Strongly Correlated Electrons
Shear viscosity at finite magnetic field for graphene, non-relativistic and ultra-relativistic cases
Cho Win Aung, Thandar Zaw Win, Subhalaxmi Nayak et al. (+1 more)
The present article has addressed the finite
magnetic field extension of the previous work by Cho et al. (Phys. Rev. B 108, 235172, 2023) on microscopic calculation of shear viscosity for electron fluid in
graphene system. Our calculation is based on the kinetic theory approach in the relaxation time approximation. In the absence of a
magnetic field, transport is governed by a single shear viscosity coefficient, whereas the application of a finite
magnetic field induces anisotropy, giving rise to five independent shear viscosity coefficients associated with distinct velocity gradient tensors. These coefficients can be physically categorized into perpendicular, parallel, and
Hall components relative to the
magnetic field direction. When the scattering time equals the cyclotron time, the perpendicular component is suppressed by 80% and the parallel component by 50% and the
Hall effect can reach maximum. Corresponding
magnetic field strength for electron fluid in
graphene is around 0.01-0.1 Tesla, and the same for non-relativistic electron fluid and ultra-relativistic
quark fluid are around 10 Tesla and 10^{14} Tesla respectively. They may be considered as the required
magnetic field strength in three different fluid systems to observe noticeable
magnetic field response in their shear viscosity coefficients.
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All authors Cho Win Aung, Thandar Zaw Win, Subhalaxmi Nayak, Sabyasachi Ghosh
Soft Condensed Matter
Ferrofluids under oscillatory magnetic fields
Taige Wang, Kaiyuan Gu, Anzhou Wang et al. (+1 more)
Ferrofluids exhibit two canonical interfacial instabilities, a static Rosensweig (normal-field) instability that produces a
lattice of peaks and a dynamical Faraday instability that produces parametrically excited standing waves. Here we present a systematic phase diagram of ferrofluid surface states driven by a purely AC vertical
magnetic field with zero mean. Scanning a broad range of frequencies and field amplitudes, we resolve two robust branches: a Faraday-wave regime that includes a stable square
lattice and a Rosensweig-like peak–valley regime indistinguishable in morphology from Rosensweig peaks. The Faraday-onset boundary is well described by a power law close to $\sqrt{f}$, while the Rosensweig-like peak onset becomes essentially frequency independent at low viscosity. The wave vector of the square
lattice grows linearly with frequency over our accessible band. We present a surface-wave theory that captures the full phenomenology, including the emergence of Rosensweig peaks under zero-mean AC driving, the near-$\sqrt{f}$ scaling of the phase boundaries, the linear growth of the selected wave vector with frequency, and the preference for square over hexagonal
lattices.
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All authors Taige Wang, Kaiyuan Gu, Anzhou Wang, Zhentang Wang
Mesoscale and Nanoscale Physics
Electronic states at twist stacking faults in rhombohedral graphite
Xiaoqian Liu, Yifei Guan and Oleg V. Yazyev
Flat bands in graphitic materials emerged as a platform for realizing tunable correlated physics. As a nodal-line semimetal, rhombohedral graphite features flat drumhead surface states in the vicinity of the Dirac points, which carry a nontrivial topological charge. We present a comprehensive study on rhombohedral graphite with twist stacking faults. Using both the continuum models and the realistic tight-binding models, we show that the twist angle between the
graphene layers can tune the interface states at such stacking faults. The
evolution of interface states originates from the interplay between the moiré periodicity and Zak phase
topology, predicting the occurrence of nearly flat bands throughout the moiré Brillouin zone. We further investigate the disorder-induced layer polarization and tunable Chern number for flat band, and characterize the relationship between the disorder strength and Chern number in twisted rhombohedral graphite.
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Soft Condensed Matter
Optoelectronically Directed Self-Assembly of Active and Passive Particles into Programmable and Reconfigurable Colloidal Structures
Donggang Cao, Sankha Shuvra Das and Gilad Yossifon
Controlled assembly of active-passive colloidal mixtures offers a route to reconfigurable microscale machines, but their self-assembly pathways remain poorly understood. We study the directed assembly of metallo-dielectric Janus particles (JPs) and passive polystyrene (PS) beads using optoelectrically reconfigurable AC-field patterning, which allows precise control over particle composition and binding sequence. Through experiments, analytical modeling, and simulations, we show that dipolar interactions drive robust JP-JP and JP-PS dimer formation with frequency-dependent stability. At intermediate and high frequencies, JP-PS binding is strongly attractive, whereas at low frequencies it becomes effectively repulsive due to electrical double-layer screening and electrohydrodynamic flows at the metallic hemisphere. In multi-particle systems, PS beads act as cooperative hubs that hierarchically recruit JPs, yielding higher-order hybrid structures. We identify structural isomers - for example, 3JP + 1PS clusters can form chain-like or triangular configurations depending on assembly sequence. Simulations confirm both as
equilibrium states, with the triangular isomer slightly more stable. Similar polymorphism appears in larger clusters (4JPs). Overall, we establish a framework for controlled active-passive colloidal assembly, showing how frequency-tunable interactions and structural polymorphism enable the design of reconfigurable colloidal machines for applications in microrobotics, targeted delivery, and adaptive materials.
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Strongly Correlated Electrons
Quantum vs thermal fluctuations in phase transitions of two-dimensional superconductors
Andrea Ponticelli, Francesco Giuseppe Capone, Vittorio Cataudella et al. (+3 more)
We investigate the impact of
quantum and thermal phase fluctuations on the suppression of superconducting order in two-dimensional systems. Within the two-dimensional
quantum XY model in the phase representation, where on-site interaction terms govern
quantum phase fluctuations, we perform extensive path-integral
quantum Monte Carlo simulations. The resulting temperature-interaction phase diagram establishes the presence of a well-defined critical line ending at a
quantum critical point at vanishing temperature with no indication of reentrant behavior. We further demonstrate that the resistance above the critical line reproduces the two expected different critical behaviors. For stronger interactions, above the
quantum critical point, the system exhibits a crossover to an insulating regime at low temperatures. Finally, Monte Carlo calculations of current-current correlation functions enable us to extract the frequency-dependent conductivity in both superconducting and normal regimes, revealing a finite-frequency response that we attribute to
quantum phase fluctuations.
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All authors Andrea Ponticelli, Francesco Giuseppe Capone, Vittorio Cataudella, Giulio De Filippis, Antonio De Candia, Carmine Antonio Perroni
Strongly Correlated Electrons
Tensor-network study of the ground state of maple-leaf Heisenberg antiferromagnet
Samuel Nyckees, Pratyay Ghosh and Frédéric Mila
We study the
quantum phase diagram of the
spin-$1/2$ nearest-neighbor Heisenberg model on the maple-leaf
lattice using infinite projected entangled pair states (iPEPS) combined with a corner transfer
matrix renormalization group scheme adapted to $C_3$-symmetric
lattices. Focusing on the fully
antiferromagnetic $J$-$J_d$ model with $J_h = J_t := J$, we map out the ground-state phase diagram as a function of the dimer coupling $J_d$. Our results show that the system hosts only two phases: a magnetically ordered canted-$120^\circ$ phase and an exact dimer singlet product phase. We identify a first-order transition between these two phases at $J_d/J \approx 1.45$. Within the magnetically ordered phase, we observe small but finite
magnetic moments. We also resolve the
quantum renormalization of the canting angle, which deviates from the classical prediction over almost the entire magnetically ordered phase.
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Quantum Gases
Opening a gap in the dispersion of the collective excitations of a driven-dissipative condensate subject to an external coherent drive
E. Stazzu, G. A. P. Sacchetto and I. Carusotto
We build a minimal theoretical model to describe the opening of a gap in the dispersion of the collective excitations of a driven-dissipative condensate when the condensate phase is fixed by an additional coherent phase-locking drive. We map out the phase diagram as a function of the amplitude and frequency of the coherent drive, identifying distinct regions corresponding to different steady-state regimes. For each region, we analyze the dispersion of the collective excitations and determine whether the spectrum is gapped, with either a purely imaginary gap or a finite real part. When the coherent drive is unable to lock the condensate phase, a gapless Goldstone mode is recovered. Within the same phase diagram, we further identify regions of finite-wavevector dynamical instability, where the condensate tends to develop a supersolid-like spatial modulation. While our theoretical framework is directly related to recent experiments with
exciton-polariton condensates, it can be applied to describe the effect of external injection also in a variety of spatially extended optical parametric oscillators or
laser devices.
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Strongly Correlated Electrons · Cross-listed from math-ph
On the Hartree-Fock phase diagram for the two-dimensional Hubbard model
Christophe Charlier, Edwin Langmann and Jonatan Lenells
We propose an analytical method for the construction of Hartree-Fock phase diagrams for the (
fermion) Hubbard model and various generalizations thereof. Such phase diagrams are traditionally constructed numerically, but we argue that, by using asymptotic techniques, it is possible to obtain analytic formulas approximating the curves separating the different phases to very high accuracy. To illustrate the new method, we apply it to the two-dimensional Hubbard model on the square
lattice at zero temperature. This yields formulas for the Hartree-Fock phase boundaries that agree with, but also improve on, earlier numerical results. In particular, our results provide the first rigorous proof of the existence of mixed phases in this model.
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Materials Science
Iterative learning scheme for crystal structure prediction with anharmonic lattice dynamics
Hao Gao, Yue-Wen Fang and Ion Errea
First-principles based
crystal structure prediction (CSP) methods have revealed an essential tool for the discovery of new materials. However, in solids close to displacive phase transitions, which are common in ferroelectrics, thermoelectrics, charge-density wave systems, or superconducting hydrides, the ionic contribution to the free energy and
lattice anharmonicity become essential, limiting the capacity of CSP techniques to determine the thermodynamical stability of competing phases. While variational methods like the
stochastic self-consistent harmonic approximation (SSCHA) accurately account for anharmonic
lattice dynamics ab initio, their high computational cost makes them impractical for CSP. Machine-learning interatomic potentials offer accelerated sampling of the energy landscape compared to purely first-principles approaches, but their reliance on extensive training data and limited generalization restricts practical applications. Here, we propose an iterative learning framework combining evolutionary
algorithms, atomic foundation models, and SSCHA to enable CSP with anharmonic
lattice dynamics. Foundation models enable robust relaxations of random structures, drastically reducing required training data. Applied to the highly anharmonic H$_3$S system, our framework achieves good agreement with the
benchmarks based on density functional theory, accurately predicting phase stability and vibrational properties from 50 to 200 GPa. Importantly, we find that the statistical averaging in the SSCHA reduces the error in the free energy evaluation, avoiding the need for extremely high accuracy of machine-learning potentials. This approach bridges the gap between data efficiency and predictive power, establishing a practical pathway for CSP with anharmonic
lattice dynamics.
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Materials Science
Surface Exciton Polaritons and Near-Zero Permittivity Surface Waves Supported by Artificial Organic Hyperbolic Metamaterials
José N. Gama, Diogo Cunha, Carla Estévez-Varela et al. (+11 more)
Hyperbolic metamaterials enable extreme light confinement and control of photonic states, but their realization has been restricted to inorganic architectures. Here, a fully organic route to fabricate artificial
hyperbolic metamaterials based on multilayered thin films of J-aggregate carbocyanine dyes alternated with polyelectrolytes is introduced. These structures exhibit strong optical anisotropy and experimentally support
hyperbolic surface
exciton polaritons and, for selected dyes, additional surface waves in near-zero permittivity regimes. Spectroscopic ellipsometry confirms a uniaxial dielectric tensor with negative in-plane and positive out-of-plane components, close to the absorption peaks of the constituent J-aggregates. This anisotropy is preserved across individual layers, demonstrating the robustness of the layer-by-layer approach and enabling the coupling of surface
exciton polaritons and near-zero permittivity modes even in films only a few nanometres thick. Transfer-
matrix simulations based on the obtained dielectric tensor reproduce the coupling conditions for all thicknesses, validating the optical model. Structural characterization reveals the link between optical anisotropy and supramolecular order, with preferential in-plane molecular orientation and the
evolution from discrete nanostructures to continuous films as deposition progresses. These organic
hyperbolic metamaterial architectures, associated with narrow excitonic resonances from J-aggregates, offer a unique platform for tailoring emission, energy transport, and exploring polariton dynamics at the nanoscale.
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All authors José N. Gama, Diogo Cunha, Carla Estévez-Varela, Marina García-Pardo, Pablo Pedreira, Adelaide Miranda, M. Carmen López-González, Pieter A.A. De Beule, Eduardo Solano, Rosalia Serna, Mikhail Vasilevskiy, Martin Lopez-Garcia, Isabel Pastoriza-Santos, Sara Núñez-Sánchez
Disordered Systems and Neural Networks
Isotropic conductivity of two-dimensional three- and four-phase symmetric composites: duality and universal bounds
Leonid Fel
We consider the problem of isotropic effective conductivity $\sigma_e(\sigma_1,\ldots,\sigma_n)$ in two-dimensional three- and four-phase symmetric composites with a partial isotropic conductivity $\sigma_j$ of the $j$-th phase. The upper $\Omega(\sigma_1,\ldots,\sigma_n)$ and lower $\omega(\sigma_1,\ldots,\sigma_n)$, $n=3,4$, bounds for effective conductivity, found by the algebraic approach, are universal (independent of the composite micro-structure) and possess all algebraic properties of $\sigma_e(\sigma_1,\ldots,\sigma_n)$ that follow from physics: first-order homogeneity, full permutation invariance, Keller's self-duality, positivity, and monotony. The bounds are compatible with the trivial solution $\sigma_e(\sigma,\ldots,\sigma)=\sigma$ and satisfy Dykhne's ansatz. Their comparison with previously known numerical calculations, asymptotic analysis, and exact results for isotropic effective conductivity $\sigma_e(\sigma_1,\ldots,\sigma_n)$ of two-dimensional three- and four-phase composites showed complete agreement. The bounds $\Omega(\sigma_1,\ldots,\sigma_n)$ and $\omega(\sigma_1,\ldots,\sigma_n)$ in both cases $n=3,4$ are stronger than the currently known variational bounds.
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Quantum Gases · Cross-listed from quant-ph
Profusion of Symmetry-Protected Qubits from Stable Ergodicity Breaking
Thomas Iadecola and Rahul Nandkishore
We show how combining a discrete
symmetry with topological
Hilbert space fragmentation can give rise to exponentially many topologically stable
qubits protected by a single discrete
symmetry. We illustrate this explicitly with the example of the $\mathsf{CZ}_p$ model, where the encoded
qubits are stable to arbitrary
symmetry-respecting perturbations for parametrically long times, substantially enhancing the robustness of a recently proposed construction based on nontopological fragmentation. In this model, the encoded
qubits naturally come in pairs for which a universal set of transversal logical gates can be performed, ruling out (by the Eastin-Knill
theorem) the possibility of using them for
quantum error correction. We also comment on the combination of
symmetry enrichment and topological fragmentation more generally, and the implications for use of systems exhibiting
Hilbert space fragmentation as
quantum memories.
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Superconductivity
Electrical drive of a Josephson junction array using a cryogenic BiCMOS pulse generator
Yerzhan Kudabay, Oliver Kieler, Michael Starkloff et al. (+5 more)
We have combined a cryogenic BiCMOS integrated
circuit with a superconducting Josephson junction array. The BiCMOS
circuit serves as an on-chip pulse generator delivering return-to-zero pulses with pulse frequencies of up to 15 GHz. With this microwave drive, we observe wide and flat Shapiro steps in the voltage-versus-current characteristics of the Josephson junction array. To the best of our knowledge, this is the first integration of a Josephson junction array with a cryogenic BiCMOS chip. Our results pave the way to a hybrid and fully integrated Josephson arbitrary waveform synthesizer with possible applications in
quantum electronics and
quantum voltage metrology.
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All authors Yerzhan Kudabay, Oliver Kieler, Michael Starkloff, Marco Schubert, Michael Haas, Johannes Kohlmann, Vadim Issakov, Mark Bieler
Mesoscale and Nanoscale Physics
Intercalant-induced Kekule ordering and gap opening in quasi-free-standing graphene
Huu Thoai Ngo, Zamin Mamiyev, Niklas Witt et al. (+2 more)
We present a comprehensive investigation of the structural and electronic properties of Sn intercalated buffer layers on SiC(0001) using low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS), spot-profile analysis low-energy electron diffraction (SPA-LEED), and density functional theory (DFT) calculations. Sn intercalation effectively decouples the buffer layer, yielding quasi-free-standing monolayer
graphene (QFMLG) while introducing local
lattice distortions. Bias-dependent STM imaging revealed the coexistence of conventional and Kekule-ordered
graphene domains, governed by the underlying Sn(1x1) reconstruction at the SiC interface. The measured STS spectra exhibit good agreement with DFT results. However, achieving homogeneous Sn(1x1) domains remains challenging, apparently, due to strain within the Sn monolayer, which drives the emergence of Kekule distortions and the associated electronic band-gap opening omogeneously in
graphene. These findings highlight the crucial role of intercalant homogeneity and strain in tuning
graphene`s structural and electronic properties.
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All authors Huu Thoai Ngo, Zamin Mamiyev, Niklas Witt, Tim Wehling, Christoph Tegenkamp
Superconductivity
Distinct Suppression Mechanisms of Superconductivity by Magnetic Domains and Spin Fluctuations in EuFe2(As1-xPx)2 superconductors
Mengju Yuan, Nan Zhou, Ruixia Ti et al. (+10 more)
Using ac composite magnetoelectric technique, we map the phase diagrams of EuFe(As1-xPx)2 to resolve the interplay between superconductivity and ferromagnetism. For samples with Tc<TFM, the transition to a
ferromagnetic multi-domain state suppresses Hc2 through the breakdown of Jaccarino-Peter compensation and enhanced
magnetic scattering from inter-domain disorder, while Hirr is reduced due to
vortex-antivortex pair nucleation at domain walls disrupting the
vortex lattice. Conversely, for samples with Tc>TFM, strong short-range
spin correlations and phase boundaries within a multiphase coexistence regime near the triple point act as potent pair-breaking centers, leading to pronounced Hc2 suppression.
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All authors Mengju Yuan, Nan Zhou, Ruixia Ti, Long Zhang, Chenyang Zhang, Tian He, Deliu Ou, Jingchun Gao, Mingquan He, Aifeng Wang, Jun-Yi Ge, Yue Sun, Yisheng Chai
Materials Science
Co$_2$MnZ (Z = Al, Si, Ga, Ge, Sn) Heusler alloys as candidate materials for spintronic and microelectronic applications: Electronic structure, transport, and magnetism
Vyacheslav V. Marchenkov, Alena A. Semiannikova, Evgenii D. Chernov et al. (+4 more)
Magnetic and electronic transport properties of Co$_2$MnZ (Z = Al, Ga, Ge, Si, Sn) Heusler
alloys were experimentally investigated. Electrical resistivity, in the temperature range from 4.2 to 300 K, as well as field dependences of the
Hall effect and magnetization at T = 4.2 K in
magnetic fields up to 100 kOe and 70 kOe, respectively, were measured. Experimental data are in good agreement with the results of the theoretical DFT calculations of the electronic structure and
magnetic moments. In the band structure of Co$_2$MnSi, half-
metallicity is formed with the full
spin polarization and the half-metallic gap of about 0.6 eV. In Co$_2$MnZ (Z = Al, Ge, Sn), it is shifted from the
Fermi energy by the hole pockets at the point $\Gamma$, preventing thereby the formation of the half-metallic state. In a peculiar case of Co$_2$MnGa, the antisite defects are expected to determine structural and electronic properties. For the Co$_2$MnAl and Co$_2$MnGa topological semimetals, Weyl topological points are found at the
Fermi energy; however, for Z = Si, Ge, Si, these features are located deeper within to the valence band. The results show that Co$_2$MnGe and Co$_2$MnSn are usual ferromagnets, Co$_2$MnAl and Co$_2$MnGa
alloys are topological semimetals that can find application in microelectronics, while Co$_2$MnSi is a half-metallic ferromagnet that is in high demand in spintronics.
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All authors Vyacheslav V. Marchenkov, Alena A. Semiannikova, Evgenii D. Chernov, Alexey V. Lukoyanov, Valentin Yu. Irkhin, Yulia A. Perevozchikova, Elena B. Marchenkova
Mesoscale and Nanoscale Physics
Optical cooling of nuclear spins in GaAs/(Al,Ga)As quantum wells at subkelvin temperatures: Evidence of the dynamic self-polarization of nuclear spins
M. Kotur, D. Kudlacik, N. E. Kopteva et al. (+4 more)
We investigate the dynamic polarization of
nuclear spins in a nominally undoped GaAs/Al$_{0.35}$Ga$_{0.65}$As
quantum well using two complementary experimental approaches: time-resolved Kerr rotation and optical orientation measurements of photoluminescence. Using the first technique, we measure a remarkably large Overhauser field of 3.1 T in a geometry close to the Faraday configuration for a 19.7 nm wide
quantum well at a temperature of 1.6 K. A
nuclear spin temperature of 6.4 $\mu$K is measured at an external
magnetic field of 0.006 T following an adiabatic sweep from 0.6 T. Despite the quadrupole-induced
nuclear spin splitting inherent to nanostructures, the
nuclear spin system is found to follow the predictions of
spin temperature theory. Using the optical orientation of the photoluminescence, we investigated
nuclear spin dynamics at millikelvin temperatures down to 300 mK. At a temperature of 500 mK, an Overhauser field of 160 mT is generated in an oblique but nearly Voigt
magnetic field using low optical power to avoid heating. The
nuclear polarization build-up time is of 150 s, consistent with earlier reports at higher temperatures, where hyperfine scattering on free photoexcited electrons governs relaxation. At 500 mK, the onset of dynamic self-polarization of
nuclear spins is observed, which becomes more pronounced as the
lattice temperature is further reduced to 300 mK. The estimated
nuclear spin temperature in the dynamic self-polarization regime can be as low as 200 nK.
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All authors M. Kotur, D. Kudlacik, N. E. Kopteva, E. Kirstein, D. R. Yakovlev, K. V. Kavokin, M. Bayer
Statistical Mechanics
Optimal navigation in a noisy environment
Abhijit Sinha, Sandeep Jangid, Tridib Sadhu et al. (+1 more)
Navigating toward a known target in a noisy environment is a fundamental problem shared across biological, physical, and engineered systems. Although optimal strategies are often framed in terms of continuous, fine-grained feedback, we show that efficient
navigation emerges from a far simpler principle: natural wandering punctuated by intermittent course corrections. Using a controlled robotic platform, active Brownian particle simulations, and scaling theory, we identify a universal trade-off between noise-induced deviation and the finite cost of reorientation, yielding an optimal course correction frequency governed by only a few system parameters. Despite their differing levels of complexity, our experiment and theory collapse onto common quantitative signatures, including first-passage time distribution and non-Gaussian angular dispersion. Our results establish intermittent course-correction as a minimal and robust alternative to continuous feedback, offering a unifying guiding principle for point-to-point
navigation in complex environments.
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All authors Abhijit Sinha, Sandeep Jangid, Tridib Sadhu, Shankar Ghosh
Strongly Correlated Electrons · Cross-listed from physics.chem-ph
Finite-Temperature Thermally-Assisted-Occupation Density Functional Theory, Ab Initio Molecular Dynamics, and Quantum Mechanics/Molecular Mechanics Methods
Shaozhi Li and Jeng-Da Chai
Recently, thermally-assisted-occupation density functional theory (TAO-DFT) [J.-D. Chai, J. Chem. Phys. 136, 154104 (2012)] has been demonstrated to be an efficient and accurate electronic structure method for studying the ground-state properties of large multi-reference (MR) systems at absolute zero. To explore the thermal
equilibrium properties of large MR systems at finite electronic temperatures, in the present work, we propose the finite-temperature (FT) extension of TAO-DFT, denoted as FT-TAO-DFT. Besides, to unlock the dynamical information of large MR systems at finite temperatures, FT-TAO-DFT is combined with ab initio molecular dynamics, leading to FT-TAO-AIMD. In addition, we also develop FT-TAO-DFT-based
quantum mechanics/molecular mechanics (QM/MM), denoted as FT-TAO-QM/MM, to provide a cost-effective description of the thermal
equilibrium properties of a QM subsystem with MR character embedded in an MM environment at finite temperatures. Moreover, the FT-TAO-DFT, FT-TAO-AIMD, and FT-TAO-QM/MM methods are employed to explore the radical nature and infrared (IR) spectra of n-acenes (n = 2–6), consisting of n linearly fused benzene rings, in
vacuum and in an argon (Ar)
matrix at finite temperatures. According to our calculations, for n-acenes at 1000 K or below, the electronic temperature effects on the radical nature and IR spectra are very minor, while the
nuclear temperature effects on these properties are noticeable. For n-acene in an Ar matrx at absolute zero, the Ar
matrix has minimal impact on the radical nature of n-acene, while the co-deposition procedure of n-acene and Ar atoms may affect the IR spectrum of n-acene.
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Statistical Mechanics · Cross-listed from gr-qc
Entropy of matter on the Carroll geometry
Saurav Samanta and Bibhas Ranjan Majhi
Two prescriptions for the construction of Carroll geometries, the expansion of
geometric variables near horizon and the expansion of metric with zero limit of the expansion parameter $c$ (speed of light in
vacuum), are known to complement each other. The
entropy of an ideal gas, confined in a box and kept very close to the horizon, depends on the transverse area of the container. We show this by using the Carroll geometry constructed through the expansion of the metric and then taking the zero limit of the expansion parameter $c$. Therefore, the present analysis assures the complementing nature of two ways of finding the Carroll geometry from the thermodynamical point of view.
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Soft Condensed Matter
Local composition fluctuations act as precursors for crystal nucleation in polydisperse hard spheres
Marjolein de Jager, Antoine Castagnède, Frank Smallenburg et al. (+1 more)
We revisit the effect of polydispersity on the
crystal nucleation of hard spheres. Using event-driven molecular dynamics simulations, we obtain the nucleation rate as a function of the supersaturation for a range of polydispersities, and demonstrate that the nucleation rate of polydisperse hard spheres deviates from the trend of monodisperse hard spheres, even when mapped to the effective packing fraction. Furthermore, we show that nucleation tends to originate in regions with on average more larger-sized particles, indicating that such regions act as precursors for nucleation in systems of polydisperse hard spheres.
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All authors Marjolein de Jager, Antoine Castagnède, Frank Smallenburg, Laura Filion
Strongly Correlated Electrons
Multiple topological phases of magnons induced by Dzyaloshinskii-Moriya and pseudodipolar anisotropic exchange interactions in Kagome ferromagnets
Jin-Yu Ni, Xia-Ming Zheng, Peng-Tao Wei et al. (+2 more)
Kagome magnets naturally hosting Dirac points and flat bands exhibit novel topological phases, enabling rich interplays between interactions and
topologies. The discovery of two-dimensional (2D) magnets generally coexisting with different types of
magnetic interactions poses a challenge for topological magnonic manipulation. Here we investigate the topological
magnon phases of 2D Kagome ferromagnet with multiple
magnetic anisotropic interactions, i.e. Dzyaloshinskii-Moriya interaction (DMI) and pseudo-dipolar interaction (PDI). It is found that the different sole
magnetic anisotropic interactions introduce completely distinct topological phase diagrams and topological states. The multiple topological
magnon phases with high Chern number emerge due to the distinct anisotropic interactions. Moreover, the interplay of the multiple anisotropic DMI and PDI interactions involved with Dirac and flat bands controls a variety of topological phase transitions, implying greater manipulation potential. In addition, the sign reversal of thermal
Hall and Nernst conductivities induced by temperature is found in particular topological phase regions, namely topological origin, relating to the energy gap and Berry
curvature (Chern number) in the vicinity of
magnetic phase transition from the thermal fluctuations, providing a possible explanation for the experimental puzzles. All these results demonstrate that the novel topological magnonic properties in Kagome magnet with multiple
magnetic anisotropic interactions can realize a potential platform for magnonic devices and
quantum computing.
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All authors Jin-Yu Ni, Xia-Ming Zheng, Peng-Tao Wei, Da-Yong Liu, Liang-Jian Zou
Statistical Mechanics
Critical Temperature(s) of Sierpinski Carpet(s)
Riccardo Ben Alì Zinati, Giacomo Gori and Alessandro Codello
We present a key algorithmic improvement to the generalized combinatorial Feynman–Vdovichenko method for calculating the critical temperature of the Ising model on Sierpinski carpets $SC_k(a,b)$, originally introduced in arxiv:1505.02699. By reformulating the method in terms of purely real-valued transfer
matrices, we substantially reduce their dimension. This optimization, together with modern computational resources, enables us to reach generation $k=10$ for the canonical $SC_k(3,1)$ carpet. Extrapolation from these data yields the most accurate estimate to date of the critical temperature $T_c^{(3,1)} = 1.4782927(26)$. We further extend the analysis to additional members of the $SC_k(a,b)$ family and report their corresponding critical temperatures.
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Soft Condensed Matter
Spatiotemporal Chaos and Defect Proliferation in Polar-Apolar Active Mixture
Partha Sarathi Mondal, Tamas Vicsek and Shradha Mishra
Chaotic transitions in inertial fluids typically proceed through a direct energy cascade from large to small scales. In contrast, active systems, composed of self propelled units, inject energy at microscopic scales and therefore exhibit an inverse cascade, giving rise to distinctly unconventional flow patterns. Here, we investigate an active mixture consisting of both apolar and polar self driven components, a setting expected to display richer behaviours than those found in living
liquid crystal (LLC) systems, where the apolar constituent is passive. Using numerical solutions of the corresponding hydrodynamic equations, we uncover a variety of complex dynamical states. Our results reveal a non-monotonic response of the apolar species to changes in the density and activity of the polar component. In an intermediate regime, reminiscent of LLC-induced disorder, the system develops a dynamically disordered phase characterised by high-density, chaotically evolving band-like structures and by the continual creation and annihilation of half integer topological defects. We show that this regime exhibits spatiotemporal chaos, which we quantify through two complementary measures: the spectral properties of density fluctuations and the maximal Lyapunov exponent. Together, these findings broaden the understanding of complex transitions in active matter and suggest potential experimental realisations in bacterial suspensions or synthetic microswimmer assemblies.
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Superconductivity
Universal quasi-degenerate orbital origin of two-dome phases in iron pnictide superconductors
Da-Yong Liu, Zhe Sun, Feng Lu et al. (+2 more)
A series of experiments revealed that novel bipartite
magnetic and superconducting (SC) phases widely exist in the phase diagrams of iron pnictides and chalcogenides. Nevertheless, the origin of the two-dome
magnetic and SC phases in iron-based compounds remains unclear. Here we theoretically investigated the electronic structures,
magnetic and SC properties of three representative iron-based systems, i.e. LaFeAsO$_{1-x}$H$_{x}$, LaFeAs$_{1-x}$P$_{x}$O and KFe$_{2}$As$_{2}$. We propose a unified quasi-degenerate orbital mechanism for the emergence of the two-dome parent
magnetic/structural phase and the subsequent two-dome SC phase. It is found that the degenerate in-plane anisotropic $d_{xz/yz}$ orbitals dominate the first
magnetic/structural and SC phases, while in-plane isotropic orbitals $d_{xy}$ or $d_{3z^{2}-r^{2}}$ with quasi-degeneracy originating from quasi-
symmetry drive the emergence of the second
magnetic/SC dome phase. Moreover, a matching rule of
spin and orbital modes for SC pairing state is proposed in multi-orbital iron-based systems. These results imply an orbital-driven mechanism as well as an orbital-selective scenario, and shed light on the understanding of the multi-dome
magnetic and SC phases in multi-orbital systems.
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All authors Da-Yong Liu, Zhe Sun, Feng Lu, Wei-Hua Wang, Liang-Jian Zou
Soft Condensed Matter
Dynamics of Marangoni-Driven Elliptical Janus Particles
Pabitra Masanta, Ratan Sarkar, Punit Parmananda et al. (+1 more)
We investigate the spontaneous motion of an elliptical Janus particle, driven by Marangoni forces, on a water surface to understand how particle shape and size influence its dynamics. The Janus particle is one-half infused with a substance such as camphor, which lowers the surface tension upon release onto the water surface. The resulting surface tension gradient generates Marangoni forces that propel the particle. For fully camphor-infused (non-Janus) particles, previous studies have shown that motion occurs along the short axis of the ellipse. However, for Janus particles, our experiments reveal a much richer steady-state dynamics, depending on both the particle's eccentricity and size. To understand these dynamics, we develop a numerical model that captures the connection between the spatio-temporal
evolution of the camphor concentration field and the Marangoni force driving the particle. Using this model, we simulate the motion of particles with varying eccentricities - from nearly circular to highly elongated shapes. The simulations qualitatively reproduce all the trajectories observed in experiments and provide insights into how particle geometry influences the dynamics of chemically driven anisotropic particles. With the help of the numerical model, we compute a full phase diagram characterising the dynamical states as a function of surfactant properties.
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All authors Pabitra Masanta, Ratan Sarkar, Punit Parmananda, Raghunath Chelakkot
Strongly Correlated Electrons · Cross-listed from nucl-th
Towards compressed baryonic matter densities: thermodynamics and transport coefficients
Anand Rai, Dani Rose J Marattukalam, Prasanta Murmu et al. (+3 more)
We study the thermodynamic and transport properties of hot and dense
quantum chromodynamic matter expected to be produced in low-energy heavy-ion collisions, using three different effective
quantum chromodynamic frameworks: the Nambu–Jona-Lasinio model, the
chiral effective model, and the
hadron resonance gas model. We briefly outline the theoretical formulation of thermodynamic quantities and transport coefficients within these approaches, where
quarks are treated with effective masses in the Nambu–Jona-Lasinio and
chiral effective models, and hadronic degrees of freedom are employed in the
hadron resonance gas model. The transport coefficients are evaluated using the Boltzmann transport equation in the relaxation-time approximation. Following the theoretical overview, we present a comprehensive analysis of the behavior of these quantities as functions of the
baryon chemical potential or net
baryon density. The Lorenz ratio $\kappa/(\sigma T)$ is found to increase rapidly-indicating a strong violation of the Wiedemann-Franz law in the low-$\mu_{B}$ regime–while approaching the universal value at higher
baryon chemical potentials or densities. The shear-viscosity-to-
entropy-density ratio $\eta/s$ remains nearly constant at low $\mu_{B}$ but exhibits a gradual increase as $\mu_{B}$ grows. We also discuss the qualitative similarities of these trends with those observed in the electron-hole
plasma of
graphene, an emergent quasi-relativistic system characterized by massless energy-momentum dispersion.
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All authors Anand Rai, Dani Rose J Marattukalam, Prasanta Murmu, Ashutosh Dwibedi, Rishabh Sharma, Sabyasachi Ghosh
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Non-Hermitian Exceptional Topology on a Klein Bottle Photonic Circuit
Ze-Sheng Xu, J. Lukas K. König, Andrea Cataldo et al. (+8 more)
Non-Hermitian physics has unlocked a wealth of unconventional wave phenomena beyond the reach of Hermitian systems, with exceptional points (EPs) driving enhanced sensitivity, nonreciprocal transport, and topological behavior unique to non-Hermitian degeneracies. Here, we present a scalable and reconfigurable silicon photonic integrated
circuit capable of emulating arbitrary non-Hermitian time
evolution with high precision. Using this programmable platform, we implement a two-band non-Hermitian
Hamiltonian defined on a Klein-bottle
topology a nonorientable parameter space that enables exceptional phases forbidden on orientable
manifolds. Through an on-chip amplitude-and-phase reconstruction protocol, we retrieve the full complex
Hamiltonian at multiple points in parameter space and experimentally map the associated
Fermi arc where the imaginary
eigenvalue gap closes. The orientation of the measured
Fermi arc reveals a nontrivial exceptional
topology: it implies the presence of same-charge EPs (or an EP monopole) that cannot annihilate locally on the Klein bottle. Our results demonstrate the first photonic realization of exceptional
topology on a nonorientable
manifold and establish a versatile platform for exploring exotic non-Hermitian and topological models relevant to classical and
quantum photonics.
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All authors Ze-Sheng Xu, J. Lukas K. König, Andrea Cataldo, Rohan Yadgirkar, Govind Krishna, Venkatesh Deenadayalan, Val Zwiller, Stefan Preble, Emil J. Bergholtz, Jun Gao, Ali W. Elshaari
Materials Science
Reductive Contact and Dipolar Interface Engineering Enable Stable Flexible CsSnI3 Nanowire Photodetectors
Letian Dai, Wanru Chen, Quanming Geng et al. (+4 more)
Lead-free tin-based halide perovskites are attractive for flexible and environmentally benign optoelectronics, but their application is limited by the rapid oxidation of Sn2+ to Sn4+ and poor operational stability. Here, we report a flexible CsSnI3 nanowire photodetector that achieves both high near-infrared photoresponse and long-term stability through synergistic aluminium-substrate contact engineering and dipolar interface modification. A 0.2 mm anodized aluminium foil serves as the flexible substrate, where localized
laser ablation exposes metallic aluminium regions that act as reductive sites, effectively suppressing Sn2+ oxidation during nanowire growth. Simultaneously, a polar interlayer of 3-fluoro-2-nitroanisole is introduced to improve energy-level
alignment, suppress interfacial deprotonation, and enhance charge extraction. The resulting device exhibits a responsivity of 0.39 A W-1, a specific detectivity of 1.38 * 10^13 Jones, and a wide linear dynamic range of 156 dB under 850 nm illumination. Moreover, the device retains over 85% of its initial photocurrent after 60 days in ambient air and maintains 94% of its initial photocurrent after 1000 bending cycles. This work establishes an effective strategy for stabilizing Sn-based perovskites toward high-performance flexible optoelectronic devices.
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All authors Letian Dai, Wanru Chen, Quanming Geng, Ying Xu, Guowu Zhou, Nuo Chen, Xiongjie Li
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Quantum Geometric Tensor in the Wild: Resolving Stokes Phenomena via Floquet-Monodromy Spectroscopy
Prasoon Saurabh
Standard topological invariants, such as the Chern number and Berry phase, form the bedrock of modern
quantum matter classification. However, we demonstrate that this framework undergoes a catastrophic failure in the presence of essential singularities – ubiquitous in open, driven, and non-Hermitian systems ("Wild" regime). In these settings, the local
geometric tensor diverges, rendering standard invariants ill-defined and causing perturbative predictions to deviate from reality by order unity ($\sim 100\%$). We resolve this crisis by introducing the Floquet-Monodromy Spectroscopy (FMS) protocol, a pulse-level control sequence, which experimentally extracts the hidden Stokes Phenomenon – the "missing"
geometric data that completes the topological description. By mapping the singularity's Stokes multipliers to time-domain observables, FMS provides a rigorous experimental bridge to Resurgence Theory, allowing for the exact reconstruction of non-perturbative physics from divergent asymptotic series. We validate this framework on a superconducting qudit model, demonstrating that the "Stokes Invariant" serves as the next-generation
quantum number for classifying phases of matter beyond the reach of conventional
topology.
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