Mesoscale and Nanoscale Physics
Direct visualization of gate-tunable flat bands in twisted double bilayer graphene
Souvik Sasmal, Ryan Muzzio, Ahmed Khalifa Paulina Majchrzak et al. (+10 more)
The
symmetry-broken correlated states in twisted double
bilayer graphene (TDBG) can be tuned via several external knobs, including twist angle, displacement field, and carrier density. However, a direct, momentum-resolved characterization of how these parameters reshape the flat-band structure remains limited. In this study, we employ micro focused angle-resolved photoemission spectroscopy to investigate the flat-band dispersion of TDBG at a twist angle of 1.6, systematically varying the displacement field and carrier density via electrostatic gating. We directly observe multiple flat moir'e minibands near charge neutrality, including a flat remote valence band residing below the low-energy flat-band
manifold. Furthermore, the dominant Coulomb repulsive energy over the flat- band bandwidth suggests favorable conditions for the emergence of interaction-driven correlated phenomena in TDBG. These findings establish that the formation and
evolution of flat bands in TDBG arises from the interplay between the electron filling and the displacement field.
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All authors Souvik Sasmal, Ryan Muzzio, Ahmed Khalifa Paulina Majchrzak, Alfred J.H. Jones, I-Hsuan Kao Kenji Watanabe, Takashi Taniguchi, Simranjeet Singh, Eli Rotenberg, Aaron Bostwick, Chris Jozwiak, Søren Ulstrup, Shubhayu Chatterjee, Jyoti Katoch
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Twisted Superconducting Quantum Diodes for High Fidelity Anharmonic Qubits
Han Zhong, Denis Kochan, Igor Zutic et al. (+1 more)
In superconducting
circuits, bidirectional signal propagation can cause back-reflections and back-action that couple environmental noise back to coherent elements, degrading fidelity. Nonreciprocal superconducting diodes provide an intrinsic route to suppress such backscattering at the
circuit level. However, their diode efficiency and
quantum integration remain limited. Here, we realize a
quantum diode in twisted NbSe2 under in-plane and out-of-plane
magnetic fields. A mere 1 degree twist yields an efficiency enhancement over pristine devices, reaching 27.6 percent.
Quantum simulations reveal that this intermediate efficiency, well below 100 percent ideal, is both experimentally practical and optimal for preserving
qubit anharmonicity and stabilizing two-level systems. These findings show that maximal rectification is not always beneficial for
quantum information, establishing a new principle for designing the fundamental properties of twisted
superconductors towards low-power, high-fidelity
quantum circuits.
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All authors Han Zhong, Denis Kochan, Igor Zutic, Yingying Wu
Superconductivity · Cross-listed from physics.optics
The Eckhaus instability: from initial to final stages
Michael I. Tribelsky
A systematic analysis of the Eckhaus instability in the one-dimensional Ginzburg-Landau equation is presented. The analysis is based on numerical integration of the equation in a large (xt)-domain. The initial conditions correspond to a stationary, unstable spatially periodic solution perturbed by "noise." The latter consists of a set of spatially periodic modes with small amplitudes and random phases. The
evolution of the solution is examined by analyzing and comparing the dynamics of three key characteristics: the solution itself, its spatial spectrum, and the value of the Lyapunov functional. All calculations exhibit four distinct, mutually agreed, well-defined regimes: (i) rapid decay of stable perturbations; (ii) latent changes, when the solution and the Lyapunov functional undergo minimal alterations while the
Fourier spectrum concentrates around the most unstable perturbations; (iii) a phase-slip period, characterized by a sharp decrease in the Lyapunov functional; (iv) slow relaxation to a final stable state.
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Materials Science
Atomic displacements drive flat band formation and lateral electron and hole separation in near-60 degree twisted MoSe2/WSe2 bilayers
Madeleine Phillips and C. Stephen Hellberg
Transition metal dichalcogenide (TMD)
bilayers with an interlayer twist exhibit a moire super-period, whose effects can manifest in both structural and electronic properties. Atomic displacements can lead to reconstruction into domains of aligned stacking, and flat bands can form that may host correlated electron states. In heterobilayers angular mismatch is nearly unavoidable, so understanding the consequences of an interlayer twist is essential. Using ab initio density functional theory, we find that in near-60 degree twisted MoSe2/WSe2
bilayers valence and conduction band flat bands emerge at ~3 degree twist. Despite relatively limited reconstruction at these angles, atomic displacement creates a polarization gradient that forms a confining potential, localizing and laterally separating electrons and holes within the moire supercell.
Excitons formed from flat band electrons and holes should therefore have not only the out-of-plane dipole moment familiar from MoSe2/WSe2 interlayer
excitons, but an in-plane dipole moment as well.
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Mesoscale and Nanoscale Physics
Universal valley filtering via uniform dissipation and velocity contrast
Sijie Yue, Wentao Xie, Kai Shao et al. (+6 more)
Valley, as a ubiquitous degree of freedom in
lattices, has found wide applications in both electronic and classical-wave devices in recent years. However, achieving valley-polarized states, a prerequisite for valley-based operations, still remains challenging. Here, we propose and experimentally demonstrate a universal non-Hermitian mechanism for valley filtering using only uniform background dissipation, which creates a propagation length contrast between valleys through their intrinsic group velocity differences. We implement this concept in an acoustic
crystal, observing switchable and robust valley polarization of sound through large-scale field mapping. Remarkably, our approach is solely based on uniform loss, without the need for any special
lattice structures, tailored excitations, or external fields. We further provide designs of our non-Hermitian valley filter on photonic and electronic platforms. Our results offer a simple and effective solution to valley-polarized state generation and may advance the development of novel valley-based devices in both classical and
quantum regimes.
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All authors Sijie Yue, Wentao Xie, Kai Shao, Hong-yu Zou, Bingbing Wang, Hong-xiang Sun, Y. X. Zhao, Wei Chen, Haoran Xue
Statistical Mechanics
Time crystalline solitons and their stochastic dynamics in a driven-dissipative \phi^4 model
Xingdong Luo and Zhizhen Chen
Periodically driven systems provide unique opportunities to investigate the dynamics of topological excitations far from
equilibrium. In this paper, we report a time-crystalline
soliton (TCS) state in a driven-dissipative $\phi^4$ model. This state exhibits spontaneous breaking of discrete time-translational
symmetry while simultaneously displaying spatial
soliton behavior. During time
evolution, the
soliton pattern periodically oscillates between kink and anti-kink configurations. We further study TCS dynamics under noise, demonstrating that
soliton random walk can induce a dynamical transition between two distinct $Z_2$
symmetry-breaking time-crystalline phases in time domain. Finally, we examine the annihilation of two spatially separated TCSs under noise. Importantly, in contrast to the confined behavior of time-crystalline monopoles reported in [Phys. Rev. Lett. 131, 056502 (2023)], the dynamics of time-crystalline
solitons is deconfined despite the nonequilibrium nature of our model: the statistically averaged annihilation time scales as a power law with the
solitons' initial separation.
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Soft Condensed Matter · Cross-listed from physics.flu-dyn
From Interface Dynamics to Darcy Scale Description of Multiphase Flow in Porous Media
Steffen Berg, Ryan T. Armstrong, Maja Rücker et al. (+3 more)
An outstanding characteristic of porous media, desired in many applications, is the large surface area, which facilitates solid-fluid interactions, making porous media an extreme case in colloid and interface science. In two-fluid systems, wetting and the balance of capillary and viscous forces control fluid displacement processes, leading to a wide range of complex flow regimes with rich spatio-temporal dynamics. Macroscopic two-phase flow is historically described through the phenomenological extensions of Darcy's law. Besides many other shortcomings and inconsistencies, it covers only connected pathway flow in the capillary-dominated flow regime in a rigorous manner while other flow regimes with moving interfaces and associated topological changes are entirely implicit. Given the lack of adequate descriptions, upscaling multiphase flow from pore to Darcy scale represents a long-standing challenge paving into the fields of thermodynamics, statistical mechanics and integral geometry. In this review, we compare novel concepts which have been largely motivated by experimental insights, enabled by significant advances in pore-scale imaging and modeling over the last decade.
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All authors Steffen Berg, Ryan T. Armstrong, Maja Rücker, Alex Hansen, Signe Kjelstrup, Dick Bedeaux
Mesoscale and Nanoscale Physics
Thermal Hall conductivity of semimetallic graphite dominated by ambipolar phonon drag
Qiaochao Xiang, Xiaokang Li, Xiaodong Guo et al. (+2 more)
It is now known that in addition to electrons, other quasi-particles such as
phonons and
magnons can also generate a thermal
Hall signal. Graphite is a semimetal with extremely mobile charge carriers of both signs and a large
lattice thermal conductivity. We present a study of the thermal
Hall effect in highly oriented pyrolytic graphite (HOPG) samples with electronic, phononic and
phonon drag contributions to the thermal
Hall signal. The measured thermal
Hall conductivity ($\kappa_{xy}$) is two orders of magnitude higher than what is expected by electronic carriers according to the electrical
Hall conductivity and the Wiedemann-Franz law, yielding a record
Hall Lorenz number of $164.9\times10^{-8}V^2 K^{-2}$ ($\sim$67$L_0$) - the largest ever observed in a metal. The temperature dependence of the thermal
Hall conductivity significantly differs from its longitudinal counterpart, ruling out a purely phononic origin of the non-electronic component. Based on the temperature dependence and the amplitudes of the Seebeck and Nernst responses, we demonstrate that ambipolar
phonon drag dominates the thermal
Hall response of graphite.
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All authors Qiaochao Xiang, Xiaokang Li, Xiaodong Guo, Zengwei Zhu, Kamran Behnia
Other Condensed Matter
Triple-core structure of the double-core vortex in superfluid $^3$He-B
Riku Rantanen
The order parameter of superfluid $^3$He involves nine complex components, and the multicomponent structure allows quantized
vortices in superfluid $^3$He to have complicated cores. One of the
vortices found in the B phase is the double-core
vortex, which has been often described as a pair of two half-
quantum vortices (HQVs) connected by a domain wall. Our numerical calculations of the core structure suggest an alternative representation of the
vortex as a combination of three
vortices, one in each component of the
spin-triplet superfluid. Based on the results we present a qualitative analytical model for the triple-core structure of the double-core
vortex. Additionally we numerically calculate the structure of a double-core
vortex stretched between pinning sites, and show that the HQV picture becomes more applicable when separation between subcores becomes large.
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Disordered Systems and Neural Networks
Demonstrating Real Advantage of Machine-Learning-Enhanced Monte Carlo for Combinatorial Optimization
Luca Maria Del Bono, Federico Ricci-Tersenghi and Francesco Zamponi
Combinatorial optimization problems are central to both practical applications and the development of optimization methods. While classical and
quantum algorithms have been refined over decades, machine learning–assisted approaches are comparatively recent and have not yet consistently outperformed simple, state-of-the-art classical methods. Here, we focus on a class of Quadratic Unconstrained Binary Optimization (QUBO) problems, specifically the challenge of finding minimum energy configurations in three-dimensional Ising
spin glasses. We use a Global Annealing Monte Carlo
algorithm that integrates standard local moves with global moves proposed via machine learning. We show that local moves play a crucial role in achieving optimal performance. Benchmarking against Simulated Annealing and Population Annealing, we demonstrate that Global Annealing not only surpasses the performance of Simulated Annealing but also exhibits greater robustness than Population Annealing, maintaining effectiveness across problem hardness and system size without hyperparameter tuning. These results provide clear and robust evidence that a machine learning–assisted optimization method can exceed the capabilities of classical state-of-the-art techniques in a combinatorial optimization setting.
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Quantum Gases
Quantum Monte Carlo study of low-dimensional Fermi fluids of dipolar atoms
Clio Johnson, Neil D. Drummond, James P. Hague et al. (+1 more)
Fermionic cold atoms in optical traps provide viable
quantum simulators of correlation effects in electronic systems. For dressed Rydberg atoms in two-dimensional traps with out-of-plane dipole moments, a realistic model of the pairwise interaction is of repulsive dipolar $1/r^3$ form at long range, softened to a constant at short range. This study provides parameterizations of fixed-node
diffusion Monte Carlo energy data for
ferromagnetic (one-component) and paramagnetic (two-component) two-dimensional homogeneous
Fermi fluids of interacting dipolar atoms. We find itinerant ferromagnetism to be unstable within our parameter spaces for dipolar interactions both with and without softening. Our parameterization of the energy as a function of density will enable density functional theory to support experimental studies of inhomogeneous fermionic cold atom systems.
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All authors Clio Johnson, Neil D. Drummond, James P. Hague, Calum MacCormick
Strongly Correlated Electrons
Applied electric and magnetic field effects on the bandgap formation and antiferromagnetic ordering in AA-stacked Bilayer Graphene
V.Apinyan and T. Kopeć
In this study, we consider a two-layer
graphene structure stacked in the AA form and exposed to the influence of two different electric fields applied to different layers. The
graphene layers are also subjected to an external
magnetic field perpendicular to the planes of the layers. We investigate the possible effects of the applied in-plane fields and the
magnetic field on excitonic pairing,
antiferromagnetic order, and the chemical potential. Simultaneously, we analyze the effects of the interlayer Coulomb interaction potential on the physical properties of the considered system. We demonstrate that the application of planar electric fields leads to the formation of an unusually large bandgap in the electronic band structure, which is not typical for AA-stacked
bilayer graphene. We discuss various values of the applied electric field potentials and show their influence on the electronic band structure of the system. Additionally, we identify the existence of a critical value of the
magnetic field above which Wigner crystallization-like effect is present for the electrons, also affecting the excitonic gap in one
spin channel. The results obtained in this study could be important for applications of AA-stacked
bilayer graphene as a large band-gap material.
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Materials Science
Intrinsic nonlinear Hall effect beyond Bloch geometry
Raffaele Resta
The theory of the intrinsic
Hall effect, both linear and nonlinear, is rooted in a geometry which is defined in the Bloch-vector parameter space; the formal expressions are mostly derived from semiclassical concepts. When disorder and interaction are considered there is no Bloch vector to speak of; one needs a more general
quantum geometry, defined in a different parameter space. The nonlinear
Hall effect is a fundamental
geometric response of the many-body ground state, not a band-structure peculiarity. The higher-level geometrical formulation of the intrinsic
Hall effect provides very compact expressions, which have the additional virtue – in the Bloch special case – of yielding the known results in a straightforward way: the logic is not concealed by the
algebra.
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Disordered Systems and Neural Networks
Fock-space fragmentation in quenches of disordered interacting fermions
Ishita Modak, Rajesh Narayanan, Ferdinand Evers et al. (+1 more)
Fock-space fragmentation, as it is currently investigated, primarily originates from specific kinematic constraints or emergent conservation laws in many-body systems with translation invariance. It leads to non-ergodic dynamics and possible breakdown of the eigenstate thermalization hypothesis. Here, we demonstrate that also in disordered systems, such as the XXZ model with random on-site fields, fragmentation appears as a natural concept offering fresh perspectives, for example, on many-body localization (MBL). Specifically, for a given quenched initial state, we identify a potential-energy shell in Fock space, defined by its energy and energy uncertainty, which represents the energetically accessible part of the many-body configuration space. For example, the drastic sample-to-sample fluctuations observed in the weak disorder regime, $W<W_{\mathrm{frag}}$, represent fluctuations of the mass of the shell. Upon increasing disorder, the potential-energy shell becomes increasingly fragmented. Its finite-size
evolution exhibits a turnaround flow; extrapolating this flow to the disorder at which the turnaround vanishes provides a heuristic estimate of the strong-fragmentation scale $W_{\mathrm{frag}}$. We
conjecture that the fragmentation identified here provides a
geometric mechanism contributing to the finite-time slowing down of relaxation observed in studies of disordered interacting systems.
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All authors Ishita Modak, Rajesh Narayanan, Ferdinand Evers, Soumya Bera
Mesoscale and Nanoscale Physics · Cross-listed from physics.chem-ph
Mechanism of the electrochemical hydrogenation of graphene
Y.-C. Soong, H. Li, Y. Fu et al. (+17 more)
The electrochemical hydrogenation of
graphene induces a robust and reversible conductor-
insulator transition, of strong interest in logic-and-
memory applications. However, its mechanism remains unknown. Here we show that it proceeds as a reduction reaction in which
proton adsorption competes with the formation of H2 molecules via an Eley-Rideal process.
Graphene's electrochemical hydrogenation is up to $10^6$ times faster than alternative hydrogenation methods and is fully reversible via the oxidative desorption of
protons. We demonstrate that the
proton reduction rate in defect-free
graphene can be enhanced by an order of magnitude by the introduction of nanoscale corrugations in its
lattice, and that the substitution of
protons for deuterons results both in lower potentials for the hydrogenation process and in a more stable compound. Our results pave the way to investigating the chemisorption of ions in 2D materials at high electric fields, opening a new avenue to control these materials' electronic properties.
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All authors Y.-C. Soong, H. Li, Y. Fu, J. Tong, S. Huang, X. Zhang, E. Griffin, E. Hoenig, M. Alhashmi, Y. Li, D. Bahamon, J. Zhong, A. Summerfield, R. N. Costa Filho, C. Sevik, R. Gorbachev, E. C. Neyts, L. F. Vega, F. M. Peeters, M. Lozada-Hidalgo
Strongly Correlated Electrons
Practical algorithm for simulating thermal pure quantum states
Wei-Bo He, Yun-Tong Yang and Hong-Gang Luo
The development of novel
quantum many-body computational
algorithms relies on robust benchmarking. However, generating such
benchmarks is often hindered by the massive computational resources required for exact diagonalization or
quantum Monte Carlo simulations, particularly at finite temperatures. In this work, we propose a new
algorithm for obtaining thermal pure
quantum states, which allows efficient computation of both mechanical and thermodynamic properties at finite temperatures. We implement this
algorithm in our open-source C++ template library, Physica. Combining the improved
algorithm with state-of-the-art software engineering, our implementation achieves high performance and numerical stability. As an example, we demonstrate that for the $4 \times 4$ Hubbard model, our method runs approximately $10^3$ times faster than $\mathcal{H}\Phi$ 3.5.2. Moreover, the accessible temperature range is extended down to $\beta = 32$ across arbitrary doping levels. These advances significantly push forward the frontiers of benchmarking for
quantum many-body systems.
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Soft Condensed Matter
Counting, Computing, and Pattern Recognition with Self-Assembling Non-Reciprocal DNA Tiles
Tim E. Veenstra, René van Roij and Marjolein Dijkstra
Harnessing the intrinsic dynamics of physical systems for information processing opens new avenues for computation
embodied in matter. Using simulations of a model system, we show that assemblies of DNA tiles capable of self-organizing into multiple target structures can perform basic computational tasks analogous to those of finite-state automata when equipped with programmable non-reciprocal interactions that drive controlled dynamical transitions between these structures. By establishing design rules for multifarious self-assembly while budgeting the energy input required to drive these non-
equilibrium transitions, we demonstrate that these systems can execute a wide variety of tasks including counting, computing modulo functions, and recognizing specific input patterns. This framework integrates
memory, sensing, and actuation within a single physical platform, paving the way toward energy-efficient physical computation embedded in materials ranging from DNA and enzymes to
proteins and colloids.
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Materials Science
Active high-entropy photocatalyst designed by incorporating alkali metals to achieve d0+d10+s0 cationic configurations and wide electronegativity mismatch
Jacqueline Hidalgo-Jimenez, Taner Akbay, Tatsumi Ishihara et al. (+1 more)
Photocatalytic hydrogen (H2) production and carbon dioxide (CO2) conversion to methane (CH4) are considered promising solutions for reducing CO2 emissions. However, the development of highly active photocatalysts is essential to efficiently drive these reactions without harming the environment. In this study, we introduce a strategy that incorporates elements with both low and high electronegativities into catalysts based on transition metals, thereby enhancing both reactant adsorption and charge transfer. This strategy is implemented in a high-
entropy oxide (HEO) by adding cesium, an alkali metal with very low electronegativity, and gallium, a metal with high electronegativity, to transition metals titanium, niobium and tantalum. The resulting
oxide, TiNbTaGaCsO9 with a large concentration of oxygen vacancies, exhibits strong light absorption, a low bandgap and a suitable band structure for both hydrogen
evolution and CO2 conversion. Compared to HEOs with only d0 or d0+d10 cationic configurations, the synthesized
oxide with a wide electronegativity difference and mixed d0+d10+s0 cationic configurations shows significantly higher activity for both H2 and CH4 production, even without using a cocatalyst. These results demonstrate a design strategy for creating highly active HEOs containing alkali metals by taking advantage of the electronegativity mismatch across the periodic table.
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All authors Jacqueline Hidalgo-Jimenez, Taner Akbay, Tatsumi Ishihara, Kaveh Edalati
Strongly Correlated Electrons
Discrete Shift and Polarization from Response to Symmetry Defects in Interacting Topological Phases
Lu Zhang, Min Long, Yuxuan Zhang et al. (+2 more)
We extend the previous study of extracting crystalline
symmetry-protected topological invariants to the correlated regime. We construct the interacting Hofstadter model defined on square
lattice with the rotation and translation
symmetry defects: disclination and dislocation. The model realizes Chern
insulator and the charge density wave state as one tunes interactions. Employing the density
matrix renormalization group (DMRG) method, we calculate the excess charge around the defects and find that the topological invariants remain quantized in both phases, with the topological quantity extracted to great precision. This study paves the way for utilizing
matrix product state, and potentially other
quantum many-body computation methods, to efficiently study crystalline
symmetry defects on 2D interacting
lattice systems.
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All authors Lu Zhang, Min Long, Yuxuan Zhang, Zi Yang Meng, Xue-Yang Song
Statistical Mechanics
Monte Carlo study of the $O(2)$-invariant $\phi^4$ theory with a cubic perturbation in three dimensions
Martin Hasenbusch
We study the $2$-component $\phi^4$ model on the simple cubic
lattice in the presence of a cubic, or equivalently, a $\mathbb{D}_4$ invariant perturbation. To this end, we perform Monte Carlo simulations in conjunction with a finite size scaling analysis of the data. We follow previous work on the $3$-component case. We study the RG flow from the decoupled Ising fixed point into the $O(2)$-invariant one and towards the fluctuation induced first order transition. To this end we study the behavior of phenomenological couplings. At the $O(2)$-invariant fixed point we obtain the estimate $Y_4=-0.1118(10)$ of the RG-exponent of the perturbation. Note that the small modulus of $Y_4$ means that the RG flow is slow. Hence, in order to interpret experiments or Monte Carlo simulations of
lattice models, which are effectively described by the $\phi^4$ model with a cubic term, we have to consider the RG flow beyond the neighborhood of the fixed points.
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Statistical Mechanics · Cross-listed from quant-ph
Absence of measurement- and unraveling-induced entanglement transitions in continuously monitored one-dimensional free fermions
Clemens Niederegger, Tatiana Vovk, Elias Starchl et al. (+1 more)
Continuous monitoring of one-dimensional free fermionic systems can generate phenomena reminiscent of
quantum criticality, such as logarithmic
entanglement growth, algebraic correlations, and emergent conformal invariance, but in a nonequilibrium setting. However, whether these signatures reflect a genuine phase of nonequilibrium
quantum matter or persist only over finite length scales is an active area of research. We address this question in a free fermionic chain subject to continuous monitoring of
lattice-site occupations. An unraveling phase $\varphi$ interpolates between measurement schemes, corresponding to different
stochastic unravelings of the same Lindblad master equation: For $\varphi = 0$, measurements disentangle
lattice sites, while for $\varphi = \pi/2$ they act as
unitary random noise, yielding volume-law steady-state
entanglement. Using replica Keldysh field theory, we obtain a nonlinear sigma model describing the long-wavelength physics. This analysis shows that for $0 \leq \varphi < \pi/2$,
entanglement ultimately obeys an area law, but only beyond the exponentially large scale $\ln(l_{\varphi,*}) \sim J/[\gamma \cos(\varphi)]$, where $J$ is the hopping amplitude and $\gamma$ the measurement rate. Resolving $l_{\varphi, *}$ in numerical simulations is difficult for $\gamma/J \to 0$ or $\varphi \to \pi/2$. However, the theory also predicts that critical-like behavior appears below a crossover scale that grows only algebraically in $J/\gamma$, making it numerically accessible. Our simulations confirm these predictions, establishing the absence of measurement- or unraveling-induced
entanglement transitions in this model.
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All authors Clemens Niederegger, Tatiana Vovk, Elias Starchl, Lukas M. Sieberer
Mesoscale and Nanoscale Physics
Relation between structure and functionality in photosynthetic antenna complex of green sulfur bacteria: efficiency under natural sunlight pumping
Alessia Valzelli, Francesco Mattiotti, Jianshu Cao et al. (+1 more)
Large-scale simulations of light-matter interaction in natural photosynthetic
antenna complexes of the Chlorobium Tepidum green sulfur bacteria (GSB) containing more than one hundred thousand chlorophyll molecules, comparable with natural size, have been performed. Here we have modeled the entire process of the
exciton energy transfer, from sunlight absorption to
exciton trapping in the reaction centers (RCs) in presence of a thermal bath. The energy transfer has been analyzed using the radiative non-Hermitian
Hamiltonian and solving the rate equations for the populations. Sunlight pumping has been modeled as black-body radiation with an attenuation factor that takes the Sun-Earth distance into account. Cylindrical structures typical of GSB
antenna complexes, and the dimeric baseplate comparable to natural size have been considered. Our analysis shows that under natural sunlight, in photosynthetic
antennae of GSB the number of excitations reaching the RC per unit time matches the RC closure rate and the internal efficiency shows values close to 80%. We also considered cylindrical structures where the orientation of the dipoles does not reflect the natural one. Specifically, we vary continuously the angle of the transition dipole with respect to the cylinder main axis, focusing on the case where all dipoles are parallel to the cylinder axis. We also consider the important case where the dipoles are randomly oriented. In all cases the light-harvesting efficiency is lower than in the natural structure, showing the high sensitivity of light harvesting to the specific orientation of the dipole moments. Our results allow for a better understanding of the relationship between structure and functionality in photosynthetic
antennae of GSB and could drive the design of efficient light-harvesting devices.
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All authors Alessia Valzelli, Francesco Mattiotti, Jianshu Cao, G. Luca Celardo
Materials Science
Spin injection and emission helicity switching in a 2D perovskite/WSe2 heterostructure
Jakub Jasinski, Francesco Gucci, Thomas Brumme et al. (+16 more)
The initialization and control of a long-lived
spin population in lead halide perovskites are prerequisites for their use in spintronic applications. Here, we demonstrate circular polarization of the interlayer
exciton emission in a (BA)2PbI4/WSe2 monolayer
heterostructure. The helicity of this emission is controlled by tuning the energy of the excitation
laser through the
manifold of
exciton resonances of the WSe2 monolayer, together with an emerging interlayer absorption feature of the
heterostructure. Theoretical calculations show that this resonance arises from hybridized (BA)2PbI4/WSe2 states in the valence band. This hybrid character enables its observation in both linear absorption and ultrafast pump-probe spectroscopies, and plays a key role in controlling the sign of the helicity of the interlayer
exciton emission. The tunable
spin polarization demonstrated here, with the WSe2 monolayer effectively acting as a tunable
spin filter, represents an important step toward the use of 2D perovskites in opto-spintronic applications.
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All authors Jakub Jasinski, Francesco Gucci, Thomas Brumme, Swaroop Palai, Armando Genco, Alessandro Baserga, Jonas D. Ziegler, Takashi Taniguchi, Kenji Watanabe, Mateusz Dyksik, Christoph Gadermaier, Michal Baranowski, Duncan K. Maude, Alexey Chernikov, Giulio Cerullo, Agnieszka Kuc, Stefano Dal Conte, Paulina Plochocka, Alessandro Surrente
Statistical Mechanics · Cross-listed from quant-ph
Krylov Complexity Under Hamiltonian Deformations and Toda Flows
Kazutaka Takahashi, Pratik Nandy and Adolfo del Campo
The
quantum dynamics of a complex system can be efficiently described in Krylov space, the minimal subspace in which the dynamics unfolds. We apply the Krylov subspace method for
Hamiltonian deformations, which provides a systematic way of constructing solvable models from known instances. In doing so, we relate the
evolution of deformed and undeformed theories and investigate their complexity. For a certain class of deformations, the resulting Krylov subspace is unchanged, and we observe time evolutions with a reorganized basis. The tridiagonal form of the generator in the Krylov space is maintained, and we obtain generalized Toda equations as a function of the deformation parameters. The imaginary-time-like evolutions can be described by real-time
unitary ones. As possible applications, we discuss coherent Gibbs states for thermodynamic systems, for which we analyze the survival probability, spread complexity, Krylov
entropy, and associated time-averaged quantities. We further discuss the statistical properties of random
matrices and supersymmetric systems for quadratic deformations.
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Statistical Mechanics
Lattice-reflection symmetry in tensor-network renormalization group with entanglement filtering in two and three dimensions
Xinliang Lyu and Naoki Kawashima
Tensor-network renormalization group (TNRG) is an efficient real-space renormalization group method for studying the criticality in both classical and
quantum lattice systems. Exploiting
symmetries of a system in a TNRG
algorithm can simplify the implementation of the
algorithm and can help produce correct tensor RG flows. Although a general framework for considering a global on-site
symmetry has been established, it is still unclear how to incorporate a
lattice symmetry in TNRG. As a first step for
lattice symmetries, we propose a method to incorporate the
lattice-reflection
symmetry in the context of a TNRG with
entanglement filtering in both two and three dimensions (2D and 3D). To achieve this, we write down a general definition of
lattice-reflection
symmetry in tensor-network
language. Then, we introduce a transposition trick for exploiting and imposing the
lattice-reflection
symmetry in two basic TNRG operations: projective truncations and
entanglement filtering. Using the transposition trick, the detailed
algorithms of the TNRG map in both 2D and 3D are laid out, where the
lattice-reflection
symmetry is preserved and imposed. Finally, we demonstrate how to construct the linearization of the TNRG maps in a given
lattice-reflection sector, with the help of which it becomes possible to extract scaling dimensions in each sector separately. Our work paves the way for understanding the
lattice-rotation
symmetry in TNRG.
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Soft Condensed Matter
Three-dimensional formulation of curved nematic shells
Mathieu Dedenon
In soft matter, the phase of nematic
liquid crystals can be made from anisotropic molecules in single component materials, or as a suspension of mesoscopic nematogens. The later offers more versatility in the experimental design of complex shapes, in particular thin curved shells, and is often found in biological systems at multiple scales from
cells to tissues. Here, we investigate theoretically the transition from three-dimensional nematics to a two-dimensional description restricted to a tangent plane, using a mean-field approach. We identify a transition from first to second order isotropic-nematic transition in presence of weak tangential anchoring. Then, we clarify the conditions under which a two-dimensional description of thin nematic shells is relevant. Nonetheless, using the example of active nematic stress, we identify physical differences between two- and three-dimensional descriptions in curved geometry. Finally, we construct a thin film approximation of nematohydrodynamics for a nematic shell in contact with a curved substrate. All together, those results show that a tangential restriction of nematic orientation must be used with care in presence of
curvature, activity, or weak anchoring boundary conditions.
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Strongly Correlated Electrons
Pairing Symmetry Crossover from $d$-wave to $s_{\pm}$-wave in a Bilayer Nickelate Driven by Hund's Coupling and Crystal Field Splitting
Yicheng Xiong, Yanmei Cai and Tianxing Ma
The pairing
symmetry of the recently discovered
bilayer nickelate
superconductor La$_3$Ni$_2$O$_7$ is a subject of intense debate in condensed matter physics, with the two leading theoretical candidates being a sign-reversing $s_{\pm}$-wave and a $d$-wave state. To investigate its ground-state properties in the intermediate coupling regime which is critical for real materials, we construct a two-orbital
bilayer Hubbard model and employ the constrained-path
quantum Monte Carlo method for large-scale simulations. By systematically calculating ground-state pairing correlation functions across parameter spaces, we map its pairing
symmetry phase diagram. We find that an increasing Hund's coupling selectively enhances the interlayer $s_{\pm}$-wave pairing while suppressing the intralayer $d$-wave pairing. Similarly, a larger
crystal field splitting drives a transition from $d$-wave- to $s_{\pm}$-wave-dominant states. Further analysis reveals that the strength of the intralayer $d$-wave pairing is strongly correlated with the $(\pi, \pi)$
antiferromagnetic spin fluctuations, which are in turn effectively suppressed by a large
crystal field splitting, thereby weakening the $d$-wave pairing channel. Additionally, the dominant pairing
symmetry transition region roughly overlaps with the inversion of orbital occupancy response to Hubbard $U$, suggesting an intrinsic link between pairing competition and orbital physics. Our results indicate that, within the parameter regime relevant to the actual material, the $s_{\pm}$-wave is the most probable pairing
symmetry.
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Strongly Correlated Electrons
Anisotropic collapse of electronic correlations in the ferromagnet UGe$_2$ under high magnetic field
K. Somesh, T. Thebault, V. Taufour et al. (+5 more)
We present electrical-resistivity measurements on the prototypical heavy-
fermion ferromagnet UGe$_2$ under pulsed
magnetic field up to 60~T. An anisotropic field-induced suppression of the electronic correlations is revealed. The electrical resistivity strongly decreases when a
magnetic field $\mathbf{H}$ is applied along the easy
magnetic axis $\mathbf{a}$, while it remains almost unchanged when $\mathbf{H}$ is applied along the hard
magnetic axes $\mathbf{b}$ and $\mathbf{c}$. The field-induced destabilization of the
ferromagnetic state is also anisotropic: the anomaly at the Curie temperature $T_C$ disappears in fields higher than $\gtrsim1$~T for $\mathbf{H}\parallel\mathbf{a}$ and in fields higher than $\gtrsim20$~T for $\mathbf{H}\parallel\mathbf{b},\mathbf{c}$. At temperatures below 2~K, we observe
quantum oscillations in fields larger than 50~T applied along $\mathbf{b}$, which support the presence of a two-dimensional
Fermi surface similar to that previously observed at low fields.
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All authors K. Somesh, T. Thebault, V. Taufour, D. Aoki, F. Duc, G. Knebel, D. Braithwaite, W. Knafo
Quantum Gases
Lattice Unitarity: Saturated Collisional Resistivity in Hubbard Metals
Frank Corapi, Robyn T. Learn, Benjamin Driesen et al. (+5 more)
We investigate the interaction-induced resistivity of ultracold
fermions in a three-dimensional optical
lattice. In situ observations of transport dynamics enable the determination of real and imaginary resistivity. In the strongly interacting metallic regime, we observe a striking saturation of the current-dissipation rate towards a value that is independent of the interaction strength. This phenomenon is quantitatively captured by a dissipation model that uses a renormalized two-body scattering
matrix. We further measure the temperature dependence of resistivity in the strongly interacting limit and discuss the predicted asymptotic high-temperature behavior. Our results provide a clear microscopic understanding of bounded resistivity of low-density metals, thus providing a useful
benchmark for studies of strongly correlated atomic and electronic systems.
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All authors Frank Corapi, Robyn T. Learn, Benjamin Driesen, Antoine Lefebvre, Xavier Leyronas, Frédéric Chevy, Cora J. Fujiwara, Joseph H. Thywissen
Quantum Gases · Cross-listed from math.NA
Discrete normalized gradient flow for two-component Bose-Einstein condensates: Energy dissipation, global convergence and sharp local convergence behavior
Zixu Feng, Lunxu Liu and Qinglin Tang
The gradient flow with semi-implicit discretization (GFSI) is the most widely used
algorithm for computing the ground state of Gross-Pitaevskii energy functional. We apply GFSI to the two-component scenario with Josephson junction and rotating term, which is one of the most important and topical models in multi-component Bose-Einstein condensates (MBECs), and rigorously establish the following fundamental results for the first time. By introducing a Lagrange multiplier to reformulate GFSI into an equivalent form, we prove its energy dissipation property and global convergence to stationary states. More significantly, we uncover an intrinsic connection between this classical numerical PDE discretization rooted in imaginary-time
evolution and Riemannian optimization, a state-of-the-art mathematical framework for
manifold-constrained optimization. This connection enables us to fully characterize the local convergence behavior of GFSI within the Riemannian optimization framework. Together with the aforementioned global convergence result, this yields a complete global–local convergence theory for GFSI. Finally, numerical experiments comprehensively validate the theoretically predicted energy dissipation and convergence properties.
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