Superconductivity
Superconductivity and geometric superfluid weight of a tunable flat band system
M. A. Mojarro and Sergio E. Ulloa
We study superconductivity and superfluid weight of the two-dimensional $\alpha$-$\mathcal{T}_3$
lattice with on-site asymmetries, hosting an isolated quasi-flat band with tunable bandwidth via a parameter $\alpha$. Within a mean-field approximation of the attractive Hubbard model, we obtain the superconducting order parameters on the three inequivalent sublattices and show their strong dependence on $\alpha$, interaction strength, and electron filling. At quasi-flat band filling, a superconducting gap opens and grows power-law fast with interaction strength, instead of the usual slow exponential growth, due to diverging density of states. We calculate the superfluid weight from linear response theory and study its band dispersion and
geometric contributions. While the conventional part proportional to band derivatives is suppressed in the quasi-flat band regime, the contribution dominated by the
quantum metric grows linearly for small interaction strength. We further demonstrate how tuning $\alpha$ enhances the
quantum metric and thus the
geometric superfluid weight especially near half-filling, while increasing on-site asymmetries increases the conventional contribution by broadening the quasi-flat band. We obtain the Berezinskii-Kosterlitz-Thouless transition temperature and demonstrate its strong dependence and enhancement with the parameter $\alpha$. Our results establish a tunable flat band system, the $\alpha$-$\mathcal{T}_3$
lattice model, as a candidate for tunable
quantum geometry and superfluid weight and as a prototype of related behavior in tunable
quantum materials.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Tomographic characterization of non-Hermitian Hamiltonians in reciprocal space
Francesco Di Colandrea, Fabrizio Pavan, Sarvesh Bansal et al. (+6 more)
Non-Hermitian
Hamiltonians enrich
quantum physics by extending conventional phase diagrams, enabling novel topological phenomena, and realizing exceptional points with potential applications in
quantum sensing. Here, we present an experimental photonic platform capable of simulating a non-
unitary quantum walk generated by a peculiar type of non-Hermitian
Hamiltonian, largely unexplored in the literature. The novelty of this platform lies in its direct access to the reciprocal space, which enables us to scan the quasi-momentum across the entire Brillouin zone and thus achieve a precise tomographic reconstruction of the underlying non-Hermitian
Hamiltonian, indicated by the comparison between theoretical predictions and experimental measurements. From the inferred
Hamiltonian, it is possible to retrieve complex-valued band structures, resolve exceptional points in momentum space, and detect the associated parity-time
symmetry breaking through eigenvector coalescence. Our results, presented entirely in quasi-momentum space, represent a substantial shift in perspective in the study of non-Hermitian phenomena.
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All authors Francesco Di Colandrea, Fabrizio Pavan, Sarvesh Bansal, Paola Savarese, Grazia Di Bello, Giulio De Filippis, Carmine Antonio Perroni, Donato Farina, Filippo Cardano
Quantum Gases
Atom and spin resolved imaging in a single shot
Tobias Hammel, Maximilian Kaiser, Daniel Dux et al. (+2 more)
We report on an imaging scheme for
quantum gases that enables simultaneous detection of two
spin states with single-atom resolution. It utilizes the polarization of the emitted
photons during fluorescence by choosing appropriate internal states of lithium-6 atoms in a
magnetic field. This scheme can readily be implemented to obtain in-situ
spin correlations in a wide variety of experimental settings.
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All authors Tobias Hammel, Maximilian Kaiser, Daniel Dux, Matthias Weidemüller, Selim Jochim
Quantum Gases
Programmable Assembly of Ground State Fermionic Tweezer Arrays
Naman Jain, Jin Zhang, Marcus Culemann et al. (+1 more)
We demonstrate deterministic preparation of arbitrary two-component product states of fermionic $^6$Li atoms in an 8$\times$8 optical tweezer array, achieving motional ground-state fidelities above $98.5\,\%$. Leveraging the large differential
magnetic moments for
spin-resolution, with parallelized site- and number-resolved control, our approach addresses key challenges for low-
entropy quantum state engineering. Combined with high-fidelity
spin-, site-, and density-resolved readout within a single $20\,\mathrm{\mu s}$ exposure, and $3\,\mathrm{s}$ experimental cycles, these advances establish a fast, scalable, and programmable architecture for fermionic
quantum simulation.
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All authors Naman Jain, Jin Zhang, Marcus Culemann, Philipp M. Preiss
Soft Condensed Matter
Multimodal motion and behavior switching of multistable ciliary walkers
Sumit Mohanty, Paul Baconnier, Harmannus A.H. Schomaker et al. (+3 more)
The collective motion of arrays of cilia - tiny, hairlike protrusions - drives the locomotion of numerous microorganisms, enabling
multimodal motion and autonomous switching between gaits to navigate complex environments. To endow minimalist centimeter-scale
robots with similarly rich dynamics, we introduce millimeter-scale flexible cilia that buckle under the
robots weight, coupling multistability and actuation within a single physical mechanism. When placed on a vibrating surface, these ciliary walkers select their propulsion direction through the buckled states of their cilia, allowing
multimodal motion and switching between modes in response to perturbations. We first show that bimodal walkers with left-right symmetric cilia can autonomously reverse direction upon encountering obstacles. Next, we demonstrate that walkers with isotropic cilia exhibit both translational and rotational motion and switch between them in response to environmental interactions. At increasing densities, swarms of such walkers collectively transition from predominantly spinning to translational motion. Finally, we show that the shape, placement and number of cilia controls the modes of motion of the walkers. Our results establish a rational, physically grounded strategy for designing minimalist soft
robots where complex behaviors emerge from feedback between internal mechanical states and environmental interactions, laying the foundation for autonomous robotic collectives without the need for centralized control.
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All authors Sumit Mohanty, Paul Baconnier, Harmannus A.H. Schomaker, Alberto Comoretto, Martin van Hecke, Johannes T.B. Overvelde
Materials Science
The Impact of Magnons, Defects, and Rapid Energy Migration on the Optical Properties of the 2D Magnet CrPS4
Jacob T. Baillie, Eden Tzanetopoulos, Rachel T. Smith et al. (+2 more)
Strong coupling between optical and
magnetic excitations could enable contactless, spatially resolved, or ultrafast interrogation and control of magnetism in two-dimensional (2D) materials and devices. The layered 2D A-type antiferromagnet CrPS4 stands out among van der Waals (vdW) magnets for its rich optical fine structure, but its spectroscopy is not yet understood and has so far been interpreted without consideration of
magnetic exchange. Here, we show that this fine structure comes primarily from exchange-mediated coupling between on-site optical "
spin-flip" transitions of Cr3+ and low-energy
spin transitions involving the surrounding
lattice. Well-resolved
magnon sidebands to optical 4A2 <–> 2E transitions are observed in photoluminescence (PL) and PL excitation spectra, as well as a pronounced PL sideband due to short-range exchange splitting. Energy migration is probed using Yb3+ dopants as traps, revealing sub-picosecond inter-site excitation hopping. Formation of dispersive Frenkel
excitons of coupled on-site d-d transitions due to inter-site exchange is discussed. In addition to impacting how optical fine structure is interpreted in this and potentially other vdW magnets, these findings may have ramifications for future applications of layered 2D magnets by revealing new opportunities to drive mode-specific
spin-wave excitations using light.
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All authors Jacob T. Baillie, Eden Tzanetopoulos, Rachel T. Smith, Remi Beaulac, Daniel R. Gamelin
Materials Science
Linear and Nonlinear Optical Properties of SiO$_2$/TiO$_2$ Heterostructures Grown by Plasma Enhanced Atomic Layer Deposition
Jinsong Liu, Martin Mičulka, Raihan Rafi et al. (+7 more)
Second harmonic (SH) radiation can only be generated in non-centrosymmetric bulk
crystals under the electric-dipole approximation. Nonlinear thin films made from bulk
crystals are technologically challenging because of complex and high temperature fabrication processes. In this work,
heterostructures made of amorphous materials SiO$_2$ and TiO$_2$ were prepared by a CMOS-compatible technique named
plasma enhanced atomic layer deposition (PEALD) with deposition temperature at 100 {\deg}C. By using the uniaxial dispersion model, we characterized the form-birefringence properties, which can enable the phase matching condition in waveguides or other nonlinear optical applications. By applying a fringe-based technique, we determined the largest diagonal component of the effective second-order bulk susceptibility $\chi_{zzz}^{(2)}$ = 1.30$\pm$0.13 pm/V at a wavelength of 1032 nm. Noteworthy, we observed strong SH signals from two-component nanolaminates, which are several orders of magnitude larger than from single layers. The SH signals from our samples only require the broken inversion
symmetry at the interface. Here optical properties of nanocomposites can be precisely tuned by the promising PEALD technology.
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All authors Jinsong Liu, Martin Mičulka, Raihan Rafi, Sebastian Beer, Denys Sevriukov, Stefan Nolte, Sven Schröder, Andreas Tünnermann, Isabelle Staude, Adriana Szeghalmi
Statistical Mechanics
Burgers dynamics for Poisson point process initial conditions of the Weibull class
Patrick Valageas
We derive the statistical properties of one-dimensional Burgers dynamics with
stochastic initial conditions for the velocity potential defined by a Poisson point process whose intensity follows a power law with exponent $\alpha > -1$. Working in the inviscid limit and exploiting the geometrical construction of solutions in terms of first-contact parabolas, we derive explicit analytical expressions for a broad set of statistical quantities. These include the one- and two-point probability distributions of the velocity, the multiplicity functions of voids and shocks, and the velocity and density correlation functions together with their associated power spectra. We also show that the full hierarchy of $n$-point distributions factorizes into a sequence of two-point conditional probabilities. This class of initial conditions leads to self-similar
evolution and produces probability distributions characterized by stretched-exponential tails, with tail exponents spanning the full range from unity to infinity. The associated characteristic length scale grows as a power law of time, with an exponent lying between zero and one half.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.chem-ph
Frequency-Dependent Polarization Propagator Calculation for Quantum Dots Using Optimized Inverse Krylov Subspace and Folded-Spectrum Method
Chandler Martin, Nicole Spanedda, Anaira Jalan et al. (+3 more)
Accurate prediction of the frequency response of
quantum dots under electromagnetic radiation is essential for investigating absorption spectra, excitonic effects, and nonlinear optical behavior in
quantum dots and
semiconductor nanoparticles. The polarization propagator provides a rigorous framework for evaluating these properties, but its construction is computationally demanding. Challenges arise from the level of electron correlation, the size of the excitonic basis, and the cost of evaluating two-electron integrals. This work addresses these difficulties by developing first- and second-order frequency-dependent polarization propagator calculations for PbS and CdS
quantum dots. The propagator is formulated using the electron propagator approach and expressed as the resolvent of the
Hamiltonian superoperator. Light-matter interaction is treated using the dipole approximation and represented in a particle-hole excitation operator basis. The correlated ground state is treated at the MP2 level, and all response-
matrix terms up to second order in the fluctuating potential are included. A frequency-dependent inverse Krylov subspace method is derived and combined with the folded-spectrum technique to isolate excitation energies within a chosen frequency window. This strategy avoids full diagonalization of the response
matrix and significantly reduces computational cost for large systems. The method is implemented in a
matrix-free manner in which no explicit response
matrix is assembled, and all operations rely on
matrix-vector products. UV-VIS excitation spectra of PbS and CdS
quantum dots were computed, demonstrating that the inverse Krylov subspace projection approach provides an efficient and accurate approximation for excitation spectra when full diagonalization is computationally prohibitive.
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All authors Chandler Martin, Nicole Spanedda, Anaira Jalan, Emily Schafer, Jessica Beyer, Arindam Chakraborty
Materials Science
A Rapid-prototyping CMOS-RRAM Integration Strategy
Andreas Tsiamis, Spyros Stathopoulos and Themis Prodromakis
Moore's law has long served the
semiconductor industry as the driving force for producing ever-advancing electronics technologies. However, given the economic implications and technological challenges associated with the present
semiconductor scaling constraints, a shift from a traditional more Moore approach to a beyond Moore paradigm is desirable for sustaining the current pace of innovation beyond the established development route. Resistive random-access
memories (RRAM) are one such beyond Moore technology that offers many avenues for innovation, and when integrated with mature complementary metal
oxide semiconductors (CMOS), can extend CMOS capabilities in a scalable and power-efficient manner, both in terms of
memory and computation. Nevertheless, as emerging and established technologies fuse, existing
semiconductor-optimised manufacturing faces significant challenges, while the methodologies and complexities of integration are often not highlighted in depth, or overlooked at the expense of demonstrating the application-specific integrated-technologies. In this article, we focus on the integration, and detail a cost-effective, rapid-prototyping, and technology agnostic CMOS-RRAM integration strategy that employs hybridised wafer-level and multi-reticle processing techniques, supported by a systematic increased complexity approach. Leveraging the fact that CMOS technologies can be readily realised by taking advantage of mature front-end-of-line fabrication processes offered by
semiconductor foundries, we establish an in-house RRAM development program that allows to combine fundamental material and device-level knowledge with custom-designed CMOS electronics. This approach utilises fully CMOS-compatible and transferable processes, ultimately enabling a seamless transition from research and development to volume production.
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Superconductivity
Evolution of the pseudogap and excess conductivity of YBa$_2$Cu$_3$O$_{7-\delta}$ single crystals in the course of long-term aging
A. L. Solovjov, L. V. Bludova, M. V. Shytov et al. (+3 more)
The temperature dependences of both fluctuation conductivity (FLC) $\sigma^\prime(T)$ and pseudogap (PG) $\Delta^*(T)$ derived from measurements of resistivity $\rho(T)$ of an optimally doped YBa$_2$Cu$_3$O$_{7-\delta}$ single
crystal subjected to long-term storage have been studied. The as-grown sample S1 exhibits characteristics typical of optimally doped YBa$_2$Cu$_3$O$_{7-\delta}$ single
crystals containing twins and twin boundaries. Analysis of both FLC and PG showed an unexpected improvement in all characteristics of the sample after 6 years of storage (sample S2), indicating that the effect of twin boundaries is somehow limited. After 17 years of storage, all characteristics of the sample changed dramatically, which indicates a strong influence of internal defects formed during the aging process. For the first time, the temperature dependences of both FLC and PG were obtained after 17 years of storage.
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All authors A. L. Solovjov, L. V. Bludova, M. V. Shytov, S. N. Kamchatnaya, Z. F. Nazyrov, R. V. Vovk
Materials Science
Mechanical Detuning of Exciton-Phonon Resonance in WS2
Álvaro Rodríguez, Carmen Munuera and Andres Castellanos-Gomez
Controlling resonant Raman scattering in two-dimensional
semiconductors typically requires tuning the excitation energy to match excitonic transitions. Here we show that mechanical deformation can achieve the same effect without changing the
laser energy, enabling a controlled transition between resonant and non-resonant Raman scattering at fixed excitation. By applying biaxial strain up to 1.3% to WS2, the B
exciton is red-shifted by 180 meV. This large excitonic shift leads to a pronounced collapse of the double-resonant 2LA(M) mode under 532 nm excitation, quantitatively described by a resonance model formulated in terms of the B
exciton energy. Meanwhile, first-order
phonons remain narrow and reversible, confirming elastic deformation and efficient strain transfer. These results establish mechanical strain as an effective knob to control
exciton-
phonon mediated light-matter interactions. They enable deterministic and reversible tuning of resonance-enhanced Raman scattering and excitonic optical responses in layered
semiconductors.
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Quantum Gases
Confinement and finite-range effects in a quasi-two-dimensional gas of fermionic dimers
Giovanni Midei, Jordi Boronat and Grigory E. Astrakharchik
We investigate the ground-state properties of ultracold two-component
Fermi gases in the presence of a transverse harmonic potential, focusing on the strongly interacting regime in which pairs of
fermions form tightly bound molecules. Using the fixed-node
diffusion Monte Carlo method, we calculate the equation of state and density profiles for the full fermionic system, which allows us to address the importance of finite-range corrections arising from the internal fermionic structure of the dimers. We interpret the results in terms of a molecular Bose gas in quasi-two-dimensional confinement and compare them with theoretical predictions for a weakly interacting two-dimensional Bose gas, identifying the range of validity of mean-field and beyond-mean-field descriptions. We also develop an analytical theory for the transverse density profile, capturing its broadening with increasing interaction strength. This work provides a
benchmark for an effective bosonic description of strongly bound fermionic dimers and offers new insights into confinement-induced dimensional effects.
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Materials Science
Gate tuning of coupled electronic and structural phase transition in atomically thin Ta$_2$NiSe$_5$
Keyu Wei, Yixuan Luo, Kenji Watanabe et al. (+3 more)
Realizing an excitonic
insulator phase from narrow-gap
semiconductors remains challenging, as unambiguous experimental signatures are difficult to establish. Ta$_2$NiSe$_5$ has been widely regarded as a leading candidate, yet the nature of its phase transition and insulating state remains controversial. Here, we report a systematic Raman spectroscopy study of Ta$_2$NiSe$_5$ as a function of thickness and field-effect doping, complemented by electrical transport measurements. The phase transition persists down to the monolayer limit, with the critical temperature increasing as thickness decreases. In
bilayer samples, both electron and hole doping suppress the insulating state, with electron doping lowering and hole doping raising the transition temperature. Importantly, the quasi-elastic scattering, previously attributed to excitonic fluctuations, evolves monotonically across the entire doping range, inconsistent with the expected suppression of excitonic correlations by Coulomb screening. These findings rule out a dominant excitonic mechanism and instead point to a coupled electronic and structural phase transition, whose stability is tunable by carrier doping. Our doping-based approach offers a general strategy for evaluating the role of excitonic effects in candidate excitonic
insulators.
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All authors Keyu Wei, Yixuan Luo, Kenji Watanabe, Takashi Taniguchi, Yanfeng Guo, Xiaoxiang Xi
Strongly Correlated Electrons · Cross-listed from quant-ph
Quantum error correction via purification using a single auxiliary
Chandrima B. Pushpan, Tanoy Kanti Konar, Aditi Sen De et al. (+1 more)
We propose a single auxiliary-assisted purification-based framework for
quantum error correction, capable of correcting errors that drive a system from its ground-state subspace into excited-state sectors. The protocol consists of a joint time
evolution of the system-auxiliary duo under a specially engineered interaction
Hamiltonian, followed by a single measurement of the auxiliary in its energy eigenbasis and a subsequent post-selection of one of the measurement outcomes. We show that the resulting purified state always achieves unit fidelity, while the probability of obtaining any energy of the auxiliary other than its ground state energy yields the success rate of the protocol. We demonstrate the power of this proposed method for several low-distance
quantum codes, including the three-, four-, and five-
qubit codes, and for the one-dimensional isotropic Heisenberg model, subjected to bit-flip, phase-flip, and amplitude-damping noises acting on all
qubits. Notably, the protocol expands the class of correctable errors for a given code, particularly in the presence of amplitude-damping noise. We further analyze the impact of replacing the auxiliary qudit with a single auxiliary
qubit, and the changes in the performance of the protocol under the realistic scenario where noise remains active during the correction cycle.
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All authors Chandrima B. Pushpan, Tanoy Kanti Konar, Aditi Sen De, Amit Kumar Pal
Statistical Mechanics
Hitting the blinking target under stochastic resetting
Bartosz Zbik, Bartłomiej Dybiec, Karol Capała et al. (+2 more)
The first hitting times of a
stochastic process, i.e., the first time a process reaches a particular level, are of significant interest across various scientific disciplines, including biology, chemistry, and economics. We modify the standard setup by allowing the target to spontaneously switch between two states, either active or inactive, and investigate the distribution of first hitting times accrued while the target is active. For this setup, we provide closed formulas for the distribution of the first hitting time. Additionally, we can introduce
stochastic resetting to the underlying process and, utilizing our results, derive the formulas for the first time the active target is hit by the process under
stochastic resetting. Interestingly, we show that resetting in this setup still leaves some
memory; the system is no longer Markovian, which prevents a straightforward application of standard techniques. The analytical results are accompanied by computer simulations of Langevin dynamics.
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All authors Bartosz Zbik, Bartłomiej Dybiec, Karol Capała, Zbigniew Palmowski, Igor M. Sokolov
Materials Science
Structural Optimization in Tensor LEED Using a Parameter Tree and $R$-Factor Gradients
Alexander M. Imre, Paul Haidegger, Florian Kraushofer et al. (+10 more)
Quantitative low-energy electron diffraction [LEED $I(V)$] is a powerful method for surface-structure determination, based on a direct comparison of experimentally observed $I(V)$ data with computations for a structure model. As the diffraction intensities $I$ are highly sensitive to subtle structural changes, local structure optimization is essential for assessing the validity of a structure model and finding the best-fit structure. The calculation of diffraction intensities is well established, but the large number of evaluations required for reliable structural optimization renders it computationally demanding. The computational effort is mitigated by the tensor-LEED approximation, which accelerates optimization by applying a perturbative treatment of small deviations from a reference structure. Nevertheless, optimization of complex structures is a tedious process. Here, the problem of surface-structure optimization is reformulated using a tree-based data structure, which helps to avoid redundant function evaluations. In the new tensor-LEED implementation presented in this work, intensities are computed on the fly, eliminating limitations of previous
algorithms that are limited to precomputed values at a grid of search parameters. It also enables the use of state-of-the-art optimization
algorithms. Implemented in Python with the JAX library, the method provides access to gradients of the $R$ factor and supports execution on graphics processing units (GPUs). Based on these developments, the computing time can be reduced by more than an order of magnitude.
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All authors Alexander M. Imre, Paul Haidegger, Florian Kraushofer, Ralf Wanzenböck, Tobias Hable, Sarah Tobisch, Marie Kienzer, Florian Buchner, Jesús Carrete, Georg K. H. Madsen, Michael Schmid, Ulrike Diebold, Michele Riva
Statistical Mechanics
Burgers equation from non-thermal stationary states in nearly-integrable gases
Paweł Lisiak, Maciej Łebek and Miłosz Panfil
When a gas of particles interacts with much a larger reservoir the density dynamics on large scales is typically governed by
diffusion. We study this paradigmatic problem for weakly coupled integrable systems and show that this picture gets altered, when transport is investigated on top of long-lived non-thermal states. Remarkably, for states non-invariant under parity we find Burgers equation arising in the hydrodynamic limit. We explicitly compute the
diffusion constant and nonlinear advective coefficient of the Burgers equation using a variant of the Chapman-Enskog theory. We find an excellent agreement between our theory and numerical simulations of a simplified model of
stochastic two-body collisions. Our conclusions are based only on Galilean invariance, existence of a small system-bath coupling parameter and a small momentum exchange between the system and the bath particles during two-body scattering.
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Statistical Mechanics
Synchronization of thermodynamically consistent stochastic phase oscillators
Maciej Chudak, Massimiliano Esposito and Krzysztof Ptaszynski
We consider a toy model of two kinetically coupled
stochastic oscillators whose dynamics is described as a Markov jump process among $N$ discrete phase states. For large $N$, it maps onto the deterministic two-oscillator Kuramoto model of synchronization. Despite its simplicity, we postulate its relevance for understanding more complex and realistic oscillator systems. In the thermodynamic limit, the model exhibits a continuous nonequilibrium phase transition between the unsynchronized and synchronized states. We show that this transition is not governed by any extremum dissipation principle – depending on system parameters, synchronization may either reduce or enhance the dissipation. Close to the phase transition, we observe a divergent behavior of fluctuations and responses with $N$ and characterize their universal scaling behavior. In particular, the covariances of the oscillator phases and the local
entropy productions are shown to diverge towards $-\infty$, a phenomenon that has not been reported before. Finally, we study the behavior of information-theoretic quantities, demonstrating that mutual information and information flow between oscillators display different scaling with $N$ in synchronized and unsynchronized states, and thus can act as order parameters of synchronization.
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Quantum Gases
Time-dependent condensation of bosonic dysprosium
Max Regalado Kloos and Georg Wolschin
We investigate thermalization and time-dependent Bose-Einstein condensate formation in ultracold Dy-164 using a nonlinear
boson diffusion equation. As compared to alkali atoms such as K-39 or Rb-87, the strong
magnetic dipole interaction modifies the scattering-length dependence of the transport coefficients that govern thermalization and condensate formation. A prediction for the time-dependent condensate fraction in Dy-164 is made.
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Mesoscale and Nanoscale Physics
Reinterpreting Landauer conductance, solving the quantum measurement problem, grand unification
Kanchan Meena, Souvik Ghosh and P. Singha Deo
In a series of recent papers we have proved rigorously that time travel is a reality and very much feasible by using
quantum mechanical processes. There are plenty of indirect experimental support untill a direct experiment is conducted. The process crucially depend on the reality of a local time as well as a local partial density of states (LPDOS) that can become negative very easily in the
quantum regime of mesoscopic systems. Mesoscopic systems are small enough to allow us to experimentally access the intermediate regime between the classical and
quantum worlds. This LPDOS is in every sense a hidden variable in
quantum mechanics that does not show up in the axiomatic framework of
quantum mechanics. It can be inferred through physical clocks obeying
quantum dynamics and can be rigorously justified from the properties of the
Hilbert space that is uniquely isomorphic to the complex plane. Therefore one can naturally guess that LPDOS will have something important to say about
quantum measurement as well as the unification of classical and
quantum laws. We therefore undertake the exercise to show that LPDOS can very much allow us to re-interpret the enormously successful phenomenological Landauer-Buttiker formalism for mesoscopic systems and put it on firm theoretical ground as a bridge between classical and
quantum mechanics, thereby unifying them. Essentially the local time calculated
quantum mechanically can dilate exactly like the proper time of relativity and be consistent with the coordinate time of relativity. Also the measured conductance of mesoscopic samples is a deterministic
quantum measurement outcome from a linear superposition of states, essentially because of LPDOS, which solves the
quantum measurement problem. For this we analyze the three probe conductance formula in details and give our arguments for the general case.
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Materials Science
Molecular Dynamics Simulations of $\gamma$-Belite(010)-Water Interfaces with High-Dimensional Neural Network Potentials
Bernadeta Prus and Jörg Behler
Belite – dicalcium silicate Ca$_2$SiO$_4$ – is a main constituent of low-carbon cement. In this work, we study several terminations of the (010) surface of $\gamma$-belite, its most stable polymorph, by molecular dynamics simulations. The energies and forces are provided by a high-dimensional neural network potential trained to density functional theory data. Water can interact in molecular form as well as dissociatively with the investigated interfaces, and the degree of dissociation is determined primarily by the protonation of SiO$_4$ groups accessible at the surface. A major part of the simultaneously formed hydroxide ions is adsorbed at surface calcium atoms, whose octahedral coordination spheres are completed by additional water molecules. The T3 termination, which is most stable in
vacuum, shows only little reactivity in water. For the only slightly less stable T2 termination, however, two distinct types of surface defects are observed. The type I defect is even stable in
vacuum and leads to a reconstruction of the entire surface, while the type II defect is only found in the presence of water. Overall, our results suggest that a variety of structures may be formed at the Ca$_2$SiO$_4$(010) surface, which are stabilized in the presence of water.
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Strongly Correlated Electrons
Contrasting magnetic behavior in MnSc_2X_4 (X = S, Se) spinel compounds investigated by magnetoelastic studies
J. Grumbach, J. Sourd, M. Deeb et al. (+12 more)
The spinel compounds MnSc_2X_4 are highly frustrated and candidate materials for
vortex-like 3q
magnetic states, such as skyrmions, with propagation vectors in the [111] plane. Because of the strong magnetoelastic coupling, we could extract a refined
magnetic (H, T) phase diagram for MnSc_2S_4 from ultrasound and dilatometry measurements. We found a variety of
magnetic phases, including the skyrmion phase, which is stable down to lowest temperatures. In comparison, we investigated MnSc_2Se_4 , having a larger distance between the
magnetic Mn^3+ ions using the same methods. Unlike in MnSc_2S_4 , we found no skyrmion phase and overall a lack of sharp anomalies indicative of phase transitions, neither in dilatometry nor ultrasound nor in specific heat and ac-susceptibility data. Motivated by our findings, we performed model calculations, which reproduced the experimentally observed magnetostriction and specific-heat results reasonably well.
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All authors J. Grumbach, J. Sourd, M. Deeb, A. Miyata, H. Suwa, T. Gottschall, A. Hauspurg, S. Chattopadhyay, M. Rotter, S. Granovsky, L. Prodan, V. Tsurkan, S. Zherlitsyn, M. Doerr, J. Wosnitza
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Three-body interaction in a magnon-Andreev-superconducting qubit system: collapse-revival phenomena and entanglement redistribution
Sheng Zhao and Peng-Bo Li
Three-body interactions are fundamental for realizing novel
quantum phenomena beyond pairwise physics, yet their implementation – particularly among distinct
quantum systems – remains challenging. Here, we propose a hybrid
quantum architecture comprising a magnonic mode (in a YIG sphere), an Andreev
spin qubit (ASQ), and a superconducting
qubit (SCQ), to realize a strong three-body interaction at the single-
quantum level. Leveraging the
spin-dependent supercurrent and
circuit-integration flexibility of the ASQ, it is possible to engineer a strong tripartite coupling that jointly excites both
qubits upon
magnon annihilation (or excites
magnons and SCQs upon ASQ deexcitation). Through analytical and numerical studies, we demonstrate that this interaction induces synchronized collapse and revival in
qubit populations when the
magnon is initially prepared in a coherent state. Notably, during the collapse region – where populations remain static – the
entanglement structure undergoes a dramatic and continuous reorganization. We show that the genuine tripartite
entanglement is redistributed into bipartite
entanglement between the two
qubits, and vice versa, with the total
entanglement conserved. These phenomena, unattainable via two-body couplings, underscore the potential of three-body interactions for exploring intrinsically new
quantum effects and advancing hybrid
quantum information platforms.
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Mesoscale and Nanoscale Physics
Domain Wall Control of Topological Qubits in the Kitaev SSH Chain
Griffith Rufo, Sabrina Rufo, Heron Caldas et al. (+1 more)
Zero energy states in one dimensional SSH Kitaev hybrid systems have emerged as promising candidates for topological
qubits. In our work, we show that introducing a domain wall into a chain with anisotropic superconducting correlations provides a powerful way to control both the number and the nature of these boundary modes. The defect acts as a digital knob: its presence or absence flips the parity of zero modes and thus decides whether an isolated Majorana exists at the chain ends. This on/off mechanism is significantly more robust and simpler than fine-tuning global parameters such as chemical potential or hopping amplitudes. Moreover, anisotropy provides an additional lever to calibrate the effect of the defect, opening a pathway to architectures where topological
qubits can be locally addressed by domain walls. This proposal reframes defects not as imperfections, but as useful resources for
quantum information and computation.
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All authors Griffith Rufo, Sabrina Rufo, Heron Caldas, Rosiane de Freitas
Materials Science
Resistance Switching Properties of Stoichiometric and Nitrogen Implanted Silicon Nitride Nanolayers on N and P-Type Si Substrates
A. E. Mavropoulis, P. Karakolis, N. Vasileiadis et al. (+6 more)
This paper examines the resistive switching characteristics of LPCVD SiNx MNOS ReRAM
cells on both heavily doped n- and p-type silicon substrates, focusing on the effects of nitrogen doping. Detailed comparisons of electrical properties through nitrogen implantation reveal variations in trap density and SET-RESET voltages between n and p conductivity Si substrates. Impedance spectroscopy further elucidates the conductive path formation and its resistance.
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All authors A. E. Mavropoulis, P. Karakolis, N. Vasileiadis, L. Sygellou, E. Stavroulakis, V. Ioannou-Sougleridis, P. Normand, G. Ch. Sirakoulis, P. Dimitrakis
Materials Science
Breakdown characteristics of SiNx with different stoichiometries for resistive memories
A.E. Mavropoulis, I. Kanellopoulos, G. Pissanos et al. (+6 more)
The breakdown characteristics of SiNx layers with different stoichiometries are explored. The stoichiometry of SiNx is modified by changing the gas flow rates during the LPCVD deposition. These layers are suitable for RRAM
cells.
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All authors A.E. Mavropoulis, I. Kanellopoulos, G. Pissanos, G. Samara, N. Vasileiadis, E. Stavroulakis, P. Normand, G. Ch. Sirakoulis, P. Dimitrakis
Materials Science
SiNx RRAMs performance with different stoichiometries
A.E. Mavropoulis, G. Pissanos, N. Vasileiadis et al. (+3 more)
The microstructure of SiNx is strongly affected by its stoichiometry, x. The stoichiometry of SiNx thin films can be modified by adjusting the gas flow rates during LPCVD deposition. The deficiency or excess of Si atoms enhance the formation of defects such as nitrogen vacancies, silicon dangling bonds etc., and thus can enable performance tuning of the resulting MIS RRAM devices. DC electrical characterization, impedance spectroscopy and constant voltage stress measurements were carried out to investigate the properties of non-stoichiometric silicon nitride films as resistive switching material. The average SET time for each device was measured by applying voltage ramps. Improvement in the SET/RESET voltages and SET time is observed. Finally, the stoichiometric film exhibits the lowest breakdown acceleration factor, while the Si-rich film the highest.
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All authors A.E. Mavropoulis, G. Pissanos, N. Vasileiadis, P. Normand, G.Ch. Sirakoulis, P. Dimitrakis
Disordered Systems and Neural Networks
Topological boundaries in non-Hermitian p-wave Kitaev chains with Rashba spin-orbit coupling
Shahroze Shahab, Aditi Chakrabarty and Sanjoy Datta
In this work, we investigate the combined effects of Rashba
spin-orbit coupling (RSOC) and non-Hermiticity on topological phase transitions in spinful p-wave Kitaev chains. While previous studies have separately examined non-Hermitian (NH) extensions of Kitaev chains and the effects of RSOC in Hermitian systems, the interplay between these two mechanisms remains largely unexplored. We analyze this interplay by considering two distinct types of complex on-site potentials: (i) a uniform gain/loss term and (ii) a complex quasiperiodic potential. We demonstrate that the impact of RSOC is highly model-dependent. In particular, RSOC does not affect the topological phase boundary in the Hermitian limit of the uniform gain/loss model (provided the
spin-flip hopping is weaker than the pairing strength), but significantly alters the topological landscape in the NH regime. In contrast, for the quasiperiodic model, RSOC modifies the phase boundaries in both the Hermitian and non-Hermitian cases. Notably, we find that the combined interplay of non-Hermiticity and RSOC drives topological transitions at significantly lower potential strengths compared to the Hermitian limit. We derive analytical expressions for the topological phase transitions in both cases and validate our predictions through numerical calculations of energy spectra and real-space winding numbers. This work provides a comprehensive understanding of how non-Hermiticity and RSOC cooperatively reshape topological phase diagrams in one-dimensional superconducting systems.
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Materials Science
Theoretical Characterization of the Magnetic Properties of Vanadium-doped Ti2C MXenes
Carlos Patiño, Pablo Díaz, Nicolás Vidal-Silva et al. (+3 more)
MXenes are two-dimensional materials composed of transition metals and light elements, known for their high conductivity and versatile surface chemistry. The introduction of
spin centers via doping can lead to promising materials for spintronics,
magnetic sensing, and data storage. We study the effect of V doping in Ti2C using first principle and Monte-Carlo simulations. Our results show that pristine Ti2C exhibits
ferromagnetic intralayer and
antiferromagnetic interlayer exchange interactions, yielding an
antiferromagnetic ground state. Vanadium incorporation alters these couplings, yet all doped configurations - Ti7VC4 and three Ti6V2C4 variants - retain predominantly
antiferromagnetic order. Despite the preserved ground state, V doping enhances the
magnetic response, most notably in the p-Ti6V2C4 configuration, which displays increased low-field susceptibility and partial
spin alignment across layers. As experimentally isolating individual doped phases is unlikely, samples will consist of mixed configurations whose collective behavior nonetheless exhibits clear signatures of V-induced
magnetic modification. These results reveal how transition-metal substitution tunes exchange interactions in MXenes and offer guidance for engineering their
magnetic functionalities.
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All authors Carlos Patiño, Pablo Díaz, Nicolás Vidal-Silva, Eduardo Cisternas, Eugenio Vogel, Fabian Dietrich