Materials Science
Physical and Dielectric Properties of Polycrystalline LaV$_{0.5}$Nb$_{0.5}$O$_4$
Ashok Kumar, Simranjot K. Sapra, Ramcharan Meena et al. (+3 more)
We report a detailed investigation of the structural, electronic, vibrational, and dielectric properties of polycrystalline LaV$_{0.5}$Nb$_{0.5}$O$_4$ samples, prepared at two sintering temperatures (1000\degree C and 1250\degree C). The introduction of Nb$^{5+}$ at the V$^{5+}$ site leads to notable structural and vibrational changes, which can be attributed to their isoelectronic nature and the comparatively larger ionic radius of Nb$^{5+}$. The Rietveld refinement of the X-ray diffraction patterns confirms a coexistence of monoclinic ($P$2$_{1}$/$n$) and scheelite-type tetragonal ($I$4$_{1}$/$a$) phases; for example, with a fraction of 4% and 96% for the sample annealed at 1250\degree C. The particle morphology has altered from spherical (1000\degree C) to irregular-shaped (1250\degree C) as a result of increase in annealing temperature. The Raman spectroscopy,
Fourier Transform Infrared spectroscopy and X-ray Photoemission Spectroscopy have been used to understand the vibrational and electronic properties. An optical band gap of 2.7~eV for the sample sintered at 1250\degree C is calculated using Ultraviolet-vis diffuse reflectance spectroscopy measurements. The dielectric studies shows the higher dielectric permittivity ($\epsilon$$_{r}$) and lower dielectric loss for the sample annealed at 1250\degree C.
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All authors Ashok Kumar, Simranjot K. Sapra, Ramcharan Meena, Vinod Singh, Anita Dhaka, Rajendra S. Dhaka
Mesoscale and Nanoscale Physics
Helical Current of Propagating Dirac Electrons and Geometric Coupling to Chiral Environments
Ju Gao and Fang Shen
We show that a propagating Dirac electron with intrinsic
spin generically carries a real–space helical conserved current, even in the absence of orbital angular momentum. Using exact Dirac eigenstates in cylindrical confinement, we demonstrate that this helical structure possesses definite handedness, persists into evanescent regions, and is characterized by a
geometric helix pitch independent of the longitudinal de~Broglie wavelength. This intrinsic helical geometry enables a local
geometric coupling between a propagating electron and a
chiral environment, yielding chirality–dependent
spin selectivity through current geometry rather than through a
spin–orbit coupling term.
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Materials Science
Facile Optimization of Combinatorial Sputtering Processes with Arbitrary Numbers of Components for Targeted Compositions
Shelby Sutton Fields, Christopher David White, Keith Knipling et al. (+1 more)
Combinatorial sputtering is a physical vapor deposition method that enables the high-throughput synthesis of compositionally varied thin films. Using this technique, the effects of stoichiometry on specific properties of
alloy thin films with analog composition gradients can be mapped using high-throughput characterization. To obtain specific stoichiometries, such as those desired for an equiatomic, intermetallic, or doped compounds, the sputter power of each target must be simultaneously tuned to optimize the deposition rate of each component. This optimization problem increases in complexity with the number of components, which commonly leads to iterative guess-and-check processing and can limit the intrinsic high-throughput advantages of this synthesis method. To circumvent this challenge, this work introduces a composition optimization procedure that enables the facile synthesis of sputtered combinatorial films with targeted compositions. This procedure leverages the expeditious mapping of composition using wavelength dispersive x-ray fluorescence and is capable of optimizing processing for an arbitrary number of components. As a demonstration, this method is leveraged to sputter a combinatorial Cr$_{v}$Fe$_{w}$Mo$_{x}$Nb$_{y}$Ta$_{z}$ film with an equiatomic composition near the wafer center.
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All authors Shelby Sutton Fields, Christopher David White, Keith Knipling, Steven Bennett
Materials Science
Electric-Switchable Chiral Magnons in PT-Symmetric Antiferromagnets
Jinyang Ni, Congzhe Yan, Peiyuan Cui et al. (+3 more)
The
magnons in
antiferromagnetic insulators (AFIs) exhibit dual chirality, each carrying opposite
spin angular momentum. However, in PT-symmetric AFIs, the
magnon bands remain degenerate. In this work, we introduce a new class of PT-preserving AFIs in which the
giant chiral splitting of
magnons can be induced and controlled by an external electric field. Unlike conventional cases, such AFIs host a hidden dipole coupled to the
antiferromagnetic order, which allows an external electric field to break the
magnon sublattice
symmetry and thereby largely lift the band degeneracy. Group theoretical analysis identifies the possible
magnetic layer groups, while first-principles calculations and
spin-wave theory reveal band splittings up to 20meV in Cr2CCl2 and Cr2CBr2 under the electric field of 0.2 V/Å, corresponding to an effective
magnetic field of 200T. In addition, the electrically controlled
magnon chiral splitting enables reversible switching of
magnon-mediated
spin currents. These findings open a new route toward nonvolatile spintronics based on
magnons.
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All authors Jinyang Ni, Congzhe Yan, Peiyuan Cui, Zhijun Jiang, Yuanjun Jin, Guoqing Chang
Materials Science
Towards a Modern Theory of Chiralization
Nicola A. Spaldin
The Modern Theory of Polarization, which rigorously defines the spontaneous electric polarization of a periodic solid and provides a recipe for its computation in electronic structure codes, transformed our understanding of ferroelectricity and related dielectric properties. Here we call for the development of an analogous Modern Theory of Chiralization. We review earlier attempts to quantify chirality, highlight the fundamental and practical developments that a modern theory would facilitate, and suggest possible promising routes to its establishment.
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Statistical Mechanics
The flux of particles in a one-dimensional Fleming-Viot process
Éric Brunet and Bernard Derrida
The Fleming-Viot process describes a system of $N$ particles diffusing on a graph with an absorbing site. Whenever one of the particles is absorbed, it is replaced by a new particle at the position of one of the $N-1$ remaining particles. Here we consider the case where the particles lie on the semi-infinite line with a biased
diffusion towards the origin which is the absorbing site. In the large $N$ limit, the
evolution of the density becomes deterministic and has a number of characteristics similar to the Fisher-KPP equation: a one-parameter family of steady state solutions, dependence of the long time asymptotics on the initial conditions, Bramson logarithmic shift, etc. One noticeable difference, however, is that in the Fleming-Viot case, the solution can be computed explicitly for arbitrary initial conditions and at an arbitrary time. By modifying the
diffusion rule near the origin, one can produce a transition in the flux of absorbed particles, very similar to the pushed-pulled transition in travelling waves. Lastly, using a cut-off approximation (which is known to be correct in the theory of travelling waves), we derive a number of predictions for the leading large $N$ correction of the flux of absorbed particles.
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Strongly Correlated Electrons
The role of the apical oxygen in cuprate high-temperature superconductors
Samuel Vadnais, Rémi Duchesne, Kristjan Haule et al. (+3 more)
Scanning tunneling microscopy measurements exploiting the natural superstructure modulation of the cuprate
superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi-2212) have revealed a possible correlation between the Cu-apical-O distance $\delta_{\mathrm{api}}$ and the superconducting order parameter $m_{\mathrm{SC}}$, as reported recently by O'Mahony et al. (Proc. Natl. Acad. Sci. 119, e2207449119 (2022)). These observations were interpreted as evidence for a direct link between superconductivity and the charge-transfer gap, and more broadly revived the long-standing question of the role of apical oxygens in cuprate superconductivity. Using a combination of density-functional theory and cluster dynamical mean-field theory, we compute from first principles the variations of $m_{\mathrm{SC}}$ induced solely by apical oxygen displacement in Bi$_2$Sr$_2$CuO$_{6+\delta}$, Bi-2212, and HgBa$_2$CuO$_{4+\delta}$. The quantitative agreement between our calculations and experiments allows us to unambiguously attribute the observed variations of $m_{\mathrm{SC}}$ to changes in $\delta_{\mathrm{api}}$. We demonstrate, however, that these variations of $m_{\mathrm{SC}}$ originate predominantly from changes in the effective hole-doping of the CuO$_2$ planes, with negligible effect on the charge-transfer gap. The modest magnitude of the $m_{\mathrm{SC}}$ modulation induced by apical-oxygen displacement alone therefore warrants caution in interpreting correlations between $T_c$ and $\delta_{\mathrm{api}}$ inferred from comparisons across different cuprate compounds. Our work demonstrates that the present ab initio framework can quantitatively resolve the influence of specific structural degrees of freedom on superconductivity in correlated
oxides.
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All authors Samuel Vadnais, Rémi Duchesne, Kristjan Haule, A.-M. S. Tremblay, David Sénéchal, Benjamin Bacq-Labreuil
Mesoscale and Nanoscale Physics
Alexander S. Mayorov, Ping Wang, Xiaokai Yue et al. (+16 more)
Graphene enables precise carrier-density control via gating, making it an ideal platform for studying electronic interactions. However, sample inhomogeneities often limit access to the low-density regimes where these interactions dominate. Enhancing carrier mobility is therefore crucial for exploring fundamental properties and developing device applications. Here, we demonstrate a significant reduction in external inhomogeneity using a double-layer
graphene architecture separated by an ultra-thin hexagonal boron nitride layer. Mutual screening between the layers reduces scattering from random Coulomb potentials, resulting in a
quantum mobility exceeding. Shubnikov de-Haas oscillations emerge at
magnetic fields below 1 mT, while integer
quantum Hall features are observed at 0.002T. Furthermore, we identify a fractional
quantum Hall plateau at a filling factor of at 2T. These results demonstrate the platform's suitability for investigating strongly correlated electronic phases in
graphene-based
heterostructures.
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All authors Alexander S. Mayorov, Ping Wang, Xiaokai Yue, Biao Wu, Jianhong He, Di Zhang, Fuzhuo Lian, Siqi Jiang, Jiabei Huang, Zihao Wang, Qian Guo, Kenji Watanabe, Takashi Taniguchi, Renjun Du, Rui Wang, Baigeng Wang, Lei Wang, Kostya S. Novoselov, Geliang Yu
Soft Condensed Matter
Coarsening dynamics of fingerprint labyrinthine patterns: Machine learning assisted characterization
Supriyo Ghosh, Vinicius Yu Okubo, Kotaro Shimizu et al. (+3 more)
Fingerprint labyrinthine patterns exhibit a level of structural complexity beyond simple stripe phases, combining local stripe order with a dense network of point-like defects. Unlike
symmetry-breaking phases, where coarsening proceeds via diffusive defect annihilation, or conventional stripe phases, where
curvature-driven motion of extended grain boundaries dominates, the coarsening of fingerprint labyrinths is governed primarily by localized junction and terminal defects. Using the Turing-Swift-Hohenberg equation, we study the nonequilibrium relaxation of fingerprint labyrinthine patterns following a quench. To go beyond conventional
Fourier-based diagnostics, we employ a template-matching convolutional neural network (TM-CNN) to identify and track junctions and terminals directly in real space, enabling a quantitative characterization of defect statistics and spatial correlations. We show that, although these point-like defects drive coarsening, their motion is strongly constrained by the surrounding stripe geometry, leading to slow, nondiffusive dynamics that are qualitatively distinct from both conventional phase ordering and stripe coarsening. Together, these results establish defect-mediated dynamics as the central organizing principle of fingerprint labyrinthine coarsening and demonstrate the effectiveness of machine-learning-assisted approaches for complex pattern-forming systems.
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All authors Supriyo Ghosh, Vinicius Yu Okubo, Kotaro Shimizu, B. S. Shivaram, Hae Yong Kim, Gia-Wei Chern
Quantum Gases
Critical speed of a binary superfluid of light
Pierre-Élie Larré, Claire Michel and Nicolas Cherroret
We theoretically study the critical speed for superfluid flow of a two-dimensional miscible binary superfluid of light past a polarization-sensitive optical obstacle. This speed corresponds to the maximum mean flow velocity below which dissipation is absent. In the weak-obstacle regime, linear-response theory shows that the critical speed is set by Landau's criterion applied to the density and
spin Bogoliubov modes, whose relative ordering can be inverted due to saturation of the optical nonlinearity. For obstacles of arbitrary strength and large spatial extent, we determine the critical speed from the conditions for strong ellipticity of the stationary hydrodynamic equations within the hydraulic and incompressible approximations. Numerical simulations in this regime reveal that the breakdown of superfluidity is initiated by the nucleation of
vortex-antivortex pairs for an impenetrable obstacle, and of Jones-Roberts
solitons for a penetrable obstacle. Beyond superfluids of light, our results provide a general framework for the critical speed of two-dimensional binary nonlinear Schrödinger superflows, including Bose-Bose
quantum mixtures.
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Mesoscale and Nanoscale Physics
Hysteretic Excitation in Non-collinear Antiferromagnetic Spin-Torque Oscillators: A Terminal Velocity Motion Perspective
Hao-Hsuan Chen and Ching-Ming Lee
We present a theoretical framework for non-collinear
antiferromagnetic spin torque oscillators (NC-AFM STO) by unifying
spin dynamics under the Poisson Bracket formalism. Shifting from traditional torque-based descriptions to an operational
symmetry perspective, we develop two complementary viewpoints: a vector perspective identifying infinite degenerate Rigid Body Precession (RBP) states where exchange energy depends solely on the total
magnetic momentum, and a particle perspective decomposing dynamics into Center-of-Mass (CM) translation and Relative Motion (RM) oscillation. Using time-dependent rotational and translational transformation techniques, we analytically resolve the rapid (~10 ps) transient
evolution into a stable RBP state driven by SOT and damping. We demonstrate that the out-of-plane anisotropy (OPA) lifts the exchange degeneracy, triggering a long-term (~1 ns) oscillatory decay toward a steady state characterized by uniform
spin z-components and a 120-degree inter-
spin locking angle. This state is accurately governed by our Terminal Velocity Motion (TVM) model [arXiv:2305.14013], where exchange coupling transforms into kinetic energy with a light effective mass. The model precisely predicts SOT-driven transients, hysteretic excitation, and the dynamic phase diagram. Finally, we account for the sub-critical current regime mismatch by identifying a 'Rigid-Body Breaking' effect: a surge in effective friction caused by the self-resonance of RM variables induced by CM translation, mediated by the in-plane anisotropy (IPA).
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Statistical Mechanics · Cross-listed from quant-ph
Universal Digitized Counterdiabatic Driving
Takuya Hatomura
Counterdiabatic driving realizes parameter displacement of an energy eigenstate of a given parametrized
Hamiltonian using the adiabatic gauge potential. In this paper, we propose a universal method of digitized counterdiabatic driving, constructing the adiabatic gauge potential in a digital way with the idea of universal counterdiabatic driving. This method has three advantages over existing universal counterdiabatic driving and/or digitized counterdiabatic driving: it does not introduce any many-body and/or nonlocal interactions to an original target
Hamiltonian; it can incorporate infinite nested commutators, which constitute the adiabatic gauge potential; and it gives explicit expression of rotation angles for digital implementation. We show the consistency of our method to the exact theory in an analytical way and the effectiveness of our method with the aid of numerical simulations.
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Superconductivity
Reaching the intrinsic performance limits of superconducting nanowire single-photon detectors up to 0.1 mm wide
Kristen M. Parzuchowski, Eli Mueller, Bakhrom G. Oripov et al. (+13 more)
Superconducting nanowire single-
photon detectors (SNSPDs) combine high detection efficiency, low noise, and excellent timing resolution, making them a leading platform for
photon-counting applications. However, despite decades of materials and fabrication research, detector performance has never been shown to match theoretical performance expectations. Here, we demonstrate for the first time in situ tuning of a detector from its typical, suboptimal operation, to a regime limited only by material quality, allowing the device to reach its intrinsic performance limit. Our approach is based on current-biased superconducting "rails" placed on either side of the detector that redistribute current across its width to achieve its peak performance. This technique reduces the dark count rate by ten orders of magnitude. Further, we show operation at this intrinsic performance limit for devices up to 0.1 mm wide, and also demonstrate near-unity internal detection efficiency (IDE) at a wavelength of 4um for a 20um-wide detector–a factor of 20 wider than the current state of the art. This work enables future detectors to overcome the Pearl limit for device width, paving the way for arbitrarily large detectors.
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All authors Kristen M. Parzuchowski, Eli Mueller, Bakhrom G. Oripov, Benedikt Hampel, Ravin A. Chowdhury, Sahil R. Patel, Daniel Kuznesof, Emma K. Batson, Ryan Morgenstern, Robert H. Hadfield, Varun B. Verma, Matthew D. Shaw, Jason P. Allmaras, Martin J. Stevens, Alex Gurevich, Adam N. McCaughan
Soft Condensed Matter · Cross-listed from physics.chem-ph
Response of fluorescent molecular rotors in ternary macromolecular mixtures
Mingshan Chi, Anh-Thy Bui, Pierre Lidon et al. (+1 more)
For a few decades, Fluorescent Molecular Rotors have been commonly employed as local probes of microviscosity in complex materials. However, without proper calibration, relating microviscosity to a physical parameter is unclear, which strongly limits their quantitative use in biological media for instance. In this study, the response of a molecular rotor in binary and ternary macromolecular aqueous solutions of polyethylene glycol (PEG) of different molecular weights is investigated in order to better rationalize the sensitivity of rotors to their cybotactic environment. More precisely, for the investigated composition range of ternary mixtures, it is shown that a linear mixing rule applies for fluorescence lifetime with the proportion of the two PEG, and with an increasing ratio of heavy PEG leading to larger lifetimes. These results allow to test more precisely the free volume theory, which has been proposed in the context of probing glass transition. Analysis show that while this theory semi-quantitatively captures the observation, its precise use raises some questions.
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All authors Mingshan Chi, Anh-Thy Bui, Pierre Lidon, Yaocihuatl Medina-Gonzalez
Disordered Systems and Neural Networks · Cross-listed from physics.soc-ph
Partitioning networks into clusters of synchronized nodes via the message-passing algorithm: an unbiased scalable approach
Massimo Ostilli
Partitioning large networks into stable clusters of synchronized nodes is a challenging task. Recent approaches based on spectral analysis can provide exact results on specific dynamics but remain unfeasible for very large networks. Moreover, within a
stochastic framework, it is unclear which dynamics should be chosen to study synchronization. Here we propose an unbiased and scalable method based on the message-passing
algorithm. By exploiting the collective behavior emerging across critical points of an effective Ising-like model, we identify dynamically coherent clusters of synchronized nodes and illustrate the approach on some large real-world networks. We find that, unlike continuous-time dynamics, abrupt desyncrhronization occurs even in simple graphs, without the need to invoke higher order interactions. However, when noise is included, the transition to synchronization becomes smoother and proceeds through the formation of plateaus, albeit at the cost of requiring larger coupling strengths.
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Statistical Mechanics · Cross-listed from quant-ph
Frictional work and entropy production in integrable and non-integrable spin chains
Vishnu Muraleedharan Sajitha, Matthew J. Davis and L. A. Williamson
The maximum work extractable from a
quantum system is achieved when the system is driven adiabatically. Frictional work $\langle W\rangle_\mathrm{fric}$ then quantifies the difference in work output between adiabatic and non-adiabatic driving. Here we show that frictional work in a non-integrable
spin chain is well-characterized by the diagonal
entropy production $\Delta S_\mathrm{d}$ associated with the build up of
quantum coherence. We show that, over a broad range of parameters, $\langle W\rangle_\mathrm{fric}\approx T_\tau\Delta S_\mathrm{d}$, with $T_\tau$ the effective temperature of the final time-evolved state. The relationship breaks down for fast protocols at low temperatures, in which case frictional work is instead well-described by the
quantum relative
entropy between the time-evolved state and a Gibbs-state approximation of the adiabatic state. We compare our results to those obtained from an integrable
spin chain, in which case the system is no longer described by a single temperature. In this case, the frictional work is described by a sum of terms for each independent subspace of the
spin chain, which are at different effective temperatures. Finally, we show how integrability breaking can enhance work extraction in the adiabatic limit, but degrade work extraction in sufficiently non-adiabatic regimes.
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Materials Science
CVD grown bilayer MoS2 based artificial optoelectronic synapses for arithmetic computing and image recognition applications
Umakanta Patra, Subhrajit Sikdar, Roshan Padhan et al. (+3 more)
Demand for lower computing power has rapidly increased. In this context,
brain-inspired neuromorphic computing, which integrate data storage and processing, has attracted significant
attention. Here, our study reveals that field effect transistors fabricated on chemical vapor deposited
bilayer (2L) MoS2 films can mimic the functions of biological synapse. These devices demonstrate high level of pair pulse facilitation (PPF), short term to long term
memory (STM-to-LTM) transition as well as learning-forgetting-relearning properties. Effect of light intensity, pulse number, pulse width and
photon energy on the STM-to-LTM transition is studied. It has been found that the rate of depression of the
memory state can be controlled using the gate bias. Electrical and optical energy consumptions per synaptic event are estimated to be as low as 280 fJ and 20 nJ, respectively. Furthermore, photocurrent in these devices is observed to increase linearly with the number of the excitation pulses. This property has been exploited to demonstrate different arithmetic operations by the device. Moreover, these devices show great potential for image recognition. Artificial neural network simulation has returned an image recognition accuracy of ~85%. All these findings show a great prospect of 2L-MoS2 for developing low power, transparent and flexible neuromorphic devices.
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All authors Umakanta Patra, Subhrajit Sikdar, Roshan Padhan, Amandeep Kaur, Satyaprakash Sahoo, Subhabrata Dhar
Materials Science
Strain as a topological selector in altermagnetic CrSb
Sumohan Giri and Nirmal Ganguli
Altermagnetism combines fully compensated
magnetic order with a
magnetic symmetry that relates inequivalent
spin sublattices, offering a promising, still underexplored platform for unconventional topological phases. Here we show that both isotropic tensile strain and electron localization, controlled by an effective Hubbard interaction $U_{\text{eff}}$, can act as efficient and systematic topological control parameters in the altermagnetic Weyl semimetal CrSb. While CrSb hosts Weyl
fermions at
equilibrium, modest tensile strain of 4-5% stabilizes additional
symmetry allowed Dirac crossings and triple-point
fermions, with further strain selectively favoring the triple-point phase. We propose a 3D low-energy
Hamiltonian that captures the interplay between the Hubbard interaction $U$ and the sublattice
symmetry of the altermagnet, giving rise to an interaction-driven Dirac crossing. Our results establish CrSb as a model altermagnet in which either strain or electron localization can selectively access and control the distinct
topologies inherent to the altermagnets.
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Soft Condensed Matter
Viscoelasticity and elastoplasticity in the power law creep and yielding of gels and fibre network materials under stress
Michael J. Hertaeg and Suzanne M. Fielding
We study computationally the creep and yielding of athermal gels and fibre network materials under a constant imposed shear stress, within a minimal model of interconnected filaments with central forces in $d=2$ spatial dimensions. Each filament is assumed Hookean initially, then breaks irreversibly above a threshold strain. At early times after the imposition of a small stress, we find purely viscoelastic creep response associated with non-affine deformations within the material, with solid terminal behaviour for a network coordination $Z>2d=4$ and initially floppy response for $Z<4$. For a marginally connected network, $Z=4$, we find sustained power law creep with a strain rate $\dot{\gamma}\sim t^{-1/2}$ and strain $\gamma \sim t^{1/2}$ as a function of time $t$ after the imposition of the stress. This viscoelastic regime gives way at later times to elastoplastic creep arising from filament breakage, broadening the range of values of $Z$ and time over which power law creep occurs, compared to a network with filament breakage disallowed. This accumulating filament breakage can weaken the network to such an extent that catastrophic material failure then occurs after a long delay, which we characterise. Finally, we consider the implications of viscoelastic versus elastoplastic deformation for the extent to which a material will recover its original shape if the load is removed after some interval of creep.
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Materials Science · Cross-listed from physics.optics
Size-dependent Dielectric Permittivity of Perovskite Nanocrystals
Jehyeok Ryu, Victor Krivenkov, Vitaly Goryashko et al. (+2 more)
Perovskite nanocrystals (PNCs) are promising building blocks for
quantum photonic devices. Optical properties of PNCs can be enhanced by integration with optical cavities or nanoantennas. Designing such structures requires accurate size dependent dielectric permittivity of PNCs. However, current reports provide primarily ensemble averaged values with limited access to the intrinsic response of individual PNCs. Here we suggest a methodology to reconstruct the size dependent complex dielectric permittivity of CsPbBr3 PNCs from the measured absorbance spectrum of colloidal solution. The permittivity of PNCs is modeled as a sum of Voigt profile oscillators, with the size dependent transition energies governed by the
exciton effective mass. Using a transmission electron microscopy derived size distribution of the PNCs, the solution permittivity is obtained via Maxwell Garnett effective medium approximation. This permittivity is used in a transfer
matrix method to simulate and fit the absorbance spectrum, from which the permittivity of PNCs is reconstructed. The extracted spectral linewidth from the imaginary part of the permittivity (78.4 meV) is consistent with single nanocrystal emission linewidths at room temperature. Finite element simulations show enhanced absorption cross section of a single PNC coupled to a nanoantenna, demonstrating applicability of the extracted permittivity. More generally, these findings provide a route to extract intrinsic permittivity of individual nanocrystals from absorbance measurements of their ensembles.
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All authors Jehyeok Ryu, Victor Krivenkov, Vitaly Goryashko, Yury Rakovich, Alexey Y. Nikitin
Superconductivity
Topological Semimetal Transport Modulated by Interstitial Fe in Ba(Fe$_{1-x}$Co$_x$)$_{2+\delta}As$_2$ Superconductors
Ze-Xian Deng, Qiang-Jun Cheng, Jing Jiang et al. (+14 more)
Topological semimetals are renowned for exhibiting large, unsaturated magnetoresistance arising from ultrahigh carrier mobility and electron-hole compensation. However, such behaviors remain poorly understood in iron-based
superconductors that have been recently recognized to harbor rich nontrivial
topology. Here, we combine angle-resolved magneto-transport measurements with first principles calculations to reveal the emergence and tunability of topological semimetals in ferropnictide Ba(Fe$_{1-x}$Co$_x$)$_{2+\delta}As$_2$ epitaxial films, modulated by interstitial Fe. These states exhibit ultralow residual resistivity, coexisting high-mobility electron and hole carriers, and linear positive magnetoresistance below 110 K. Remarkably, the magnetoresistance becomes more pronounced when the
magnetic field is applied parallel to the film plane, reaching an unsaturated 1206% at 56 T. Furthermore, superconductivity persists in these ferropnictide films, establishing them as a tunable platform for investigating the interplay among electron correlation,
topology, and superconductivity.
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All authors Ze-Xian Deng, Qiang-Jun Cheng, Jing Jiang, Yong-Wei Wang, Xi Zhou, Ming-Qiang Ren, Cong Cong Lou, Xiao-Xiang Chen, Bin-Jie Wu, Zeng-Wei Zhu, Qing-Hua Zhang, Lin Gu, Ding Zhang, Kai Liu, Xu-Cun Ma, Qi-Kun Xue, Can-Li Song
Superconductivity
Intertwined Charge Stripes and Majorana Zero Modes in An Iron-Based Superconductor
Yu Liu, Li-Xuan Wei, Qiang-Jun Cheng et al. (+12 more)
In type-II
superconductors,
magnetic fields modulate the amplitude and phase of the superconducting order parameter, forming quantized
vortices where superconductivity is locally suppressed and exotic bound states or competing electronic orders emerge. Using spectroscopic-imaging scanning tunneling microscopy on epitaxial Ba(Fe$_{0.94}Co$_{0.06})$_2$As$_2$ films, we discover an incommensurate charge-stripe order aligned with the Fe-Fe bond direction. These charge modulations become strongly enhanced at the
vortex core and extend far into the
vortex halo. Strikingly, the charge order modulates Andreev bound states of
vortices at non-zero energies, producing abelian
vortices with half-odd-integer level quantization and non-abelian
vortices with integer-quantized core states that host a Majorana zero mode. The distinct
vortex types are distinguished by the registry of their centers relative to the charge-stripe pattern and remain robust in ultrathin (2.5-unit-
cell) films. Our findings reveal a density-wave-textured
vortex matter and provide fresh insights into intertwined phenomena in iron-based
superconductors.
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All authors Yu Liu, Li-Xuan Wei, Qiang-Jun Cheng, Zhenhua Zhu, Xin-Yu Shi, Cong-Cong Lou, Yong-Wei Wang, Ze-Xian Deng, Ming-Qiang Ren, Dong E. Liu, Ziqiang Wang, Xu-Cun Ma, Jin-Feng Jia, Qi-Kun Xue, Can-Li Song
Quantum Gases · Cross-listed from physics.atom-ph
Dynamics of antiferromagnetic Dimers in Rydberg Atom Chains
Feng-Yuan Kuang, Lin Li and Weibin Li
We investigate the dynamics of
antiferromagnetic dimers within a Rydberg atom chain in the regime where
laser detuning compensates for nearest-neighbor (NN) interactions. Using an effective PXQ model, we demonstrate that the associated
Hilbert space decomposes into disconnected, dimer-conserving subspaces. The classification of these subspaces is provided, and the computational basis states spanning them are identified. Through a combination of analytical mapping and numerical simulations, we compare the dynamics of the PXQ model with those of the full Rydberg atom chain. The deviations are attributed to two factors,
laser-induced leakage from the constrained
Hilbert subspace and the influence of long-range interactions beyond the NN limit. Our results indicate that subspace leakage can be mitigated by increasing the NN interaction strength. While this simultaneously amplifies the effects of long-range interactions, the conservation of the dimer number remains. Our study opens up possibilities for exploring the dynamics of
antiferromagnetic dimers using the Rydberg atom
quantum simulator.
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Materials Science
Structural stability, electronic structure, and magnetic properties of the single-layer trilayer La3Ni2O7 polymorph
Shekhar Sharma, Yi-Feng Zhao and Antia S. Botana
A polymorph of the
bilayer nickelate La3Ni2O7 that displays an alternating single-layer (SL) and trilayer (TL; 1313) stacking pattern has recently been discovered. Signatures of superconductivity under pressure have been found in this phase. At ambient pressure, La3Ni2O7-1313 has been reported to crystallize in three different space-group
symmetries Cmmm, Imma, and Fmmm. Unlike the commonly observed tilted NiO6 octahedra in perovskite nickelates, the Cmmm phase exhibits no NiO6 tilts, implying that this structural feature alone may be insufficient to give rise to superconductivity in Ruddlesden-Popper nickelates. Here, we employ first-principles calculations and group theory analysis to study the pressure dependence of the structural instabilities in this SL-TL La3Ni2O7 polymorph. At ambient pressure, we identify multiple unstable
phonon branches in the highest
symmetry (Cmmm) structure at various high-
symmetry points of the Brillouin zone. Distortions associated with these instabilities lead to one of the other experimentally reported space groups (Imma) that does display octahedral tilts. The
magnetic tendencies indicate that the electronic structure of La3Ni2O7-1313 at ambient pressure is dominated by the TL block, as the SL is in a Mott-insulating regime. Under pressure, a tetragonal P4/mmm structure becomes stable, in agreement with experiments.
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Materials Science
Hybrid films of Co - C60 preparation and changes induced by external stimuli
Giovanni Ceccio, Jiri VAcik, Yuto Kondo et al. (+9 more)
In this work, we report on the study on organic-metal hybrid systems, in particular Co-C60 fullerene thin films. This study mainly focused on the investigation of the morphological and structural
evolution of the film surface after various external stimuli designed to provide energy to the system. For film growth, we adopted an innovative approach, combining ion-beam sputtering of a pure metal target with thermal evaporation of C60 in a co-deposition setup. The films underwent a series of treatments to induce modifications.
Laser and ion irradiations were performed using a pulsed
laser, a continuous Ar beam, and a pulsed C beam. In addition, thermal annealing in
vacuum was performed to examine the long-term effects of temperature. The composition of deposited film was investigated using Ion Beam Analysis, the morphology and the structure, and the effects of treatments on the films were studied using SEM and TEM microscopies and Raman spectroscopy. Changes in electrical resistance were also measured to explore potential applications of these films after treatment.
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All authors Giovanni Ceccio, Jiri VAcik, Yuto Kondo, Kazumasa Takahashi, Romana Miksova, Eva Stepanovska, Josef Novak, Petr Malinsky, Barbara Fazio, Catia Cannilla, Alena Michalcova, Sebastiano Vasi
Mesoscale and Nanoscale Physics
Localized emission in MoSe$_2$ monolayers on GaN nanopillars
Abderrahim Lamrani Alaoui, Álvaro Moreno, Maximilian Heithoff et al. (+12 more)
Solid-state
quantum emitters (QEs) in two-dimensional
semiconductors offer compact, chip-compatible sources for
quantum photonics. In transition-metal dichalcogenides (TMDs), nanopillars are widely used to induce localized emission, yet the underlying confinement mechanism and the relative roles of strain versus dielectric environment remain unclear. The general problem addressed here is whether strain alone explains
quantum emitter formation and placement in MoSe$_2$, or whether dielectric contrast at suspended-supported interfaces is also required. Here, we combine hyperspectral superlocalization of photoluminescence with co-registered AFM topography and phase to map the positions of localized states (LS) in MoSe$_2$ suspended on GaN pillars and correlate them with bending strain and the local dielectric context. Contrary to the common assumption of purely strain-driven activation, LS frequently occur at suspended–supported interfaces around the pillar apex and span a broad strain range without a clear threshold, while being scarce along high-strain ripples. Our data indicate that deterministic emitter positioning in Mo-based TMDs benefits from co-engineering both strain gradients and nanoscale dielectric heterogeneity, rather than strain alone. More broadly, this combined optical-mechanical characterization approach provides a general framework for mapping structure-property relationships in 2D
quantum materials at the single-emitter level.
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All authors Abderrahim Lamrani Alaoui, Álvaro Moreno, Maximilian Heithoff, Virginie Brändli, Aimeric Courville, Maksym Gromovyi, Sébastien Chenot, Mahima-Ravi Srivastava, Stéphane Vézian, Benjamin Damilano, Frank Koppens, Yannick Chassagneux, Christophe Voisin, Philippe Boucaud, Antoine Reserbat-Plantey
Materials Science
NASICON solid-electrolyte modification and analysis using ion and neutron beams
Giovanni Ceccio, Jiri Vacik, Mykhailo Drozdenko et al. (+7 more)
Solid electrolytes (SEs) for sodium-based superionic conductors (NaSICON) are widely recognized for their excellent ionic conductivity and application in sodium based energy storage systems. While considerable effort has been made to develop thin electrolytes for all-solid-state batteries (ASSBs) for lithium ions, only a few sodium-based SEs have been successfully fabricated as thin films. These thin films are particularly desirable for their reduced electrical resistance, which typically increases with the thickness of the SE. By reducing the thickness of the SEs to the nanometer scale, their ionic conductivity can be significantly enhanced. In this study, the NASICON composite was initially prepared in the form of pellets using the mixed
oxide technique with a planetary ball mill and synthesized by the solid-state method at 1250 {\deg}C. The resulting pellets were used as sputtering targets in a low-energy ion facility to prepare continuous and uniform NASICON nanofilms. To explore the effect of ion implantation on the electrical properties of NASICON, the prepared films were bombarded with Ni ions at 1.1 MeV and varying fluences, using the Tandetron accelerator at the CANAM infrastructure (NPI Řež). The electrical properties of both the synthesized and implanted films were analyzed through electrochemical impedance spectroscopy (EIS). The results, describing the impact of irradiation on NASICON's properties, are presented here.
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All authors Giovanni Ceccio, Jiri Vacik, Mykhailo Drozdenko, Romana Miksova, Ivan Mastronardo, Dejan Prokop, Benedetta Brancato, Eva Stepanovska, Claudia D'Urso, Leone Frusteri
Materials Science
Effects of pulsed and continuous light and heavy ion irradiation on the morphology and electrical properties of Ag+C60 and Au+C60 composite thin films
Giovanni Ceccio, Kazumasa Takahashi, Yuto Kondo et al. (+5 more)
Metal - organic nanocomposite thin films represent a versatile class of materials whose properties can be effectively tuned through external stimuli. In this study, Ag+C60 and Au+C60 nanocomposite thin films were briefly investigated to elucidate the effects of ion irradiation on both their morphology and electrical properties. The films were synthesized by co-deposition of noble metals and fullerenes, using ion beam sputtering of metal targets combined with simultaneous thermal evaporation of C60. The as - deposited films were characterized by ion beam analysis to determine their composition and element depth distributions. Subsequently, the samples were irradiated at room temperature with either a continuous Ar ion beam or a pulsed C ion beam, both at an energy of 20 keV and a fluence of 1 x 1015 ions/cm2. Irradiation-induced morphological changes were examined by scanning electron microscopy. While the C-irradiated films retained compact and homogeneous surface morphologies, Ar irradiation induced pronounced surface restructuring, resulting in highly corrugated and porous-like surfaces. In addition to morphology, the electrical resistance of the films was measured. The results indicate that C-irradiated samples exhibit only minor changes in resistivity, whereas Ar irradiation strongly affects the electrical properties, with the most significant impact observed for the Au+C60 system. The observed changes in electrical resistance closely correlate with the irradiation-induced surface morphology. The measurement results are briefly discussed below.
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All authors Giovanni Ceccio, Kazumasa Takahashi, Yuto Kondo, Romana Miksova, Vasily Lavrentiev, Josef Novak, Eva Stepanovska, Jiri Vacik
Soft Condensed Matter
Orientational ordering and correlations in a quasi-one-dimensional hard-dumbbell fluid
Ana M. Montero, Péter Gurin, Szabolcs Varga et al. (+1 more)
We study a quasi-one-dimensional fluid of hard dumbbells with continuous orientational degrees of freedom using an exact transfer-
matrix formulation. The model allows for a complete analytical characterization of thermodynamic properties, orientational ordering, and correlation functions in terms of the spectral properties of an integral operator. We derive exact expressions for the equation of state, the orientational distribution function, and both partial and total radial distribution functions. Their asymptotic behavior is governed by the complex poles of the Laplace-transformed correlation functions, which determine the positional and orientational correlation lengths. As density increases, the system exhibits a continuous crossover from a weakly ordered regime with a unimodal orientational distribution to a strongly constrained regime characterized by bimodal orientational ordering. This crossover is accompanied by a nonmonotonic behavior of the pressure relative to the Tonks gas and by a qualitative change in the decay of correlation functions from oscillatory to monotonic. In the high-pressure limit, we show that orientational and positional fluctuations contribute equally to the pressure, leading to a universal ratio of twice the Tonks pressure. The theoretical predictions are supported by numerical solutions of the discretized transfer operator and by scaling arguments that elucidate the high-pressure behavior of ordering and correlation lengths.
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All authors Ana M. Montero, Péter Gurin, Szabolcs Varga, Andrés Santos
Strongly Correlated Electrons
Magnetoelastic coupling at the field-induced transition in EuAl$_{12}$O$_{19}$
T. Haidamak, G. Bastien, P. Proschek et al. (+9 more)
Magnetoelastic coupling plays a crucial role in
magnetic-field-induced transitions in anisotropic ferromagnets. Ultrasonic methods are suitable for experimental investigations of these phenomena. We investigate elastic constants in EuAl$_{12}$O$_{19}$, a quasi-two-dimensional anisotropic ferromagnet, by measuring sound velocity in
magnetic fields perpendicular to spontaneous magnetization. The shear modulus $C_{44}$ exhibits dramatic softening at the field-induced transition from the
ferromagnetic to a paramagnetic phase with
magnetic moments forced to polarize along the applied transverse field. The softening is attributed to strong
magnetic fluctuations near a second-order phase transition. Theoretical calculations based on magnetization data qualitatively reproduced the observed behavior within a strain-exchange mechanism. These results demonstrate that magnetoelastic coupling in EuAl$_{12}$O$_{19}$ arises primarily from exchange striction and provide a framework for modeling similar transitions in other anisotropic ferromagnets.
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All authors T. Haidamak, G. Bastien, P. Proschek, A. Eliáš, R.H. Colman, D. Gorbunov, S. Zherlitsyn, A.A. Zvyagin, G.A. Zvyagina, J. Prokleška, V. Sechovský, M. Vališka