Disordered Systems and Neural Networks · Cross-listed from quant-ph
Optimizing the dynamical preparation of quantum spin lakes on the ruby lattice
DinhDuy Vu, Dominik S. Kufel, Jack Kemp et al. (+3 more)
Quantum spin liquids are elusive long-range entangled states. Motivated by experiments in Rydberg
quantum simulators, recent excitement has centered on the possibility of dynamically preparing a state with
quantum spin liquid correlation even when the ground state phase diagram does not exhibit such a topological phase. Understanding the microscopic nature of such
quantum spin "lake" states and their relationship to
equilibrium spin liquid order remains an essential question. Here, we extend the use of approximately symmetric neural
quantum states for real-time
evolution and directly simulate the dynamical preparation in systems of up to $N=384$ atoms. We analyze a variety of
spin liquid diagnostics as a function of the preparation protocol and optimize the extent of the
quantum spin lake thus obtained. In the optimal case, the prepared state shows
spin-
liquid properties extending over half the system size, with a topological
entanglement entropy plateauing close to $\gamma = \ln 2$. We extract two physical length scales $\lambda$ and $\xi$ which constrain the extent of the
quantum spin lake $\ell$ from above and below.
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All authors DinhDuy Vu, Dominik S. Kufel, Jack Kemp, Lode Pollet, Chris R. Laumann, Norman Y. Yao
Strongly Correlated Electrons
Microscopic Theory Revealing Ising Criticality with Distinct Sublattice Orders in Pseudospin-1/2 Chain
Mandev Bhullar, Philip Richard and Hae-Young Kee
The one-dimensional transverse Ising model is a paradigmatic example of
quantum criticality. In
spin-orbit coupled systems, however, effective Ising interactions arise alongside bond-dependent couplings such as Kitaev ($K$) and $\Gamma$ terms in addition to the Heisenberg ($J$) interaction, leading to complex
magnetic orders beyond the pure Ising limit. We first explore how the generic $J-K-\Gamma$ model with four-fold screw
symmetry in a
spin-orbit-entangled pseudospin-1/2 chain manifests via sublattice order, and then test whether field-driven transitions retain Ising universality. We find sublattice-dependent
magnetic order below the critical field and a distinct sublattice pattern persisting above it. Despite these complex
magnetic order structures, the transition remains in the Ising universality class with central charge $c=1/2$. Our work provides a route to the microscopic
Hamiltonian and emergent Ising criticality while allowing microscopic physics of the sublattice orders to manifest at low and high fields. Application to
antiferromagnetic Ising materials such as BaCo$_2$V$_2$O$_8$ is also discussed.
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Statistical Mechanics
Universal spectral correlations in open Floquet systems with localized leaks
Edson M. Signor, Miguel A. Prado Reynoso, Bidhi Vijaywargia et al. (+2 more)
We show that introducing a localized leak in Floquet systems with time-reversal
symmetry leads to universal spectral correlations governed by the non-Hermitian
symmetry class $\mathrm{AI}^{\dagger}$, associated with complex-symmetric Ginibre random
matrices, rather than by the unconstrained Ginibre ensemble. As a concrete example, we analyze the leaky
quantum standard map (L-QSM) of the kicked rotor. Since the closed map exhibits circular orthogonal ensemble (COE) statistics, the open system is naturally compared with the truncated circular orthogonal ensemble (TCOE), which models localized leakage by removing columns from a COE
matrix. We find excellent agreement between the bulk spectral properties of the L-QSM and the TCOE, and demonstrate that their short-range spectral correlations follow the universal statistics of the non-Hermitian
symmetry class $\mathrm{AI}^{\dagger}$. This agreement holds for smaller leak sizes as the
matrices increase, while the COE limit is recovered only when the truncation is smaller than one full column. In contrast to local properties, the global density of states of the L-QSM and the TCOE approaches the Ginibre circular law only when the leakage becomes sufficiently strong.
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All authors Edson M. Signor, Miguel A. Prado Reynoso, Bidhi Vijaywargia, Sandra D. Prado, Lea F. Santos
Statistical Mechanics · Cross-listed from quant-ph
Persistent coherent quantum dynamics in 2D long-range magnets via magnon binding
Vighnesh Dattatraya Naik and Markus Heyl
The dynamics of 2D long-range
quantum magnets represents a current frontier in experimental physics such as in Rydberg atomic systems or trapped ions. In this work we address theoretical challenges in understanding these dynamics by combining large-scale neural
quantum state simulations with an effective theory. Our findings uncover a mechanism for persistent coherent
quantum dynamics and slow relaxation in 2D long-range
quantum magnets. Demonstrated on the 2D transverse-field
quantum Ising model with power-law decaying interactions, we observe long-lived oscillatory behavior after quenching the system from a
ferromagnetic product state. We explain this phenomenon by the formation of
magnon bound states, generated by effective attractive long-range
magnon interactions. Our results highlight a generic mechanism for long-lived
quantum coherence in 2D
quantum magnets that can be directly observed in current
quantum simulation platforms.
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Disordered Systems and Neural Networks
Extreme statistics as a probe of the superfluid to Bose-glass Berezinskii-Kosterlitz-Thouless transition
Jeanne Colbois, Natalia Chepiga, Shaffique Adam et al. (+2 more)
Recent studies of delocalization-localization transitions in disordered
quantum chains have highlighted the role of rare, chain-breaking events that favor localization, in particular for high-energy eigenstates related to many-body localization. In this context, we revisit the random-field XXZ
spin-1/2 chain at zero temperature with
ferromagnetic interactions, equivalent to interacting
fermions or hard-core
bosons in a random potential with attractive interactions. We argue that localization in this model can be characterized by chain-breaking events, which are probed by the extreme values of simple local observables, such as the on-site density or the local magnetization, that are readily accessible in both experiments and numerical simulations. Adopting a bosonic
language, we study the disorder-induced Berezinskii-Kosterlitz-Thouless (BKT)
quantum phase transition from superfluid (SF) to Bose glass (BG), and focus on the strong disorder regime where localization is driven by weak links. Based on high-precision density
matrix renormalization group simulations, we numerically show that extreme local densities accurately capture the BKT transition, even for relatively short chains ranging from a few dozen to a hundred sites. We also discuss the SF-BG transition in the weak disorder regime, where finite-size effects pose greater challenges. Overall, our work seeks to establish a solid foundation for using extreme statistics of local observables, such as density, to probe delocalization-localization transitions in disordered
quantum chains, both in the ground state and at high energy.
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All authors Jeanne Colbois, Natalia Chepiga, Shaffique Adam, Gabriel Lemarié, Nicolas Laflorencie
Quantum Gases
Swimming against a superfluid flow: Self-propulsion via vortex-antivortex shedding in a quantum fluid of light
Myrann Baker-Rasooli, Tangui Aladjidi, Tiago D. Ferreira et al. (+4 more)
A superfluid flows without friction below a critical velocity, exhibiting zero drag force on
impurities. Above this threshold, superfluidity breaks down, and the internal energy is redistributed into incoherent excitations such as
vortices. We demonstrate that a finite-mass, mobile
impurity immersed in a flowing two-dimensional paraxial superfluid of light can swim against the superfluid current when this critical velocity is exceeded. This self-propulsion is achieved by the periodic emission of quantized
vortex-antivortex pairs downstream, which impart an upstream
recoil momentum that results in a net propulsive force. Analogous to biological systems that minimize effort by exploiting wake
turbulence, the
impurity harnesses this
vortex backreaction as a passive mechanism of locomotion. Reducing the
impurity dynamics to the motion of its center of mass and using a point-
vortex model, we quantitatively describe how this mechanism depends on the
impurity geometry and the surrounding flow velocity. Our findings establish a fundamental link between internal-energy dissipation in
quantum fluids and concepts of self-propulsion in active-matter systems, and opens new possibilities for exploiting
vortices for controlled
quantum transport at the microscale.
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All authors Myrann Baker-Rasooli, Tangui Aladjidi, Tiago D. Ferreira, Alberto Bramati, Mathias Albert, Pierre-Élie Larré, Quentin Glorieux
Strongly Correlated Electrons
Origin of superconductivity in bilayer nickelates: a Quantum Monte Carlo study for a sign-problem-free effective model
Xu Zhang
Using determinant
Quantum Monte Carlo, we investigate the interplay between doping, inter-layer tunneling and onsite Hund's coupling in stabilizing superconductivity (SC) in a two-orbital model for the
bilayer nickelate $\text{La}_3\text{Ni}_2\text{O}_7$. With realistic dispersion and for certain values of the interaction parameters, the auxiliary-field-decoupled
fermion Hamiltonian has Kramers anti-
unitary symmetries which guarantee the absence of a sign problem. The same anti-
unitary symmetries can also be used to show there is a second instability towards $(\pi,\pi)$ inter-layer bond order (BO) in the strong interaction limit. We indicate the possible connection between this bond order and the enigmatic density wave state observed in experiment, and clarify the decisive role played by the inter-layer tunneling in the competition between SC and BO. Finally, possible directions on how to enhance the SC transition temperature and stabilize the SC phase are also discussed.
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Strongly Correlated Electrons
Anisotropic scattering rates in strain-tuned Sr$_2$RuO$_4$
Ben Currie, David T. S. Perkins, Evgeny Kozik et al. (+2 more)
Motivated by recent angle-resolved photoemission spectroscopy (ARPES) experiments, we analyze the temperature, frequency, and momentum dependence of the single-particle scattering rate in a model of the $\gamma$-band of Sr$_2$RuO$_4$ under strain, with particular emphasis on the behavior near the Lifshitz transition where the
Fermi energy crosses a single Van Hove point. While the scattering rate is only moderately anisotropic at zero strain, we find that it becomes strongly anisotropic at the Lifshitz point. At the lowest energies, we recover the expected universal behavior: the scattering rate varies (ignoring logarithmic corrections) as $\tau^{-1}\sim \omega $ at the Van Hove point and as $\tau^{-1}\sim \omega^{3/2}$ away from it. At higher energies, however, corrections of order $\omega^2$ become important in both regimes. We show that the experimentally observed behavior $\tau^{-1} \sim \omega^{\alpha}$ with $\alpha \approx 1.4(2)$ at the Van Hove point can be quantitatively explained by a superposition of linear and quadratic contributions to the scattering rate, which are comparable in magnitude at the intermediate energies probed by experiment, rather than in terms of a new universal power law. We further predict a distinctive anisotropy, strain dependence, and a non-monotonic frequency dependence of the scattering rate at a Lifshitz transition, all of which may be directly tested in experiments.
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All authors Ben Currie, David T. S. Perkins, Evgeny Kozik, Joseph J. Betouras, Jörg Schmalian
Materials Science
Phonon-assisted tunneling in Jahn-Teller E$ \times $e impurity centers in crystals
V. Hizhnyakov
Tunnel transitions between various distorted states of
impurity centers in
crystals with the E$ \times $e Jahn-Teller effect are considered, taking into account changes in the dynamics of
phonons caused by this effect. Both linear and quadratic vibrational interactions are taken into account. It was found that
phonon scattering accompanying tunneling leads not only to a broadening of the energy spectrum of the transitions, but also to a deterioration in resonance. The results obtained are consistent with measurements of ultrasonic attenuation in Al2O3:Ni, GaAs:Mn and in GaAs:Cu doped
crystals. A notable feature of E$ \times $e tunneling is the existence of a range of values for quadratic vibration interaction, in which the tunneling remains coherent at sufficiently high temperatures.
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Soft Condensed Matter · Cross-listed from physics.geo-ph
A microstructural rheological model for transient creep in polycrystalline ice
Alex J. Vargas, Ranjiangshang Ran and Justin C. Burton
The slow creep of glacial ice plays a key role in sea-level rise, yet its transient deformation remains poorly understood. Glen's flow law, where strain rate is simply a function of stress, cannot predict the time-dependent creep behavior observed in experiments. Here we present a physics-based rheological model that captures all three regimes of transient creep in polycrystalline ice. The key components of the model are a series of Kelvin-Voigt mechanical elements that produce a power-law (Andrade) creep, and a single viscous element with microstructure and stress dependence that represents reorientation in the polycrystalline grains. The interplay between these components produces a minimum in the strain rate at approximately 1% strain, which is a universal but unexplained feature reported in experiments. Due to its transient nature, the model exhibits fractional power-law exponents in the stress dependence of the strain rate minimum, which has been conventionally interpreted as independent physical processes. Taken together, we provide a compact, mechanistic framework for transient ice rheology that generalizes to other polycrystalline materials and can be integrated into constitutive laws for ice-sheet models.
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Materials Science
A Unified Symmetry Classification of Magnetic Orders via Spin Space Groups: Prediction of Coplanar Even-Wave Phases
Ziyin Song, Ziyue Qi, Chen Fang et al. (+2 more)
Spin space groups (SSGs) impose fundamentally different constraints on
magnetic configurations in real and reciprocal spaces. As a consequence, the correspondence between real-space and momentum-space
spin arrangements is far richer than traditionally assumed. Building on the complete enumeration of SSGs, we develop a systematic,
symmetry-based framework that classifies all possible
spin arrangements allowed by these groups. This unified approach naturally incorporates conventional
magnetic orders, altermagnetism, and p-wave magnetism as distinct
symmetry classes. Crucially, our classification predicts a variety of novel
magnetic phases, highlighted by the discovery of the coplanar even-wave magnet: a state that is non-collinear in real space but hosts a collinear even-wave
spin polarization in k-space. Analysis of a minimal model reveals that this phase is characterized by non-quantized
spin polarization and exhibits a novel mechanism for
symmetry-enforced zero polarization on non-degenerate bands. Extending the framework from bulk
crystals to layer SSGs appropriate for two-dimensional systems, we further predict layered counterparts and provide
symmetry guidelines for designing
bilayer coplanar p-wave and even-wave magnets. We further validate this finding through first-principles calculations and propose CoCrO4 as a promising candidate for its experimental realization, thereby demonstrating the completeness and predictive power of the SSG-based classification of
magnetic orders.
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All authors Ziyin Song, Ziyue Qi, Chen Fang, Zhong Fang, Hongming Weng
Mesoscale and Nanoscale Physics
Non-linear transport in multifold semimetals
Andrea Kouta Dagnino, Xiaoxiong Liu and Titus Neupert
Transport measurements are a powerful way to probe the electronic structure of
quantum materials, but the information they contain is often convoluted. Yet, in particular for simple low-energy fermiologies, and by combining linear and non-linear responses, definite conclusions can be drawn – such as, for instance, in the case of the circular photogalvanic effect in Weyl semimetals. Here, we derive the complete DC transport response functions up to third order in the applied electric field within Boltzmann theory that encode combined information about
quantum geometry and band dispersion. We discuss the responses for multifold
fermions at high-
symmetry momenta in time-reversal symmetric
crystals as well as their reduction by
symmetry constraints. We exemplify in detail the cases of space group $P2_13$ and $I4_132$, which realize different multifold
fermions, and show under which conditions these low-energy excitations can be differentially addressed through their bulk non-linear responses, enabling non-linear valley-tronics. We show that in the latter space group, a purely transverse third order valley current can be produced, leading to an accumulation of electrons of different valleys on opposite surfaces of the material.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Floquet Topological Frequency-Converting Amplifier
Adrian Parra-Rodriguez, Miguel Clavero-Rubio, Philippe Gigon et al. (+3 more)
We introduce a driven-dissipative Floquet model in which a single harmonic oscillator, with both frequency and decay rate modulated, realizes a non-Hermitian synthetic
lattice with an effective electric-field gradient in frequency space. Using the Floquet-Green's function and the doubled
Hamiltonian representation of non-Hermitian
matrices, we show that the linear response of this system is characterized by a local winding number. Nontrivial values of the winding number induce directional amplification in the synthetic dimension, thereby converting input signals to different frequencies. The underlying mode structure is well described by a Jackiw-Rebbi-like continuum theory with Dirac cones and solitonic topological zero modes in synthetic frequency. Our results establish a simple and experimentally feasible route to non-Hermitian topological amplification, naturally implementable in current
quantum technologies such as superconducting
circuits.
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All authors Adrian Parra-Rodriguez, Miguel Clavero-Rubio, Philippe Gigon, Tomás Ramos, Álvaro Gómez-León, Diego Porras
Materials Science
Low Resistance Non-Alloyed Ohmic Contacts to High Al Composition n-type AlGaN
Joseph E. Dill, Xianzhi Wei, Changkai Yu et al. (+6 more)
Ohmic contacts to high (>70%) Al content n-type Al$_x$Ga$_{1-x}$N ultra-wide bandgap
semiconductor layers in nitride electronic and photonic devices are typically fabricated by a lift-off process and high temperature ($>700^\circ$C) thermal alloying. These conditions often result in significant structural deformations of the fabricated structures and impose a harsh thermal budget on all other aspects of the device. Here, we report the fabrication of non-alloyed as-deposited ohmic contacts to 71% n+AlGaN ($E_\text{g}\sim5.4$~eV) with a free carrier concentration of roughly $7\times 10^{19}$~cm$^{-3}$ and a resistivity of 4 - 5.5 m$\Omega$cm (among the lowest reported for Al$_{0.71}$Ga$_{0.29}$N) with linear $I-V$ characteristics and a contact resistivity of $\rho_\text{c}=(4.4\pm1.0)\times10^{-4}$~$\Omega$cm$^2$ (measured at zero voltage). Contacts with this quality are formed by two separate fabrication schemes: (i) metal-first patterning, and (ii) lift-off with an oxygen asher descum prior to metal deposition. Given the low threading dislocation density in the single-
crystal AlN substrate used for epitaxy, the smooth morphology of the contacted epitaxial surface, and the non-alloyed nature of the contacts, this contact resistivity is attributed purely to thermionic field emission through the metal-
semiconductor junction. Contact resistivity extraction at low current injection enables us to model these results using a thermionic field-emission model of contact resistivity, yielding a barrier height for Ti/Al$_{0.71}$Ga$_{0.29}$N of $(0.81\pm0.02)$ eV.
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All authors Joseph E. Dill, Xianzhi Wei, Changkai Yu, Akhansha Arvind, Shivali Agrawal, Debaditya Bhattacharya, Keisuke Shinohara, Debdeep Jena, Huili Grace Xing
Quantum Gases
Low Energy Excitations of a 1D Fermi Gas with Attractive Interactions
Aashish Kafle, Ruwan Senaratne, Danyel Cavazos-Cavazos et al. (+5 more)
The low-energy excitations of a two-component repulsive
Fermi gas confined to one dimension are linear dispersing
spin- and charge-density waves whose respective propagation velocities depend on the strength and sign of their interaction. Quasi-1D
fermions with attractive interaction realize the Luther-Emery
liquid, which exhibits a rich array of phenomena, many of which are qualitatively different from those exhibited by their repulsive counterpart. We use a Feshbach resonance to access attractive interactions with $^6$Li atoms. We measured the
spin and charge dynamic structure factors using Bragg spectroscopy and find that, contrary to repulsive interactions, the
spin wave propagates faster than the charge density wave, thus producing an inversion of the classic
spin-charge separation. We also find that a small
spin polarization strongly suppresses the
spin gap in the measured Bragg spectra. Evidence for pairing are a reduction in
spin correlations with increasing attraction and RF spectra consistent with an atom/molecule mixture.
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All authors Aashish Kafle, Ruwan Senaratne, Danyel Cavazos-Cavazos, Hai-Ying Cui, Thierry Giamarchi, Han Pu, Xi-Wen Guan, Randall G. Hulet
Materials Science
An accurate alternative to hybrid functionals for germanium: DFT+$\alpha$
Abdulgaffar Abdurrazaq, Ruggero Lot, Antoine Jay et al. (+5 more)
The accuracy of bulk property predictions in density functional theory (DFT) calculations depends on the choice of exchange-correlation functional. While the Perdew-Burke-Ernzerhof (PBE) functional systematically overestimates
lattice parameters and strongly underestimates electronic band gaps, hybrid functionals such as Heyd-Scuseria-Ernzerhof (HSE) offer better overall agreement across a broad range of materials. Using germanium as a critical test case, we challenge the ability of both functionals to capture
semiconductor properties. Although HSE improves PBE's gap error, it fails to reproduce germanium's correct $\Gamma$-L indirect and $\Gamma$-$\Gamma$ band gaps simultaneously. Noting that the PBE underestimated energy separation between the 4p valence-band maximum and 4s conduction-band minimum causes unphysical $sp$ mixing, we propose DFT+$\alpha$, a semi-empirical correction scheme applied selectively to 4s-like orbitals. For germanium, DFT+$\alpha$ restores the proper ordering and orbital character of the band edges and yields accurate
lattice constant, bulk modulus, elastic constants and
phonon frequencies at a fraction of hybrid-functional computational cost.
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All authors Abdulgaffar Abdurrazaq, Ruggero Lot, Antoine Jay, Gabriela Herrero-Saboya, Nicolas Richard, Layla Martin-Samos, Anne Hémeryck, Stefano de Gironcoli
Statistical Mechanics
Langevin equation with potential of mean force: The case of anchored bath
Alex V. Plyukhin
The potential of mean force (PMF) is an effective average potential acting on an open system, renormalized due to the interaction with the surrounding thermal bath. The PMF determines the correction to the
equilibrium Gibbs distribution, but it is generally unclear how to implement the concept for time-dependent phenomena described by a (generalized) Langevin equation. We study a model where the system is a single particle (so there are no complications related to internal forces) and a non-trivial PMF is due to the presence of on-site (anchor) potentials applied to the bath particles. We found that the PMF does not merely replace the external potential, but also makes the dissipation kernel and statistical properties of noise dependent on the system's position. That dependence is determined by the internal bath and system-bath interactions and is a priori unknown. Therefore, in the general case the Langevin equation with the PMF is not closed and thus inoperable. However, for systems with linear forces the aforementioned dependence on the system's position is canceled. As an example, we consider a model where the bath is formed by the Klein-Gordon chain, i. e. a harmonic chain with on-site harmonic potentials. In that case, the generalized Langevin equation has the standard form with an external potential replaced by a quadratic PMF.
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Statistical Mechanics
Commissioning of an experiment for thermodynamic and spectroscopic studies of hydrogen isotopologues at cryogenic conditions
Joshua Kohpeiß, Dominic Batzler, Beate Bornschein et al. (+7 more)
To study thermodynamic properties and dynamic phase space behavior of hydrogen isotopologues (Q$_2$) at cryogenic temperatures and at high density, the Tritium Absorption InfraRed Spectroscopy 2 (T$_2$ApIR) experiment has been set up and commissioned at Tritium Laboratory Karlsruhe (TLK). In the frame of the experiment, Q$_2$ behavior in different phases, ortho/para states, temperatures (10 K - 300 K) and pressures (up to 2.5 bar a) will be investigated with optical methods, infrared and Raman spectroscopy. The facility consists of a fully tritium compatible cryostat, which includes an optical
cell, ortho/para converter and windows for optical and spectroscopic studies. The cryostat can be cooled below the H$_2$ triple point by a two-stage cryocooler and contains openings in the cryogenic shielding for the optical access. The challenge of combining these scientific requirements in a design with high amounts of tritium (14 g), in a limited space, all while maintaining the TLK safety philosophy was solved by the presented design. The experiment is ready to be fully integrated into the TLK closed loop tritium infrastructure. This contribution reports a comprehensive overview of the commissioning phase of the experimental facility and the results of the first commissioning experiments, including cryogenic performance tests, commissioning experiments with non-radioactive gases, and tests of the analytical instruments.
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All authors Joshua Kohpeiß, Dominic Batzler, Beate Bornschein, Lutz Bornschein, Robin Größle, Daniel Kurz, Ralph Lietzow, Alexander Marsteller, Michael Sturm, Stefan Welte
Superconductivity
Dominant Excitonic Superconductivity in a Three-component Hubbard Chain
Sheng Chen, Qiao Yang, Wéi Wú et al. (+1 more)
Understanding superconductivity emerging from repulsive
fermions remains a major challenge in condensed matter physics. In this paper, we investigate the pairing tendencies in a one-dimensional, three component repulsive Hubbard model, using the density
matrix renormalization group method. At half-filling, the system exhibits density wave ground state due to strong Hubbard repulsions. Upon doping, we find that Cooper pairs can emerge, whose fluctuations predominate the long-range physics in the system across a wide parameter range. The effective attractions between Cooper pairs are mediated by the particle-hole fluctuations in the third non-pairing component, resembling an excitonic mechanism of superconductivity. The coexistence of multiple density waves and superconductivity at different
fermion fillings is explored. We also present an analytical study of the pairing mechanism in both weak and strong coupling limits. Our results provide a new perspective for understanding and exploring unconventional superconductivities in strongly correlated fermionic systems.
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All authors Sheng Chen, Qiao Yang, Wéi Wú, Fadi Sun
Materials Science
Molybdenum Disulfide Bilayers Hybridized with Reduced Graphene Oxide Nanosheets for Enhanced Hydrogen Evolution Reaction
Bruno Ferreira Brischi, Gabriela Frajtag, João Pedro da Silva Mariano et al. (+6 more)
Two-dimensional (2D) molybdenum disulfide (MoS2) nanosheets have attracted
attention as a promising and cost-effective alternative catalyst for the hydrogen
evolution reaction (HER). However, their aggregation and poor conductivity limit their catalytic activity. Consequently, researchers are exploring ways to improve the conductivity and density of electroactive edges of MoS2 through hybridization with akin advanced 2D materials. Here, reduced
graphene oxide (rGO) nanosheets are added to a
liquid-phase-exfoliated MoS2 dispersion to create drop-casting hybrid MoS2@rGO electrodes for HER. The findings reveal the formation of ~1.1 nm-thick MoS2
bilayers, with the catalytic performance of MoS2@rGO dependent on the degree of
graphene oxide reduction. The rGO moderate reduction prevents the MoS2
bilayers from restacking, improves conductivity, retains oxygenated groups that enhance interlayer spacing, and exposes more electroactive edges. When hybridized with rGO crafted at optimal reduction time, the hybrid system eclipses the efficiency of pristine MoS2
bilayers by attaining the lowest overpotential (~70 mV) and the lowest Tafel slope (~46 mV dec-1). This shows that MoS2
bilayers hybridized with rGO offer a promising method to outperform the electrocatalytic efficiency of MoS2-based electrodes. These findings expand opportunities for future strain engineering, defect engineering, and high-end twist-angle assemblies for hybrid systems combining MoS2
bilayers and rGO.
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All authors Bruno Ferreira Brischi, Gabriela Frajtag, João Pedro da Silva Mariano, Laís Fernanda Medeiros Ruela, Gustavo Duarte Verçosa, Camila Desiderio Fernandes, Murilo Santhiago, Letícia Mariê Minatogau Ferro, Leandro Merces
Strongly Correlated Electrons
Triangular $J_1$-$J_2$ Heisenberg Antiferromagnet in a Magnetic Field
Thomas Bader, Shi Feng, Sasank Budaraju et al. (+3 more)
The behavior of the paradigmatic $J_1-J_2$ triangular
lattice Heisenberg antiferromagnet in a
magnetic field remains unsettled despite decades of study. We map out the phase diagram using three complementary approaches, including self-consistent nonlinear
spin-wave theory, density-
matrix renormalization group, and variational Monte Carlo. This combined analysis resolves the competition among different field-induced
magnetic orders and magnetization plateaux across the classically frustrated parameter range. In particular, there is a finite range in the parameter regime around $J_2/J_1=\frac{1}{8}$ in which i) upon the application of the external field, the gapless
quantum spin liquid acquires a finite density of monopoles, and ii) by further increasing the field, two plateaux are clearly obtained at $m=\frac{1}{3}$ and $m=\frac{1}{2}$. We discuss the experimental importance of the consecutive magnetization plateaux transitions as a signature of an underlying
quantum spin-
liquid phase.
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All authors Thomas Bader, Shi Feng, Sasank Budaraju, Federico Becca, Johannes Knolle, Frank Pollmann
Statistical Mechanics
Spontaneous Ratchet Currents and Transition Dynamics in Active Wetting
Noah Grodzinski, Robert L. Jack and Michael E. Cates
Self-propelled particles accumulate on repulsive barriers in so-called active wetting, whose relationship with
equilibrium wetting remains unclear. Using an exact (noiseless) hydrodynamic framework for an active
lattice gas, we show, using a slit geometry with periodic boundary conditions, that active matter exhibits both fully-wet and partially-wet states, with a critical wetting transition between them. Furthermore, we demonstrate the existence of a spontaneous-
symmetry-breaking ratchet current in the partially-wet state, leading to departure of the bulk densities from their binodal values and the emergence of a novel dynamical pathway for the full-to-partial wetting transition. We elucidate this modified dynamical pathway using a minimal model. The results, while establishing a direct connection between active and
equilibrium wetting, also identify the nonequilibrium consequences of activity.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Non-abelian quantum double models from iterated gauging
David Blanik and José Garre-Rubio
We reconstruct all (2+1)D
quantum double models of finite groups from their boundary
symmetries through the repeated application of a gauging procedure, extending the existing construction for abelian groups. We employ the recently proposed categorical gauging framework, based on
matrix product operators (MPOs), to derive the appropriate gauging procedure for the $\mathsf{Rep}\, G$
symmetries appearing in our construction and give an explicit description of the dual emergent $G$
symmetry, which is our main technical contribution. Furthermore, we relate the possible gapped boundaries of the
quantum double models to the
quantum phases of the one-dimensional input state to the iterated gauging procedure. Finally, we propose a gauging procedure for 1-form $\mathsf{Rep}\, G$
symmetries on a two-dimensional
lattice and use it to extend our results to the construction of (3+1)D
quantum doubles models through the iterative gauging of (2+1)-dimensional
symmetries.
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Soft Condensed Matter
Two-phase hydrodynamic model of active colloid motion
A. Kiverin, S. Luguev and I. Yakovenko
The paper presents a two-phase hydrodynamic model for the numerical simulation of collective motion in a thin layer of active colloids containing spherical microswimmers. The model accounts for three fundamental mechanisms governing the dynamics of the active colloid: the random motion of the microswimmers, their mutual collisions, and their interaction with the surrounding fluid phase. The accurate resolution of the characteristic time scales associated with each mechanism is crucial for reproducing the different dynamic modes. The model reproduces two primary modes of motion: Brownian and collective, as well as the transition between them. It is demonstrated that hydrodynamic interactions begin to play a significant role when the microswimmer velocity exceeds a critical threshold. At this point, the kinetic energy transferred to the fluid phase is sufficient to generate a noticeable feedback effect on the swimmers' motion. Conversely, a further increase in microswimmers' velocity enhances the role of collisions, causing the system to revert from a collective mode back to a Brownian-like state. A similar transition occurs at higher volume fractions of microswimmers within the colloid.
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Quantum Gases
Fluctuation-Induced Supersolidity at the Superfluid-Solid Interface
Baptiste Coquinot, Ragheed Alhyder, Alberto Cappellaro et al. (+1 more)
Supersolidity, combining superfluid and crystalline orders, has been realized in dipolar Bose-Einstein condensates by tuning interatomic interactions. Here we show that supersolidity can also emerge from mode coupling at a superfluid-solid interface, without modifying bulk interactions and for a broad class of superfluids. Using an analytical and numerical treatment of the coupled superfluid and
phonon fields, we derive the criterion for a density-modulation instability driven by interfacial coupling and dependent on dimensionality. In superfluid helium, the instability first appears at the roton mode, while in a Bose-Einstein condensate with contact interactions it occurs at the lowest accessible wave vector set by the system size. Beyond the threshold, the ground state acquires an interfacial density modulation while the bulk remains superfluid, forming a hybrid superfluid-supersolid phase. Our results identify interfacial mode coupling as a promising route to supersolidity, enabling the simultaneous exploitation of interfacial supersolid and bulk superfluid
quantum properties.
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All authors Baptiste Coquinot, Ragheed Alhyder, Alberto Cappellaro, Mikhail Lemeshko
Strongly Correlated Electrons
Disentangling the unusual magnetic anisotropy of the near-room-temperature ferromagnet Fe$_{4}$GeTe$_{2}$
Riju Pal, Joyal J. Abraham, Alexander Mistonov et al. (+9 more)
In the quest for two-dimensional conducting materials with high
ferromagnetic ordering temperature the new family of the layered Fe$_{n}$GeTe$_{2}$ compounds, especially the near-room-temperature ferromagnet Fe$_{4}$GeTe$_{2}$, receives a significant
attention. Fe$_{4}$GeTe$_{2}$ features a peculiar
spin reorientation transition at $T_\mathrm{SR} \sim 110$ K suggesting a non-trivial temperature
evolution of the
magnetic anisotropy (MA) - one of the main contributors to the stabilization of the
magnetic order in the low-D systems. An electron
spin resonance (ESR) spectroscopic study reported here provides quantitative insights into the unusual
magnetic anisotropy of Fe$_{4}$GeTe$_{2}$. At high temperatures the total MA is mostly given by the demagnetization effect with a small contribution of the counteracting intrinsic
magnetic anisotropy of an easy-axis type, whose growth below a characteristic temperature $T_{\rm shape} \sim 150$ K renders the sample seemingly isotropic at $T_\mathrm{SR}$. Below one further temperature $T_{\rm d} \sim 50$ K the intrinsic MA becomes even more complex. Importantly, all the characteristic temperatures found in the ESR experiment match those observed in transport measurements, suggesting an inherent coupling between
magnetic and electronic degrees of freedom in Fe$_{4}$GeTe$_{2}$. This finding together with the observed signatures of the intrinsic two-dimensionality should facilitate optimization routes for the use of Fe$_{4}$GeTe$_{2}$ in the magneto-electronic devices, potentially even in the monolayer limit.
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All authors Riju Pal, Joyal J. Abraham, Alexander Mistonov, Swarnamayee Mishra, Nina Stilkerich, Suchanda Mondal, Prabhat Mandal, Atindra Nath Pal, Jochen Geck, Bernd Büchner, Vladislav Kataev, Alexey Alfonsov
Materials Science
Computational Screening and Discovery of Silver-Indium Halide Double Salts
Christos Tyrpenou, G. Krishnamurthy Grandhi, Paola Vivo et al. (+2 more)
Perovskite-inspired materials have emerged as promising candidates for both outdoor and indoor photovoltaic applications owing to their favorable optoelectronic properties and reduced toxicity. Here, we employ the experimentally realized AgBiI$_4$ double salt as a structural prototype and replace Bi$^{3+}$ with In$^{3+}$ to design a novel lead-free halide compound, AgInI$_4$. First-principles calculations predict that AgInI$_4$ is both chemically and dynamically stable, exhibiting a direct band gap of 1.72 eV, comparable to its bismuth analogue. However, its predicted photovoltaic performance, evaluated using the spectroscopic limited maximum efficiency metric, is lower under both
solar and LED illumination. This reduction arises primarily from
symmetry-forbidden optical transitions and the absence of Bi-derived 6s$^2$ lone-pair states at the valence band maximum. High-throughput screening of the Ag-In-I ternary phase-space reveals several more stable and metastable compounds that fall into two structural families: tetrahedrally and octahedrally coordinated, with characteristic band gaps near 3.0 eV and 2.0 eV, respectively. Despite multiple synthetic attempts, the predicted AgInI$_4$ phase could not be experimentally realized, underscoring the challenges of stabilizing indium-based halide double salts. While these materials are unlikely to serve as efficient photovoltaic absorbers, their tunable band gaps and stability make them promising candidates for charge transport and other optoelectronic applications.
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All authors Christos Tyrpenou, G. Krishnamurthy Grandhi, Paola Vivo, Mikaël Kepenekian, George Volonakis
Materials Science · Cross-listed from physics.app-ph
Reducing dislocation defect levels via sub-melt nanosecond pulsed-laser induced densification of diamond
Adam H. Khan, Tae Sung Kim, Gabe Guss et al. (+4 more)
Dislocations and polishing-induced defect networks in synthetic diamond generate local strain fields that broaden Raman features and limit optical, thermal, and electronic performance. Sub-melt
laser annealing has emerged as a route to repair near-surface defects without graphitization, yet quantitative evidence of densification, defect depletion, and property recovery remains limited. Here, we show that nanosecond pulsed-
laser annealing (PLA) can relax dislocation-associated strain in single-
crystal CVD diamond by compacting and reorganizing the damaged near-surface region. Single- and two-pulse PLA were applied, and structural
evolution was quantified using co-registered ISO 25178 white-light interferometry, depth-resolved Raman spectroscopy, and cross-sectional STEM with
geometric phase analysis (GPA). Across a 5x6 grid(n = 30), responsive regions show large reductions in local slope (Sdq 45-65%), developed area (Sdr 60-90%), height spread (Sp, Sz 30-65%), void volume (Vv 57-60%), and roughness amplitude (Sa, Sq 48-57%), consistent with densification of ~4-6.5 nm. Raman profiling reveals narrowing of the diamond line and improved spectral uniformity to depths of ~2-3 {\mu}m, indicating relaxation of dislocation-mediated strain beyond the compaction layer. STEM-GPA strain maps confirm smoother strain fields, reduced hotspots, and redistribution of localized strain concentrations after PLA. These results show that sub-melt PLA reduces dislocation-driven strain by compacting surface-connected free volume and reorganizing defect networks. The approach provides a scalable path to upgrade industrial-grade diamond including homoepitaxial, heteroepitaxial, and polycrystalline CVD to low-defect, device-ready surfaces relevant to high-power electronics, photonics, and
quantum substrates.
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All authors Adam H. Khan, Tae Sung Kim, Gabe Guss, Ted A. Laurence, Sonny S. Ly, Thejaswi U. Tumkur, Afaq H. Piracha
Strongly Correlated Electrons
Diffusion and relaxation of topological excitations in layered spin liquids
Aprem P. Joy, Roman Lange and Achim Rosch
Relaxation processes in topological phases such as
quantum spin liquids are controlled by the dynamics and interaction of fractionalized excitations. In layered materials hosting two-dimensional topological phases, elementary quasiparticles can diffuse freely within the layer, whereas only pairs (or more) can hop between layers - a fundamental consequence of topological order. Using exact solutions of emergent nonlinear
diffusion equations and particle-based
stochastic simulations, we explore how pump-probe experiments can provide unique signatures of the presence of $2d$ topological excitations in a $3d$ material. Here we show that the characteristic time scale of such experiments is inversely proportional to the initial excitation density, set by the pump intensity. A uniform excitation density created on the surface of a sample spreads subdiffusively into the bulk with a mean depth $\bar z$ scaling as $\sim t^{1/3}$ when annihilation processes are absent. The propagation becomes logarithmic, $\bar z \sim \log t$, when pair-annihilation is allowed. Furthermore, pair-
diffusion between layers leads to a new decay law for the total density, $n(t) \sim (\log^2 t)/t$ - slower than in a purely $2d$ system. We discuss possible experimental implications for pump-probe experiments in samples of finite width.
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Quantum Gases · Cross-listed from quant-ph
Geometry-driven transitions in sparse long-range spin models with cold atoms
Alex Gunning, Aydin Deger, Sridevi Kuriyattil et al. (+1 more)
We explore the influence of geometry in the critical behavior of sparse long-range
spin models. We examine a model with interactions that can be continuously tuned to induce distinct changes in the metric,
topology, and dimensionality of the coupling graph. This underlying geometry acts as the driver of criticality, with structural changes in the graph coinciding with and dictating the phase boundaries. We further discuss how this framework connects naturally to realizations in tweezer arrays with Rydberg excitations. In certain cases, the effective geometry can be incorporated in the layout of atoms in tweezers to realize phase transitions that preserve universal features, simplifying their implementation in near-term experiments.
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All authors Alex Gunning, Aydin Deger, Sridevi Kuriyattil, Andrew J. Daley