Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el
Bound states, resonances, and their thermodynamic properties in pseudospin-1 systems with short-range impurities
E. V. Gorbar and Pavlo Sukhachov
Bound states and resonances induced by short-range impurities modeled by circular potential wells are analyzed in the vicinity of flat and dispersive bands in gapped and gapless pseudospin-1 systems. We find that the bound and resonant states derived from the flat band show unusual characteristics originating from the multicomponent structure of pseudospin-1
fermions, which are distinct from those for pseudospin-$\tfrac{1}{2}$
fermions. Contrary to gapped Dirac systems and unlike bound states in the vicinity of the upper dispersive band, the bound states derived from the flat band occur for any value of the total angular momentum. The energies of these bound states with higher angular momentum $j$ tend to decrease with $|j|$. In addition, it is found that their wave functions are localized at the potential well edge and the localization increases with $|j|$. The signatures of the impurity states in the local density of states are determined. Using the Anderson model for independent electrons in the disorder potential, the thermodynamic potential,
entropy density, and heat capacity are obtained. In the regime dominated by bound states derived from the flat band, the
entropy density monotonically increases with temperature and saturates, whereas the heat capacity exhibits a single maximum.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Chiral phonons driven by chiral cavities
V. A. S. V. Bittencourt, N. Shabala, R. M. Geilhufe et al. (+1 more)
Lattice vibrations carrying angular momentum give rise to fundamental phenomena such as the
phonon Hall effect and the Einstein-de Haas effect, offering new opportunities for manipulating angular momentum in condensed-matter systems. Generating such circularly polarized
phonons requires either the use of an external
magnetic field, or of polarized light pulses. The latter approach does not require the use of any
magnetic response of the material, but it has limitations, in particular regarding the duration of the pulse. Consequently, any effect stemming from
phonons generated by light pulses is transient. In this paper, we propose the use of a driven electromagnetic cavity as a route to generate a steady-state population of chiral
phonons. We derive a general description of cavity-chiral
phonon interaction, with a particular focus on modes of chiral cavities. We show that, under optimized conditions, a significant effective
phonon-induced
magnetic field can be generated by means of an external drive with realistic power. Our approach is specially tailored for Gamma point
phonons with THz frequencies, and opens a new route for investigating chiral
phonons with electromagnetic cavities.
Read the full abstract ▾
All authors V. A. S. V. Bittencourt, N. Shabala, R. M. Geilhufe, A. Metelmann
Mesoscale and Nanoscale Physics
Entanglement from particle number fluctuations in a second-order topological insulator
Mahla Moridi Farimani and Kim Pöyhönen
Higher-order topological
insulators are materials with a bulk energy gap featuring gapless modes at $(d-n)$-dimensional edges, where $n > 1$. Despite this modified bulk-boundary correspondence, their nontrivial
topology can nevertheless be observed through the bipartite
entanglement spectrum. Inspired by works suggesting fluctuations in conserved quantities could be used to study
topology in one-dimensional systems, which likewise feature zero-dimensional edge modes, we extend this treatment to a two-dimensional second-order topological
insulator where corner states play an analogous role. We show that the standard bipartite
entanglement entropy and particle number fluctuation lack striking signals of topological phase transitions, both in the static case and in the time
evolution after a quench, obscured by an area-law term from the subsystem edges. By introducing a quadripartite construction of the subsystem, we show that it is possible to isolate the topological contributions, producing sharp transition peaks in both quantities, observable by studying subsystems much smaller than the full system. As particle number fluctuations are accessible in existing experiments, these results establish a concrete and scalable path to experimental detection of the
entanglement in higher-order topological
insulators.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.stat-mech
Exact joint eigenvalue densities of non-Hermitian random matrices are Calogero scattering states
Zhenyu Xiao, Ze Chen and Shinsei Ryu
Determining exact joint
eigenvalue densities is central to random
matrix theory. We solve this long-standing problem for non-Hermitian
matrices with transposition
symmetry (complex symmetric and complex self-dual) at arbitrary
matrix size. Up to a Vandermonde factor, they are scattering-state wave functions of the Calogero model, a line of particles interacting through an inverse-square potential, with the coupling strength set by the
symmetry. In contrast to many previously known joint densities, the densities cannot be written as a gas of
eigenvalues with pairwise interactions. We further compute the complex level spacing distributions and two-point spectral correlation functions, which carry power-law tails, absent in a Coulomb gas. Our results shed light on the interplay among random
matrices, integrability, and
symmetry.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.stat-mech
Duality between the level statistics of Hermitian and non-Hermitian random matrices
Ze Chen, Zhenyu Xiao, Yifei Liu et al. (+1 more)
The complex spectral statistics of non-Hermitian random
matrices provide a standard diagnostic of dissipative
quantum chaos. Yet an analytical understanding of how
symmetry enriches these universal correlations remains limited. We establish an exact duality between the spectral statistics of Hermitian and non-Hermitian random
matrices in the limit of large
matrix size. This duality resolves a longstanding analytical problem by yielding the previously unknown
eigenvalue pair-correlation functions for complex symmetric (class AI$^\dagger$) and complex self-dual
matrices (class AII$^\dagger$), completing the analytical description of bulk pair correlations in the non-Hermitian threefold way. It further gives closed-form spectral densities near the origin for seven additional
symmetry classes. Numerical tests in interacting and dissipative
quantum models support the universality of these predictions beyond Gaussian ensembles. The duality suggests a deeper connection between chaos in closed and open
quantum systems.
Read the full abstract ▾
All authors Ze Chen, Zhenyu Xiao, Yifei Liu, Shinsei Ryu
Mesoscale and Nanoscale Physics
How Landau caterpillars turn into Hofstadter butterflies by tuning the periodic potential strength
Ivo A. Gabrovski and Louk Rademaker
It is well-known that the spectrum of two-dimensional electrons in a perpendicular
magnetic field is given by discrete flat Landau levels. By contrast, electrons in a two-dimensional tight-binding model give rise to a fractal Hofstadter butterfly spectrum. In this paper, we connect these two opposite limits by showing how a butterfly spectrum emerges from broadened Landau `caterpillars', by continuously increasing the periodic potential strength. We identify a series of topological transitions that isolate a lowest trivial band, a necessary condition for the butterfly to emerge. The resulting butterfly is topologically distinct from the Hofstadter butterfly at fluxes $\phi>1$, due to anomalous behavior of diagonal hopping. Moreover, the hopping parameters of an effective tight-binding model, obtained by a Wannierization procedure at large
magnetic field, are highly dependent on the flux, revealing that Wannier orbitals themselves change under the applied
magnetic field. Our methods and results are relevant for artificial materials, such as moiré systems, where a full
quantum of flux per
lattice unit
cell is experimentally accessible. On a theoretical level, having Wannierization methods for each specific flux allows more accurate many-body calculations in large
magnetic fields.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el
Higher-Winding Fractionalization
Kishore Iyer, Christophe Mora and Daniele Guerci
Higher-winding skyrmion textures can generate emergent
magnetic fields with multiple flux quanta per unit
cell. This opens an intriguing route toward fractionalization, allowing fractionalized
quantum anomalous Hall states to arise even at integer filling of the microscopic unit
cell. We show that, in this setting, increasing
lattice-scale inhomogeneity of the emergent
magnetic field drives a Berezinskii–Kosterlitz–Thouless (BKT) transition between a fractionalized
liquid and a crystalline dielectric state. This transition carries a topological signature: under flux insertion, the many-body polarization defines a quantized winding number that is nonzero in the fractionalized phase and vanishes in the dielectric
crystal.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Engineering multi-photon dissipation with a dc-voltage-biased Josephson junction
Marco Paradina, Ambroise Peugeot, Roberto Negrin et al. (+8 more)
Multi-
photon dissipation – a key resource for bosonic
qubits – is usually realized by parametrically pumping a Josephson coupler at the cost of spurious nonlinear terms. Here we instead engineer it using a dc-voltage-biased SQUID, such that these parasitic terms average out. We activate the conversion of one, two, or four
photons of a high-Q mode into a single
photon of a lossy mode. We characterize the two-
photon dissipation by Wigner
tomography, establishing dc-biased junctions as a resource for reservoir engineering and a viable route to cat-
qubit stabilization.
Read the full abstract ▾
All authors Marco Paradina, Ambroise Peugeot, Roberto Negrin, Oscar Novat, Tristan Villain, Anil Murani, Jean-Loup Ville, Sébastien Jezouin, Raphaël Lescanne, Audrey Bienfait, Benjamin Huard
Mesoscale and Nanoscale Physics
Device characterization of Si$/$SiGe double quantum dots using exchange oscillations in Earth's magnetic field
Holly G. Stemp, Harry Hanlim Kang, Chih Hwan Yang et al. (+6 more)
Exchange-based
semiconductor qubits encompass a broad family of encodings constructed from singlet- and triplet-like
spin states, several of which are compatible with operation at zero applied
magnetic field. Their reliable operation requires characterization of environmental noise, residual idle interactions, and exchange-dependent decay, but this characterization often relies on multi-axis control calibration or deliberately engineered
magnetic-field gradients. A simpler zero-applied-field diagnostic is particularly valuable for hybrid
semiconductor-
superconductor systems, in which
magnetic fields can degrade superconducting components. Here, we use the intrinsic
magnetic-field gradient produced by residual nuclear
spins in isotopically enriched Si/SiGe to implement exchange oscillations between two
quantum dots as a characterization tool without a micromagnet, dynamic nuclear polarization, or prior multi-axis calibration. Using Carr-Purcell-Meiboom-Gill exchange sequences, we extend the singlet coherence from $T_2^*=1.17\pm0.02~\mu$s to $T_2^{\mathrm{CPMG}}=74.8\pm1.8~\mu$s with $N=70$ refocusing pulses. The oscillation phase resolves residual exchange in the tens-of-kilohertz regime and enables it to be mapped across the $(1,1)$ charge
cell. These results establish intrinsic-gradient exchange oscillations as a simple, more relevant zero-field diagnostic for exchange-only and related
semiconductor qubit encodings that is amenable to rapid, high-throughput device characterization.
Read the full abstract ▾
All authors Holly G. Stemp, Harry Hanlim Kang, Chih Hwan Yang, Gabriel D. Cutter, Frederike Brockmeyer, Patrick J. Strohbeen, Max Hays, Jeffrey A. Grover, William D. Oliver
Mesoscale and Nanoscale Physics
Interfacial Spin-to-Charge Conversion in Sputtered MoTe2 Heterostructures Probed by Spin Pumping and Spin-Torque Ferromagnetic Resonance
J. L. Costa, E. Santos, E. L. T. França et al. (+2 more)
Transition metal dichalcogenides (TMDs) and their Weyl semimetal phases, such as MoTe$_2$, have attracted significant
attention for
spin-orbit torque applications due to their efficient charge-to-
spin conversion. However, whether this conversion originates predominantly from the bulk or the interface remains unclear. Here, we investigate
spin-charge interconversion in MoTe$_2$ using
spin-pumping and
spin-torque ferromagnetic resonance (SP-FMR and ST-FMR). Thickness-dependent measurements reveal large
spin-to-charge conversion and
spin-torque efficiencies that are essentially independent of MoTe$_2$ thickness, indicating that the conversion is predominantly governed by the Rashba-Edelstein effect at the Py/MoTe$_2$ interface rather than by bulk
spin transport. This behavior contrasts with the characteristic thickness dependence observed in Pt
heterostructures and is further supported by bidirectional SP-FMR and interface-separation measurements. Our results highlight the dominant role of the Py/MoTe$_2$ interface in enabling efficient
spin-charge conversion and
spin-orbit torques in TMD-based spintronic devices. These findings highlight the potential of sputtered MoTe$_2$/Py
heterostructures for low-power spintronic applications, including
magnetic memory and logic devices.
Read the full abstract ▾
All authors J. L. Costa, E. Santos, E. L. T. França, J. B. S. Mendes, A. Azevedo
Mesoscale and Nanoscale Physics
Breakdown of Charge-Conjugation Symmetry of Disclinations in 2D Crystals
Ruslan Yamaletdinov, Mikhail I. Katsnelson and Oleg V. Yazyev
Disclinations are elementary topological defects in two-dimensional (2D) crystalline membranes, yet their elastic properties remain largely unexplored. Using atomistic simulations, we address the energetics, morphology, and interactions of disclinations in free-standing
graphene, a prototypical 2D
crystal. We find that while disclinations with positive topological charges follow an expected behavior, negative disclinations exhibit sublinear energy scaling with charge as well as
equilibrium shape that deviates sharply from the conventional saddle ansatz. This breakdown of charge-conjugation
symmetry leads to qualitatively distinct interactions: positive disclinations repel, whereas negative disclinations display a robust long-range attraction. These trends are shown to be further amplified by self-adhesion in folded membranes. Our results uncover a fundamentally different energetic landscape for negative
curvature defects and provide a basis for understanding the stability, self-folding behavior, and defect-driven morphology of
graphene and other 2D membranes.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Signatures of inter-sideband coherence in the resonance fluorescence spectrum of an acoustically-modulated quantum dot
Rafał A. Bogaczewicz, Hubert J. Krenner and Paweł Machnikowski
We theoretically investigate the inter-sideband phase coherence within the resonance fluorescence spectrum of an acoustically modulated
quantum dot using a filtered-field formalism for a Mach-Zehnder configuration. We demonstrate that
geometric slant of the interferograms provides an indicator of phase coherence that is resilient to environmental white noise. Specifically, noise-induced spectral
diffusion reduces the global fringe intensity, while leaving the characteristic inclination strictly invariant. Our findings establish a framework for verifying single-
photon coherence between spectral sidebands, essential for frequency-bin encoding and scalable
quantum networking in realistic, noisy solid-state architectures.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Local phase-space Berry curvature and Hall transport in textured twisted bilayer graphene
Tohid Farajollahpour
Slow twist-angle and heterostrain textures in twisted bilayer
graphene provide a natural route to phase-space Berry geometry. We show that a purely
geometric tetrad/shift sector does not generate mixed Berry
curvature once the
spin connection is treated consistently. By contrast, a projected textured mini-Dirac cone in twisted bilayer
graphene acquires genuine mixed phase-space
curvature. We analyze a controlled local Hall-bar limit with a one-dimensional texture and mirror $M_x$. In that limit the pseudogauge gradient renormalizes only the longitudinal conductivity along the textured direction, while a dc nonlinear Hall response appears only when an additional valley-odd tilt generates a Berry-
curvature dipole. Both
geometric responses peak at the same local filling, $\mu_{\rm loc}=\sqrt{2}\,m$, providing a gate-tunable fingerprint of their common origin. All local-cone parameters and their texture susceptibilities are extracted from a heterostrained Bistritzer-MacDonald model at $\theta=1.3^\circ$. The tilt invoked in the transport estimates corresponds to heterostrain of only $0.03\%-0.2\%$, below values routinely imaged in devices. The resulting theory provides a local analytic framework for textured moiré Dirac materials and cleanly separates
geometric, texture-induced, and transport-level ingredients relevant to realistic TBG.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Supermoiré Reconstruction and Topological Mosaics in Twisted Trilayer WSe$_2$ and MoTe$_2$
Hai Meng, Yang Xu and Fengcheng Wu
We investigate
lattice relaxation and band structures of helical and alternating twisted trilayer WSe$_2$ and MoTe$_2$ using machine-learning force fields and large-scale ab initio calculations. Interference between the two bilayer moiré
lattices generates a supermoiré
lattice that, upon relaxation, reconstructs into a few dominant domain types with locally commensurate bilayer moiré
lattices. Because the systems lack $C_{2z}$
symmetry, domains otherwise related by this
symmetry become energetically and topologically distinct, unlike in twisted trilayer
graphene. Band structure calculations show that the topmost valence bands originate from the $K$ ($K'$) valleys and carry domain-dependent valley Chern numbers. The resulting supermoiré
lattice hosts a mosaic of topologically inequivalent domains, offering a platform for exploring correlated and topological physics.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Coexistence of polariton bound states in the continuum and 2D radiative excitons
Simone Zanotti, Marco Liscidini, Dario Gerace et al. (+1 more)
Bound states in the continuum (BICs) enable optical modes with ideally infinite radiative lifetimes despite lying within the radiation continuum. Radiation-matter interaction in periodically patterned planar waveguides
embedding two-dimensional (2D) optically active excitations can be described
quantum mechanically by diagonalizing a non-Hermitian operator, known as the Hopfield
matrix, which can be generalized to incorporate independent photonic and excitonic losses into the polaritonic states. However, since 2D
excitons undergo intrinsic wavevector-dependent radiative decay within the light cone, whether the Hopfield formalism can consistently account for this process while preserving polariton BICs has remained an open question. Here we show that a non-Hermitian Hopfield formalism incorporating excitonic radiative losses correctly captures the existence of genuine $k=0$ polariton BICs with diverging radiative lifetimes. The theory provides a unified microscopic framework for radiative
excitons and polariton BICs, and an efficient predictive tool for designing photonic-
crystal platforms coupled to
quantum wells, transition-metal dichalcogenides, and other 2D excitonic materials.
Read the full abstract ▾
All authors Simone Zanotti, Marco Liscidini, Dario Gerace, Lucio C. Andreani
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Emergence and suppression of phonon vortices in two-dimensional crystals: Interplay of lattice symmetry, heavy impurities, and shear
Yu-Tian Zhang, Deng Pan and Yuliang Jin
Phonon vortices are
vortex-like displacement fields that appear in the vibrational modes of two- dimensional materials. Here, we demonstrate that these
vortices arise as
symmetry-adapted linear combinations of degenerate planar
phonon modes, with the superposition coefficients uniquely de- termined by the
lattice point group. This
symmetry principle establishes that
vortices are intrinsic standing-wave solutions in perfect
crystals, requiring neither impurities nor disorder. A heavy mass impurity favors
vortex modes over planar modes through stronger resonance-induced frequency soft- ening, whereas shear deformation suppresses
vortex modes by breaking rotational
symmetry. The competition between these two effects gives rise to a precisely predictable strain threshold. The proposed framework, grounded in
symmetry and energy-minimization, provides a useful basis for understanding vibrational topological defects induced by other types of impurities or defects. This study further suggests that defect and shear engineering constitutes an effective tuning strategy for controlling vibrational modes and the associated thermal and mechanical properties of
crystals.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Predictive wavelength tailoring of uniform GaSb-based quantum dots for emission at 1.55 um
Markus Peil, Maja Wasiluk, Ziemowit Olinkiewicz et al. (+11 more)
A detailed study of emission wavelength tailoring of GaSb-based QDs formed by InGaSb-filling of droplet-etched nanoholes in AlGaSb is presented. The study shows that the emission wavelength can be modified from 1.48 um to the center of the telecom C-band at 1.55 mm by independently varying the QD composition and size. More specifically, the optical transition energy shifts linearly as a function of In-content of the QD material at a rate of -4.4 meV/In-percentage, and with the number of monolayers (ML) of material used for filling the nanoholes, at -2.0 meV/ML. These experimentally observed energy shifts are well predicted by simulations yielding rates of -4.3 meV/In-percentage and -2.1 meV/ML, respectively. For the simulation, a uniform In composition, low intermixing, and microscopically measured QD geometry is considered. Additionally, excellent ensemble QD uniformity, with unprecedented inhomogeneous broadening well-below 7 meV across all samples is demonstrated. Finally, photoluminescence of single-QDs reveals narrow excitonic emission lines of 13.8+/-6.7 ueV and low fine-structure splitting values reaching <10 ueV. These results identify GaSb-based LDE QDs as a tunable telecom platform for scaling
quantum-photonic applications over long-haul optical fiber networks.
Read the full abstract ▾
All authors Markus Peil, Maja Wasiluk, Ziemowit Olinkiewicz, Tymon Przychodni, Robert Matysiak, Teemu Taskinen, Joona Salonen, Abhiroop Chellu, Metin Patli, Joonas Hilska, Anna Musiał, Michał Gawełczyk, Mircea Guina, Teemu Hakkarainen
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Layer Axial Phonons and Dipolar Thermal Response in Centrosymmetric Thin Films
Madhubanti Mukherjee, Kapil Gope and Barun Ghosh
In nonmagnetic centrosymmetric materials, $\mathcal{PT}$
symmetry enforces vanishing total
phonon angular momentum (
phonon AM) at every wave vector, making them appear unsuitable as hosts of axial
phonons. Here, using first-principles calculations for BaAgAs and representative van der Waal's layered materials, we show that centrosymmetric slabs can still host large hidden layer-resolved
phonon AM with both chiral and cycloidal modes. This hidden
phonon AM texture produces layer resolved
phonon thermal Edelstein-like responses and a real-space
phonon AM dipole response, both tunable by strain. Our results establish centrosymmetric layered materials as an exciting platform for hidden axial
phonon and multipolar
phonon thermal response.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Exact fluctuation relations in voltage- and temperature-biased Laughlin-edge constrictions
Gu Zhang, Gabriele Campagnano, Domenico Giuliano et al. (+2 more)
We present a comprehensive analysis of non-
equilibrium fluctuation-dissipation relations connect- ing experimentally accessible chiral-current auto- and cross-correlations to the tunneling-current noise and conductance in Laughlin edge states coupled through a
quantum point contact (QPC). We examine their validity for two chiral Laughlin edges held at different temperatures and voltages and show that the relations remain exact for arbitrary tunneling strength, voltage bias, and edge- state temperatures. We further generalize them to spatially extended QPCs and to tunneling am- plitudes with an explicit voltage dependence, and discuss the conditions and limitations associated with these generalizations. Our results establish that the local tunneling-current noise generated at the QPC can be reliably reconstructed from experimentally accessible auto- and cross-correlations measured downstream, providing a robust route to characterize non-
equilibrium transport in chiral edge states.
Read the full abstract ▾
All authors Gu Zhang, Gabriele Campagnano, Domenico Giuliano, Igor Gornyi, In`es Safi
Mesoscale and Nanoscale Physics
Moiré-induced lattice reconstruction at buried atomic interfaces
Nicholas Clark, Frederick Allars, Isaac Soltero et al. (+18 more)
Atomic reconstruction at twisted two-dimensional interfaces governs many of their emergent optical, electronic, and mechanical properties, including sliding ferroelectricity. Despite recent progress in understanding
lattice reconstruction in suspended twisted bilayers, structural changes at van der Waals heterointerfaces between multilayer
crystals remain largely unexplored. Here we use multi-slice electron ptychography to non-invasively recover the three-dimensional atomic structure at marginally twisted rhombohedral interfaces between thick transition-metal dichalcogenide
crystals. With a position precision of ~3 pm and a depth resolution ~1 nm, we resolve the twist-induced
lattice reconstruction field per layer, and the resulting dislocation network at the buried interface. Despite the bulk nature, we observe markedly strong in-plane interfacial reconstruction due to suppression of the out-of-plane bending by outer layers, exceeding predictions from our three-dimensional modelling. Furthermore, we extract the strain tensor
evolution during the decay of the reconstruction into the bulk, providing a structural foundation for understanding multi-layer moiré systems.
Read the full abstract ▾
All authors Nicholas Clark, Frederick Allars, Isaac Soltero, Wendong Wang, David Hopkinson, Hugo de Latour, James G. McHugh, William Talbott, Sam Sullivan-Allsop, Rongsheng Cai, Astrid Weston, Xiao Li, Gareth Tainton, Casey K. Cheung, Francisco Selles, Alex Summerfield, Andrey Kretinin, Christopher S. Allen, Vladimir Falko, Sarah J. Haigh, Roman Gorbachev
Mesoscale and Nanoscale Physics
Dynamics of a nanoscale ferromagnetic vortex
Jun Seok Seo and Se Kwon Kim
We propose a ferromagnetic
vortex stabilized by the interfacial Dzyaloshinskii–Moriya interaction (iDMI) and investigate its properties through theoretical analysis and micromagnetic simulations. Our results demonstrate that this
vortex can remain stable even in nanoscale ferromagnetic disks with radii below $5\,\text{nm}$—far smaller than those of conventional nanodot
vortices having about $1\,\mu\text{m}$ radius. We analytically solve the nonlinear equation of motion describing the anharmonic
vortex oscillation, and identify the critical frequency that determines the stability of the driven oscillation of the
vortex. This nanoscale
vortex exhibits conventional properties of microscale
vortices, including gyrotropic oscillation and resonance frequency shift under an out-of-plane
magnetic field. It also exhibits unconventional behaviors, such as a strongly anharmonic potential, nonlinear oscillations, and a Duffing-oscillator-like response under the external AC bias.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Evanescent-mode Casimir-Josephson force and gate-controlled resonances in ballistic graphene Josephson junctions
Shahrukh Salim
We develop a microscopic scattering theory of the phase-dependent
equilibrium mechanical response of a ballistic
superconductor-
graphene-
superconductor Josephson junction. The calculation is based on an energy-dependent Dirac scattering
matrix embedded in a normalized Matsubara determinant, so the reported force correction contains the complete Bogoliubov-de Gennes spectrum of the stated ideal model. At charge neutrality the full determinant approaches a closed-form evanescent-mode result proportional to $\Delta W/L^2$, reaching $2\ln 2\,\Delta W/(\pi L^2)$ at phase difference $\pi$ in the zero-temperature short-junction limit. Gate doping produces propagating channels and Fabry-Pérot structure, causing large oscillations and sign reversals of the phase-dependent force correction $\delta F=F(\phi)-F(0)$. We distinguish the interband-to-intraband Andreev crossover, controlled by $|\mu|/\Delta$, from the evanescent-to-propagating crossover, controlled by $|\mu|L/(\hbar v_F)$. Exact real-energy subgap poles obtained from the same energy-dependent scattering
matrix are used to diagnose specular/interband and retro/intraband character; these labels are not treated as separately measurable thermodynamic forces in the mixed regime. We also quantify the difference between the complete determinant result and the frozen-scattering short-junction approximation without identifying that difference with a pure continuum force. The resulting gate- and phase-dependent mechanical signal provides a Dirac-material extension of earlier superconductivity-induced mechanical-force proposals.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el
Holographic Representations of Topological Quantum Criticality: Emergent Symmetry Approach around the Bott Clock
Fan Yang and Fei Zhou
In this article, we apply the idea of emergent
symmetries to construct holographic representations of a broad class of topological
quantum critical points (tQCPs) that appear in fermionic classes in the Bott clock. We show explicitly that around the Bott clock, an emergent
symmetry $U_{EM}$ exists at a tQCP between different
symmetry protected gapped phases with protecting
symmetry $G_p$ in $d$ spatial dimensions. This emergent
symmetry can be used to construct a $(d+1)$ spatial dimensional
lattice model with a properly upgraded
symmetry such as $U_{EM}\times G_p$ or $U_{EM} \rtimes G_p$, etc. By doubling the degrees of freedom of the adjacent topological class in $d$-dimensions, we successfully show that the $(d+1)$-dimensional
lattice models constructed in this way have the desired enlarged
symmetry groups that precisely belong to the adjacent topological classes, counterclockwise around the Bott clock. Furthermore, $d$-dimensional boundaries of these $(d+1)$ dimensional
lattice models of gapped topological classes are shown to exhibit identical infrared dynamics as the corresponding tQCPs in the $d$-dimensional adjacent topological phases in the Bott clock, with lower
symmetries.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Scalar Spin Chirality from Dissipative Pumping and Lamb Shift Precession
YuanDong Wang and JianHua Wei
Circulating currents in triangular triple
quantum dots reverse repeatedly with bias even at zero
magnetic flux and for a real
Hamiltonian, a phenomenon whose origin has remained unclear. We show that dissipative tunneling prepares an orbital pseudospin, while virtual charge fluctuations generate a noncollinear Lamb field that rotates it toward the chiral direction. Bias changes their relative orientation and thereby reverses the current. This reservoir-induced orbital Hanle effect converts a nonchiral orbital polarization into scalar
spin chirality, which an exact ground-multiplet identity links to the circulating current. Hierarchical-equations-of-motion calculations show that the low-bias reversal survives beyond the second-order weak-coupling description, while the quadratic growth of chirality after a sudden voltage switch identifies precession. More broadly, time-reversal-odd responses can emerge in open
quantum systems from the interplay between dissipative state preparation and coherent precession.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Singlet-doublet transitions and Josephson currents in a superconducting ring with a quantum dot
Guo-Hui Ding, Fei Ye and Bing Dong
We investigate the ground state properties of a superconducting ring embedded with a
quantum dot (QD) by using a variational wave-function approach. A theoretical formulation for the treatment of the finite-U Anderson impurity coupled with a superconducting ring are presented. We demonstrate singlet-doublet transitions of the ground state for this system with the QD in the mixed valence regime. It is shown that the supercurrent in the
superconductor ring shows oscillations with the external enclosed
magnetic flux and exhibits abrupt jumps at the singlet-doublet phase transition points.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Switchable Magnetoelectric Transport in Graphene via a Van der Waals Multiferroic
Miuko Tanaka, Shunta Aoki, Ikoi Sato et al. (+12 more)
Electric and
magnetic control of transport properties at atomic interfaces is central to the development of next generation electronics and spintronics. Van der Waals multiferroics materials that simultaneously host dielectric and
magnetic orders down to the monolayer limit offer a promising platform for such interfacial control, yet the realization of electronic functionalities that exploit the unique attributes of van der Waals multiferroics has largely remained elusive. Here, we realize a van der Waals
heterostructure comprising
graphene and the multiferroic CuCrP2S6, enabling gate-switchable magnetoelectric transport in
graphene, mediated by the multiferroic layer. The charge-neutrality resistance peak of
graphene exhibits pronounced hysteresis arising from polarization flip in the multiferroic state. Application of an in-plane
magnetic field shifts this peak in a polarization-dependent manner, revealing
magnetic-field-induced polarization modulation a direct signature of the magnetoelectric effect. Furthermore, cooling the device under an applied electric field enables domain control of the multiferroic order, allowing reversible switching of the interfacial magnetoelectric transport. These results provide the first demonstration of interfacial magnetoelectric transport in a vdW
heterostructure, and establish a pathway for engineering two-dimensional van der Waals interfaces for functional device applications.
Read the full abstract ▾
All authors Miuko Tanaka, Shunta Aoki, Ikoi Sato, Hao Ou, Itishree Pradhan, Ngoc Han Tu, Yangsong Chen, Tomohiro Ishii, Kenji Watanabe, Takashi Taniguchi, Michihisa Yamamoto, Masayuki Hashisaka, Jiang Pu, Naoki Ogawa, Toshiya Ideue
Mesoscale and Nanoscale Physics
Universal tuning of Förster resonance energy transfer in gate-programmable conductor-dielectric-conductor heterostructures
Alexis J. Agosto, Daniel Gunlycke and Michael N. Leuenberger
We develop a
quantum-electrodynamical theory for universal tuning of spontaneous emission and Förster resonance energy transfer (FRET) in a material-agnostic conductor-dielectric-conductor
heterostructure. The platform consists of a dielectric spacer of thickness $W$ bounded by two gate-tunable two-dimensional conductors. The only microscopic input from the surrounding materials is the transverse-
magnetic and transverse-electric reflection amplitudes $r_{\TM/\TE}(q_\rho,\omega)$ of the two sheets. Starting from the QED
photon propagator, we derive the retarded Maxwell dyadic, the
vacuum/Hadamard field propagator, and the time-ordered Feynman propagator in the same geometry. The spontaneous-emission rate is controlled by the local
vacuum spectral density, while FRET is controlled by the nonlocal retarded/advanced product $\obG_{\text R}(\bx_D,\bx_A;\omega_D)\Im\,\balpha_A(\omega_D)\obG_{\text A}(\bx_A,\bx_D;\omega_D)$. In the transparent limit $r_{\TM}\to 0$, the near-field FRET rate recovers the bulk $x_\rho^{-6}$ law. In the Dirichlet/PEC branch $r_{\TM}\to -1$, the gapless transverse mode is removed and the donor-acceptor coupling acquires a Bessel-$K$ envelope, giving an exponentially screened FRET rate $\Gamma_{D\to A}\propto\exp(-2\pi x_\rho/W)$ at large lateral separation. In the opposite Neumann/PMC-like branch $r_{\TM}\to 1^{-}$, a nearly gapless transverse mode survives and produces a wide quasi-two-dimensional logarithmic propagator, enhancing the nonlocal electromagnetic coupling over a gate-programmable range $x_{\rho,*}\sim W/(1-r_{\TM})$. For
graphene-Er implementations, the same retarded Green tensor also separates dissipative on-shell Er-to-
graphene decay, governed by its absorptive part, from dispersive virtual-plasmon-mediated Er-Er coupling, governed by its reactive part; a plasmonic band gap can suppress the former while retaining the latter.
Read the full abstract ▾