical properties of amorphous solids. We also highlight pressing open questions and some promising directions for future research in the field.
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Superconductivity

Influence of the Ortho-II superstructure in the YBa$_2$Cu$_3$O$_{7-\delta}$ Orthorhombic phase after annealing

Roberto F. Luccas, Lorenzo Gallo, Cesar E. Sobrero et al. (+1 more)

Based on experimental results, this work proposes the influence of the Oxygen order present in the Ortho-II superstructure of YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO), on the final ordering of Oxygens in its Orthorhombic phase for $\delta$ $\approx$ 0. Isothermal oxygenation (oxyg) of YBCO powder material is performed, starting from non-oxygenated material ($\delta$ $=$ 1) and evolving until saturation in an oxygen atmosphere. The oxyg process is carried out within a temperature range from 300 $^o$C to 800 $^o$C (300 $^o$C $<$ T$_O$ $<$ 800 $^o$C). During the oxyg process, and using a thermogravimetric balance, the evolution of mass (m) and the differential thermal analysis (DTA) of the material are monitored with respect to an inert reference material subjected to the same conditions as the YBCO powder. These results allow observation of the Tetragonal-Orthorhombic (T-O) transition occurring in the YBCO material. From these results, oxygenated YBCO material is obtained by working at different temperatures and under two different conditions: through a direct T-O transition into the Ortho-I superstructure, and by passing through the Ortho-II superstructure along the transition. The material obtained under these two conditions is studied by X-Ray diffraction, revealing differences in the resulting diffractograms. Furthermore, we propose that, for low values of T$_O$ (T$_O$ $<$ 400 $^o$C), the T-O transition proceeds through the region of the phase diagram where the Ortho-II superstructure is present, leading to progressive ordering of the Oxygen atoms within the material. This ordering leaves a fingerprint in the final configuration reached by the YBCO material, even beyond the region where the Ortho-II superstructure is stable. Finally, we suggest that this mechanism is responsible for the differences observed between the diffractograms obtained under both conditions.
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All authors Roberto F. Luccas, Lorenzo Gallo, Cesar E. Sobrero, Jorge A. Malarría

Soft Condensed Matter

Using test particle sum rules to improve approximations in classical DFT : White-Bear and White-Bear mark II versions of the Lutsko Functional

Melih Gül, Roland Roth and Robert Evans

In a recent paper [M. Gül et al., Phys. Rev. E, 110 (6), 064115] we showed that test particle sum rules, which address the excess chemical potential and isothermal compressibility, could be used to develop new and accurate classical density functionals for hard-sphere (HS) fluids. Here we extend our approach to the construction of HS functionals building upon the state of art White-Bear (WB) and White-Bear mark II functionals. Employing the same test-particle sum rules we determine the two free parameters in the Lutsko [James F. Lutsko, Phys. Rev. E, 102, 062137] formulation of fundamental measure theory (FMT) by minimizing the relative errors between different routes to the two thermodynamic quantities. The resulting optimized Lutsko WB functionals, especially Lutsko WB mark II, are generally more accurate and consistent than those obtained in earlier treatments.
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Materials Science · Cross-listed from physics.chem-ph

Self-consistent Hessian-level meta-generalized gradient approximation

Pooria Dabbaghi, Juan Maria García Lastra and Piotr de Silva

The $\vartheta$-MGGA class of density functionals is formally reformulated as Hessian-level meta-generalized gradient approximations (HL-MGGAs). In contrast to standard meta-GGAs that rely on the orbital-dependent kinetic-energy density or the density Laplacian, HL-MGGAs utilize the full density Hessian. We introduce a simplified, non-empirical functional, $\vartheta$-PBE, and present a roadmap for its self-consistent implementation within the projector augmented-wave (PAW) method. By utilizing the complete set of spatial second-order density derivatives, the functional's underlying descriptor successfully distinguishes between distinct one-electron density limits, such as single-center atomic densities and two-center bonds, that standard iso-orbital indicators often conflate. Benchmarks across molecular and solid-state datasets reveal that while $\vartheta$-PBE delivers accurate chemisorption energies and molecular properties, challenges remain in predicting bulk lattice constants. Ultimately, this work demonstrates the physical utility and feasibility of designing orbital-independent, Hessian-based exchange-correlation functionals.
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Other Condensed Matter

Identifying Topological Invariants of Non-Hermitian Systems via Domain-Adaptive Multimodal Model for Mathematics

Jiuchun Meng, Lichao Sun, Xiumei Wang et al. (+2 more)

Identifying topological invariants are endowed with profound physical connotations in the fields of condensed matter physics. However, they are often limited by the failure of standard theorems and high computational costs. Traditional machine learning methods typically treat this problem as a black-box regression, which fails to learn the underlying mathematical structures of lattices. To this end, we propose a straightforward yet powerful multimodal model that fundamentally improves topological invariants discovery through two key methodological innovations. First, instead of feeding raw data into a standard network, our model introduces a dual-track alignment mechanism. This mechanism treats eigenvalues as context sequences and eigenvectors as matrix structures, enabling the model to naturally capture the interrelated algebraic and geometric properties of topological states. Second, to resolve the common problem where deep learning models make numerical mistakes in exact mathematical calculations, we use a tool-integrated reasoning paradigm. Within this paradigm, the neural network acts as a logical controller to calculate discrete topological indices. This design eliminates the uncertainty of deep learning, ensuring zero-error calculations from continuous physical data. We demonstrate that our model can accurately reconstruct complex three-dimensional generalized Brillouin zones and achieve 97% accuracy in calculating non-Bloch Chern numbers in long-range transition systems. By combining the flexible logic of multimodal artificial intelligence with the rigorous precision of symbolic computation, this work provides a reliable and highly versatile tool for exploring exotic topological phases.
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All authors Jiuchun Meng, Lichao Sun, Xiumei Wang, Dandan Zhu, Xingping Zhou

Soft Condensed Matter

Frictional sliding strength of knotted and capstan configurations along the axis of a cylinder

Javier Sabater, Ji-Sung Park, Jérôme Crassous et al. (+2 more)

We investigate the sliding strength of thin filaments in frictional contact with a translating cylinder, perpendicular to the filaments' axes, in knotted (clove hitch) and unknotted (capstan) configurations. Recent work reported superlinear scaling for surgical knots with elasto-plastic filaments [1]. Testing the clove hitch with various materials (elastomeric rods, metallic wires, braided ropes) reveals similar nonlinear behavior, ruling out plasticity. To explore the source of the previously reported nonlinear behavior, we perform three-dimensional FEM simulations (resolving full 3D mechanics) and reduced-order DER simulations (isolating geometric effects by neglecting cross-sectional deformation). Both FEM and DER simulations reproduce the experimental scaling. Simplifying the knot topology by studying capstan angles from $\pi/4$ to $4\pi$ yields comparable superlinear behavior, transitioning to linearity at smaller angles. We rationalize the results by developing an analytical model based on planar elastica theory for the capstan configuration (which exhibits behavior similar to the clove hitch but with a simpler topology). The model reproduces the observed superlinear behavior and rationalizes it by coupling the evolution of normal forces and contact arclength during tightening. The analysis further predicts transition to linearity when full contact between the filament and the cylinder is established, providing a mechanical framework applicable across materials, geometries, and topologies.
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All authors Javier Sabater, Ji-Sung Park, Jérôme Crassous, Sébastien Neukirch, Pedro M. Reis

Mesoscale and Nanoscale Physics

Microscopic evidence of spin-driven multiferroicity and topological spin textures in monolayer NiI2

Haitao Wang, Tianxing Jiang, Weiyi Pan et al. (+12 more)

In type II multiferroics, noncollinear spin textures are expected to induce electric polarization directly, leading to strong magnetoelectric coupling. Realizing such spin driven multiferroicity in two-dimensional systems, and elucidating the interplay between local spins and electric polarization, are of both fundamental and technological importance. Here, using vectorial spin polarized scanning tunneling microscopy, we investigated the spin-driven multiferroicity in monolayer NiI2 at atomic scale. We identify a canted spin-spiral state with fully determined spin rotation plane, accompanied by a 2Q charge modulation. At spin spiral domain walls, we discover topological spin textures that composed of meron/antimeron pairs. These textures are associated with distinct charge pattern and notable band shifts, indicating local bound charges induced by variations of ferroelectricity at domain wall. Our observations are well captured by a realistic spin model incorporating Kitaev interactions and generalized spin-current model of type II multiferroicity. The findings provide microscopic evidence of spin-driven multiferroicity in an extreme 2D system and establish a platform for low-dissipation, electric-field control of topological spin textures.
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All authors Haitao Wang, Tianxing Jiang, Weiyi Pan, Xu Wang, Hongyu Wang, Junchao Tian, Lianchuang Li, Dongming Zhao, Qingle Zhang, Chenxi Wang, Ying Yang, Hongjun Xiang, Changsong Xu, Donglai Feng, Tong Zhang

Mesoscale and Nanoscale Physics

Tensor-network simulation of quantum transport in many-quantum-dot systems

Maximilian Streitberger and Marko J. Rančić

Transport through correlated nanoscale systems underpins the operation of quantum-dot and molecular-scale devices, yet accurate simulations of large open quantum systems remain computationally challenging as system size increases. Tensor-network methods offer a promising route past this scaling barrier by efficiently compressing quantum states. Here we extend a tensor-based solver with a jump-counting estimator that enables direct computation of steady-state electron currents from lead-induced tunneling events. We benchmark the resulting currents against the state-of-the-art master-equation solver QmeQ across a range of lead-dot and inter-dot coupling parameters and find quantitative agreement in the tractable regime. Compared with classical approaches, TJM reduces memory requirements and wall-clock time by orders of magnitude, enabling simulations of interacting quantum-dot arrays far beyond the range accessible to density-matrix-based transport solvers and systematic studies of size-dependent nonequilibrium transport in larger arrays. Our approach allow us to model quantum transport in an array of up to fifty (50) quantum dots.
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Strongly Correlated Electrons

Development of ab initio Hubbard parameter calculation schemes in the k-point sampling real-time TDDFT program in CP2K

Kota Hanasaki and Sandra Luber

We implemented ab initio Hubbard parameter calculation schemes in the k-point sampling real-time TDDFT (RT-TDDFT) program in CP2K. We propose a new linear-response-based calculation scheme for energy-dependent Hubbard parameters. Our scheme extends the minimum-tracking linear-response method proposed in [Moynihan et al., arXiv preprint arXiv:1704.08076(2017); E. B. Linscott et al., Phys. Rev. B 98, 235157 (2018)] to realize the calculation of energy-dependent Hubbard parameters that reflect the exchange-correlation (xc) effects included in the xc-functional. We discuss the properties of the minimum-tracking linear-response method in comparison to another promising scheme, ACBN0 [Agapito et al., Phys. Rev. X, 5, 011006 (2015)]. We show that, while neither clearly outperforms the other in the accuracy of static property calculations, each has a distinct dynamical application depending on its theoretical formulation.
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Strongly Correlated Electrons

A Practical Introduction to Tensor Network Renormalization with TNRKit.jl

Victor Vanthilt, Adwait Naravane, Chenqi Meng et al. (+1 more)

We present TNRKit, an open-source Julia package for Tensor Network Renormalization (TNR) of two- and three-dimensional classical statistical models and Euclidean lattice field theories. Built on top of TensorKit, it provides a symmetry-aware framework for constructing tensor-network representations of partition functions and coarse-graining them using methods such as TRG, HOTRG, and LoopTNR. Beyond thermodynamic quantities, the package enables the extraction of universal conformal data – including scaling dimensions and the central charge – directly from fixed-point tensors. TNRKit is designed with both usability and extensibility in mind, offering a practical platform for applying, benchmarking, and developing modern tensor renormalization algorithms. This paper also serves as a self-contained introduction to the TNR framework.
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All authors Victor Vanthilt, Adwait Naravane, Chenqi Meng, Atsushi Ueda

Mesoscale and Nanoscale Physics

Excitonic Mott transition without population inversion

Oleg Dogadov, Armando Genco, Allison R. Cadore et al. (+12 more)

Exciton dissociation via the excitonic Mott transition (EMT) governs the high-density optical response of semiconductors and sets fundamental limits for optoelectronic devices. The EMT is conventionally linked to the onset of population inversion and the emergence of optical gain. Here, we demonstrate that this paradigm can break down under ultrafast non-equilibrium excitation. Using femtosecond pump-probe optical spectroscopy, we drive a monolayer transition metal dichalcogenide into a dense photoexcited state in which the excitonic resonance is completely quenched within ~100 fs, while the optical gain is entirely absent across the explored fluence range. State-of-the-art real-time ab initio simulations reveal that the EMT is governed by an interplay of strongly nonthermal carrier populations and nonequilibrium dynamical screening of the Coulomb interaction. The quantitative agreement between theory and experiment identifies a distinct, ultrafast pathway to exciton ionization beyond quasi-equilibrium descriptions and demonstrates that population inversion is not a universal prerequisite for the EMT.
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All authors Oleg Dogadov, Armando Genco, Allison R. Cadore, James A. Kerfoot, Evgeny M. Alexeev, Osman Balci, Chiara Trovatello, Kenji Watanabe, Takashi Taniguchi, Seth Ariel Tongay, Andrea C. Ferrari, Giulio Cerullo, Stefano Dal Conte, Gianluca Stefanucci, Enrico Perfetto

Materials Science

Microscopic contributions to the deviation from Amontons friction law

Suresh Ravisankar, Ravikant Kumar, Antonio Cammarata et al. (+2 more)

We investigate the nanoscale friction behaviour of MX2 monolayers (M = Mo, W; X = S, Se) on Au(111) and Ag(111) substrates with a silicon tip using classical molecular dynamics simulations with machine-learning-based force fields. This approach enables an accurate description of tip-surface interactions and friction mechanisms at the atomic scale. We observe a pronounced non-monotonic dependence of the friction force on the applied normal load, indicating a breakdown of Amontons's law at the nanoscale. Analysis of lateral force' signals and their spatial Fourier transforms reveals the coexistence of multiple sliding modes, including longitudinal sliding, lateral slip, and zig-zag motions. We show that the overall friction response is governed by the relative contributions of these motions. While the qualitative features of friction are largely substrate-independent, both the magnitude of friction and the balance between sliding modes depend sensitively on the substrate-monolayer combination. In particular, Au/MoSe2/Si exhibits significantly reduced friction due to suppression of lateral slip motion. Our results indicate that the method is broadly applicable for probing nanoscale friction in related heterostructures.
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All authors Suresh Ravisankar, Ravikant Kumar, Antonio Cammarata, Thilo Glatzel, Tomas Polcar

Mesoscale and Nanoscale Physics

Millisecond spin relaxation times of distinct electron and hole subensembles in MA$_x$FA$_{1-x}$PbI$_3$ perovskite crystals

Rongrong Hu, Sergey R. Meliakov, Dmitri R. Yakovlev et al. (+4 more)

The unique combination of outstanding optical quality and attractive spin properties opens new avenues for optical spin control in hybrid organic-inorganic perovskite semiconductors. Using the optically detected magnetic resonance technique, we study the spins of electrons and holes in mixed-cation MA$_x$FA$_{1-x}$PbI$_3$ single crystals with $x = 0.4$ and 0.8. Multiple distinct spin subensembles with $g$-factors spanning from 2.9 to 3.6 for electrons and from 0.5 to 1.2 for holes are resolved, revealing diverse localization environments. We measure the longitudinal spin relaxation times, $T_1$, reaching 2 ms and remaining in the $\mu$s range even for weakly localized carriers at the cryogenic temperature of 1.6 K. The magnetic-field dependence of $T_1$ is dominated by the random nuclear (Overhauser) fields with strengths of $\sim 0.4-0.8$ mT for electrons and $\sim 4-12$ mT for holes, corresponding to $\mu$s-long correlation times of the hyperfine field determined by carrier hopping between shallow localization sites. The temperature dependence of $T_1$ reveals a weak localization potential of the charge carriers and shows a correlation between $T_1$ and the inhomogeneity of the spin ensemble. These results establish mixed-A-site perovskite single crystals as a promising solid-state platform with long-lived spin states for quantum information applications.
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All authors Rongrong Hu, Sergey R. Meliakov, Dmitri R. Yakovlev, Bekir Turedi, Maksym V. Kovalenko, Manfred Bayer, Vasilii V. Belykh

Strongly Correlated Electrons

Between Mott and cluster Mott: spin-orbit entangled dimer singlets in Ba$_3$CeRu$_2$O$_9$

L. Pätzold, A. Sandberg, H. Schilling et al. (+8 more)

The hexagonal 4d ruthenates Ba3MRu2O9 host structural dimers and exhibit a delicate balance of competing interactions. Hund's coupling, trigonal crystal-field splitting, and hopping for $a_{1g}$ and $e_g^\pi$ orbitals all fall within a narrow energy window. This yields a series of possible ground states, ranging from the localized Mott limit with (anti-) ferromagnetic exchange coupling via orbital-selective behavior to the cluster Mott limit with quasimolecular orbitals that are delocalized over the two dimer sites. Using resonant inelastic x-ray scattering, we show that Ba3CeRu2O9 with four holes per dimer resides in the intricate crossover regime between the localized Mott case and the quasimolecular limit. The spin-orbit entangled singlet ground state predominantly shows a Mott-like charge distribution with two holes per Ru site. At the same time, spin and orbital occupation contradict an exchange-based Mott scenario but agree with a cluster Mott approach. A quasimolecular trial wave function describes more than 70% of the ground state. In this crossover regime, small changes of, e.g., the crystal field may strongly affect the character of electronic states.
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All authors L. Pätzold, A. Sandberg, H. Schilling, H. Gretarsson, E. Bergamasco, M. Magnaterra, P. Becker, P. H. M. van Loosdrecht, J. van den Brink, M. Hermanns, M. Grüninger

Mesoscale and Nanoscale Physics

Telecom C-band single-photon sources with a semiconductor-dielectric microresonator

Yuriy Serov, Aidar Galimov, Sergey Sorokin et al. (+19 more)

Secure communications with quantum key distribution over fiber-optic links is one of the few recognized applications of quantum physics at the level of individual quanta – single C-band photons. Currently, the widely used sources of such photons are highly attenuated laser pulses, featured by a low probability of single photon occurrence. Here, we present an efficient source with an InAs/GaAs quantum dot on a metamorphic buffer layer inside a micropillar-shaped microcavity. The key innovation is the use of different semiconductor and dielectric materials to form the lower (GaAs/AlGaAs) and upper (Si/SiO$_2$) Bragg reflectors. Compatibility of these materials in a monolithic source is achieved by depositing a small amount of Si/SiO$_2$ pairs on an incomplete micropillar made from a coherent heterostructure grown by molecular beam epitaxy. This design enables resonant excitation with $\pi$-pulses and generation of polarized photons with a record-breaking end-to-end efficiency of 11%.
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All authors Yuriy Serov, Aidar Galimov, Sergey Sorokin, Nikolai Maleev, Marina Kulagina, Yuriy Zadiranov, Grigorii Klimko, Maxim Rakhlin, Alexey Veretennikov, Gleb Veyshtort, Olga Lakuntsova, Yuliya Salii, Daria Berezina, Sergey Troshkov, Demid Kirilenko, Alexey Blokhin, Alexei Vasil'ev, Alexander Kuzmenkov, Mikhail Bobrov, Irina Sedova, Tatiana V. Shubina, Alexey A. Toropov

Strongly Correlated Electrons

Proximate quantum spin liquid state in the frustrated HoInCu$_4$ metal

I. Ishant, T. Shiroka, O. Stockert et al. (+2 more)

We conducted a comprehensive and comparative muon-spin relaxation and rotation ($\mu$SR) investigation on two fcc-lattice metallic compounds, HoCdCu$_4$ ($T_\mathrm{N}\approx 8$ K) and HoInCu$_4$ ($T_\mathrm{N}\approx 0.76$ K), to elucidate the nature of their magnetic ground states and the role of frustration in stabilizing them. Our $\mu$SR results reveal that, in contrast to HoCdCu$_4$, strong magnetic frustration exists in HoInCu$_4$. Notably, in HoInCu$_{4}$, only 30% of the Ho-moments participate in the static magnetic ordering below $T_\mathrm{N}$, while the remaining 70% of the Ho-moments exhibit dynamic correlations and persistent spin dynamics down to 0.3 K, resembling a quantum spin-liquid (QSL) behavior. By contrast, in HoCdCu$_{4}$, all the Ho-moments contribute to the magnetic order below $T_\mathrm{N}$. Furthermore, in HoInCu$_{4}$, the temperature dependence of the relaxation rate indicates the presence of quantum critical fluctuations in the paramagnetic state near $T_\mathrm{N}$, suggesting the proximity to a quantum critical point (QCP). These observations suggest that the ground state of HoInCu$_{4}$ is a proximate quantum spin liquid (PQSL), a state that has not been reported before in frustrated metallic systems. Our $\mu$SR findings are further corroborated by recent inelastic neutron results on HoInCu$_4$, which show similarities to other insulating PQSL candidates, thus reinforcing our conclusions.
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All authors I. Ishant, T. Shiroka, O. Stockert, V. Fritsch, M. Majumder

Strongly Correlated Electrons · Cross-listed from physics.chem-ph

Spin-adapted neural network backflow for symmetry-preserving simulations of strongly correlated electrons

Yunzhi Li, Zibo Wu, Bohan Zhang et al. (+2 more)

Strongly correlated molecules often contain dense manifolds of low-lying spin states, making total-spin symmetry essential for predictive electronic-structure theory. Neural-network quantum states provide flexible variational wavefunctions, but commonly used fermionic architectures do not enforce this symmetry and can therefore converge to spin-contaminated states with misleading energies and properties. Here we introduce a spin-adapted neural-network backflow (SA-NNBF) ansatz in second quantization, which combines configuration-dependent spatial orbitals with a compressed spin eigenfunction. A projected tensor compression scheme for spin eigenfunctions and a particle-hole representation make variational Monte Carlo calculations with SA-NNBF practical for active spaces containing more than one hundred electrons. Across hydrogen chains and iron-sulfur clusters, SA-NNBF eliminates spin contamination and consistently achieves lower variational energies than standard NNBF with a comparable number of parameters. For the CAS(113e,76o) active-space model of FeMoco, SA-NNBF yields a highly compact spin-adapted variational state, achieving an energy competitive with recent spin-adapted DMRG calculations at bond dimension $D=10000$ while using orders of magnitude fewer parameters. Our work establishes a general framework for developing spin-symmetry-preserving neural-network quantum states for chemically realistic strongly correlated electrons.
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All authors Yunzhi Li, Zibo Wu, Bohan Zhang, Wei-Hai Fang, Zhendong Li

Strongly Correlated Electrons

Magnetic-field switching of exciton-magnon coupling in LiNiPO$_4$

Bei Sun, Zhuo Yang, Julian Shibuya et al. (+3 more)

Exciton-magnon transitions provide a fundamental optical fingerprint of coupled excitonic and magnetic excitations in antiferromagnets. However, controlling such coupled excitations by external fields remains a key challenge. Here we report the temperature and magnetic-field evolution of exciton-magnon coupling in the magnetoelectric antiferromagnet LiNiPO$_4$ using pulsed magnetic fields up to 50 T. The magnon sideband intensity exhibits sharp switching across field-induced magnetic phases, with strong suppression in plateau phases and enhancement in canted spin states. This behavior is attributed to the interplay between the thermal magnon population and the spin-dependent optical transition matrix element. These results demonstrate that magnetic-field control of spin degrees of freedom enables selective switching of exciton-magnon coupling in antiferromagnets.
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All authors Bei Sun, Zhuo Yang, Julian Shibuya, Koichi Kindo, Kenta Kimura, Atsuhiko Miyata

Materials Science

Volume Collapse Without a Structural Transition in Shock-Compressed FeO

C. Crépisson, T. Stevens, M. Fitzgerald et al. (+121 more)

We report x-ray diffraction and emission spectroscopy of FeO under laser-driven shock compression between 31-199 GPa. FeO retains the B1 (rocksalt) structure along the Hugoniot to the melt boundary at 191 GPa. While the phase and volume are broadly consistent with results from static compression, we observe an anomalous 7-10% volume collapse around 60 GPa absent in static experiments. We identify this as an isostructural high-spin to low-spin metallic transition in FeO. The low-spin state is directly evidenced by x-ray emission spectroscopy at 180 GPa.
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All authors C. Crépisson, T. Stevens, M. Fitzgerald, C. Camarda, P. G. Heighway, D. Peake, D. McGonegle, A. Descamps, A. Amouretti, D. A. Chin, K. K. Alaa El-Din, S. Azadi, E. Brambrink, K. Buakor, L. Pennacchioni, M. Sieber, A. Coutinho Dutra, J. Hernandez Gordillo, K. Yamamoto, J.-A. Hernandez, R. Torchio, T. Tschentscher, Y. Wang, H. Taylor, J. Pintor, O. S. Humphries, M. Andrzejewski, C. Baehtz, E. Barraud, A. B. Belonoshko, D. S. Bespalov, E. Boulard, R. Briggs, D. Cabaret, O. Castelnau, A. Chakraborti, J. Chantel, D. M. Cheshire, G. Collins, T. E. Cowan, Y. J. Deng, S. Di Dio Cafiso, L. Dresselhaus-Marais, X. Fang, A. Forte, S. Galitskiy, E. Galtier, T. Gawne, H. Ginestet, F. Hanby, A. Hari, N. J. Hartley, H. Höppner, N. Jaisle, J. Kim, Z. Konôpková, A. Krygier, J. Kuhlke, C. M. Lonsdale, S-N. Luo, J. Lütgert, M. Masruri, E. E. McBride, J. D. McHardy, M. I. McMahon, R. S. McWilliams, S. Merkel, T. Michelat, J-P. Naedler, B. Nagler, M. Nakatsutsumi, A-M. Norton, I. K. Ocampo, I. I. Oleynik, C. Otzen, N. Ozaki, C. A. J. Palmer, S. E. Parsons, A. Pelka, A. Phelipeau, C. Prescher, N. Pulver, C. Prestwood, C. Qu, D. Ranjan, R. Redmer, C. Sahle, A. A. Sanjuan Mora, S. Schumacher, J-P. Schwinkendorf, N. Sévelin-Radiguet, G. Shoulga, R. F. Smith, S. Singh, C. N. Somarathna, M. Stevenson, C. V. Storm, C. Strohm, T-A. Suer, M. X. Tang, A. Tipeev, M. Toncian, T. Toncian, U. Trdan, J. D. Tunacao, J. D. Umpleby-Thorp, L. Wang, M. Wilke, U. Zastrau, G. Gregori, D. Polsin, C. Sternemann, J. S. Wark, T. M. Hutchinson, C. McGuire, S. Pandolfi, A. Sollier, A. Higginbotham, T. R. Preston, D. Kraus, J. H. Eggert, K. Appel, M. Harmand, S. M. Vinko

Mesoscale and Nanoscale Physics

Self-Assembled Telecom Color Centers in Silicon and Their Growth Environment

Jacqueline Marböck, Enrique Prado Navarrete, Merve Karaman et al. (+6 more)

Artificial atoms based on color centers in silicon (SiCCs) have recently emerged as promising candidates for highly integrable and scalable key components in photonic quantum technology, including telecom single-photon sources and spin memory devices. A novel all-epitaxial fabrication technique for SiCCs, based on ultra-low-temperature (ULT) molecular beam epitaxy (MBE), addresses limitations of conventional fabrication via ion implantation, such as vertical ion straggle and collateral crystal lattice damage. This method solely relies on self-assembly of SiCCs during kinetically-limited growth of (carbon-doped) Si(:C) at ULTs <~350{\deg}C. The latter requires an extraordinary pristine growth environment to prevent unintended defect formation caused by the incorporation of impurities from the background vapor; however, so far, no study has specifically addressed how exactly the vacuum conditions during epitaxy influence SiCC formation, their optical properties, and the quality of the surrounding crystal matrix. Here, we investigate the impact of the growth pressure and the substrate temperature on the self-assembly and photoluminescence (PL) properties of important SiCCs, such as W, G, G', and T centers. Further, we use PL and Doppler broadening variable energy positron annihilation spectroscopy to emphasize the role of the growth pressure in suppressing the luminescence background, which is crucial for advancing quantum photonics applications.
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All authors Jacqueline Marböck, Enrique Prado Navarrete, Merve Karaman, Oliver E. Lang, Thomas Fromherz, Maciej O. Liedke, Andreas Wagner, Moritz Brehm, Johannes Aberl

Superconductivity

Nonlinear phononics in LaFeAsO: Optical control of the crystal structure toward possible enhancement of superconductivity

Shu Kamiyama, Tatsuya Kaneko, Kazuhiko Kuroki et al. (+1 more)

Nonlinear phononics provides a route to control crystal structures through light-induced phonon excitation. In this study, we apply nonlinear phononics to an iron-based superconductor, LaFeAsO, with the aim of tuning its crystal structure toward the ideal one to enhance superconductivity. We simulate light-induced phonon dynamics on the anharmonic lattice potential determined by first-principles calculations. We find that the anion height $h$, a key structural parameter in iron-based superconductors, approaches its ideal value when an appropriate infrared-active phonon mode is selectively excited. This result suggests the possibility of controlling crystal structures and enhancing superconductivity in iron-based superconductors based on the concept of nonlinear phononics.
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All authors Shu Kamiyama, Tatsuya Kaneko, Kazuhiko Kuroki, Masayuki Ochi

Mesoscale and Nanoscale Physics

Resolving Single-Peptide Phosphorylation Dynamics in Plasmonic Nanopores using Physics-Informed Bi-Path Model

Mulusew W. Yaltaye, Yingqi Zhao, Kuo Zhan et al. (+2 more)

Protein phosphorylation provides a dynamic readout of cellular signaling yet remains difficult to detect at low abundance and stoichiometry. Single-molecule surface-enhanced Raman spectroscopy (SM-SERS) using particle-in-pore plasmonic nanopores offers label-free molecular detection with submolecular sensitivity. However, reliable identification of subtle post-translational modifications (PTMs) is hindered by the stochastic nature of SM-SERS signals, partial excitation of peptide residues within the plasmonic hotspot, and background interference. Here, we introduce a physics-informed deep learning framework to decode complex SM-SERS dynamics and identify single-peptide PTMs. The model integrates multiple-instance learning with a temporal encoder combining temporal convolutional networks and bidirectional gated recurrent units to capture both local spectral variability and long-range blinking dynamics. To address diffusion-driven spectral heterogeneity, long spectral trajectories are segmented using Pearson-correlation, enabling weakly supervised training under label ambiguity. This framework robustly distinguishes single peptide phosphorylation despite strong background interference and stochastic signal fluctuations. By coupling nanoplasmonic confinement with spatiotemporal deep learning, our approach enables high-fidelity detection of single-molecule phosphorylation events and advances ultrasensitive phosphoproteomic analysis.
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All authors Mulusew W. Yaltaye, Yingqi Zhao, Kuo Zhan, Vahid Farrahi, Jian-An Huang

Disordered Systems and Neural Networks

Projector, Neural, and Tensor-Network Representations of $\mathbb{Z}_N$ Cluster and Dipolar-cluster SPT States

Seungho Lee, Daesik Kim, Hyun-Yong Lee et al. (+1 more)

The $\mathbb{Z}_N$ cluster-state wavefunction, a paradigmatic example of symmetry-protected topological (SPT) order with $\mathbb{Z}_N \times \mathbb{Z}_N$ symmetry, is expressed in various equivalent ways. We identify the projector-based scheme called the $P$-representation as the efficient way to express cluster and dipolar cluster state's wavefunctions. Employing the restricted Boltzmann machine scheme to re-write the interaction matrix in the $P$-representation in terms of neural weight matrices allows us to develop the neural quantum state (NQS) and the matrix product state (MPS) representations of the same state. The NQS and MPS representations differ only in the way the weight matrices are split and grouped together in a matrix product. For both $\mathbb{Z}_N$ cluster and dipolar cluster states, we derive in closed form the weight function $W(s,h)$ that couples physical spins $s$ to hidden variables $h$, generalizing the previous construction for $Z_2$ cluster states to $\mathbb{Z}_N$. For the dipolar cluster state protected by two charge and two dipole symmetries, the procedure we have developed leads to the tensor product state (TPS) representation of the wavefunction where each local tensor carries three virtual indices connecting a given site to two nearest neighbors and one further neighbor. We benchmark the resulting TPS construction against conventional MPS representation using density-matrix renormalization group simulations and argue that the TPS could offer a more efficient representation for some modulated SPT states. As a by-product of the investigation, we generalize the previous $Z_2$ matrix product operator construction of the Kramers-Wannier (KW) operator to $\mathbb{Z}_N$ and interprets it as the dipolar generalization of the discrete Fourier transform on $\mathbb{Z}_N$ variables. The new interpretation naturally explains why the KW map is non-invertible.
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All authors Seungho Lee, Daesik Kim, Hyun-Yong Lee, Jung Hoon Han

Materials Science

Bond-Strength-Based Understanding of Oxygen Vacancy Migration Barriers in Rutile Oxides

Inseo Kim and Minseok Choi

We carry out bond-strength based analysis for the migration barrier ($E_{\rm B}$) of oxygen vacancies in rutile-type 3$d$ transition-metal dioxides by combining density-functional theory (DFT) and the bond-valence model. The covalent and ionic contributions to chemical bonding are explicitly decomposed and quantified by the sum of the integrated crystal orbital Hamilton population ($S_c$) and the Madelung energy ($S_i$), respectively. Both $S_c$ and $S_i$ exhibit strong correlations with the $E_{\rm B}$ from DFT ($E_{\rm B}^{\rm DFT}$), and their average $\bar{S}$ provides a reasonable estimate of $E_{\rm B}^{\rm DFT}$ across the oxide series. Inspired by the bond-valence model, two parameters are extracted by fitting to a large dataset of 3$d$ transition-metal dioxides. Our results show that using these parameters, $E_{\rm B}$ of oxygen vacancies can be efficiently estimated.
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Mesoscale and Nanoscale Physics

Exact Solution for Current-Driven Domain-Wall Dynamics Beyond Lorentz Contraction in Antiferromagnets with Dzyaloshinskii-Moriya Interaction

Mu-Kun Lee, Rubén M. Otxoa and Masahito Mochizuki

We study current-driven domain-wall (DW) dynamics in antiferromagnets (AFMs) with Dzyaloshinskii-Moriya interaction (DMI). We obtain an exact analytical solution for spiral DW dynamics, applicable to both head-to-head DWs under bulk DMI and up-down DWs under interfacial DMI when the magnetic easy axis is aligned with the DMI vector. For the latter case experimentally relevant to synthetic AFMs with in-plane anisotropy, the solution predicts a constant DW velocity driven by nonadiabatic spin-transfer torque together with a steady rotation of the DW tilt angle induced by damping-like spin-orbit torque. Remarkably, the DW width shows unconventional current dependence, either pure elongation or contraction followed by elongation depending on damping and torque parameters, in sharp contrast to the Lorentz-type contraction known for antiferromagnetic (AF) DWs without DMI. These results provide an exact description of current-driven AF-DW dynamics and suggest experimentally accessible signatures of DMI-modified DW dynamics in synthetic AFMs.
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Superconductivity

Directional Andreev-Reflection Signatures of Inter-Orbital Pairing in Sr$_2$RuO$_4$

G. Csire, Y. Fukaya, M. Cuoco et al. (+6 more)

Unconventional superconductivity in quasi–two-dimensional systems is commonly identified through the emergence of Andreev bound states (ABS) at in-plane edges, while surfaces perpendicular to out-of-plane direction remain fully gapped due to weak interlayer coherence. This directional anisotropy has long served as a key paradigm for constraining pairing symmetries. Here, we show that Sr$_2$RuO$_4$ exhibits a striking reversal of this behavior. Using edge- and surface-sensitive spectroscopy, we observe pronounced in-gap ABS at surfaces perpendicular to the out-of-plane direction, whereas in-plane edges exhibit a reduced intensity of the in-gap spectral features. We show that this anomalous anisotropy can arise from the inter-orbital character of the superconducting pairing. Both even- and odd-parity inter-orbital pairing channels naturally generate robust surface ABS while suppressing planar edge modes and can also provide a mechanism for the appearance of a horizontal line node. Supported by ab initio and model calculations, including Sr$_2$RuO$_4$/Ag interface reconstructions, our results highlight the possible role of inter-orbital correlations in shaping the spectroscopic response and provide constraints on the structure of the superconducting order parameter in Sr$_2$RuO$_4$.
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All authors G. Csire, Y. Fukaya, M. Cuoco, Y. Tanaka, R.K. Kremer, A.S. Gibbs, G.A. Ummarino, D. Daghero, R.S. Gonnelli