Mesoscale and Nanoscale Physics
Weak localization and universal conductance fluctuations in large area twisted bilayer graphene
Spenser Talkington, Debarghya Mallick, An-Hsi Chen et al. (+7 more)
We study diffusive magnetotransport in highly p-doped large area twisted
bilayer graphene in 1{\deg}, 7{\deg}, 9{\deg} and 20{\deg} samples. We report weak localization in twisted
bilayer graphene for the first time. All samples exhibit weak localization, from which we extract the phase coherence length and intervalley scattering lengths, and from that determine that dephasing is caused by electron-electron scattering and intervalley scattering is caused by point defects. We observe signatures of universal conductance fluctuations in the 9{\deg} sample, which has high mobility and is near the van Hove singularity. Further improvements in sample quality and applications to large area moire materials will open new avenues to observe
quantum interference effects.
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All authors Spenser Talkington, Debarghya Mallick, An-Hsi Chen, Benjamin F. Mead, Seong-Jun Yang, Cheol-Joo Kim, Shaffique Adam, Liang Wu, Matthew Brahlek, Eugene J. Mele
Strongly Correlated Electrons
Characterizing Mott Insulators in the Interacting One-Body Picture
Theo N. Dionne, Santiago Villodre, Mikel Iraola et al. (+1 more)
The one-body picture underlies our understanding of weakly interacting solids but breaks down in strongly correlated systems. We develop a general framework, based on the single-particle Green's function and the one-body reduced density
matrix (1RDM), to characterize correlated electronic phases. Applying it to the Hubbard diamond chain, we combine density
matrix renormalization group and cellular dynamical mean-field theory to construct
symmetry-resolved effective orbitals and track their
evolution across its Mott transitions, while the 1RDM purity provides a scalar indicator of the phase boundaries. These tools offer a general route to extend one-body concepts to correlated materials.
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All authors Theo N. Dionne, Santiago Villodre, Mikel Iraola, Maia G. Vergniory
Mesoscale and Nanoscale Physics
Optically-Induced Faraday-Goldstone Waves
Daniel Kaplan, Pavel A. Volkov, Andrea Cavalleri et al. (+1 more)
Faraday waves, typically observed in driven fluids, result from the confluence of nonlinearity and parametric amplification. Here we show that optical pulses can generate analogous phenomena that persist much longer than the pump time-scales in ordered
quantum solids. We present a theory of ultrafast light-matter interactions within a
symmetry-broken state; dynamical nonlinear coupling between the
Higgs (amplitude) and the Goldstone (phase) modes drives an emergent phason texture that oscillates in space and in time: Faraday-Goldstone waves. Calculated signatures of this spatiotemporal order compare well with measurements on K$_{0.3}$MnO$_{3}$;
Higgs-Goldstone beating, associated with coherent energy exchange between these two modes, is also predicted. We show this light-generated crystalline state is robust to thermal noise, even when the original Goldstone mode is not. Our results offer a new pathway for the design of periodic structures in
quantum materials with ultrafast light pulses.
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All authors Daniel Kaplan, Pavel A. Volkov, Andrea Cavalleri, Premala Chandra
Superconductivity · Cross-listed from hep-ph
Phases and properties of color superconductors
Andreas Schmitt
Cold and dense matter is expected to be in a color-superconducting state. Here we review two calculations, relevant for fundamental properties and applications of color superconductivity, respectively: the weak-coupling QCD calculation of the fermionic energy gap together with the
magnetic screening masses of the gauge
bosons, and the calculation of bulk viscosity from a non-leptonic electroweak process. These calculations are supplemented by a discussion of color
superconductors with mismatched
Fermi momenta, and they are embedded in the context of the state of the art by giving an overview of previous and ongoing work and future directions.
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Statistical Mechanics
Persistence of the Berezinskii-Kosterlitz-Thouless transition with long-range couplings
Luis Walther, Josef Willsher and Johannes Knolle
The Berezinskii-Kosterlitz-Thouless (BKT) transition is an archetypal example of a topological phase transition, which is driven by the proliferation of
vortices. In this Letter, we analyze the persistence of the BKT transition in the XY model under the influence of long-range algebraically decaying interactions of the form $\sim 1/{r^{2+\sigma}}$. The model hosts a magnetized low temperature phase for sufficiently small $\sigma$. Crucially, in the presence of long-range interactions,
spin waves renormalize the interaction between
vortices, which stabilizes the BKT transition. As a result, we find that there is no direct transition from the magnetized to the disordered phase and that the BKT transition persists for arbitrary long-range exponents, which is distinct from previous results. We use both Landau-Peierls-type arguments and renormalization group calculations - including a coupling between
spin wave and topological excitations - and obtain similar results. We emphasize that Landau-Peierls-type arguments are a powerful tool for analyzing continuous
spin models. We discuss the relevance of our findings for current Rydberg atom experiments, and highlight the importance of long-range couplings for other types of topological defects.
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Strongly Correlated Electrons
Thermal Tensor Network Simulations of Lattice Fermions with Fixed Filling
Qiaoyi Li, Dai-Wei Qu, Bin-Bin Chen et al. (+2 more)
Numerical simulations of strongly correlated
fermions at finite temperature are essential for studying high-temperature superconductivity and other
quantum many-body phenomena. The recently developed tangent-space tensor renormalization group (tanTRG) provides an efficient and accurate framework by representing thermal density operators as
matrix product operators. However, the particle number generally varies during the cooling process. The conventional strategy of fine-tuning chemical potentials to reach a target filling is computationally demanding. Here we propose a fixed-$N$ tanTRG
algorithm that stabilizes the average particle number by adaptively tuning the chemical potential within the imaginary-time
evolution. We
benchmark its accuracy on exactly solvable free
fermions, and further apply it to the square-
lattice Hubbard model. For hole-doped cases, we study the temperature
evolution of charge and
spin correlations, identifying several characteristic temperature scales for stripe formation. Our results establish fixed-$N$ tanTRG as an efficient and reliable tool for finite-temperature studies of correlated
fermion systems.
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All authors Qiaoyi Li, Dai-Wei Qu, Bin-Bin Chen, Tao Shi, Wei Li
Materials Science
Oxygen vacancies in vanadium dioxide: A DFT$+V$ study
Oskar Leibnitz, Peter Mlkvik, Nicola A. Spaldin et al. (+1 more)
We present a density-functional theory study of the effects of oxygen vacancies on the structural and electronic properties of vanadium dioxide (VO$_2$). Our motivation is the reported suppression of the metal-
insulator transition by oxygen vacancies and the lack of a clear consensus on its origin. We use the DFT$+V$ method with a static intersite vanadium-vanadium interaction term, $V$, to calculate the properties of the oxygen-deficient metallic rutile and insulating monoclinic M1 phases of VO$_2$ on the same footing. We find that oxygen vacancies induce local distortions in the M1 phase, but do not destroy the dimerization usually associated with the insulating behavior. In spite of this, we find that the M1 phase becomes metallic as a result of the partial filling of the conduction band due to a rigid-band-like doping effect.
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All authors Oskar Leibnitz, Peter Mlkvik, Nicola A. Spaldin, Claude Ederer
Soft Condensed Matter
From Fresh to Salty: How Ions Modulate Solvent-Mediated Interactions between Grafted Silica Nanoparticles in Water
Yuvraj Singh, Chandan K. Choudhury and Rakesh S. Singh
Nanoparticles (NPs) are fundamental building blocks for engineering functional soft materials, where precise control over the solvent-mediated inter-particle effective interaction (Ueff) is essential for tailoring bulk structure and properties. These solvent-mediated interactions are strongly influenced by NP's surface chemistry, solvent properties, and thermodynamic conditions such as temperature (T) and pressure (P). However, despite considerable progress, a general predictive framework for tuning Ueff and guiding self-assembly remains lacking. In this work, using all-atom molecular dynamics simulations, we investigated the alteration of Ueff between silica nanoparticles (Si-NPs) functionalized with polyethylene (PE) and polyethylene glycol (PEG) by salt (sodium chloride) across a range of thermodynamic conditions. At ambient thermodynamic conditions, bare (not functionalized) Si-NPs exhibit minimal variation in Ueff even at high salt concentrations. In contrast, PE-grafted Si-NPs display strong salt-induced attractions, while PEG-grafted Si-NPs show an intermediate, more gradual response. To asses the transferability of these salt-induced effects on effective interactions, we further examined the effects of salt on Ueff under different (T,P) conditions. Our results indicate that the salt-induced modulation of Ueff between both bare and grafted Si-NPs is largely invariant across the explored (T,P) conditions. Molecular-level analysis reveals that salt promotes solvent depletion within the interparticle cavity for both hydrophobic PE and hydrophilic PEG grafts, with the strongest effect observed in the PE case. In general, this study highlights the coupled roles of surface chemistry, ion-
polymer interactions, and solvent structuring in the regulation of Ueff, and provides important insights into the predictable control of interparticle interactions for soft material engineering.
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Strongly Correlated Electrons
Machine Learning Green's Functions of Strongly Correlated Hubbard Models
Mateo Cárdenes Wuttig
We demonstrate that a machine learning framework based on kernel ridge regression can encode and predict the self-energy of one-dimensional Hubbard models using only mean-field features such as static and dynamic Hartree-Fock quantities and first-order GW calculations. This approach is applicable across a wide range of on-site Coulomb interaction strengths $U/t$, ranging from weakly interacting systems ($U/t \ll 1$) to strong correlations ($U/t > 8$). The predicted self-energy is transformed via Dyson's equation and analytic continuation to obtain the real-frequency Green's function, which allows access to the spectral function and density of states. This method can be used for nearest-neighbor interactions $t$ and long-range hopping terms $t'$, $t''$, and $t'''$.
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Materials Science
A Linear-Scaling, Charge-Aware Foundation Potential for Atomistic Simulations
Tsz Wai Ko, Runze Liu, Adesh Rohan Mishra et al. (+3 more)
Electrostatics govern charge transfer and reactivity in materials. However, most foundation potentials (FPs) either neglect explicit electrostatic interactions or come at prohibitive computational cost. Here, we introduce charge-equilibrated TensorNet (QET), an equivariant, charge-aware architecture that achieves linear scaling with system size via an analytically solvable charge-equilibration scheme. We demonstrate that a trained QET FP matches state-of-the-art FPs on materials property
benchmarks but delivers qualitatively different predictions in systems dominated by electrostatic interactions. The QET FP reproduces the correct structure and density of the NaCl-CaCl2 ionic
liquid and the crystallization of Ge1Sb2Te4 phase change
memory, which charge-agnostic FPs miss. We further show that a fine-tuned QET captures reactive processes at the Li/Li6PS5Cl solid-electrolyte interface and supports simulations under applied electrochemical potentials. These results remove a fundamental constraint in large-scale atomistic simulations of electrostatics and establish a general, data-driven framework for charge-aware FPs with transformative applications in energy storage, catalysis, and beyond.
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All authors Tsz Wai Ko, Runze Liu, Adesh Rohan Mishra, Zihan Yu, Ji Qi, Shyue Ping Ong
Strongly Correlated Electrons
Kondo cloud conductance in cavity-coupled quantum dots with asymmetric barriers
D. Fossion, V. Champain, S. Mohapatra et al. (+9 more)
The Kondo effect emerges when a localized
spin is screened by conduction electrons, giving rise to a strongly-correlated many-body ground state. In this work, we investigate this phenomenon in a GaAs/AlGaAs
quantum dot, focusing on the spatial extension of the Kondo screening cloud in the electron reservoirs. To probe its properties, the dot is coupled to an electronic Fabry-Pérot interferometer, enabling controlled modulation of the density of states at the
Fermi level. The observation of Kondo temperature oscillations indicates a Kondo screening length comparable to the cavity size. Furthermore, we explore how the coupling asymmetry with the two reservoirs affects both the amplitude and the phase of the conductance oscillations, revealing a subtle interplay between coherent transport and Kondo effect.
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All authors D. Fossion, V. Champain, S. Mohapatra, A. Cavanna, U. Gennser, D. Mailly, B. Hackens, L. Jansen, X. Jehl, S. De Franceschi, B. Brun-Barrière, H. Sellier
Statistical Mechanics · Cross-listed from quant-ph
Matrix-product state skeletons in Onsager-integrable quantum chains
Imogen Camp and Nick G. Jones
Matrix-product state (MPS) skeletons are connected networks of
Hamiltonians with exact MPS ground states that underlie a phase diagram. Such skeletons have previously been found in classes of free-
fermion models. For the translation-invariant BDI and AIII free-
fermion classes, it has been shown that the underlying skeleton is dense, giving an analytic approach to MPS approximation of ground states anywhere in the class. In this paper, we partially expose the skeleton in certain interacting
spin chains: the $N$-state Onsager-integrable
chiral clock families. We construct MPS that form a dense MPS skeleton in the gapped regions surrounding a sequence of fixed-point
Hamiltonians (the generators of the Onsager
algebra). Outside these gapped regions, these MPS remain eigenstates, but no longer give the many-body ground state. Rather, they are ground states in particular sectors of the spectrum. Our methods also allow us to find further MPS eigenstates; these correspond to low-lying excited states within the aforementioned gapped regions. This set of MPS excited states goes beyond the previous analysis of ground states on the $N=2$ free-
fermion MPS skeleton. As an application of our results, we find a closed form for the disorder parameter in a family of interacting models. Finally, we remark that many of our results use only the Onsager
algebra and are not specific to the
chiral clock model representation.
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Statistical Mechanics
Dynamical universality class for competing short- and long-range interactions
Jean-François de Kemmeter, Stefano Ruffo and Stefano Gherardini
Understanding the dynamical universality classes of systems with long-range interactions remains a key challenge in statistical physics. In this Letter, we analytically and numerically investigate the non-
equilibrium critical dynamics of the one-dimensional
spin-$1/2$ Nagle-Kardar model, which is characterized by the competition between short- and long-range interactions and the presence of a tricritical point. We focus on the slowing-down of the magnetization $m$ at criticality under Glauber dynamics. Starting from the corresponding master equation, we perform a coarse-graining procedure to obtain a Fokker-Planck equation for the macroscopic variables. Then, the asymptotic decay of the magnetization is derived using central
manifold theory. We find that $m$ decays as $t^{-1/2}$ along the critical line and as $t^{-1/4}$ precisely at the tricritical point. This finding confirms that the dynamical critical exponent is $z=2$ as for mean-field models, proving that the macroscopic critical dynamics of the Nagle-Kardar model falls within the dynamical universality class of purely relaxational, non-conserved order parameters (model A). While Kardar proved that the
equilibrium Curie-Weiss theory extends to Ising models where nearest-neighbor interactions are included, we here show that such result is valid also for critical dynamics. Our work provides the semi-analytical solution for the critical dynamics of a model with mixed-range interactions, assigning its universality class.
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Mesoscale and Nanoscale Physics
Controlling Quantum Transport in a Superconducting Device via Dissipative Baths
S. V. Aksenov, M. S. Shustin and I. S. Burmistrov
Within the
quantum field-theoretical approach describing the
evolution of a quadratic Liouvillian in the basis of Keldysh contour coherent states, we investigate the spectral and transport properties of a dissipative superconducting system coupled to normal
Fermi reservoirs. We derive a generalization of the Meir-Wingreen formula and Onsager
matrix for a superconducting system subject to an arbitrary number of fermionic baths. Following Kirchhoff's rule, we obtain an expression describing the dissipation induced loss current and formulate modified
quantum kinetic equations. For wide-band contacts locally coupled to individual sites, we find that each contact reduces the degeneracy multiplicity of the non-
equilibrium steady state by one. These results are numerically verified through several cases of the extended Kitaev model at symmetric points with a single contact. Furthermore, in the linear response regime at low temperatures, we demonstrate that (non-)degenerate non-
equilibrium steady states correspond to (non-)quantized conductance peaks. Revisiting a paradigmatic problem of resonant transport in the Majorana mode of the Kitaev model we demonstrate that the dissipation accounts for the zero-bias peak suppression and its asymmetry.
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Materials Science
Domain Walls and Defects in Ferroelectric Inorganic Halide Perovskites CsGeX$_3$ (X = Cl, Br, I)
Kristoffer Eggestad, Benjamin A. D. Williamson and Sverre M. Selbach
Among all-inorganic halide perovskites, the only known ferroelectrics are the family of CsGeX$_3$ (X = Cl, Br, I). Here, we study their ferroelectric domain walls (DWs) and common point defects by density functional theory (DFT) calculations and investigate the interplay between DWs and defects. The most stable defects are V$_{\text{X}}$ and V$_{\text{Cs}}$ and the former shows low migration barriers and high mobility. In contrast to
oxide ferroelectrics, the affinity between point defects and DWs is negligible, reflecting the subtle structural distortions at CsGeX$_3$ DWs. Concomitantly, the formation energies and migration energy barriers of CsGeX$_3$ DWs are small compared to
oxides, and neither V$_{\text{X}}$ nor V$_{\text{Cs}}$ pin migrating DWs. The band gap invariance across DWs and the lack of affinity towards intrinsic charged point defects imply that conducting DWs for nanoelectronics may be challenging to realise in CsGeX$_3$. However, shallow $p$-type defect levels and low hole effective masses suggest that high $p$-type conductivity may be achievable in nominally ferroelectric CsGeX$_3$. The low DW migration energy barriers and insignificant DW pinning by point defects make CsGeX$_3$ promising materials as robust soft ferroelectrics for high-frequency switching applications with low energy dissipation.
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Materials Science
A Strain-Engineered 0D/1D Heterojunction of InVO4/Cu-TbFeO3 for High- Selectivity CO2 Photoreduction
Muneeb ur Rahman
The catalytic CO2 photoreduction to CO is significantly hindered by the pervasive kinetic bottleneck of *CO-desorption and inefficient charge separation. Surpassing the conventional single photocatalytic strategy, herein, a multi-synergetic 0D/1D S-scheme heterojunction by precisely assembling 0D InVO4 nanoparticles on 1D Cu-doped TbFeO3 (IVO/CTFO). This nano-heterojunction is rationally designed at multiple steps where Cu2+ substitution at the Fe3+ site induces a compression in
lattice strain and oxygen vacancies (VO), acting as electron traps and CO2 chemisorption sites, which breaks
spin-polarization of pristine TbFeO3 to facilitate multichannel charge flow. The 0D/1D strategy couples the maximum surface active-sites and short charge
diffusion routes with directional charge migration. Moreover, a 0D/1D
lattice mismatch creates a built-in electric field at the interface, resulting in an enhanced lifetime (64.70 ns) of charged species, an efficient CO yield (65.75 mmole g-1.h-1), and high selectivity (95.93%). DFT calculations and experimental findings confirmed the
Fermi level shift toward the conduction band and the existence of
spin-hybridization. Operando-DRIFTS and the free-energy diagram unveil a H+ mediated mechanism at the interface, alongside a reduction in energy barrier for CO2 photoreduction from *COOH to *CO. Thus, this study presents an excellent approach that integrates defect-engineering, strain-compression, and interfacial design in advancing
solar fuels production.
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Materials Science
Effect of Misfit and Threading Dislocations on Surface Energies of PbTe-PbSe Interfaces
Emir Bilgili, Nicholas Taormina, Yang Li et al. (+3 more)
This work quantifies the effect of misfit and threading dislocations on the surface energies of PbTe-PbSe interfaces, with the defect structures of the interfaces being obtained from atomistic and multiscale simulations of their manufacturing processes. Simulation results show that direct bonding produces semi-coherent interfaces with two-dimensional misfit dislocation networks, while heteroepitaxial processes produce complex three-dimensional dislocation structures with both misfit and threading dislocations. Surface energies at these interfaces were determined by computing the interaction energies across these interfaces. Compared with coherent interfaces, directly bonded interfaces exhibit up to ~23% lower surface energy, while the surface energies of epitaxially grown interfaces can be nearly 50% lower. The results demonstrate the significant effects of dislocations on interfacial energy.
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All authors Emir Bilgili, Nicholas Taormina, Yang Li, Adrian Diaz, Simon R. Phillpot, Youping Chen
Mesoscale and Nanoscale Physics
Direct imaging of magnetotransport at graphene-metal interfaces with a single-spin quantum sensor
C. Ding, M. L. Palm, K. Kohli et al. (+3 more)
Magnetotransport underlines many important phenomena in condensed matter physics, such as the
Hall effect and magnetoresistance (MR) effect. Thus far, most magnetotransport studies are based on bulk resistance measurements without direct access to microscopic details of the spatial transport pattern. Here, we report nanoscale imaging of magnetotransport using a scanning single-
spin quantum magnetometer, which is demonstrated in a
graphene-metal hybrid device at room temperature. By visualizing the current flow at elevated
magnetic fields (~0.5 T), we directly observe the Lorentz deflection of current near the
graphene-metal interface, which is a hallmark of magnetotransport. Combining the local current distribution with global resistance measurements, we reveal that transport properties of the hybrid are governed by a complex interplay of intrinsic MR around the Dirac cone, carrier hydrodynamics, interface resistance, and the nanoscale device geometry. Furthermore, accessing the local transport pattern across the interface enables quantitative mapping of spatial variations in contact resistance, which is commonly present in electronic devices made from two-dimensional materials yet non-trivial to characterize. Our work demonstrates the potential of nanoscale current imaging techniques for studying complex electronic transport phenomena that are difficult to probe by resistance-based measurements.
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All authors C. Ding, M. L. Palm, K. Kohli, T. Taniguchi, K. Watanabe, C. L. Degen
Statistical Mechanics · Cross-listed from quant-ph
Finite-Bath Open Quantum Systems: Exact Dynamics
Devvrat Tiwari and Subhashish Banerjee
In this work, we introduce a method for deriving exact master equations from the dynamical map for finite open
quantum systems coupled to (in)finite reservoirs, using the principle of minimal dissipation. The exact dynamics of the central
spin model, which models a finite-bath open
quantum system, is developed for two interaction types: Heisenberg and
stochastic pure-dephasing interactions. The Heisenberg interaction yields a novel phase-covariant
quantum channel in the strong-coupling regime, offering a new platform for studying a range of
quantum information protocols. The
stochastic pure-dephasing interaction provides the microscopic derivation of the paradigmatic non-Markovian random telegraph noise (RTN) channel, establishing its
quantum foundation and offering insight into
stochastic couplings. We derive the closed-form master equations for both models. As a demonstration, we explore the thermodynamic performance of these systems as
quantum batteries. A direct relationship between
quantum heat current and charging power is revealed, and RTN
quantum batteries are shown to have advantages in charge storage.
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Materials Science
Defect-Mediated Phase Engineering of 2D Ag at the Graphene/SiC Interface
Arpit Jain, Boyang Zheng, Sawani Datta et al. (+23 more)
Atomically thin silver (Ag) films offer unique opportunities in plasmonic,
quantum optics, and energy harvesting, yet conventional growth methods struggle to achieve structural control at the monolayer limit. Here, we demonstrate phase-selective synthesis of large-area, crystalline 2D Ag films via defect-engineered confinement heteroepitaxy (CHet) at the epitaxial
graphene/silicon carbide (EG/SiC) interface. By tuning
graphene growth and post-growth defect introduction, two distinct Ag phases are achieved with disparate properties: a nearly commensurate Ag(1)
lattice stabilized by vacancy and line defects in epitaxial
graphene, and a denser Ag(2) phase preferentially grown with sp3-rich zero-layer
graphene. Structural and spectroscopic characterization confirm
lattice registry with the SiC substrate, while theoretical calculations reveal a thermodynamic preference for Ag(2) but an easier nucleation for Ag(1). Both phases are found to be semiconducting, with the Ag(2) phase exhibiting slightly enhanced n-doping of
graphene. Notably, nonlinear optical measurements reveal a three-order magnitude difference in second-order susceptibility between the two phases, demonstrating promise for phase-tunable 2D metals in reconfigurable optoelectronic and metamaterial platforms.
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All authors Arpit Jain, Boyang Zheng, Sawani Datta, Kanchan Ulman, Jakob Henz, Matthew Wei-Jun Liu, Van Dong Pham, Wen He, Chengye Dong, Li-Syuan Lu, Alexander Vera, Nader Sawtarie, Wesley Auker, Ke Wang, Bob Hengstebeck, Zachary W. Henshaw, Shreya Mathela, Maxwell Wetherington, William H. Blades, Kenneth Knappenberger, Ursula Wurstbauer, Su Ying Quek, Ulrich Starke, Shengxi Huang, Vincent H. Crespi, Joshua A. Robinson
Quantum Gases
Pattern formation in ring condensates subjected to bichromatic driving
Premabrata Manna, S. I. Mistakidis, P. G. Kevrekidis et al. (+1 more)
We investigate the dynamical formation of nonlinear patterns in one-dimensional ring condensates under bichromatic periodic modulation of the interaction strength. The stability phase diagram of the condensate's homogeneous density state is analytically derived through a suitable biharmonic variant of the Mathieu equation and computing the associated Floquet spectrum. It reveals the complex interplay between the driving parameters, i.e., amplitude, frequencies, and the so-called frequencies' mixing angle, which dictate the instability onset and the selective enhancement of higher-order resonance tongues, thus offering precise control over the excited modes. These results are in agreement with time-dependent mean-field simulations evidencing the emergence of density wave modulations of specific momenta, while enabling a deeper understanding of the nonlinear stage of the relevant instability. Further insights on the ensuing unstable nonlinear dynamics are provided through a reduced {five-mode} model which captures the instability onset, the oscillatory behavior of the mode populations and the phase-space dynamics, in agreement with the mean-field predictions. Our study highlights the versatility of bichromatic driving to generate and control complex nonlinear patterns that are within reach in present day ultracold atom experiments.
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All authors Premabrata Manna, S. I. Mistakidis, P. G. Kevrekidis, Pankaj Kumar Mishra
Mesoscale and Nanoscale Physics
Complementary and Asymmetric Tapered Bent Mid-Infrared Waveguide Arrays for Subwavelength-Pitch Integration and Crosstalk Minimization
Humaira Zafar and Mauro Fernandes Pereira
This paper delivers the first report of a mid-infrared (MIR) waveguide array design that employs complementary and asymmetric tapered Euler-shaped bends. These provide greater fabrication flexibility to achieve subwavelength-pitch integration while reducing crosstalk to below 30 dB across the 3.1 to 3.6 micron wavelength range. Unlike previous designs, which maintained constant waveguide widths, the Euler waveguide bends are characterized by asymmetric and complementary tapered waveguide widths. This approach significantly reduces crosstalk to below 30 dB for both the first and second neighboring waveguides across a 500 nm wavelength range, enhancing the efficiency of optical phased arrays (OPA) with a large field of view, optimizing light propagation and minimizing crosstalk. The waveguide array is fabricated on a silicon-on-
insulator platform, with a 2-micron buried
oxide layer and a 500 nm-thick silicon layer. The design is highly tolerant to fabrication variations, maintaining consistent performance even with width variations. The spectral responses, simulated using the 3D finite-difference time-domain method, demonstrate negligible coupling and low insertion loss across the wavelength range. This work offers a robust and CMOS-compatible solution for MIR integrated photonic
circuits.
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Mesoscale and Nanoscale Physics
Synchronizing microwave cQED limit-cycle oscillators
Cecilie Hermansen and Jens Paaske
Self-sustained oscillators play a central role in the stabilization and synchronization of complex dynamical systems. A number of different physical systems are currently being investigated to clarify the importance of such active components in the
quantum realm. Here we explore the properties of a driven dissipative electron-
photon hybrid system based on superconducting microwave resonators coupled resonantly to a voltage-biased double
quantum dot (DQD). First, we establish a
Hopf bifurcation at a critical value of the electron-
photon coupling, beyond which an effective negative friction sustains steady limit-cycle oscillations of individual resonators. Second, we show that two such limit-cycle resonators coupled via the same voltage-biased DQD synchronize for small enough frequency detuning. A nonlinear
photon Keldysh action is derived by perturbation theory in the effective
circuit fine-structure constant, and the limit-cycle dynamics is analyzed in terms of resulting saddle-point, and Fokker-Planck equations. In the Markovian limit of infinite bias voltage, these results are shown to agree well with the solution of a corresponding Lindblad master equation for the DQD resonator system.
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Statistical Mechanics
Projection Operator The Mori-Zwanzig method of projection operators:Generalized Langevin equation.(Lecture Notes)
Nail Fatkullin
A fairly brief and complete presentation of the Zwanzig-Mori projection operator technique is given.
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Biphoton state generation and engineering with bright hybrid III-V/Silicon photonic devices
Lorenzo Lazzari, Jérémie Schuhmann, Othmane Meskine et al. (+7 more)
Hybrid photonic
circuits, harnessing the complementary strengths of multiple materials, represent a key resource to enable compact, scalable platforms for
quantum technologies. In particular, the availability of bright sources of tunable biphoton states is eagerly awaited to meet the variety of applications currently under development. In this work we demonstrate a heterogeneously integrated device that merges biphoton generation and on-chip
quantum state engineering, combining an AlGaAs
photon-pair source with a CMOS-compatible silicon-on-
insulator (SOI)
circuit.
Photon pairs are generated in the C telecom band via spontaneous parametric down-conversion and transferred to the SOI chip through a multimode evanescent coupling scheme. This design achieves a pair generation rate above 10$^{6}$ s$^{-1}$mW$^{-1}$ and a coincidence-to-accidental ratio up to 600. Crucially, the coupling design induces strong and predictable transformations of the biphoton joint spectral amplitude, enabling complex
quantum state engineering entirely on-chip in a compact device compliant with electrical pumping.
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All authors Lorenzo Lazzari, Jérémie Schuhmann, Othmane Meskine, Martina Morassi, Aristide Lemaître, Maria I. Amanti, Frédéric Boeuf, Fabrice Raineri, Florent Baboux, Sara Ducci
Materials Science
Cathodoluminescence, light injection and EELS in STEM: From comparative to coincidence experiments
Luiz H. G. Tizei, Yves Auad, Florian Castioni et al. (+1 more)
Electron spectroscopy implemented in electron microscopes provides high spatial resolution, down to the atomic scale, of the chemical, electronic, vibrational and optical properties of materials. In this review, we will describe how temporal coincidence experiments in the nanosecond to femtosecond range between different electron spectroscopies involving
photons, inelastic electrons and secondary electrons can provide information bits not accessible to independent spectroscopies. In particular, we will focus on nano-optics applications. The instrumental modifications necessary for these experiments are discussed, as well as the perspectives for these coincidence techniques.
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All authors Luiz H. G. Tizei, Yves Auad, Florian Castioni, Mathieu Kociak
Strongly Correlated Electrons
Effect of uniaxial stress on helimagnetic phases in the square-lattice itinerant magnet EuAl$_{4}$
Masaki Gen, Takuya Nomoto, Hiraku Saito et al. (+5 more)
We investigate uniaxial-stress effects on the
magnetic phase diagram of the square-
lattice itinerant magnet EuAl$_{4}$, where strong coupling among
spin,
lattice, and charge produces a variety of helimagnetic phases, including rhombic and square skyrmion
lattices. Combining resistivity and magnetization measurements with
neutron scattering, we find that compressive stresses of only several tens of megapascal along [010] enhance
antiferromagnetic character and shorten the
magnetic modulation period in the lowest-temperature single-Q spiral state, thereby driving the critical temperatures and fields of multiple phases to higher values. First-principles calculations show that increasing orthorhombic
lattice distortion deforms the
Fermi surface relevant to the magnetism, providing compelling evidence that
Fermi-surface nesting plays a crucial role in stabilizing the helical
magnetic modulations in EuAl$_{4}$.
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All authors Masaki Gen, Takuya Nomoto, Hiraku Saito, Taro Nakajima, Yusuke Tokunaga, Rina Takagi, Shinichiro Seki, Taka-hisa Arima
Strongly Correlated Electrons
Magnetic anisotropy and intermediate valence in CeCo$_5$ ferromagnet
Alexander B. Shick and Evgenia A. Tereshina-Chitrova
The intermediate valence of Ce in CeCo$_5$ challenges standard density functional theory (DFT) and static DFT+$U$ approaches, which fail to capture its
magnetic properties. By combining DFT+$U$ with exact diagonalization of the Anderson
impurity model for the Ce 4$f$ shell, we find a substantial reduction of Ce
spin and orbital moments, consistent with DFT+DMFT, arising from Ce$^{4+}$ - Ce$^{3+}$ valence fluctuations. The total
magnetic moment of 6.70 $\mu_B$ agrees with experiment, and the calculated $4f$ density of states reproduces photoemission and Bremsstrahlung isochromat spectra. The uniaxial
magnetic anisotropy energy reaches 4.8 meV/f.u. when Coulomb correlations on both Ce 4$f$ and Co 3$d$ shells are included, in very good agreement with experimental data. These results highlight the importance of dynamical correlations and provide guidance for exploring high-performance, low-rare-earth-content permanent magnets.
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Quantum Gases
Chiral phases and dynamics of dipoles in triangular optical ladders
Arjo Dasgupta, Mateusz Łącki, Henning Korbmacher et al. (+3 more)
Dipoles in triangular optical ladders constitute a flexible platform for the study of the interplay between
geometric frustration and long-range anisotropic interactions, and in particular for the observation of the spontaneous onset of chirality. Frustration magnifies the effect of the dipolar interactions in itinerant polarized dipolar
bosons. As a result, the dipole-induced transition between a
chiral superfluid and a non-
chiral two-component superfluid may be observed for current state-of-the-art temperatures even for the weak inter-site interaction characterizing
magnetic atoms in standard optical
lattices. On the other hand, pinned
spin-$1/2$ dipoles, which we discuss in the context of polar molecules in two rotational states, realize frustrated dipolar XXZ
spin models. By controlling the external electric field strength and orientation, these systems can explore a rich ground-state landscape including
chiral and nematic phases, as well as intriguing
chiral dynamics.
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All authors Arjo Dasgupta, Mateusz Łącki, Henning Korbmacher, Gustavo A. Domínguez-Castro, Jakub Zakrzewski, Luis Santos
Soft Condensed Matter
Sedimentation profiles and phase stacking diagrams in polydisperse hard rounded rectangle fluids
Tobias Eckert, Daniel de las Heras, Enrique Velasco et al. (+1 more)
We analyze the sedimentation behavior of a polydisperse two-dimensional
liquid-
crystal fluid using a local density functional theory based on scaled particle theory. Polydispersity is incorporated through variations in the roundness of hard rectangular particles interacting solely via excluded area effects. Despite its simplicity, the model displays a rich phenomenology. In bulk, the fluid exhibits isotropic, nematic, and tetratic phases. In sedimentation, we obtain complex phase stacking diagrams featuring multiphasic stacking sequences with up to four stacks of different bulk phases, inverted stacking sequences such as top isotropic and bottom nematic together with top nematic and bottom isotopic, as well as stacking sequences with reentrant stacks such as tetratic and nematic stacks floating between two isotropic stacks. This phenomenology arises as a result of an intricate coupling between particle polydispersity and the effect of
gravity. Our approach can be easily adapted to investigate the sedimentation behaviour of other polydisperse colloidal systems.
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All authors Tobias Eckert, Daniel de las Heras, Enrique Velasco, Yuri Martínez-Ratón