Strongly Correlated Electrons
Dynamical control of Coulomb interactions and Hubbard bands in monolayer 1T-TaS$_2$
Niklas Notter, Markus Aichhorn and Anna Galler
Monolayer 1T-TaS$_2$ hosts a
star-of-David charge-density wave (CDW) that stabilizes a low-temperature Mott-insulating state. Recent time-resolved spectroscopies indicate a coupling between the CDW amplitude mode and the electronic correlation strength, yet the role of the screened Coulomb interaction remains unclear. Using the constrained random-phase approximation, we show that the CDW amplitude modifies the bare and screened on-site interactions, leading to sizable variations in the effective Hubbard U. Our combined density functional and dynamical mean-field theory calculations reveal that the Hubbard bands shift in concert with the CDW amplitude, and that a reduced distortion drives a transition from a Mott
insulator to a correlated metal. These results demonstrate a direct link between
lattice distortions and Coulomb interactions in transition-metal dichalcogenides, providing a microscopic mechanism for light-induced control of correlated phases in two-dimensional
quantum materials.
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Materials Science
Strain Engineering of Altermagnetic Symmetry in Epitaxial RuO$_2$ Films
Johnathas D. S. Forte, Seung Gyo Jeong, Anand Santhosh et al. (+3 more)
The
magnetic ground state of RuO$_2$ has been under intense debate. Using first-principles calculations, we show that compressive strain along [001] direction stabilizes an altermagnetic phase in RuO$_2$ thin films grown on (100) and (110) TiO$_2$ substrates. We further identify that compressive strain enhances the density of states near the
Fermi level, resulting in a
Fermi surface instability and the emergence of altermagnetism. The magnitude of strain and the associated increase in the density of states can be tuned by varying the film thickness, as systematically confirmed by x-ray diffraction and photoemission spectroscopy measurements.
Symmetry analysis further reveals that (100) RuO$_2$ hosts an ideal altermagnetic order, whereas broken
symmetry in (110) films leads to an uncompensated ferrimagnetic state. Finally, we discuss the effects of Hubbard $U$ parameters and evaluate the realistic tunneling magnetoresistance of (100) RuO$_2$.
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All authors Johnathas D. S. Forte, Seung Gyo Jeong, Anand Santhosh, Seungjun Lee, Bharat Jalan, Tony Low
Materials Science
Tunable Colloidal Synthesis Enabling {\mu}-ARPES on Individual Two-dimensional Bismuth Nanocrystals
Fagui He, Yan Yan Grisan Qiu, Simone Mearini et al. (+4 more)
Two-dimensional bismuth (Bi) is a promising platform for
quantum and energy technologies due to strong
spin-orbit coupling, high thermoelectric efficiency, and magnetoresistance. However, scalable and flexible synthesis of high-quality Bi with fast research turnaround remains challenging. We report a controlled colloidal synthesis of Bi nanosheets with tunable lateral sizes (0.6 - 4.1 um), hexagonal shape, and a layered single-crystalline structure along the {00l} planes. The nanosheets exhibit excellent oxidation resistance and ambient stability. ARPES measurements on individual nanosheets reveal a band structure in excellent agreement with DFT calculations, confirming high
crystal quality and uniformity. Our findings enable fast production and characterization of two-dimensional Bi, paving the way for fundamental studies and integration into next-generation
quantum and energy devices.
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All authors Fagui He, Yan Yan Grisan Qiu, Simone Mearini, Vitaliy Feyer, Kevin Oldenburg, Rostyslav Lesyuk, Christian Klinke
Materials Science
Understanding the swelling behavior of P(DMAA-co-MABP) copolymer in paper-based actuators
Catarina C. Ribeiro, Nele Link, Jan-Lukas Schäfer et al. (+3 more)
As interest in sustainable materials grows, paper is being reimagined as a multifunctional substrate with significant potential for future technologies for innovative, environmentally friendly solutions. This study investigates the swelling behavior and environmental responsiveness of a copolymer, poly(N,N-dimethylacrylamide-co-4-methacryloyloxybenzophenone) (P(DMAA-co-MABP)), when applied to cellulosic paper for use in humidity-sensitive actuators. The copolymer's swelling behavior was characterized using dynamic vapor sorption (DVS) and in-situ atomic force microscopy (AFM). DVS measurements demonstrated that the
polymer coating significantly enhances the hygroscopic properties of the paper, while AFM revealed the
polymer's fast response to relative humidity (RH) changes, shown by immediate height adjustments, increased adhesion, and decreased stiffness at higher RH levels.Studies on
polymer-modified paper-based
bilayer actuators demonstrate that incorporating the hydrophilic P(DMAA-co-MABP) results in actuation in response to relative humidity variations between 10% and 90% RH. From these findings, two models were proposed to assess key mechanisms in the swelling behavior: the correlation between the heterogeneity in crosslinking and the
polymer swelling behavior, and the correlation between
polymer-paper interactions and the hygro-responsive bending behavior. Additionally, thermal analysis was performed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), providing a comprehensive profile of the copolymer's behavior.
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All authors Catarina C. Ribeiro, Nele Link, Jan-Lukas Schäfer, Carina Breuer, Markus Biesalski, Robert W. Stark
Statistical Mechanics · Cross-listed from hep-th
From dual gauge theories to dual spin models
Mustafa Mullahasanoglu
This brief review surveys recent progress driven by the gauge/Yang-Baxter equation (YBE) correspondence. This connection has proven to be a powerful tool for discovering novel integrable
lattice spin models in statistical mechanics by exploiting dualities in supersymmetric gauge theories. In recent years, research has demonstrated the use of dual gauge theories to construct new
lattice spin models that are dual to Ising-like models.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
An introduction to Markovian open quantum systems
Shovan Dutta
This is a concise, pedagogical introduction to the dynamic field of open
quantum systems governed by Markovian master equations. We focus on the mathematical and physical origins of the widely used Lindblad equation, its unraveling in terms of
stochastic pure-state trajectories and the corresponding continuous measurement protocols, the structure of steady states with emphasis on the role of
symmetry and conservation laws, and a sampling of the novel physical phenomena that arise from nonunitary dynamics (dissipation and measurements). This is far from a comprehensive summary of the field. Rather, the objective is to provide a conceptual foundation and physically illuminating examples that are useful to graduate students and researchers entering this subject. There are exercise problems and references for further reading throughout the notes.
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Superconductivity
Superconductivity in hyperbolic spaces: Cayley trees, hyperbolic continuum, and BCS theory
Mykhailo Pavliuk, Tomáš Bzdušek and Askar Iliasov
We investigate $s$-wave superconductivity in negatively curved geometries, focusing on Cayley trees and the
hyperbolic plane. Using a self-consistent Bogoliubov-de Gennes approach for trees and a BCS treatment of the
hyperbolic continuum, we establish a unified mean-field framework that captures the role of boundaries in
hyperbolic spaces. For finite Cayley trees with open boundaries, the superconducting order parameter localizes at the edge while the interior can remain normal, leading to two distinct critical temperatures: $T_\textrm{c}^\textrm{edge} > T_\textrm{c}^\textrm{bulk}$. A corresponding boundary-dominated phase also emerges in
hyperbolic annuli and horodisc regions, where radial variations of the local density of states enhance edge pairing. We also demonstrate that the enhancement of the density of states at the boundary is significantly more pronounced for the discrete tree geometry. Our results show that, owing to the macroscopic extent of the boundary, negative
curvature can stabilize boundary superconductivity as a phase that persists in the thermodynamic limit on par with the bulk superconductivity. These results highlight fundamental differences between bulk and boundary ordering in
hyperbolic matter, and provide a theoretical framework for future studies of correlated phases in negatively curved systems.
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Other Condensed Matter
Bi-isotropic effects on hybrid surface polaritons in bilayer configurations
A. Nonato and Pedro D. S. Silva
In this work, we investigate the bi-isotropic effects in the formation and tunability of hybrid surface polaritons in
bilayer configurations. We consider a
heterostructure composed of a medium with bi-isotropic constitutive relations and an AFM layer. Using the transfer
matrix formalism, we derive general expressions for the dispersion relations of surface polaritonic modes, including the dependence on the bi-isotropic parameter, and analyze their coupling to bulk
magnon-polaritons. As an illustration of application, we consider a
heterostructure formed with Bi$_{2}$Se$_{3}$ interfaced with
antiferromagnetic (AFM) materials that support terahertz-frequency
magnons, specifically Cr$_{2}$O$_{3}$ and FeF$_{2}$. In the strong bi-isotropic coupling regime, the surface Dirac plasmon–
phonon–
magnon polariton (DPPMP) dispersion undergoes a pronounced
redshift, accompanied by suppression of the characteristic anticrossing between the Dirac plasmon and the
phonon. This effect, observed in all AFM materials considered, suggests a weakening of the hybrid interaction, possibly due to saturation or detuning mechanisms induced by increased $\alpha$. Furthermore, increasing the
Fermi energy of the topological
insulator enhances the surface plasmon and
phonon contributions, inducing a blueshift of the DPPP branches and bringing them closer to resonance with the
magnon mode, thereby increasing the hybridization strength. Intriguingly, this
redshift partially compensates the blueshift induced by a higher
Fermi level, restoring the system to a weak-coupling regime analogous to that observed at lower
Fermi energies. Our findings reveal that both the
Fermi level and the bi-isotropic response offer independent and complementary control parameters for tuning the strength of light–
magnon coupling in TI/AFM
heterostructures, with potential implications for reconfigurable THz spintronic and photonic devices.
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Materials Science
Magnetic Field-Controlled THz Modulation in Uniaxial Anisotropic Spin-Valves Emitters
Arseniy M. Buryakov, Anastasia V. Gorbatova, Pavel Y. Avdeev et al. (+6 more)
Uniaxial spintronic
heterostructures constitute compact THz emitters under femtosecond optical excitation, with emission amplitude and polarization governed by the applied
magnetic field is presented. We demonstrate here efficient magnetically tunable THz amplitude control in ultrathin, exchange-biased Co/Pt/Co/IrMn
spin valve. Terahertz spintronic magnetometry resolves reversible switching between parallel and antiparallel magnetization states and correlates the high- and low-emission regimes with constructive and destructive interference of charge transients generated by the inverse
spin Hall effect in the Pt spacer. A residual low-emission signal is traced to
spin-to-charge conversion in IrMn. Phase inversion under front- versus back-side excitation confirms the ISHE origin of the emission, while a macrospin Landau-Lifshitz-Gilbert model reproduces the field dependence of its amplitude and separates layer-specific contributions. Together, these results define a wafer-compatible
spin valve device architecture that enables efficient, low-field THz amplitude control.
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All authors Arseniy M. Buryakov, Anastasia V. Gorbatova, Pavel Y. Avdeev, Igor Yu. Pashen'kin, Maksim V. Sapozhnikov, Alexey A. Klimov, Elena D. Mishina, Alexandr S. Sigov, Vladimir L. Preobrazhensky
Statistical Mechanics
Spin-orbit coupled spin-boson model : A variational analysis
Sudip Sinha, Subhasis Sinha and Sushanta Dattagupta
The
spin-
boson (SB) model is a standard prototype for
quantum dissipation, which we generalize in this work, to explore the dissipative effects on a one-dimensional
spin-orbit (SO) coupled particle in the presence of a sub-ohmic bath. We analyze this model by extending the well-known variational polaron approach, revealing a localization transition accompanied by an intriguing change in the spectrum, for which the doubly degenerate minima evolves to a single minimum at zero momentum as the system-bath coupling increases. For translational invariant system with conserved momentum, a continuous magnetization transition occurs, whereas the ground state changes discontinuously. We further investigate the transition of the ground state in the presence of harmonic confinement, which effectively models a
quantum dot-like nanostructure under the influence of the environment. In both the scenarios, the
entanglement entropy of the
spin-sector can serve as a marker for these transitions. Interestingly, for the trapped system, a cat-like superposition state corresponds to maximum
entanglement entropy below the transition, highlighting the relevance of the present model for studying the effect of decoherence on intra-particle
entanglement in the context of
quantum information processing.
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Materials Science · Cross-listed from physics.chem-ph
Atomistic Simulations of Oxide-Water Interfaces using Machine Learning Potentials
Jan Elsner, K Nikolas Lausch and Jörg Behler
Oxide-water interfaces govern a wide range of physical and chemical processes fundamental to many fields like catalysis, geochemistry, corrosion, electrochemistry, and sensor technology. Near solid
oxide surfaces, water behaves differently than in the bulk, exhibiting pronounced structuring and increased reactivity, typically requiring ab initio-level accuracy for reliable modeling. However, explicit ab initio calculations are often computationally prohibitive, especially if large system sizes and long simulation time scales are required. By learning the potential energy surface (PES) from data obtained from electronic structure calculations, machine learning potentials (MLPs) have emerged as transformative tools, enabling simulations with ab initio accuracy at dramatically reduced computational expense. Here, we provide an overview of recent progress in the application of MLPs to atomistic simulations of
oxide-water interfaces. Specifically, we review insights that have been gained into the reactivity of interfacial systems involving the dissociation and recombination of water molecules,
proton transfer processes between the solvent and the surface and the dynamic nature of aqueous
oxide surfaces. Moreover, we discuss open challenges and future possible research directions in this rapidly evolving but challenging field.
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Soft Condensed Matter
Active chain spirograph: Dynamic patterns formed in extensible chains due to follower activity
Sattwik Sadhu, Nitin Kriplani, Anirban Sain et al. (+1 more)
Follower activity results in a large variety of conformational and dynamical states in active chains and filaments. These states are formed due to the coupling between chain geometry and the local activity. We study the origin and emergence of such patterns in noiseless, flexible active chains. In the overdamped limit, we observed a range of dynamical steady states for different chain lengths ($N$). The steady-state planar trajectories of the centre-of-mass of the chain include circles, periodic waves, and quasiperiodic, bound trajectories resembling spirographic patterns. In addition, out-of-plane initial configuration also leads to the formation of 3D structures, including globular and supercoiled helical structures. For the shortest chain with three segments $(N=3)$, the chain always moves in a circular trajectory. Such circular trajectories are also observed in the limit of large chain lengths $(N \gg 1)$. We analytically study the dynamical patterns in these two limiting cases, which show quantitative and qualitative matches with numerical simulations. Our analytical study also provides an estimate of the limiting $N$ where the large chain length behaviour is expected. These analyses reveal the existence of such intricately periodic patterns in active chains, arising due to the follower activity.
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All authors Sattwik Sadhu, Nitin Kriplani, Anirban Sain, Raghunath Chelakkot
Materials Science
Investigation of the intrinsic hidden spin texture and spin-state segregation in centrosymmetric monolayer dichalcogenide: effectiveness of the electric-field approach
Ameneh Deljouifar, Anita Yadav, Nataša Stojić et al. (+2 more)
The emergence of hidden
spin polarization in centrosymmetric nonmagnetic
crystals due to local
symmetry breaking has created new opportunities for potential spintronic applications and for enhancing our understanding of mechanisms to electrically manipulate
spin-related phenomena. In this work, we investigate within density functional theory the properties of the hidden
spin texture and
spin-layer segregation in a prototype centrosymmetric dichalcogenide-monolayer material using an electric-field-based method. This method is shown to yield a precise and robust alternative to traditional layer-projected
spin-polarization techniques for obtaining the intrinsic hidden
spin textures in such materials. Moreover, it gives access at the same time to the spatial distribution within the monolayer of the individual
spin-segregated states responsible for the hidden
spin textures, not provided by other techniques. With this approach we determine and study the hidden
spin textures of the upper valence bands of the PtTe2 monolayer together with the spatial behavior of the probability densities and
spin polarization densities of the corresponding maximally segregated
spin states. This combined study enabled by the electric-field method yields new insights into the mechanisms controlling the
spin-layer segregation and resulting hidden
spin texture in such systems. We also discuss the
symmetry rules governing the shape in the Brillouin zone of the hidden
spin texture, which can be straightforwardly predicted within the present framework.
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All authors Ameneh Deljouifar, Anita Yadav, Nataša Stojić, H. Rahimpour Soleimani, Nadia Binggeli
Soft Condensed Matter
Ferroelectric nematic liquid crystals: temperature-tunable electrocaloric fluids with large strength at low fields
Diana I. Nikolova, Rachel Tuffin, Mengfan Guo et al. (+5 more)
The electrocaloric (EC) effect offers a promising energy-efficient and clean cooling technology. We present the first direct measurements of EC temperature change in a new family of EC fluids, ferroelectric nematic
liquid crystals (FNLCs), demonstrating in two such materials temperature jumps of $|{\Delta}T_j|$ ~ 0.2 K for field changes as low as ${\Delta}E$ ~ 0.1 $V {\mu}m^{-1}$. Indirect measurements of adiabatic temperature change $|{\Delta}T|$ confirm that these direct measurements are an underestimate and that ${\Delta}E$ = 2 $V {\mu}m^{-1}$ can induce up to $|{\Delta}T|$ ~ 1.6 K, yielding EC strengths $|{\Delta}T/{\Delta}E|$ up to 100% higher than incumbent materials. For temperature spans of 5-10 K, we predict a coefficient of performance of ~21-40. We find $|{\Delta}T|$ ~ 1 K for >100 FNLCs that collectively span all temperatures between $0{^\circ}$C and $100{^\circ}$C. This, together with the new device concepts conceivable with fluid EC materials, offers huge potential for cooling applications.
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All authors Diana I. Nikolova, Rachel Tuffin, Mengfan Guo, Neil D. Mathur, Xavier Moya, Peter Tipping, Richard J. Mandle, Helen F. Gleeson
Materials Science · Cross-listed from physics.app-ph
Self-Assembled hBN Wrinkles as Planar Optofluidic Channels
Xiliang Yang, Tetsuo Martynowicz, Allard Katan et al. (+3 more)
Optically accessible, scalable planar nanofluidic channels are attractive for studying transport and localization under confinement. Two dimensional (2D) materials provide large area, atomically flat interfaces for generating such platforms, yet achieving long range one-dimensional (1D) confinement with top-down nanofabrication remains challenging because it requires reproducible nanoscale feature control over extended distances, high yield, and low nonspecific adsorption of analytes under aqueous conditions. Here we demonstrate that thermally induced wrinkling of exfoliated hexagonal boron nitride (hBN) produces self-assembled,
liquid-accessible, channel-like networks through a lithography-free process. By varying flake thickness and substrate choice, we quantify statistical trends in wrinkle density and morphology, thereby establishing a practical fabrication design space. Atomic force microscopy and electron microscopy reveal wrinkle-derived geometries with vertical confinement ranging from <2 nm to >100 nm depending on flake thickness and substrate. We further employ time-sequence optical imaging upon droplet-contact, which together with Raman mapping of the water OH-stretch band and capacitance-gradient mapping (dC/dz) by scanning dielectric microscopy (KPFM-based) measurements, demonstrates
liquid infiltration and long-term
liquid retention within the wrinkle network for more than 10 h. We finally show a proof-of-concept biomolecule confinement application in which we integrate a
graphene overlayer as a background suppression interface, enabling wide-field fluorescence localization of ATTO647N labeled DNA along hBN wrinkle-induced nanochannels. Overall, this work establishes self-assembled hBN wrinkles as a scalable, and optically addressable planar nanofluidic platform for confinement of fluids and biomolecules.
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All authors Xiliang Yang, Tetsuo Martynowicz, Allard Katan, Kenji Watanabe, Takashi Taniguchi, Sabina Caneva
Materials Science · Cross-listed from physics.class-ph
Momentum-Transfer Framework Unifies High-Velocity Impact and Failure Across Materials, Geometries, and Scales
Yasara Dharmadasa, Nicholas Jaegersberg, Ara Kim et al. (+2 more)
Materials that dissipate energy efficiently under high-speed impacts, from micrometeoroid strikes on spacecraft to ballistic penetration in protective systems, are essential for maintaining structural integrity in extreme environments. Yet, despite decades of study, predicting and comparing impact performance across materials, geometries, and length scales remains challenging because conventional projectile-impact models often rely on conservation-based or empirically partitioned descriptions that assume the projectile-target interaction is a closed system. Here, we relax this assumption and directly observe the momentum and energy transferred out of the projectile during impact. We find that the momentum transferred to the target consistently reaches its maximum at the ballistic-limit velocity, demonstrated through a coordinated suite of micro-projectile impact experiments spanning varied projectile diameters, target thicknesses, and impact velocities, and further supported by targeted macroscale tests. This behavior is reinforced across a broad range of independent studies encompassing metals,
polymers, composites, sandwich panels, and reinforced concrete, with thicknesses ranging from nanometers to hundreds of millimeters and projectiles of spherical, blunt, ogive, and conical shape, under both normal and oblique impacts. Together, these observations reveal a consistent impact behavior across all available data: maximum momentum transfer occurs at the ballistic limit. Extending this bound into the energy absorption landscape addresses an entrenched misconception in the field by revealing that specific energy absorption inherently inflates the performance of thinner targets due to
geometric normalization, rather than reflecting genuine material enhancement.
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All authors Yasara Dharmadasa, Nicholas Jaegersberg, Ara Kim, Jizhe Cai, Ramathasan Thevamaran
Soft Condensed Matter · Cross-listed from physics.bio-ph
Capillarity Reveals the Role of Capsid Geometry in HIV Nuclear Translocation
Alex W. Brown, Sami C. Al-Izzi, Jack L. Parker et al. (+4 more)
The protective capsid encasing the genetic material of Human Immunodeficiency Virus (HIV) has been shown to traverse the
nuclear pore complex (NPC) intact, despite exceeding the passive
diffusion threshold by over three orders of magnitude. This remarkable feat is attributed to the properties of the capsid surface, which confer solubility within the NPC's phase-separated, condensate-like barrier. In this context, we apply the classical framework of wetting and capillarity – integrating analytical methods with sharp- and diffuse-interface numerical simulations – to elucidate the physical underpinnings of HIV
nuclear entry. Our analysis captures several key phenomena: the reorientation of incoming capsids due to torques arising from asymmetric capillary forces; the role of confinement in limiting capsid penetration depths; the classification of translocation mechanics according to changes in
topology and interfacial area; and the influence of (spontaneous) rotational
symmetry-breaking on energetics. These effects are all shown to depend critically on capsid geometry, arguing for a physical basis for HIV's characteristic capsid shape.
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All authors Alex W. Brown, Sami C. Al-Izzi, Jack L. Parker, Sophie Hertel, David A. Jacques, Halim Kusumaatmaja, Richard G. Morris
Quantum Gases · Cross-listed from quant-ph
Quantum dynamics of spin-J particles in static and rotating magnetic fields: Entanglement resonances and kinks
Nargis Sultana, Siddharth Seetharaman and Rejish Nath
We examine the
quantum dynamics of both a single
spin-J particle and a pair of
spin-J particles in the presence of static and rotating
magnetic fields, which can be important for qudit-based
quantum technologies. Notably, we find resonant, periodic oscillations between two maximally stretched states, irrespective of the value of J. Additionally, we observe periodic transitions between sublevels with
magnetic quantum numbers of opposite signs. The dynamics also exhibit a periodic transfer of the
spin to the maximally stretched state, starting from the ground state of the initial
Hamiltonian. For a pair of
spins, we derive various resonance conditions and further analyze the
entanglement generated by dipole-dipole interactions. In the case of two
spin-1/2 particles, the
entanglement dynamics reveal resonances and kinks in the maximum
entanglement, and their criteria can be obtained from the energy spectrum. Strikingly, we show that the kink can be exploited to engineer the
entanglement dynamics. Finally, we briefly discuss the regime of weak dipolar interactions, which are relevant for dipolar Bose-Einstein condensates.
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Statistical Mechanics
Weak-Memory Dynamics in Discrete Time
Hugues Meyer and Kay Brandner
Discrete dynamics arise naturally in systems with broken temporal translation
symmetry and are typically described by first-order recurrence relations representing classical or
quantum Markov chains. When
memory effects induced by hidden degrees of freedom are relevant, however, higher-order discrete
evolution equations are generally required. Focusing on linear dynamics, we identify a well-delineated weak-
memory regime where such equations can, on an intermediate time scale, be systematically reduced to a unique first-order counterpart acting on the same state space. We formulate our results as a mathematical
theorem and work out two examples showing how they can be applied to
stochastic Floquet dynamics under coarse-grained and
quantum collisional models.
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Quantum Gases
Ultrafast many-body dynamics of dense Rydberg gases and ultracold plasma
Mario Großmann, Jette Heyer, Julian Fiedler et al. (+4 more)
Understanding Coulomb driven many-body dynamics in ultracold atomic systems far from
equilibrium remains an open challenge, particularly when ultrafast excitation channels create competing pathways toward Rydberg gases or ultracold
plasmas. Here, we investigate the many-body dynamics in a $^{87}$Rb Bose-Einstein condensate after exposure to a single femtosecond
laser pulse. By tuning the
laser wavelength across the two-
photon ionization threshold, we can control the initial state that is either dominated by free electrons and leads to an ultracold
plasma or dominated by electrons in excited states which leads to a dense Rydberg gas. The large bandwidth enables overcoming the Rydberg blockade that limits the excitation density for narrow-linewidth
lasers. We directly measure the kinetic energy of the released electrons and compare the final distribution of free, bound and
plasma electrons to molecular dynamics simulations where the electrons are modeled as individual particles including collisional ionization and recombination processes. We find very good agreement between the simulated electron distribution and the experimental observation. We identify charge imbalance as main driver for the decay of a dense Rydberg gas into an ultracold
plasma.
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All authors Mario Großmann, Jette Heyer, Julian Fiedler, Markus Drescher, Klaus Sengstock, Philipp Wessels-Staarmann, Juliette Simonet
Materials Science
High-temperature plasma in Casimir physics
Suman Kumar Panja and Mathias Boström
We present a short review of an unusual but important application for a high-temperature charged
plasma. The unorthodox proposition was made by Ninham concerning a contribution from Casimir forces across high-temperature electron-positron
plasma in
nuclear interactions. The key message in the current work is how high temperatures ($\sim10^{11}$ \,K) pop out as essential. Clearly, classical, semi-classical, and
quantum considerations for the background media impact both the Casimir effect and the physics of
stars and the Universe.
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Materials Science · Cross-listed from quant-ph
Fermionic dynamics on a trapped-ion quantum computer beyond exact classical simulation
Faisal Alam, Jan Lukas Bosse, Ieva Čepaitė et al. (+37 more)
Simulation of the time-dynamics of fermionic many-body systems has long been predicted to be one of the key applications of
quantum computers. Such simulations – for which classical methods are often inaccurate – are critical to advancing our knowledge and understanding of
quantum chemistry and materials, underpinning a wide range of fields, from biochemistry to clean-energy technologies and chemical synthesis. However, the performance of all previous digital
quantum simulations of
fermions has been matched by classical methods, and it has thus far remained unclear whether near-term, intermediate-scale
quantum hardware could offer any computational advantage in this area. Here, we implement an efficient
quantum simulation
algorithm on Quantinuum's System Model H2 trapped-ion
quantum computer for the time dynamics of a 56-
qubit system that is too complex for exact classical simulation. We focus on the periodic spinful 2D
Fermi-Hubbard model and present evidence of
spin-charge separation, where the elementary electron's charge and
spin decouple. In the limited cases where ground truth is available through exact classical simulation, we find that it agrees with the results we obtain from the
quantum device. Employing long-range Wilson operators to study deconfinement of the effective gauge field between spinons and the effective potential between charge carriers, we find behaviour that differs from predictions made by classical tensor network methods. Our results herald the use of
quantum computing for simulating strongly correlated electronic systems beyond the capacity of classical computing.
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All authors Faisal Alam, Jan Lukas Bosse, Ieva Čepaitė, Adrian Chapman, Laura Clinton, Marcos Crichigno, Elizabeth Crosson, Toby Cubitt, Charles Derby, Oliver Dowinton, Norhan Eassa, Paul K. Faehrmann, Steve Flammia, Brian Flynn, Filippo Maria Gambetta, Raúl García-Patrón, Max Hunter-Gordon, Glenn Jones, Abhishek Khedkar, Joel Klassen, Michael Kreshchuk, Edward Harry McMullan, Lana Mineh, Ashley Montanaro, Caterina Mora, John J. L. Morton, Alberto Nocera, Dhrumil Patel, Pete Rolph, Raul A. Santos, James R. Seddon, Evan Sheridan, Wilfrid Somogyi, Marika Svensson, Niam Vaishnav, Sabrina Yue Wang, Gethin Wright, Eli Chertkov, Henrik Dreyer, Michael Foss-Feig
Strongly Correlated Electrons
Laser-Induced Commensurate-Incommensurate Transition of Charge Order in a Hubbard Superlattice
Hua Chai, Zhenyu Cheng, Qinxin Hu et al. (+4 more)
We investigate the nonequilibrium dynamics of charge density waves in a pumped one-dimensional Hubbard superlattice with staggered onsite Coulomb interactions at half-filling, using time-dependent exact diagonalization. In
equilibrium, the system exhibits commensurate charge correlations consistent with the superlattice periodicity. Under
laser excitation, the charge correlation function exhibits distinct behaviors across four representative frequencies, spanning both linear and nonlinear optical regimes. Notably, we observe a
laser-induced commensurate-to-incommensurate transition in the charge order, manifested by a shift in the peak wavevector of the charge structure factor. This transition is driven by sublattice-selective doublon-holon dynamics, where the
laser frequency and intensity determine whether excitations predominantly destabilize the charge order on the weakly or strongly interacting sublattice. Our analysis of the excitation spectrum and site-resolved correlation dynamics reveals the underlying mechanisms of this transition. These results suggest a promising optical strategy for controlling charge order in superlattice-based
quantum materials.
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All authors Hua Chai, Zhenyu Cheng, Qinxin Hu, Zhongbing Huang, Xiang Hu, Xuedong Tian, Liang Du
Materials Science
Impact of AlN buffer thickness on electrical and thermal characteristics of AlGaN/GaN/AlN HEMTs
Minho Kim, Dat Q. Tran, Plamen P. Paskov et al. (+3 more)
We investigate the influence of AlN buffer thickness on the structural, electrical, and thermal properties of AlGaN/GaN high-electron mobility transistors (HEMTs) grown on semi-insulating SiC substrates by metal-organic chemical vapor deposition. X-ray diffraction and atomic force microscopy reveal that while thin AlN layers (120 nm) exhibit compressive strain and smooth step-flow surfaces, thicker single-layer buffers (550 nm) develop tensile strain and increased surface roughness. Multi-layer buffer structures up to 2 {\mu}m alleviate strain and maintain surface integrity. Low-temperature
Hall measurements confirm that electron mobility decreases with increasing interface roughness, with the highest mobility observed in the structure with a thin AlN buffer. Transient thermoreflectance measurements show that thermal conductivity (ThC) of the AlN buffer increases with the thickness, reaching 188 W/m.K at 300 K for the 2 {\mu}m buffer layer, which is approximately 60% of the bulk AlN ThC value. These results highlight the importance of optimizing AlN buffer design to balance strain relaxation, thermal management, and carrier transport for high-performance GaN-based HEMTs.
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All authors Minho Kim, Dat Q. Tran, Plamen P. Paskov, U.Choi, O.Nam, Vanya Darakchieva
Quantum Gases
Thermal Casimir effect in the spin-orbit coupled Bose gas
Marek Napiórkowski and Pawel Jakubczyk
We study the thermal Casimir effect in ideal Bose gases with
spin-orbit (S-O) coupling of Rashba type below the critical temperature for Bose-Einstein condensation. In contrast to the standard situation involving no S-O coupling, the system exhibits long-ranged Casimir forces both in two and three dimensions ($d=2$ and $d=3$). We identify the relevant scaling variable involving the ratio $D/\nu$ of the separation between the confining walls $D$ and the S-O coupling magnitude $\nu$. We derive and discuss the corresponding scaling functions for the Casimir energy. In all the considered cases the resulting Casimir force is attractive and the S-O coupling $\nu$ has impact on its magnitude. In $d=3$ the exponent governing the decay of the Casimir force becomes modified by the presence of the S-O coupling, and its value depends on the orientation of the confining walls relative to the plane defined by the Rashba coupling. In $d=2$ the obtained Casimir force displays singular behavior in the limit of vanishing $\nu$
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Strongly Correlated Electrons
Phases and phase transtions in one-dimensional alternating mixed spin (1/2-1) chain: effects of frustration and anisotropy
Soumya Satpathi, Suparna Sarkar and Swapan K. Pati
We investigate the phases and phase-transitions in one-dimensional alternating mixed-
spin (1/2-1) chain in the presence of both frustration and anisotropy. Frustration is introduced via next-nearest-neighbor interactions, while single-ion anisotropy is incorporated at each
lattice site. Our results show that moderate frustration can drive a phase transition from a ferrimagnetic state to an anti-
ferromagnetic ground state. Remarkably, the presence of a weak easy-plane anisotropy destabilizes the ferrimagnetic order, also leading to the emergence of an
antiferromagnetic phase. Interestingly, under strong frustration and anisotropy, the system exhibits signatures of a novel phase with
spin density wave (SDW)-like modulation . We explore these anomalous phase transitions by employing exact diagonalization (ED) for small system sizes and the density
matrix renormalization group (DMRG) method to characterize ground state properties for larger system sizes. We also investigate the finite-temperature behavior across various phases using the ancilla-based time-evolving block decimation (TEBD) approach. The primary objective of this work is to elucidate the phase structure of alternating mixed-
spin chains under the combined effects of frustration and anisotropy. The primary objective of this work is to elucidate the intricate interplay between frustration and anisotropy in identifying the exotic phases and phase-transitions in alternating mixed-
spin chains. Our findings contribute to a deeper understanding of mixed-
spin quantum systems and may offer insights for future theoretical and experimental studies.
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Materials Science
Stopping power of electron liquid for slow quantum projectiles
Vladimir U. Nazarov and E. K. U. Gross
We revisit the problem of deceleration of a charge moving in a medium. Going beyond the traditional approach, which relies on Ehrenfest dynamics, we treat the projectile fully
quantum mechanically, on the same footing as the electrons of the target. In order to separate the dynamics of the projectile from that of the electrons, we employ the Exact Factorization method. We illustrate the resulting theory by applying it to the problem of the stopping power (SP) of a jellium-model metal for slowly moving charges. The
quantum mechanical nature of particles manifests itself remarkably in the differences in the SP for projectiles of the same charge moving with the same velocity, but having different masses.
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Mesoscale and Nanoscale Physics
Exciton dynamics in equilibrium and nonequilibrium regimes
Pushpendra Yadav
The bound electron-hole pairs known as
excitons govern the optical properties of insulating solids. While their behavior in
equilibrium is well-understood theoretically, the nonequilibrium regime at high excitation densities-where phenomena like electron-hole
liquids emerge - is less explored. This thesis presents a first-principles study of
excitons in two-dimensional materials. We use the GW approximation and the Bethe-Salpeter equation to investigate their properties from
equilibrium to nonequilibrium conditions. We first demonstrate how increasing photo-excited carrier density leads to a
redshift-blueshift crossover of
excitons. We then show that electron-
phonon interactions critically modify optical spectra and
exciton lifetimes at finite temperatures. Finally, we unify these effects to demonstrate the formation of an electron-hole
liquid phase above a critical carrier density and below a critical temperature. Our work identifies how enhanced Coulomb interactions in two dimensions can stabilize this phase at significantly higher temperatures, proposing promising material candidates for observing these collective states.
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Soft Condensed Matter
Numerical Investigation of Single-Core to Split-Core Transitions in Nematic Liquid Crystals
Daniel Siebel-Cortopassi and Pei Liu
We analyze single-core and split-core defect structures in nematic
liquid crystals within the Landau-de Gennes framework by studying minimizers of the associated energy functional. A bifurcation occurs at a critical temperature threshold, below which both split-core and single-core configurations are solutions to the Euler-Lagrange equation, with the split-core defect possessing lower energy. Above the threshold, the split-core configuration vanishes, leaving the single-core defect as the only stable solution. We analyze the dependence of such temperature threshold on the domain size and characterize the nature of the transition between the two defect types. We carry out a quantitative study of defect core sizes as functions of temperature and domain size for both single and split core defects.
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Soft Condensed Matter
Melting line of silicon modelled with a machine-learning potential
Yu. D. Fomin
In the present study we investigate the phase diagram of silicon within the framework of SNAP machine learning potential model. We show that the melting line of diamond phase of silicon is a linear function of pressure, which is in good agreement with experimental data. At the same time the melting temperature is strongly underestimated. Also, this model fails to predict the high pressure phases of silicon.
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