Mesoscale and Nanoscale Physics
Reading Altermagnetic Domains with Photon Drag
Sayed Ali Akbar Ghorashi and Andrew M. Rappe
Finite
photon momentum allows second-order photocurrents in centrosymmetric space groups, where the conventional bulk photovoltaic effect is forbidden. Here we study the
photon-drag response of altermagnets and show that its angular dependence reveals both the
symmetry of the
magnetic order and the Néel domain of the sample. For example, when a
crystal rotation exchanges the two domains, the domain-even and domain-odd parts of the current appear in different angular harmonics, $4n$ and $4n+2$ for tetragonal $d$-wave altermagnets, so that two measurements rotated by $90^\circ$ on a single domain isolate the domain-odd current. We also find that these microscopic contributions exhibit opposite domain parities depending on light polarization. Under linear light, only the shift term is domain odd, while under circular light, the domain-odd channel switches to the injection, Fermi-surface, and contact principal-value terms. Mirror
symmetries fix the angular phase of each harmonic and distinguish $d_{x^2-y^2}$, $d_{xy}$, and $g$-wave order. In contrast, conventional collinear antiferromagnets show no domain-odd
photon-drag current, and in tetragonal ferromagnets the two parts share the same harmonics. Although the altermagnetic
spin splitting does not require
spin-orbit coupling (SOC), SOC is essential to observe the domain-odd charge current. Our work uncovers distinct signatures of altermagnetism in
photon drag and provides a route to all optical
magnetic readouts of altermagnets.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Band Tail States: Speed Bump or End of the Road for Two-Dimensional Semiconductors?
Zherui Han, Robert K. A. Bennett, Davide Donadio et al. (+7 more)
We propose that the path to realizing the full potential of two-dimensional (2D) electronics lies in understanding and mastering their energy band tail states (BTS). Unlike silicon, which benefits from sharp band edges (Urbach energy $E_\rm U$ ~ 10 meV), today's monolayer 2D
semiconductors have rough band edges ($E_\rm U$ ~ 100 meV) caused by spatial potential inhomogeneity. Comparing a physics-based electrical model to experiments, we demonstrate that BTS cause reduced effective mobility and "slow" transistor turn-on with excessive gate voltage in monolayer 2D transistors, which sets a fundamental limit for their energy-efficient operation. We also show that BTS effects in 2D transistors could be mitigated with higher gate capacitance, with strain engineering, and by using bilayer instead of monolayer 2D channels, as long as $E_\rm U$ is reduced below ~ 50 meV. This work provides a theoretical framework and design guidelines to navigate these fundamental limits, and to enable successful integration of 2D
semiconductors into low-power nanoelectronics.
Read the full abstract ▾
All authors Zherui Han, Robert K. A. Bennett, Davide Donadio, Maritha A. Wang, Tara Peña, Mikaël Cassé, Martin Vanbrabant, Valeriya Kilchytska, Jean-Pierre Raskin, Eric Pop
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Helicity decoupling ultrastrong Rabi splitting from quantum vacuum dressing
Ayoub El-Amrani, Nasir Boubekraoui, Zakaria Mzaouali et al. (+4 more)
Polaritons and
quantum vacuum dressing are usually regarded as intertwined consequences of ultrastrong light-matter coupling. Here we show that they can be controlled independently through helicity. We consider cyclotron resonance coupled to a chiral cavity supporting a single circular mode. When the helicity of the cavity field matches the cyclotron motion, energy is exchanged resonantly between light and matter, producing a large Rabi splitting and conventional polaritons, while the ground state remains the bare
vacuum. Reversing the
magnetic field reverses the cyclotron motion without changing the cavity. The same mode then couples through anomalous processes that create and annihilate light and matter excitations in pairs: the conventional polaritonic anticrossing disappears, while the ground state acquires squeezing and virtual excitations. These two regimes show that spectral hybridization and
quantum vacuum dressing are distinct manifestations of ultrastrong coupling, and that a large Rabi splitting alone does not imply a dressed
quantum vacuum. Helicity therefore provides a route to controlling polariton formation and
quantum correlations as distinct resources in cavity
quantum materials.
Read the full abstract ▾
All authors Ayoub El-Amrani, Nasir Boubekraoui, Zakaria Mzaouali, Houssam Sabri, Herschel Rabitz, Abdelouahed El Fatimy, Dukhyung Lee
Mesoscale and Nanoscale Physics
EPR as a probe for the mechanisms of chirality-induced spin selectivity in photoinduced charge transfer
Arianna Cantarella, D. K. Andrea Phan Huu, Paolo Santini et al. (+3 more)
Several models for chirality-induced
spin selectivity (CISS) in charge transfer have been proposed, but rarely compared directly with experiments. This step is essential for their validation and future progress of the field. Here we investigate a broad class of radical pair states associated with different microscopic models by computing the related electron-paramagnetic resonance spectra. This allows us to evidence peculiar signatures of different radical pair states, to study their experimental accessibility and identify conditions to verify proposed microscopic models.
Read the full abstract ▾
All authors Arianna Cantarella, D. K. Andrea Phan Huu, Paolo Santini, Michael R. Wasielewski, Alessandro Chiesa, Stefano Carretta
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Coherence-assisted quantum state preparation and thermal control through repeated interactions
Alessandro Prositto and Dvira Segal
We investigate the relaxation dynamics and steady state of a
qubit interacting with a coherent environment through an energy-conserving flip-flop interaction within the Markovian repeated-interaction framework. We derive an exact analytical solution for the evolving and stationary state, nonperturbative in the environmental coherence. We show that environmental coherence provides a resource for dissipative state preparation by expanding the set of accessible steady states. In particular, coherent ancillas can increase the system ground- state population beyond that of the bath, corresponding to an effective temperature below the bath temperature, and enhance its steady-state purity, with these effects controlled by the interplay between the system energy scale and the system-ancilla coupling. Nevertheless, we prove that the purity of the system can never exceed the purity of the ancilla. We further analyze the thermodynamics of the protocol and show that environmental coherence can modify and even reverse the natural direction of heat transfer, giving rise to anomalous heat flow. Remarkably, for fixed interaction parameters, the direction of the coherence-induced heat transfer is governed by the relative phase between the system and ancilla coherence, whereas their magnitudes determine the amount of heat exchanged. Our results establish environmental coherence as a resource for controlling steady-state preparation and energy transfer in repeated-interaction dynamics.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Hydrodynamic Anomalous Hall Effect in a Two-Dimensional Dirac Fluid
A. Levchenko and D. A. Pesin
In ultraclean conductors, electron-electron collisions can make transport hydrodynamic. In a Berry-curved band, these collisions can also produce two-particle coordinate shifts, which contribute to the anomalous Hall current in the presence of a transport electric field. We develop a kinetic theory of this contribution for a two-dimensional massive Dirac Fermi
liquid with weak contact interactions and weak short-range disorder. The computed response is independent of interaction strength at leading Born order. Its contribution to the anomalous Hall conductivity is comparable to the thermal correction to the intrinsic anomalous Hall conductivity. The existence of the momentum zero mode of the electron-electron collision integral leads to a nontrivial frequency dependence of the anomalous Hall response considered in this work. In particular, the limits of vanishing frequency (dc) and vanishing disorder do not commute. In the dc limit, the momentum response to the transport field grows inversely with the momentum relaxation rate. This allows arbitrarily weak, energy-dependent impurity scattering to produce a finite correction by coupling conserved momentum to the modes relaxed by electron-electron scattering. This correction disappears when the clean limit is taken before the zero-frequency limit. As a result, the interaction-induced Hall response retains information about the mechanism of momentum relaxation even as the overall disorder strength tends to zero.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el
Cooper Instability of a Magnetic Wigner Crystal
Wangqian Miao and Chunli Huang
Recent scanning tunneling microscopy has directly imaged electronic
crystals in rhombohedral hexalayer
graphene, and magnetotransport measurements suggest that superconductivity and charge-density-wave order emerge from a common
spin-valley-polarized ferromagnetic metal at nearby carrier densities. Motivated by these observations, we ask whether collective modes in a
magnetic Wigner
crystal can mediate pairing in this setting. We address this question by studying the Cooper problem for two electrons in the first conduction band of the Wigner
crystal. Unlike conventional
phonon-mediated pairing, the collective mode (
boson) energies and single-particle (
fermion) dispersion are comparable scales controlled by the electron density, leaving no small parameter for an adiabatic expansion. Moreover, because the
magnetic Wigner
crystal is not time-reversal invariant, the usual Cooper logarithmic divergence in the pairing susceptibility is absent, so the attraction must exceed a finite threshold for pairing to occur. These unusual features motivate a numerical experiment to see whether the
crystal's own vibrations can bind electrons. We obtain the crystalline ground state and its collective mode spectrum within Hartree–Fock and time-dependent Hartree–Fock approximation, and derive the electron–
phonon Hamiltonian using the quasiboson approximation. Solving the resulting two-electron problem, we find that
phonon-mediated attraction exceeds the pairing threshold, with chiral $p$-wave pairing as the leading instability. Within these approximations, we show that collective modes of a Wigner
crystal can indeed favor chiral pairing despite broken time-reversal
symmetry. Our results provide an encouraging starting point for developing a full many-body theory to study electronic crystallization and superconductivity.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el
Symmetric Mode Ansatz: Theory of Magnon Collective Modes in Chern Insulators
Miguel Gonçalves, Jonah Herzog-Arbeitman, Juan Felipe Mendez-Valderrama et al. (+3 more)
Moiré materials host integer and fractional Chern
insulators (FCIs) where time-reversal is broken spontaneously by flat band ferromagnetism. In twisted MoTe2, unlike in
quantum Hall, opposite
spins carry opposite Chern numbers and realize Ising ferromagnetism with gapped
magnon excitations. Clarifying the nature of these collective modes and the origin of the
magnon gap is key to understanding the stability of the Chern magnets in these materials. To do so, we develop a generalized single-mode approximation, which we call the symmetric mode ansatz (SyMA), to describe the low-energy
magnon spectrum. We find it to be in exceptional agreement with numerical calculations at integer filling, and qualitatively accurate across fractional fillings including FCIs. To explain the accuracy of the SyMA, we present two families of Hubbard models (including the Haldane model and continuum ideal bands) whose collective modes are analytically solvable and for which the SyMA is either exact or an accurate approximation. For a class of these models where SyMA is exact, we prove two-sided bounds on the zero-momentum
magnon gap in terms of the Chern number, Berry
curvature, and
quantum metric, revealing that uniform
quantum geometry is sufficient for stabilizing magnetism in Chern bands.
Read the full abstract ▾
All authors Miguel Gonçalves, Jonah Herzog-Arbeitman, Juan Felipe Mendez-Valderrama, Andreas Feuerpfeil, B. Andrei Bernevig, Nicolas Regnault
Mesoscale and Nanoscale Physics
Millisecond phonon lifetimes in piezoelectric nanomechanical resonators
Oliver A. Hitchcock, Matthew P. Maksymowych, Kaveh Pezeshki et al. (+5 more)
Piezoelectric nanomechanical resonators operating at gigahertz frequencies are a promising platform for
quantum information processing and precision sensing, but
phonon lifetimes have been limited to the microsecond range, widely attributed to the higher intrinsic loss of piezoelectric materials. Here we show that this limitation is not fundamental. Using a fabrication process informed by recent studies of defect-mediated loss in lithium niobate, we combine chemical restoration of ion-milled surfaces with a shadow-mask metallization process to produce lithium niobate phononic
crystal resonators with inferred internal
phonon lifetimes of up to 21 milliseconds at 3.6 gigahertz, corresponding to quality factors exceeding $4\times10^8$ ($f\cdot Q_i > 10^{18}$) at millikelvin temperatures. By systematically varying the electrode-to-resonator spacing, we demonstrate that the measured lifetime is set by external coupling between the device and the measurement
circuit rather than material loss. This establishes that lithium niobate, once fabrication-induced surface damage is removed, achieves an intrinsic quality comparable to the best mechanical materials while remaining an intrinsically piezoelectric platform with strong electromechanical coupling.
Read the full abstract ▾
All authors Oliver A. Hitchcock, Matthew P. Maksymowych, Kaveh Pezeshki, Takuma Makihara, Erik Szakiel, Chou-Wei Kiang, Daniel Rugar, Amir H. Safavi-Naeini
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el
Spin Chain with Continuous Exponential Symmetry: Topological Phase and Beyond
Biao Lian and Zhen Bi
We study symmetric gapped ground states of one-dimensional
spin $S$ chains with a continuous exponential
symmetry $U(1)\rtimes\mathbb Z_2$ with integer base $q$, where the U(1) charge has a modulated unit of charge $q^{L-j}$ decaying exponentially with site $j$. The simplest model is a
quantum breakdown model that can be viewed as a $q$-deformation of the XXZ Haldane
spin chain. We show that the
topology of their symmetric ground states crucially depends on $S$ and $q$. For integer $S$, odd $q$ allows a nontrivial $\mathbb Z_2$ Haldane-type
symmetry-protected topological (SPT) phase with protected edge modes, while even $q$ allows no nontrivial SPT phase. For half-odd integer $S$, odd $q$ prohibits any unique symmetric gapped ground state due to a Lieb-Schultz-Mattis obstruction, whereas even $q$ enforces a novel symmetric gapped phase which we name as the “half-SPT" phase. Unconventionally, the half-SPT phase only has a
symmetry protected edge mode on one edge, and has half of the string orders of an SPT phase. Our results uncover a new type of
symmetry-protected gapped phases beyond existing classification schemes.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el
SC$^\sharp$: superconductivity intertwined with topological order
Zhi-Qiang Gao, Yan-Qi Wang, Hui Yang et al. (+2 more)
Superconductivity and intrinsic topological order can intertwine in ways that go beyond simple coexistence. Here we develop a classification framework for (2+1)D gapped
superconductors with condensate charge $2ne$. By focusing on the topological properties of superconducting
vortices, we precisely characterize this interplay. We obtain a classification with increasing levels of intertwinement, from the well known invertible
superconductors without topological order, to untwisted and twisted SC$^\ast$, and finally to SC$^{\sharp}$. Our main finding is the family SC$^{\sharp}$, in which the elementary
vortex carrying $h/(2ne)$ flux cannot be factorized into an invertible
superconductor vortex dressed by bulk anyons, and every elementary
vortex is necessarily non-Abelian. For such phases, we also obtain no-go results: the elementary
vortex sector has
quantum dimension at least $\sqrt{6}$ and cannot satisfy Fibonacci fusion rules. We develop a systematic algebraic framework to obtain all these superconducting phases through anyon condensation, allowing us to construct several infinite families of examples and make connections to anyon superconductivity. Finally, we introduce primitive SC$^\sharp$ phases for which factorization of every nontrivial
vortex sector is obstructed, and argue that they cannot arise by disordering the relative phases of lower-charge superconducting condensates. Our classification scheme based on
vortex properties allows us to uncover new distinctions between topologically ordered
superconductors and constrain how they can be realized.
Read the full abstract ▾
All authors Zhi-Qiang Gao, Yan-Qi Wang, Hui Yang, Zhaoyu Han, Ashvin Vishwanath
Mesoscale and Nanoscale Physics
Pseudospin Hall Transport Induced by Berry Curvature
Qinhui Jiang, Jidong Song, Qingyang Mo et al. (+4 more)
Pseudospin-1 Dirac systems exhibit unique physics distinct from conventional Dirac cones, such as flat-band crossings and non-Abelian characteristics, yet their topological transport properties have remained largely untapped in passive, time-reversal-invariant settings. Here we uncover an in-plane polarity of the Berry-
curvature texture in a pseudospin-1 Dirac
Hamiltonian, a previously unexplored
geometric degree of freedom encoded in the sign-resolved distribution of Berry
curvature despite zero net Berry flux, and reveal a new mechanics where Berry
curvature induce pseudospin Hall behaviors in a system. We show that the oriented coupling between this momentum-space polarity and a real-space mass gradient governs a
geometric selection rule that dictates the emergence of gapless pseudospin Hall modes. By engineering the intracell couplings of a four-site planar
lattice, we independently program the Berry-
curvature polarity and the spatial mass gradient without altering the host
lattice symmetry. Acoustic experiments directly confirm this directional selection rule: reversing the mass gradient closes or reopens the dispersive gap, while pseudospin-selective source excitation launches counterpropagating pseudospin branches along arbitrary prescribed axes. Our work establishes
quantum geometric polarity as a versatile tool for reconfigurable wave routing, sensing, and high-capacity
quantum applications.
Read the full abstract ▾
All authors Qinhui Jiang, Jidong Song, Qingyang Mo, Bo Li, Dongyi Wang, Shuang Zhang, Mengyao Li
Mesoscale and Nanoscale Physics
Exciton switching and tunable exciton-phonon coupling in Oxygen doped ZnO nanorods
Aiswarya Rath, Kalyan Ghosh and Pratap K Sahoo
Self ion doping in ZnO nanorods offers a powerful route to dynamically control excitonic states and light matter interactions. Here, vertically aligned hexagonal ZnO nanorods were irradiated with 250 keV oxygen ions to establish a direct link between irradiation induced defects and excitonic and optical responses. Increasing ion fluence progressively quenches the near band edge emission at 380 nm, leading to a complete
exciton OFF state, while thermal annealing restores the emission, yielding a reversible
exciton OFF or ON response. This switching originates from defect mediated modification and thermal recovery of excitonic states. The defect band emission, between 400 to 750 nm, exhibits quasi periodic whispering gallery mode like resonances that are progressively suppressed as irradiation alters nanorod geometry and optical confinement. Low-temperature photoluminescence resolves D0X, FX 1LO, and FX 2LO transitions, whose temperature
evolution follows the Bose Einstein model. The non-monotonic variation of excition
phonon coupling strength reveals a competition among irradiation induced defects,
lattice distortion, and
exciton localization in determining
exciton phonon coupling. These results establish Oxygen ion irradiation as a means to simultaneously engineer excitonic switching,
exciton phonon interactions, and optical resonances, providing a pathway toward defect programmable ZnO nanophotonic and optoelectronic devices.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Deterministic Vortex Generation from Coupled Trapped Polariton Condensate Triad
X. Qin, N. Pitanios, S. Dam et al. (+4 more)
We present the deterministic generation and all-optical switching of ternary topologically distinct
vortex states in a triad of trapped
exciton-polariton condensates with direct state readout from momentum-space emission distribution. Tuning the non-resonant pump power controls the sign of the dissipative coupling, selecting between a ferromagnetic in-phase state and two frustrated states with global phase winding. The zero-winding ferromagnetic state has unstructured far-field emission at low momenta and forms
vortex-antivortex arrays at the Dirac points, reflecting the C_3v global
symmetry. The two frustrated states of +-2pi winding can be activated on-demand by a control beam and produce different triangular emission patterns selectively localized at the K or K' points. Although all three states share identical real-space emission distributions, their momentum-space photoluminescence profiles distinguish them unambiguously, revealing the chirality without the need for interferometry. This enables on-demand orbital angular momentum control using a pump independent of resonant phase or OAM imprinting, establishing condensate triads as a compact platform for reconfigurable chiral light generation operating on a ternary logic basis.
Read the full abstract ▾
All authors X. Qin, N. Pitanios, S. Dam, S. Betzold, S. Höfling, S.V. Koniakhin, P.G. Savvidis
Mesoscale and Nanoscale Physics
Jin-Hyung Choi, Sang-Hoon Han, Young-Kwon Han et al. (+3 more)
Optically exciting a typical low-dimensional
semiconductor produces a nodeless \(s\)-type
exciton as its lowest-energy bound state. Here, we explain how Coulomb phase matching stabilises a
quantum-
vortex exciton as the lowest bound state in flat Chern bands. Using a prototypical Yin–Yang kagome
lattice, we demonstrate that increasing the
spin–orbit coupling drives a transition of the lowest
exciton from a
quantum-
vortex state to a zero-winding state, while leaving the band Chern numbers unchanged. We trace this behaviour to a gauge-invariant combination of
exciton phase differences and Bloch-overlap phases that can reduce the Coulomb energy. By comparing states with identical wavefunction amplitudes, we isolate this phase contribution and show that it is sufficient to drive the reversal in
exciton ordering. We classify
exciton topology by the momentum-space wavefunction winding relative to the conduction–valence Chern-number difference,connecting the competing states to circular-polarisation selection rules. We then show that the resulting reordering can be tracked directly in the optical absorption spectrum, through the transition from a dark
vortex exciton to a bright zero-winding
exciton. These findings establish a microscopic link between
exciton topology, Coulomb binding, and optical response that extends beyond the information contained in the underlying electronic band Chern numbers.
Read the full abstract ▾
All authors Jin-Hyung Choi, Sang-Hoon Han, Young-Kwon Han, Jun-Won Rhim, Sun-Woo Kim, Joshua J. P. Thompson
Mesoscale and Nanoscale Physics
Beyond Equilibrium Raman Thermometry: Fermi-Level Control of the Anti-Stokes Response in Graphene
Martin Jindra, Luka Pirker, Tim Verhagen et al. (+6 more)
Non-
equilibrium electron and
phonon populations govern heat generation and dissipation in nanoscale devices, yet their direct characterization remains challenging. Anti-Stokes Raman scattering provides a sensitive probe of
phonon populations and local temperatures, although its interpretation becomes more complex when electronic and phononic populations are driven out of
equilibrium. Here, we investigate the gate-dependent anti-Stokes Raman response of monolayer
graphene and find that the anti-Stokes response deviates from that expected from an
equilibrium phonon population. Using a spatially localized microdroplet spectroelectrochemical platform, dielectric back-gates, and chemical doping, we observe a strong and reversible suppression of the G-mode anti-Stokes intensity as the Fermi level is tuned away from the Dirac point, while the Stokes intensity remains essentially unchanged. By contrast, the G-mode frequency and linewidth of both the Stokes and anti-Stokes branches evolve with doping as expected from the established Kohn-anomaly picture. The anti-Stokes/Stokes intensity ratio decreases by several-fold over the measured range and displays a pronounced, gate-dependent power response with maximum sensitivity at charge neutrality. Comparison with previous studies of non-
equilibrium carrier dynamics in doped
graphene suggests an important role of Fermi-level-dependent electronic phase space, which can influence both hot-carrier-driven
phonon populations and electronically mediated Stokes-anti-Stokes scattering. Our findings establish anti-Stokes Raman scattering as a sensitive probe of electron-
phonon coupling and non-
equilibrium phonon dynamics in
graphene.
Read the full abstract ▾
All authors Martin Jindra, Luka Pirker, Tim Verhagen, Ciarán Fowley, Martin Kalbáč, Matěj Velický, Riichiro Saito, Ado Jorio, Otakar Frank
Mesoscale and Nanoscale Physics
Gentle Floquet control of orbital Hall effect and orbital inverse Faraday effect
Pei-Han Lin, Roderich Moessner and Egor I. Kiselev
Floquet engineering controls material responses via a time-periodic electromagnetic drive. An important task in practice is to reduce the driving strengths required to implement Floquet protocols. We show that in systems with strong phase-space constraints, where the response is dominated by a small region of momentum space, the relative impact of a resonant Floquet drive is enhanced. We demonstrate this idea on the example of the orbital Hall effect, where
equilibrium occupations restrict the interband coherence to a narrow momentum interval $\hbar\Delta k$. The ratio $eE_0/(\Omega_0\hbar\Delta k)$, where $\Omega_0$ is the frequency of the drive, is considerable even at modest field amplitudes $E_0$, leading to a large relative change in the orbital Hall conductivity. Due to the non-trivial orbital texture, the circularly polarized drive induces an inverse orbital Faraday effect by magnetizing the electrons. We show that the corresponding susceptibility is controlled by the interband
quantum metric that determines the resonant Floquet hybridization.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Charge transport in two-dimensional conductors with hybrid three-component plasma
A. D. Levin, V. A. Chitta, Z. D. Kvon et al. (+2 more)
Electron–hole
plasma in two-dimensional systems has mainly been studied in two limiting cases: degenerate semimetals with parabolic bands and nondegenerate symmetric Dirac systems such as
graphene. Here we investigate a different regime realized in a gapless HgTe
quantum well: a multicomponent
plasma where massless Dirac carriers coexist with thermally activated heavy holes from lateral valence-band valleys. Near charge neutrality, the resistance increases approximately as $T^2$, in sharp contrast to the nearly temperature-independent resistivity expected for a symmetric Dirac
plasma. We show that once heavy holes are populated, charge neutrality pins the chemical potential above the Dirac point, leaving the Dirac electrons moderately degenerate while the heavy holes remain nondegenerate and obey Boltzmann statistics. The light electrons therefore scatter almost elastically from the heavy holes, allowing a relaxation-time treatment of interparticle transport. Using carrier densities from self-consistent band-structure calculations, we reproduce the data with a short-range electron–hole interaction in the weakly disordered limit, for which the conductivity scales as $T^{-2}$ and the excess resistivity is proportional to the heavy-hole density. In contrast, an unscreened Coulomb interaction would give a temperature-independent conductivity. The extracted interaction amplitude is of the expected Coulomb scale. These results establish near-critical HgTe
quantum wells as a platform for interaction-driven transport in multicomponent systems combining degenerate massless and nondegenerate massive carriers.
Read the full abstract ▾
All authors A. D. Levin, V. A. Chitta, Z. D. Kvon, N. N. Mikhailov, G. M. Gusev
Mesoscale and Nanoscale Physics
Coupled quantum critical states in a circuit simulator
D. B. Karki and Andrew K. Mitchell
Hybrid metal-
semiconductor quantum circuits offer a controlled setting for realizing and probing strongly correlated
quantum matter. A largely open question that may be addressed by such simulators is whether coupled critical states can combine into new non-Fermi
liquid (NFL) phases. Inspired by the recent realization of a two-site charge-Kondo
circuit [W. Pouse et al., \href{https://www.nature.com/articles/s41567-022-01905-4}{Nat. Phys. 19, 492 (2023)}], we uncover the fate of coupled Kondo anyons emerging from the two-channel-Kondo critical point at each site. Bosonization and
quantum Brownian motion methods yield the full quasiballistic phase diagram and low-temperature transport properties, while numerical renormalization group calculations resolve the complementary weak-coupling limit. Together, these provide a unified description, and reveal robust NFL phases with continuously tunable transport and susceptibility exponents. Stronger inter-site coupling ultimately produces a screened Fermi
liquid.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Topological and kinetic origins of fractional thermal conductance at the topological insulator–superconductor interface
Laurence A. Jacobs and Guillermo R. Zemba
A recent experiment by Roy et al. (Nat. Commun. 17, 2853 (2026)) demonstrated a robust half-integer thermal conductance plateau, \kappa_0 T/2, at a bipolar (\nu,\nu')=(2,-1) junction in bilayer
graphene, produced not by non-Abelian
topology but by full equilibration of co-propagating electron and hole edge modes. We prove a
theorem that fixes when the two origins can be told apart: under full thermal equilibration, the two-terminal thermal conductance of a network of chiral edge segments joined at ideal floating contacts is a rational function of the net chiral central charges of the segments alone, quantities pinned by the gravitational anomaly and invariant under arbitrary local boundary kinetics. The corollary is an impossibility statement: whenever two realizations present the same anomaly data to the same network, no thermal-conductance measurement can distinguish them. That the equilibrated (2,-1) value equals the central charge of a chiral Majorana mode is an arithmetic fact about one filling combination, but wherever such a coincidence occurs it is beyond the reach of thermometry, and the separation must come from the charge sector, which is not anomaly-pinned at a superconducting boundary. We develop the topological
insulator-
superconductor interface as the application: a
vortex carries fractional charge e/4 from the \theta = \pi magnetoelectric coupling, the boundary hosts a chiral Majorana mode of central charge 1/2, and a laterally adjacent integer
quantum Hall (IQH) region supplies the kinetic realization. The Lorenz ratio (anomalous for the isolated Majorana boundary, L_0 / (1 + 4|\nu_{IQH}|) in the composite device) and the excess shot noise (growing with B from e/4
vortex tunneling versus locked to IQH plateaus) together resolve the mechanism, provided the
quantum Hall edge does not abut the
superconductor.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from physics.chem-ph
Cotunneling-Assisted Redistribution of Nonpassivity in a Photosynthetic Junction
Manjet Rajak, Trishna Kalita, Debasish Sharma et al. (+1 more)
We investigate how cotunneling affects passive-state ordering in a Photosystem II reaction center modelled as a nonequilibrium molecular junction. We use a full pigment excitation
manifold, with excitonic and charge-transfer rates computed within a Nakajima-Zwanzig formalism using realistic spectral densities. Cotunneling is introduced through a microscopically constructed doubly reduced acceptor state obtained from relevant quinone-side two-electron configurations, while photoexcitation is allowed into the full excitonic
manifold. Passive-state permutations are quantified through ergotropy and energetic capacitance. We find that thermodynamic smoothness in ergotropy and energetic capacitance can conceal microscopic state rearrangements. Cotunneling redistributes the extractable nonequilibrium energy among the quinone acceptor, the donor-pheophytin radical pair, and excitonic states with strong contributions from pigments on the inactive branch. At high Coulomb interaction, cotunneling produces no passive-state reordering. Piecewise-linear relations among ergotropy, energetic capacitance, and mean energy further reveal the population reorderings generated by cotunneling.
Read the full abstract ▾
All authors Manjet Rajak, Trishna Kalita, Debasish Sharma, Himangshu Prabal Goswami
Mesoscale and Nanoscale Physics
Programmable Asymmetric Spin-Orbit Torque Switching for Spin Logic
Rongkun Han, Dahai Wei, Jianhua Zhao et al. (+1 more)
Spin logic devices provide a promising route toward ultralow-power and nonvolatile information processing. In this work, we demonstrate field-free
spin-orbit torque-induced asymmetric magnetization switching in in-plane anisotropy (IMA) and perpendicular
magnetic anisotropy
heterostructures, characterized by different critical switching currents under opposite current polarities. Combined experiments and macrospin simulations reveal that the asymmetric switching originates from an in-plane effective field Hy , which breaks the Myz mirror
symmetry of the system. By controlling the magnetization direction of the IMA layer, both the switching polarity and bias direction can be tuned. Building on four distinct types of asymmetric switching behaviors, we realize a reconfigurable
spin logic operation within a single Hall-bar device. These results clarify the physical origin of asymmetric magnetization switching and demonstrate an approach for realizing reconfigurable
spin logic devices.
Read the full abstract ▾
All authors Rongkun Han, Dahai Wei, Jianhua Zhao, Yuan Lu
Mesoscale and Nanoscale Physics
Construction-Dependent Floquet Topology in Circularly Driven $N$-Stacked Su-Schrieffer-Heeger Chains
Aayushi Agrawal and Jayendra N. Bandyopadhyay
We investigate construction-dependent Floquet
topology in a two-dimensional
lattice formed by stacking Su-Schrieffer-Heeger (SSH) chains with co-located sublattice orbitals. We present two constructions in the decoupled-chain limit. Construction-I: the constituent SSH chains are topologically trivial with winding number $w=0$. Construction-II: the constituent SSH chains are topologically nontrivial with $w=1$. Although these constructions are unitarily equivalent in the static limit, circular driving distinguishes them because the hopping processes related by the transformation correspond to different physical bond vectors and therefore acquire different Peierls phases. Using the Floquet-Sambe formalism, we determine the quasienergy spectra and phase diagrams in terms of the lower-band Chern number $C_L$ and directional Zak phases $(Z_x,\, Z_y)$. We find distinct Floquet phase structures, including low-frequency phases with $C_L = -3$ and $C_L = -4$ in the two constructions. Since the Chern number does not resolve the
topology of the two quasienergy gaps separately, we further calculate the dynamical winding numbers $W_0$ and $W_\pi$, and verify the corresponding chiral edge states. In particular, at identical driving parameters, both constructions can have the same Chern numbers $C_L=-2$, while their gap-resolved winding numbers are $(W_0,\, W_\pi)=(0,\,+2)$ and $(-2,\,0)$, respectively. We also calculate the time-averaged optical Hall conductivity and show that $ C_Le^2/h$ determines its dc value for ideal full-band occupation. At the same time, its finite-frequency response contains
photon-assisted contributions. Our results demonstrate that the physical construction of the constituent chains, although irrelevant to the static bulk spectrum, can play a decisive role in the Floquet topological structure. We discuss possible experimental realizations of the driven model.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Self-induced spin-orbit torque switching in a synthetic antiferromagnetic Co 2 MnGa /MnGa bilayer
Rongkun Han, Haohang Cheng, Dahai Wei et al. (+2 more)
The large intrinsic
spin current in
magnetic Weyl semimetals (WSMs) provides a promising platform for
spin-orbit torque (SOT) devices. Here, we demonstrate SOTdriven magnetization switching in a synthetic antiferromagnet (SAF) composed of a Co2MnGa(CMG)/MnGa bilayer. In this heavy metal-free structure, CMG film functions simultaneously as a
spin current source and as a
magnetic layer. Macrospin simulations confirm the self-induced switching mechanism in the bilayer. The SOT generated by CMG switches the MnGa layer, which in turn triggers the reversal of the CMG layer via strong antiferromagnetic exchange coupling. These results elucidate the
spin dynamics in SAFs and provide a new pathway toward SOT devices with selfinduced magnetization switching.
Read the full abstract ▾
All authors Rongkun Han, Haohang Cheng, Dahai Wei, Yuan Lu, Jianhua Zhao
Mesoscale and Nanoscale Physics
Gate-driven Switching Dynamics in a Fully Suspended Superconducting Nanowire
Matthijs Rog, Giacomo Trupiano, Filippo Antola et al. (+4 more)
A gate voltage can suppress the critical current of a superconducting nanowire, and various scenarios have been proposed to describe these observations. The key difficulty is that these scenarios, including both leakage-driven and field-driven mechanisms, are impossible to disentangle in standard experiments. Here, we resolve this issue by studying a fully suspended superconducting nanowire of amorphous MoGe, separated from the gate by
vacuum, eliminating all leakage-driven channels. We measure the phase slip escape rate $\Gamma$ and find a large gate-induced enhancement of $\Gamma$, exponential over six orders of magnitude. Fitting various escape-rate models reveals a strong deviation from simple phase slip models, hinting at a complex interaction between the electrostatic field and the phase slip centers. Surprisingly, $\Gamma$ is not invariant under reversal of the gate-voltage polarity. Our work establishes a clear and nontrivial connection between gate voltage and $\Gamma$, guiding future research into the origins of the effect.
Read the full abstract ▾
All authors Matthijs Rog, Giacomo Trupiano, Filippo Antola, Mario Cuoco, Giorgio De Simoni, Kaveh Lahabi, Francesco Giazotto
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Electronic Properties of Ladder-Type Phenylenes Studied by Thermally-Assisted-Occupation Density Functional Theory
Tsu-Hsuan Wang and Jeng-Da Chai
Accurate prediction of the electronic properties of extended $\pi$-conjugated systems with radical character remains a major theoretical challenge. To overcome this challenge, thermally-assisted-occupation density functional theory (TAO-DFT) has been developed in recent years. In this study, we employ TAO-DFT to systematically explore the electronic properties of ladder-type phenylenes ($n$-LPs), containing $n$ linearly fused four-membered carbon rings. Our calculations reveal that all investigated $n$-LPs (with $n$ = 1 ~ 40) possess singlet ground states. With increasing $n$-LP length, we observe a transition from the nonradical character of shorter $n$-LPs to the polyradical character of longer $n$-LPs. Notably, we identify a distinct damped periodic oscillation in the radical character of $n$-LPs, featuring highly correlated hotspots at specific lengths ($n = 3k - 1$, where $k$ are positive integers). The real-space representation of active orbitals confirms this global electronic behavior is governed by the intrinsic structural periodicity and completely delocalized nature of the active orbitals along the central ladder framework. These findings provide fundamental insights into the size-dependent electronic properties of $n$-LPs, guiding their rational design for future nanomaterial applications.
Read the full abstract ▾
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Phonon-Enabled Collective Strong Coupling of Color Centers in a Plasmonic Cavity
Bharti Garg, Prabhdeep Singh, Masoud Taleb et al. (+1 more)
Quantum emitters in hexagonal boron nitride (hBN) are promising building blocks for solid-state
quantum photonics because of their bright room-temperature emission. These emitters strongly interact with
lattice vibrations, which partially underpins their excitation efficiency. Here, using complementary cathodoluminescence (CL) and photoluminescence (PL) spectroscopy, we demonstrate cavity-mediated interactions between hBN
quantum emitters coupled to the same plasmonic Au void cavity at the room temperature. Cathodoluminescence measurements reveal that a vibronic transition of the 443 nm emitter hybridizes with the cavity mode, giving rise to a spectrally resolved splitting, while the neighboring 537 nm emitter remains in the weak-coupling regime despite spectral overlap. The energy split of the CL peak is at the order of 36.2 meV, whereas the PL-resolved peak is approximately 24.1 meV, which is due to the collective excitations of multiple emitters per electron excitation and their mutual interactions. Maxwell-Bloch simulations reproduce the experimental spectra and identify the observed splitting as the result of cavity-induced hybridization. Excitation-dependent PL further shows that the hybridized state can be accessed through
phonon-assisted excitations below the zero-
phonon transition. These results demonstrate that vibronic transitions provide an effective pathway for controlling interactions between multiple
quantum emitters in hybrid plasmonic nanophotonic systems.
Read the full abstract ▾
All authors Bharti Garg, Prabhdeep Singh, Masoud Taleb, Nahid Talebi
Mesoscale and Nanoscale Physics · Cross-listed from physics.chem-ph
How Good Is DFT for Solid-Liquid Interfaces? A Comparison With the Random-Phase Approximation for Water on Graphene
Xavier R. Advincula, Yair Litman, Jiuyang Shi et al. (+3 more)
Simulations of water at solid interfaces routinely disagree on basic properties, from contact angle to friction, depending on the model used, whether an empirical force field or a density functional theory (DFT) exchange-correlation (XC) approximation. Yet no accurate computational reference has been available to determine which, if any, is reliable. Here we assess XC approximations spanning the rungs of Jacob's Ladder against the random-phase approximation (RPA) at the
graphene-water interface. Using machine-learned potentials (MLPs) trained on both DFT and RPA data, we achieve the extensive sampling required to characterize interfacial structure, wettability, friction, and vibrational sum-frequency generation spectra. We find that XC approximations disagree substantially with RPA and with each other. To make sense of this, we introduce a transferable, multi-observable scoring framework that distills each functional's agreement with RPA into a single measure. Six functionals emerge as reliable starting points for studies of
graphene-water and other dispersion-dominated interfaces, namely B3LYP-D3(0), revPBE-D3(0), revPBE-D3(BJ), B97M-rV, r$^{2}$SCAN, and revPBE0-D3(0). Notably, this ranking follows no simple rule based on functional family or rung of Jacob's Ladder. What does hold across functionals is that dynamical and spectroscopic properties tend to be harder for DFT to reproduce than structural ones, with direct consequences for functional selection. Our framework also offers a general strategy for benchmarking any atomistic model, including the new generation of foundational MLPs, against high-accuracy references at solid–
liquid interfaces. Beyond simulation, this work identifies which models can be trusted to connect measured contact angles, friction, and vibrational spectra to the molecular structure behind them.
Read the full abstract ▾
All authors Xavier R. Advincula, Yair Litman, Jiuyang Shi, Flaviano Della Pia, Christoph Schran, Angelos Michaelides