Mesoscale and Nanoscale Physics
Synchronizing Spectral and Interference Criticalities at an Exceptional Point
Zeng-Zhao Li and Xiao Xue
Exceptional points (EPs) are spectral singularities, but whether they can be used to control a distinct criticality of coherent interference remains largely unexplored. Here we show in nonlocal superconducting transport how spectral and interference criticalities can be controllably synchronized. In a minimal superconducting double-
quantum-dot system, loss imbalance selectively drives one Bogoliubov sector through an EP. The spectral EP and the CAR-ECT interference criticality form distinct structures in control space whose relative ordering can be continuously tuned. At their synchronization point, the interference boundaries between crossed Andreev reflection (CAR) and elastic cotunneling (ECT) coalesce at the EP and bifurcate beyond it, creating a finite CAR-dominated window. The resulting interference window opens with a square-root critical law, whose exponent also governs the finite-temperature observability scale. Detuning unfolds the two criticalities, while retuning restores their intersection, establishing the synchronization as controlled rather than generic. The bifurcation is directly observable in nonlocal conductance. Our results establish exceptional points as spectral control points for independently defined interference criticalities, opening a route to non-Hermitian control of critical
quantum interference.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.supr-con
Imaging how fluctuations destroy superconductivity in two dimensions
Logan Bishop-Van Horn, Teng Zhang, Sara Metti et al. (+3 more)
Two-dimensional
superconductors test our understanding of
quantum phases. Low-temperature "anomalous metal" states are widely observed where conventional theories predict only superconducting or insulating ground states. In model systems based on proximity-coupled Josephson junction arrays, the critical temperature falls far faster with decreasing normal-state conductance than predicted by existing models. Whether these observations indicate a new
quantum phase, a need to refine models of disorder and fluctuations, or both remains unresolved. Using scanning
magnetic susceptometry, we image the local superfluid phase stiffness $\rho_s$ in gate-tunable Josephson junction arrays consisting of epitaxial Al islands on an InAs
quantum well. Across six arrays and more than two orders of magnitude in the zero-temperature phase stiffness $\rho_{s0}$, the diamagnetic critical temperature $T_{c,\varphi}$ is suppressed more strongly than can be explained solely by thermal phase fluctuations, scaling approximately as $T_{c,\varphi}\propto\rho_{s0}^{0.3}$. While $\rho_s$ is remarkably uniform at high carrier densities, at low carrier densities we find that anomalous metal transport emerges together with large-scale inhomogeneity that transport alone cannot directly detect. These results are inconsistent with a classical XY description within standard junction models, instead pointing to
quantum fluctuations that suppress superconductivity throughout the superconducting phase and amplify inhomogeneity near the
superconductor-
insulator transition, producing anomalous metal behavior.
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All authors Logan Bishop-Van Horn, Teng Zhang, Sara Metti, Tyler Lindemann, Michael J. Manfra, Kathryn A. Moler
Mesoscale and Nanoscale Physics
Realization of Very High Mobility InAs Quantum Wells on InP Substrates Through Convex InAlAs Graded Buffer Optimization
Tyler Lindemann, Rojila Ghimire, Alejandro Alcaraz Ramirez et al. (+4 more)
Due to strong
spin-orbit coupling, large Landé $g$-factor, and a highly transparent interface, the two-dimensional electron gas (2DEG) in InAs
quantum wells provides an ideal platform for the exploration of topological superconductivity in hybrid
semiconductor-
superconductor heterostructures. Reduction of disorder in the
semiconductor remains a primary challenge to the disambiguation of subtle interaction effects. Here we demonstrate very high mobility InAs 2DEGs grown on insulating InP substrates. Utilizing a convex compositional grading profile in an InAlAs metamorphic buffer we demonstrate InAs
quantum wells with thickness greater than 10 nm without need of Ga-containing cladding layers. We examine structural and electrical transport properties of these
heterostructures. Advances in the design of the metamorphic InAlAs buffer result in low-temperature electron mobility exceeding $1.7\times10^6$ cm$^2$ V$^{-1}$ s$^{-1}$ at 2DEG density $\leq3.2\times10^{11}$ cm$^{-2}$, the highest value yet reported for this material system.
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All authors Tyler Lindemann, Rojila Ghimire, Alejandro Alcaraz Ramirez, Ahmad Azizimanesh, Sergei Gronin, Ray Kallaher, Michael J. Manfra
Mesoscale and Nanoscale Physics
Intriguing topological superconductor phases in long-range extended Kitaev models: an interplay between sub-lattices and power-law interaction
Dharana Joshi, Amaan Khan and Tanay Nag
The power-law profile of hopping and superconductivity introduces rich critical phenomena that are not possible to explore in the nearest-neighbor models. Having this in mind, we construct the Su-Schrieffer-Heeger (SSH)-Kitaev model with mono-, bi-, and tri-partite sub-
lattices where superconductivity [hopping] is of power-law Kitaev [SSH] type. The long-range (LR) superconductivity can alone gap out the zero-momentum critical line while LR hopping alters the finite-momentum critical line. There exists open-ended critical line at vanishing superconducting gap on the phase diagram for all versions of the SSH-Kitaev model. Interestingly, LR superconductivity (hopping) promotes massive Dirac (Majorana zero) modes, while in a finite-size system, their emergence in open boundary conditions is caused by the bulk gap of the anti-periodic
Hamiltonian in momentum space. This indicates an unconventional bulk-boundary correspondence for power-law models as compared to what is seen in the short-range models. Importantly, the thermodynamic phase boundaries are correctly reproduced by the above unconventional correspondence. Intriguingly, an even (odd) number of sub-
lattices yields an integer (half-integer) winding number while the massive Dirac modes continue to survive irrespective of the sub-
lattice profile as long as there exists LR pairing only.
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Mesoscale and Nanoscale Physics
Power-law growth of shift current with superlattice period in flat Chern bands
Nianlong Zou, Cheng Xu, Ning Mao et al. (+1 more)
Quantum geometry governs a wide array of physical observables in topological
quantum materials. In its ideal limit,
quantum geometry yields exact bounds and analytical results for a growing class of observables. However, a comparable framework for the shift current remains elusive because it depends on
geometric relations between multiple bands. In this work, we show that the shift current is proportional to the cyclotron shift, the displacement of the cyclotron center induced by Landau-level mixing. This mechanism yields a universal scaling law: the integrated weight and the peak magnitude scale as $l^{i+1-n}$ and $l^{2i+1-n}$ in the
magnetic length or moiré period $l$, where $n$ is the momentum order of the
symmetry-breaking perturbation and $\Delta E \propto l^{-i}$ is the level spacing. We verify the scaling law in exactly solvable chiral-$N$ Landau levels under a uniform
magnetic field and in Schrödinger and Dirac moiré skyrmion
crystals, which capture the flat Chern bands of twisted MoTe$_2$ and twisted bilayer
graphene. For a Schrödinger flat band with a distorted skyrmion texture, the integrated weight grows linearly with the moiré period and the resonant peak grows cubically.
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All authors Nianlong Zou, Cheng Xu, Ning Mao, Yang Zhang
Mesoscale and Nanoscale Physics
Interaction induced flattening of optical transition quantum geometry
Xu Yang and Justin C. W. Song
The Riemannian geometry of optical transition dipoles has become a useful picture for understanding linear and nonlinear optical response. Here we argue that the interacting
quantum geometry of optical transitions possesses a rich structure and can be naturally delineated into two types: localized and delocalized particle-hole excitations. The former possess uniform
quantum geometry with flat (vanishing) Hermitian
curvature; the latter possess non-uniform
quantum geometry with non-vanishing Hermitian
curvature. As a striking example, we find that uniform
quantum geometry can be produced by electron-hole interactions: even when composed from extended Bloch states in the particle and hole bands, we find
excitons have uniform and flat
quantum geometry. By developing a many-body length gauge formulation of nonlinear response, we find this uniform and flat excitonic
quantum geometry zeros its third-order circular photoconductivity in non-
magnetic materials in stark contrast to its non-interacting counterparts. Similarly, the zero Hermitian
curvature of localized optical transitions locks their Hall response to that of the ground state. This demonstrates the rich landscape of many-body optical response controlled by an interacting
quantum geometry.
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Mesoscale and Nanoscale Physics
Theory of extrinsic contributions to the full orbital current
James H Cullen and Dimitrie Culcer
The orbital Hall effect (OHE) underpins the emerging field of orbitronics. A complete
quantum-mechanical evaluation of the usual orbital-current operator must retain all
matrix elements of the position operator, including its band-diagonal differential part; intrinsic calculations based on this full evaluation can differ by orders of magnitude from the conventional truncation. A relaxation-time estimate of disorder effects on the full current has been reported, but a microscopic treatment of extrinsic scattering has remained unavailable because the position operator requires wavevector-off-diagonal density-
matrix elements. Here we develop such a theory by solving the
quantum kinetic equation for the wavevector-off-diagonal density
matrix, including band-structure, field-corrected side-jump, and skew-scattering terms within the non-crossing approximation. We apply the theory to a massive Dirac cone and to the same model with a particle-hole-
symmetry-breaking quadratic term. Disorder-generated contributions of order $\tau^0$ are generically comparable to the intrinsic current in the metallic regime and cannot be separated from it by simple disorder-strength scaling. For the bare massive Dirac cone the surviving non-crossing extrinsic correction cancels the conventional intrinsic value and leaves a total current exactly twice the
quantum correction, whereas particle-hole asymmetry activates conventional skew scattering for disorder with a non-zero third moment, which dominates in sufficiently clean samples. The wavevector-off-diagonal construction is independent of the two-band model and provides a general route to disorder corrections for position-dependent observables in multiband solids.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Morphological evolution of an Au crystalline domain in a nano-particle investigated by Bragg coherent diffraction imaging
Seonghyun Han, Saehyun Kang, Ouyoung Kwon et al. (+4 more)
Understanding the dynamic structural
evolution of metallic nanoparticles is crucial for tailoring their functional properties. In this study, we utilized three-dimensional coherent X-ray diffraction to investigate the morphological transformation of Au nanocrystalline domains in a multi-domain nanoparticle during in-situ annealing. By combining Bragg coherent diffraction imaging with autocorrelation function analysis, we observed a transformation from an anisotropic multi-domain configuration toward a single crystalline
equilibrium morphology. Above 600 degrees Celsius, a small subsidiary domain merged into the primary domain, which was continuously coarsened at 625 degrees Celsius, resulting in a more isotropic morphology. Finally, at 635 degrees Celsius, the low-energy {111} and {100} facets emerged, and the
crystal shape converged toward an
equilibrium truncated octahedral geometry. This work demonstrates a framework for interpreting complex domain dynamics, offering fundamental insights into domain growth and
equilibrium shape formation.
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All authors Seonghyun Han, Saehyun Kang, Ouyoung Kwon, Wonsuk Cha, Hyon Chol Kang, Chan Kim, Do Young Noh
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Scalable simulation of non-Markovian quantum transport by stochastic-phase bath reduction
Zhen Huang, Lin Lin and Pinchen Xie
Accurate simulations of non-Markovian
quantum transport remain limited to small systems, and a key bottleneck is that each system site requires an independent set of
quantum bath orbitals. We introduce the
Stochastic Phase
Algorithm (SPA), which replaces the independent local Gaussian baths in single-quasiparticle Holstein models by $R$ shared
quantum baths with
stochastic site-dependent phases. We prove that phase averaging reproduces the target two-point bath correlation
matrix for every $R$, while increasing $R$ systematically suppresses errors from higher-order cross-site correlations. We obtain a fixed-time $O(R^{-1})$ trace-norm error bound with a prefactor independent of system size and connectivity. This spatial compression applies directly to
unitary baths and can be combined with coupled-Lindblad spectral compression [Phys. Rev. Lett. 136, 090403 (2026)], which represents each shared environment by a very small number of coupled, damped
quantum modes fitted to its thermal bath correlation over the simulation window. Numerically, SPA converges against direct
unitary benchmarks on a $3\times3$
lattice, enables full-state-vector
quantum-bath dynamics on a $100\times100$
lattice, and, with $R=1$, closely reproduces near exact
benchmarks for
exciton populations in bacteriochlorophyll aggregates and carrier mobility in rubrene.
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Mesoscale and Nanoscale Physics
Dynamic moiré-like band modulation in Dirac materials via multi-beam optical interference
Evelyn P. Sinaga, Rizky Setiawan, Herri Trilaksana et al. (+2 more)
We propose a purely optical Floquet framework to dynamically generate moiré-like superlattices and quasicrystalline potentials in a gapped Dirac material, entirely bypassing the need for physical twisting. The interference of three coherent circularly polarized beams produces a triangular, valley-dependent Floquet mass landscape that folds the Dirac spectrum into a mini-Brillouin zone, driving pronounced valley-selective miniband reconstruction. We further show that the bands near the Fermi level undergo a light-driven topological phase transition. Remarkably, interfering five or seven beams yields non-crystallographic spatial patterns, giving rise to optical quasicrystals with similar valley contrasting features. Although this purely optical approach provides a versatile route to band engineering, reaching deep subwavelength modulation requires overcoming the free-space diffraction limit. To overcome this limitation, we consider highly confined, linearly polarized surface plasmon polariton fields with controlled relative phases. Their phase-controlled interference generates a spatially alternating chiral mass with zero spatial average. Consequently, the two valleys exhibit degenerate energy spectra while hosting opposite valley-resolved miniband Chern numbers. Our findings establish a reconfigurable, all-optical platform for dynamically engineering moiré-like bands, quasicrystalline electronic states, and valley-dependent
topology without mechanical twisting.
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All authors Evelyn P. Sinaga, Rizky Setiawan, Herri Trilaksana, Lukas P. A. Krisna, Eddwi H. Hasdeo
Mesoscale and Nanoscale Physics
Active control of THz plasmon propagation in a one-dimensional electronic waveguide
Thomas Vasselon, Uzer Ahmad, Clément Geffroy et al. (+14 more)
Quantum nanoelectronics is pushing towards ever higher operating frequencies in order to realise
quantum technologies capable of processing information at unprecedented speeds. A particularly promising direction is the development of flying electron
qubits, which offer the prospect of
quantum operations on picosecond timescales. Achieving in-flight
quantum control in this regime would establish a fundamentally new paradigm for studying
quantum entanglement and enable a novel form of
quantum information processing based on propagating electronic wavepackets. Here we report a first step towards this goal by injecting ultrashort electron wavepackets into an engineered
quantum nanoelectronic device. We demonstrate active control over the propagation speed of an electron wavepacket with a temporal duration as short as 4 ps in a quasi-one-dimensional electron waveguide with a length ranging from 10 $\mathrm{\mu}$m to 40 $\mathrm{\mu}$m. This advance provides a key building block for ultrafast
quantum operations using flying electrons. Beyond its technological implications, our approach offers a platform for exploring the intrinsic dynamical processes that govern
quantum transport and coherence in nanoscale electronic systems.
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All authors Thomas Vasselon, Uzer Ahmad, Clément Geffroy, Lucas Mazzella, Matteo Aluffi, Seddik Ouacel, Jashwanth Shaju, Kevin Bredillet, Nathan Roussel, Jean-François Roux, Pierre-Baptiste Vigneron, Arne Ludwig, Andreas D. Wieck, Matias Urdampilleta, Hermann Sellier, Giorgos Georgiou, Christopher Bäuerle
Mesoscale and Nanoscale Physics
Local time-reversal-invariant topological markers in two dimensions
Thomas Klein Kvorning, Miguel F. Martínez and Julia D. Hannukainen
Local topological markers provide a real-space characterization of topological phases and are suited to noncrystalline models. We derive a local topological marker, the Chern-Simons descendant marker, for characterizing the
topology of two-dimensional time-reversal-invariant near-Gaussian states from the one-particle density
matrix \(\rho\). We construct an auxiliary three-dimensional state characterized by the local Chern-Simons marker, and use dimensional reduction to obtain the Chern-Simons descendant marker for the original two-dimensional state. This derivation introduces a local Hermitian involution \(S\) that is odd under time reversal. When \([S,\rho]=0\), the local Chern-Simons descendant marker reduces to half the difference of the local Chern markers in the \(S=\pm1\) sectors. Constructing an \(S\) that commutes exactly with \(\rho\) generally requires fine-tuning, but this is not needed—the local Chern-Simon marker remains well defined whenever \(\Gamma=\{\rho,S\}-S\) has a spectral gap around zero, even when \([S,\rho]\neq0\). This leaves the practical problem of identifying a suitable \(S\) for a given state, which, importantly, is straightforward even when
spin is not a candidate. We show this by considering both strong Rashba and Dresselhaus
spin-orbit coupling, for which knowledge of the physical origin of the state reduces the general problem of choosing $S$ to a one-parameter family \(S(\theta)\). We evaluate the optimal angle $\theta$ maximizing the spectral gap of $\Gamma$ analytically assuming translation invariance, and find that the gap of $\Gamma$ remains open for a broad range of angles around the optimum. The same value of \(\theta\) remains valid in disordered systems, providing an easy way to obtain choice of \(S\) for evaluating the local Chern-Simons descendant marker of the state.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.stat-mech
Universal splitting of nonequilibrium phase transitions in driven Potts heat engines
Vitória T. Henkes, Gustavo A. L. Forão, Andre C. Barato et al. (+1 more)
We investigate nonequilibrium phase transitions and thermodynamic properties of driven Potts models coupled to two thermal reservoirs at different temperatures. The interplay with the multi-state structure of the Potts model leads to distinct phase-transition scenarios. The proposed driving scheme breaks the
symmetry between the Potts states and gives rise to multiple transitions within the ordered phases, where the phases are characterized by different numbers of stable fixed points. This number can vary from $q$ fixed points to $1$ fixed point, corresponding to $q-1$ distinct transitions. The driving scheme strongly affects the thermodynamic operation regimes, allowing the system to operate as a heat engine. We demonstrate that these phenomena persist for both a mean-field (MF) model and a two-dimensional model, confirming the robustness of the results with respect to dimensionality. For the MF case, we also develop a phenomenological description in the strongly ordered regime that yields analytical expressions for the power, heat currents, and efficiency. Our results show how multi-state collective interactions, nonequilibrium driving, and thermal bias jointly generate a rich phase structure and the emergence of a collective heat engine.
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All authors Vitória T. Henkes, Gustavo A. L. Forão, Andre C. Barato, Carlos E. Fiore
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Beyond Antibunching: Photon Correlation Analysis Reveals Blinking Origin
Patricia Kallert, Santiago Bermúdez-Feijóo, Giorgio De Pascalis et al. (+18 more)
A variety of
quantum emitters compete in the quest for the best single-
photon source for photonic
quantum technologies. Consequently, only a consistent approach to analyze the second-order auto correlation function allows comparison of the multi-
photon contribution ($g^{(2)}(0)$) of different sources. However, the community employs different and inconsistent methods for blinking sources, leading to incomparable
benchmarks of source quality. Here, we use the emission of an inherently non-blinking
quantum dot (QD) and apply artificial blinking through two different mechanisms: masking the recorded raw data in post-processing and emulation of a blinking system by gating the
laser excitation pulses. We then compare the $g^{(2)}(0)$ values with the non-blinking result. For the analysis, we investigate five
estimators of $g^{(2)}(0)$ actively used in the literature. While fitting the envelope of the correlations on long-time scales with the correct blinking model is the best choice, normalizing to the Poisson level gives by far the worst proximity. Furthermore, we test our predictive model to identify the underlying blinking mechanism of a QD in a circular Bragg grating cavity.
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All authors Patricia Kallert, Santiago Bermúdez-Feijóo, Giorgio De Pascalis, Nicolas Claro-Rodriguez, Ioannis Caltzidis, Normen Auler, Eva Berger, Rebecca Aschwanden, Tobias Krieger, Saimon. F. Covre da Silva, Sandra Stroj, Quirin Buchinger, Michele B. Rota, Thomas Hummel, Sven Höfling, Armando Rastelli, Rinaldo Trotta, Dirk Reuter, Sonja Barkhofen, Klaus D. Jöns, Tobias Huber-Loyola
Mesoscale and Nanoscale Physics
Helical Anomaly from Concurrent $\mathbb{Z}$ and $\mathbb{Z}_2$ Topology in an Acoustic Semimetal
Hou-Yin Li, Hua-Shan Lai, Jian-Lan Xie et al. (+3 more)
Topological classification constitutes a cornerstone of modern condensed-matter physics. Historically, topological systems have been predominantly characterized by invariants confined to a single topological class, such as topological
insulators with a $\mathbb{Z}_2$ invariant and Weyl semimetals with an integer ($\mathbb{Z}$) topological charge. While such classification frameworks in principle permit gapless phases in which bulk and boundary degeneracies are protected by distinct invariants, this regime has received limited focused
attention, as coordinating the requisite
symmetries within a single band structure is highly nontrivial. Here, we realize such concurrent $\mathbb{Z}$ and $\mathbb{Z}_2$
topology in a two-dimensional acoustic semimetal, revealing pseudospin-selective topological bulk modes arising from the interplay between these distinct invariants, termed helical anomaly bulk states (HABSs). Our
lattice design exploits layer, sublattice, and gauge-staggered degrees of freedom, enabling modular control of effective time-reversal, chiral, and particle-hole
symmetries. The resulting system exhibits bulk degeneracies protected by an integer $\mathbb{Z}$ invariant and Kramers-like boundary degeneracies protected by a $\mathbb{Z}_2$ invariant, forming twisted boundary arcs. Crucially, finite-size systems manifest helical or anti-helical edge states coexisting with HABSs, a distinctive signature absent in single-invariant
topologies. Our results establish HABSs as a characteristic signature of concurrent
topology and demonstrate a new regime where bulk and boundary invariants jointly govern topological transport beyond conventional single-class frameworks.
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All authors Hou-Yin Li, Hua-Shan Lai, Jian-Lan Xie, Xiao-Chen Sun, Yan-Feng Chen, Cheng He
Mesoscale and Nanoscale Physics
Theory of optical alignment and orientation of excitons in an ensemble of semiconductor nanoplatelets
O. O. Druzhinina and A. V. Rodina
We present the theory of
exciton optical
alignment and optical orientation effects in a single
semiconductor nanoplatelet (NPL) and in an ensemble of NPLs. The theoretical model is developed to take into account the emission from both bright and dark
exciton states in the case of strong electron-hole exchange interaction and an isotropic distribution of in-plane orientations of the NPLs' edges with respect to the linear polarization axis. The conditions for the linear optical response regime on the polarized resonant excitation of the bright
exciton are considered, and the steady-state and time-dependent expressions for polarized photoluminescence are presented for the low temperature case in the Faraday
magnetic field at normal incidence. The
symmetry of the obtained optical response corresponds to the $C_{2}$ point group for the single NPL and the $C_{\infty}$ point group for the NPL ensemble. The bright-to-dark
exciton coupling mechanism allowing one to observe the optical
alignment of the dark
exciton is considered. The example calculations of the effects are presented for the parameters close to those of CdSe/CdS core/shell NPLs. The effect of the fluctuations in the
exciton parameters in the ensemble on the polarization dephasing in the transverse effective
magnetic field is demonstrated.
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Mesoscale and Nanoscale Physics
Nonabelian vortices: From topological strings to nonvolatile memory
Chau Dao, Eric Kleinherbers and Yaroslav Tserkovnyak
We investigate the topological classification and properties of nonabelian
vortices that arise in a 2-dimensional film of a two-component condensate. For a repulsive interaction between the condensates, we realize an order parameter in the ordered configuration space of three complex numbers $\mathcal C_3(\mathbb C)$. Analyzing the homotopic properties, we find the emergence of elementary nonabelian
vortex-antivortex pairs connected by energetic strings that are rooted in the repulsive interaction and carry the nonabelian information. Moreover, we predict the existence of Brunnian
vortices, which are textures exhibiting zero net winding of the condensate phases and can only be detected by a higher-order winding number. Finally, to motivate technological applications rooted in nonabelian
vortex transport, we devise a nonvolatile
memory storage device that encodes topologically robust information.
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Mesoscale and Nanoscale Physics
Correlated quasiperiodicity enables efficient thermoelectric energy conversion
Swaraj Biswas and Santanu K. Maiti
We investigate a route to enhanced thermoelectric energy conversion in nanoscale systems by exploiting a correlated quasiperiodic energy landscape in a one-dimensional chain coupled to source and drain reservoirs. The considered modulation generates a highly non-uniform electronic transmission spectrum, providing favorable conditions for achieving a large thermoelectric figure of merit. By systematically tuning the incommensurability parameter, a variety of quasiperiodic configurations are explored, several of which yield high values of the figure of merit exceeding $2$. Electronic transport properties are evaluated within a tight-binding framework using the non-
equilibrium Green's function formalism, while the thermoelectric coefficients, including electrical conductance, Seebeck coefficient, and electronic thermal conductance, are determined through the Landauer approach. The underlying quasiperiodic potential belongs to the Aubry-André-Harper (AAH) family and exhibits a weakly varying spatial profile, leading to transmission characteristics that are favorable for thermoelectric optimization. The influence of
phonon thermal conductance on the overall energy-conversion efficiency is also analyzed in detail. For the sake of completeness, we also critically inspect the effect of conductor to electrode coupling and the coupling asymmetry on $ZT$. We also check the thermoelectric response of conventional AAH system and an elaborate comparison is made with our chosen
quantum system. Our findings highlight the potential of correlated quasiperiodic nanostructures as promising candidates for efficient thermoelectric applications.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Quantum Simulation of Si/SiGe Devices with Experimentally Calibrated Micromagnet Effects
Andrii Sokolov, Conor Power, Mathieu Moras et al. (+7 more)
Silicon-based
spin qubits in Si/SiGe
heterostructures are a leading platform for scalable
quantum computing, yet bridging the gap between theoretical computer-aided design(CAD) models and experimental reality remains a significant challenge. Standard simulations often fail to capture critical physical phenomena, such as interface dipoles, parasitic charge accumulation, and the
magnetic hysteresis of on-chip micromagnets. In this work, we present a comprehensive, experimentally calibrated 3D simulation pipeline for a 6-dot Si/SiGe device. We refine the
semiconductor band
alignment and introduce a semi-empirical classical charge screening model to accurately capture the formation of parasitic wells and their suppression of gate lever-arms. Furthermore, we apply the Jiles-Atherton model to account for the hysteresis and pre-magnetization of integrated cobalt micromagnets, successfully reproducing the experimental resonant frequencies across all six
qubits. By coupling these calibrated electrostatic and
magnetic profiles into a time-dependent rotating wave approximation (RWA)
Hamiltonian, we reproduce experimental observables, including microwave power chevrons. This framework provides a robust foundation for predicting device behavior, evaluating microwave line losses, and optimizing future scalable
spin qubit architectures prior to fabrication.
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All authors Andrii Sokolov, Conor Power, Mathieu Moras, Claude Rohrbacher, Brian Malone, Sergey Amitonov, Agostino Apra, Amir Sammak, Nodar Samkharadze, Elena Blokhina
Mesoscale and Nanoscale Physics
Aharonov-Bohm interference probing of chiral Andreev edge states via scanning gate microscopy
S. Maji and M. P. Nowak
We theoretically investigate the spatial response of chiral Andreev edge states at a
quantum Hall-
superconductor interface probed by scanning gate microscopy. Using the Bogoliubov-de Gennes formalism, we demonstrate that the localized potential of the scanning gate tip decouples the chiral Andreev edge states from the
superconductor into independent electron and hole paths. In the $\nu=2$ regime, this local separation forces the quasiparticles to accumulate a relative
magnetic phase in the normal region, resulting in Aharonov-Bohm-type conductance oscillations that are captured by a
geometric analytical model. At higher filling factors (e.g., $\nu=4$), the tip progressively interacts with spatially distinct edge channels, dynamically altering the Andreev-induced mode mixing and modifying the transport resonances. Furthermore, we show that these highly localized interferometric signatures survive in the presence of disorder, even when conventional non-local transport oscillations are masked.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Direct observation of the electronic structure of even-layer puckered SnTe monolayer films on graphene
Satoru Ichinokura, Shunsuke Tsuda, Kiyohisa Tanaka et al. (+1 more)
We report a direct observation of the electronic structure of monolayer SnTe on
graphene by angle-resolved photoemission spectroscopy. By combining low-energy electron diffraction, momentum microscopy, core-level spectroscopy, and first-principles calculations, we show that the observed monolayer-limit electronic structure is consistent with a puckered even-layer biatomic-layer building block rather than a nonpuckered square-flat structure. The observed band dispersion and its polarization dependence are reproduced by a puckered structure with a substrate-renormalized buckling amplitude. We further show that
graphene actively interacts with ultrathin SnTe by selecting its in-plane orientational texture, renormalizing the buckling amplitude, and modifying the local interfacial electrostatic environment in the monolayer limit. In comparison, multilayer SnTe exhibits a more ringlike momentum-space distribution, interlayer-split valence bands, and a stronger p-type character, revealing the onset of thickness
evolution from an interface-stabilized puckered ultrathin limit toward a more bulklike state.
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All authors Satoru Ichinokura, Shunsuke Tsuda, Kiyohisa Tanaka, Koichiro Yaji
Mesoscale and Nanoscale Physics
Charge and spin qubits in interacting quantum dots coupled to Rashba-active leads
Grazia Di Bello, Fabrizio Pavan, Mattia Trama et al. (+3 more)
We present a unified study of charge and
spin qubits encoded in a single interacting
quantum dot tunnel-coupled to Rashba fermionic leads. The dot is described by an Anderson impurity
Hamiltonian with either repulsive or attractive local interactions and a
magnetic field of arbitrary orientation. In the repulsive regime, a
spin qubit is encoded in the singly occupied
spin sector, whereas in the attractive regime, close to the degeneracy between the empty and doubly occupied configurations, these two states define a charge-
qubit subspace. We combine a weak-coupling Lindblad master equation in the Markovian secular limit with numerically controlled
matrix-product-state simulations of the full dot-reservoir system. In
equilibrium, we identify
magnetic pair breaking in the attractive regime and a weak Rashba-induced
magnetic anisotropy when the
magnetic field is rotated relative to the
spin-orbit axis. In the dynamical regime, relaxation and decoherence are controlled by the energetic gap between the logical
manifold and nearby leakage states, and are further enhanced by Rashba-dependent tunneling. These findings show that even a minimal Anderson-impurity description captures key ingredients for coherent
spin and charge
qubits: the energetic structure of leakage states and
spin-orbit-dependent dot-lead hybridization.
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All authors Grazia Di Bello, Fabrizio Pavan, Mattia Trama, Roberta Citro, Giulio De Filippis, Carmine Antonio Perroni
Mesoscale and Nanoscale Physics
Observation of the orbital Nernst effect
Yuto Masuda, Takamasa Hirai, Daegeun Jo et al. (+5 more)
The Nernst effect, which converts a temperature gradient into a transverse charge current, is fundamental to thermoelectrics. Its
spin analogue, the
spin Nernst effect, enables thermal generation of transverse
spin currents and is central to
spin caloritronics. Recently, the discovery of orbital currents, the orbital counterpart of
spin currents, has extended angular-momentum transport beyond
spin, leading to the prediction of the orbital Nernst effect, in which a temperature gradient drives a transverse orbital current. However, experimental evidence for this effect has been lacking. Here, we report the observation of the orbital Nernst effect in Ti. Using Ni electrodes on Ti, we detect a thermally induced voltage that depends on the magnetization direction and scales linearly with the temperature gradient. This voltage is strongly suppressed both when Ni is replaced with Ni$_{81}$Fe$_{19}$ and when Ti is replaced with Cr, providing strong evidence that the signal originates from the orbital Nernst effect rather than the anomalous Nernst or
spin Nernst effect. These results establish thermally driven orbital transport, opening a pathway toward orbital caloritronics.
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All authors Yuto Masuda, Takamasa Hirai, Daegeun Jo, Naoki Yano, Peter M. Oppeneer, Hossein Sepehri-Amin, Ken-ichi Uchida, Kazuya Ando
Mesoscale and Nanoscale Physics
Ultrastrong coupling of topologically protected edge and bulk magnetoplasmons without a dedicated cavity
F. Velli, P. Sai, M. Dub et al. (+6 more)
In the ultrastrong light-matter coupling regime, the ability to confine the electric field to subwavelength scales and define an electromagnetic mode is essential. This task is typically achieved through dedicated cavities, such as THz metal resonators. Here, we instead introduce ultrastrong coupling directly between distinct magnetoplasmon excitations, leveraging solely the spatial
symmetry of a confined electronic medium in the presence of a
magnetic field. By patterning an AlGaN/GaN single
quantum well hosting a two-dimensional electron gas into micrometer-scale patches, we tailor the mutual interactions between topologically protected edge and bulk magnetoplasmons, achieving coupling strengths of up to 0.1. The progressive breaking of rotational
symmetry determines the coupling rules and leads to the emergence of energy gaps and unique chiral-mode hybridization. Our results highlight a path towards exploiting the
symmetry class and
topology of the magnetoplasmon wavefunction as a new parameter space for ultrastrong light-matter interaction without a dedicated cavity.
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All authors F. Velli, P. Sai, M. Dub, J. Dzian, F. Le Mardele, M. Mittendorff, M. Orlita, W. Knap, C. Lange
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Spurious spin nutation modes arising from truncated memory effects
Markus Weißenhofer, Ritwik Mondal, M. S. Mrudul et al. (+1 more)
Spin dynamics is conventionally treated as inertia-free. The inertial Landau-Lifshitz-Gilbert equation (iLLG) extends this with a second-order time derivative, predicting a high-frequency nutational mode that recent experiments have claimed to observe and interpreted as direct evidence for
spin inertia. We show that when
spin inertia is generated by eliminating additional dynamical degrees of freedom, the resulting exact
spin-only description is generally non-Markovian. The iLLG is recovered as the low-frequency, second-order truncation of the underlying
memory kernel. Using a minimal
spin–cavity model, we show that the exact eigenfrequencies and those obtained via the iLLG differ and that the
spin nutation mode predicted by the latter is a truncation-induced high-frequency artifact. This raises a broader question of the applicability of the iLLG obtained from analogous low-frequency truncations, which may likewise generate spurious high-frequency roots. Consequently, agreement of a high-frequency spectral feature with the iLLG nutation frequency does not, by itself, establish a physical nutation mode.
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All authors Markus Weißenhofer, Ritwik Mondal, M. S. Mrudul, Peter M. Oppeneer
Mesoscale and Nanoscale Physics
Strain Engineering of the Topological Gap and Tunable Chern Numbers in the 2D Kagome Metal-Organic Framework Eu$_2$(C$_6$H$_4$)$_3$
Jiaxuan Guo, Simin Nie and Fritz B. Prinz
The
quantum anomalous Hall effect carries dissipationless chiral edge currents without an external
magnetic field, yet raising its operating temperature and controlling the number of edge channels remain difficult. Using first-principles calculations, we identify the two-dimensional metal-organic kagome ferromagnet Eu$_2$(C$_6$H$_4$)$_3$ as an intrinsic Chern
insulator whose topological gap can be enlarged by mechanical strain. The monolayer has a
spin-orbit-coupling-induced gap of 72.7 meV that widens to 124.7 meV under -8% biaxial strain, realizing a
quantum anomalous Hall phase with Chern number $\mathcal{C}=-1$ and a single chiral edge state. The local moments come from the half-filled Eu $4f^{7}$ shell, while the gap-opening
spin-orbit coupling is carried by Eu $5d$ states hybridized into the carbon kagome bands. The AB-stacked bilayer couples ferromagnetically and accumulates the per-layer Chern numbers, giving $\mathcal{C}=-2$ with two co-propagating chiral channels. An out-of-plane electric field then drives the bilayer through a sequence of topological transitions among $\mathcal{C}=-2$, $-3$, and $-1$, switching the number of edge channels. Together, strain, stacking, and gating give three distinct handles on the gap and the Chern number within a single stoichiometric material.
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Mesoscale and Nanoscale Physics
Unmodeled states and uncertain action outcomes in agentic scanning tunneling microscopy
Siyu Cheng, Muxian Xu, Christopher Candelora et al. (+1 more)
In physical experiments, interventions can alter hidden experimental states in ways that cannot be predicted in advance. Autonomous scientific
agents must therefore interpret the consequences of their interventions while operating with incomplete knowledge of the experimental state. Here we investigate this problem using scanning tunneling microscopy (STM) tip conditioning, traditionally a human-expert-intensive task governed by inaccessible tip apex conditions and uncertain action outcomes. We introduce quailbot, an
agent harness that places the LLM inside the instrument feedback loop by linking physical interventions with experimental readbacks. After a brief apprenticeship with a human expert, frontier LLM
agents autonomously completed end-to-end tip conditioning on an STM and passed an independent verification. The contingencies that arose during the experiments further exposed the limits of LLM agentic autonomy when relevant experimental states or dynamics were hidden or unmodeled. Our results show that future autonomous physical experimentation requires
agents to infer hidden and unmodeled experimental states, track the outcomes of their actions, and operate within the observability and action limits of real instruments.
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All authors Siyu Cheng, Muxian Xu, Christopher Candelora, Ilija Zeljkovic