Mesoscale and Nanoscale Physics
Real-Time FPGA-Based Multi-Parameter Feedback Stabilization of a Silicon Double Quantum Dot
Johnathan Bryan, Tim J. Wilson and Hong-Wen Jiang
Long term operation of
semiconductor spin qubits requires active stabilization of
quantum dot potentials against low-frequency charge noise. Previous work demonstrated a gradient-descent feedback (GDFB) approach on a silicon double
quantum dot utilizing transport current measurements. We extend such a GDFB approach in a silicon double
quantum dot device with high-bandwidth rf-reflectometry readout by utilizing a field-programmable gate array, the OPX by
Quantum Machines, for digital signal processing. The OPX enables continuous multi-parameter gradient calculation and quick gate voltage updates, significantly increasing the effective feedback bandwidth compared to previous work. By operating with 8 steps per feedback cycle and an integration time of 25.6 $\mu$s, this high speed stabilization scheme achieves a -6 dB noise suppression up to a bandwidth of 5 kHz. This effectively suppresses low frequency 1/f noise, maintaining device stability over longer time periods, and potentially enables real-time control in large-scale
quantum dot arrays.
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Mesoscale and Nanoscale Physics
Nanoscale imaging of ferromagnetic vortex dynamics with scanning NV magnetometry
Jeffrey Rable, Jyotirmay Dwivedi, Nitin Samarth et al. (+3 more)
The generation and manipulation of
spin waves at the nanoscale via
magnetic vortices are of considerable importance because of their broad applications across magnonic and
quantum technologies. Previously, fixed nitrogen-vacancy (NV) centers in diamond have been used to locally characterize
vortex dynamics, and scanning NV magnetometry (SNVM) has been used to image
vortices' static stray fields. Here, we demonstrate SNVM imaging of both the static and microwave fields generated by
vortices in mesoscopic permalloy structures with $\sim$50 nm spatial resolution, achieving excellent agreement with micromagnetic simulations, while revealing the effects of disorder. We further demonstrate a 40$\times$ microwave field enhancement near a
vortex core and image the disorder-dependent, spatially varying, evanescent decay of these microwaves. Our ambient, tabletop technique surpasses diffraction-limited techniques' resolutions by at least 5$\times$, with far greater accessibility and throughput than synchrotron radiation-based techniques, offering new opportunities in the study and development of magnonic devices.
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All authors Jeffrey Rable, Jyotirmay Dwivedi, Nitin Samarth, Paul Stevenson, Arun Bansil, Swastik Kar
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Light Polarization Sensitive Transistor Action in the van der Waals ferroelectric 4H-SnS2
Abhishek Bajgain, Rabindra Basnet, Subhashree Chatterjee et al. (+2 more)
Van der Waals (vdW) ferroelectric
semiconductors provide a unique platform for exploring the interplay between spontaneous polarization, electronic transport, ion migration, and photocarrier generation at the nanoscale. Here, we establish a room-temperature ferroelectric state in SnS2 and its sensitivity to structural polytype by directly contrasting the centrosymmetric 2H-phase with the polar 4H-phase. Raman spectroscopy distinguishes the 2H and 4H polymorphs of SnS2 through their characteristic
phonon fingerprints. Piezoresponse force microscopy confirms room-temperature ferroelectricity in the 4H phase, while the 2H phase exhibits no ferroelectric response. The built-in polarization in a three-terminal transistor device of the 4H-SnS2 is modulated significantly by electrostatic gating and on exposure to linear and circularly polarized light. This device reveals polarization-controlled output characteristics with distinct gate-voltage induced hysteretic response and thermally activated carrier transport, confirming p-type semiconducting behavior strongly coupled to ferroelectric polarization. The photoresponse likewise exhibits polarization-assisted carrier separation, sublinear power-law scaling, a nonmonotonic temperature response correlated with the characteristic Raman modes, ferroelectric hysteresis, and a pronounced dependence on the circular and linear polarization states of the incident
laser beam. These results establish 4H-SnS2 as a promising material system for polarization-driven electronic and optoelectronic technologies, including nonvolatile
memory and photoferroelectric functionalities.
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All authors Abhishek Bajgain, Rabindra Basnet, Subhashree Chatterjee, Alexander Samokhvalov, Ramesh C. Budhani
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Degenerate high-order hybrid bound states in the continuum beyond diffraction limit
Ji Tong Wang and Nicolae C. Panoiu
We demonstrate the existence of at-$\Gamma$ degenerate hybrid bound-states in the continuum (BICs) with high-order topological charges and quadratic band degeneracy in periodic photonic structures with $C_{6v}$
symmetry above the diffraction limit. The degenerate BICs are realized by combining
symmetry protection, which suppresses radiation into zeroth-order diffraction channel, with quadratic band degeneracy and parameter tuning to eliminate radiation into first-order diffraction channels. An effective
Hamiltonian is used to investigate the band structure around the degeneracy point, and the topological dynamics in all diffraction channels are characterized. This work reveals a novel mechanism for realizing degenerate BICs above the diffraction limit, opening up opportunities for new physics and applications.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Cell Natural Orbitals in Quantum Materials
Harshitra Mahalingam, Nishchhal Verma, Daniel Muñoz-Segovia et al. (+1 more)
Understanding correlated
quantum matter starts with an accurate model of the single-particle states that interact at low energies: their dispersion, band geometry, orbital content and charge density. In many cases, notably the topological bands of moire materials, it is not straightforward to find a real-space description with a few local orbitals that accomplishes this task. Here we provide a systematic way to identify the local degrees of freedom that best capture the band geometry and charge density of any chosen set of bands. We use the unit-
cell one-particle reduced density
matrix (UC-1pRDM), obtained by restricting the projector onto the target bands to a single unit
cell. Its eigenstates, which we call
cell natural orbitals (CNOs), form a local, symmetric basis uniquely determined by the Bloch wavefunctions and the choice of real-space partition. Their
eigenvalues measure the occupation of each CNO in the target bands, quantifying
entanglement across unit-
cell boundaries and the importance of multi-orbital character. A set of CNOs that maximizes total spectral weight and reproduces the target band
symmetries provides optimal trial states for Wannierization. We exemplify this by constructing a
lattice model for twisted bilayer WSe$_2$ that tracks the orbital content across twist angles.
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All authors Harshitra Mahalingam, Nishchhal Verma, Daniel Muñoz-Segovia, Raquel Queiroz
Mesoscale and Nanoscale Physics
Complete kinematic null for local kinetic dissipation in a sixfold-driven electron fluid
P. Shubham Parashar
We identify a complete kinematic null in a two-dimensional electron fluid driven by a sixfold boundary pattern. In the $U_3^\pm$ channel of $D_{12}$, device
symmetry excludes both the vector representation $R_1$ and the full first-gradient tensor $R_1\otimes R_1$. Hence at the
symmetry-fixed center $\mathbf{j}(0)=0$ and $\partial_i j_j(0)=0$, so every local quadratic dissipative form built from the modeled charge/momentum field through first gradient order vanishes independently of the constitutive coefficients. In an $O(2)$-isotropic angular-harmonic kinetic model the first allowed local sector is $m=3$. For $\nu q^2/\gamma_3\ll1$, its heating is set by the previously derived coefficient $\kappa_4=v_F^4/(16\gamma_2^2\gamma_3)$. An explicit incompressible Stokes disk realizes a nonzero center signal, and a finite-moment kinetic boundary-value solution approaches the corresponding local
benchmark. Within the local, fixed-current momentum-conserving Stokes regime, the normalized
magnetic response can then be fitted for effective $\gamma_3$ and $\gamma_2$. Thus the sixfold drive creates a measurement point where ordinary local charge/momentum hydrodynamic dissipation is absent while a kinetic mode remains finite.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el
Cell Natural Orbitals in Interacting Topological Bands
Nishchhal Verma, Harshitra Mahalingam, Daniel Muñoz-Segovia et al. (+1 more)
Topological bands exhibit obstruction to exponentially localized and symmetric Wannier functions, challenging the standard paradigm of representing projected interactions in terms of local orbitals with finite range. To faithfully capture the form factors and
quantum geometry of topological bands we introduce a singular-value decomposition of the band-projected density form factors, enabling a geometry-based truncation scheme of the
Hilbert space, exposing an intrinsic hierarchy on band-projected interactions that is determined by the underlying wavefunctions. This decomposition is most naturally described in terms of
Cell Natural Orbitals (CNOs), as the eigenstates of the unit-
cell reduced one-particle density
matrix, whose occupation provide a measure of the minimal orbital complexity required to faithfully represent the band wavefunctions overlaps. The CNO decomposition identifies systematically the minimal number of local orbitals needed to reproduce short-ranged interactions while resolving the hierarchy of interaction strengths across CNO channels. Applied to magic-angle twisted bilayer
graphene in the chiral limit, we find that the dominant CNO is centered at the AA site, resembling the $f$-
fermion of the heavy-
fermion model. The subdominant CNO channels carry progressively weaker interaction
matrix elements, allowing them to be treated at the static mean-field level, while the dominant channel requires a dynamical self-energy. The formalism illustrates how variations of charge density within the unit
cell generate momentum dependence in the CNO envelope function and, consequently, dispersion in the single-particle spectral function. More broadly, our results establish CNOs as a geometry-informed bridge between band
topology and real-space correlations, providing a systematic framework for analyzing interactions and emergent phases in
quantum materials.
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All authors Nishchhal Verma, Harshitra Mahalingam, Daniel Muñoz-Segovia, Raquel Queiroz
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
AES-Debye: an Accurate, Efficient, and Scalable Engine for Debye Scattering Calculations
Navid Panchi, Sebastian Kuckuk, Markus Wittmann et al. (+2 more)
Total scattering models are essential for characterizing the structure and disorder of nanoscale materials. The Debye scattering equation (DSE) provides a rigorous route to elastic total scattering, but its direct evaluation is computationally demanding because pairwise contributions must be accumulated at every scattering vector, whereas common acceleration strategies based on binned pair-distance distributions or gridded fast
Fourier transforms can introduce discretization and aliasing artifacts that compromise diffuse-scattering accuracy. Here, we present AES-Debye, an accuracy-preserving DSE framework that aggregates pair distances into a pair distribution function (PDF) using corrected bin centers and numerically robust accumulation to suppress discretization and summation errors. A data-locality-aware parallel design enables efficient execution on CPUs and GPUs. We demonstrate strong scalability by computing a high-resolution total scattering profile for a system of 90 million atoms, $(0.1,\mu\mathrm{m})^{3}$, in minutes on a distributed-
memory CPU platform. These capabilities extend accurate elastic total scattering calculations to large, complex systems while simultaneously providing high-resolution PDFs for downstream structural analysis.
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All authors Navid Panchi, Sebastian Kuckuk, Markus Wittmann, Michael Engel, Alberto Leonardi
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el
Tunable Multiband Geometry and Fractional Phases in Higher Vortexable Systems
Xiaohan Wan, Siddhartha Sarkar, Ting Cao et al. (+3 more)
Higher vortexability is often viewed as a route to topological flat bands with higher-Landau-level-like
quantum geometry. Here we emphasize a complementary perspective: it provides a tunable multiband structure in which wave function geometry can be varied continuously while the band dispersion, degeneracy, and
topology remain fixed. We perform systematic exact-diagonalization studies of many-body phases in fractionally filled higher vortexable moiré systems, retaining the full flat-band
Hilbert space rather than projecting onto a single band. The multiband treatment reveals a cascade of Abelian and non-Abelian phases at zero
magnetic field, including integer and fractional
exciton insulators, Abelian fractional Chern
insulators, Moore-Read and Read-Rezayi states. At fixed filling, different phases are connected through transitions or crossovers driven solely by changes in wave function geometry, highlighting
quantum geometry itself as a direct tuning parameter between competing topological states. At fillings associated with Moore-Read and Read-Rezayi states, our calculations show that interband mixing shifts the optimal
quantum geometry regime without suppressing non-Abelian topological order under screened Coulomb interaction. Our results establish higher vortexable moiré bands as a tunable platform for exploring geometry-driven multiband topological phases at zero
magnetic field.
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All authors Xiaohan Wan, Siddhartha Sarkar, Ting Cao, Mark Rudner, Di Xiao, Kai Sun
Mesoscale and Nanoscale Physics
Topological phase rectification via Aharonov-Bohm interference in a Majorana–quantum-dot interferometer
Jia Liu, Hao-Yuan Yang, Yuan Hong et al. (+5 more)
We propose and theoretically investigate a topological superconducting rectifier based on a
quantum-dot–Majorana interferometer. The Aharonov-Bohm phase, controlled by a
magnetic flux threading the interferometer loop, tunes the
quantum interference between a trivial $2\pi$-periodic
quantum-dot channel and a topological $4\pi$-periodic Majorana channel. At non-integer flux, this interference generates a persistent current background $I_{\rm off}$ that shifts the current-phase relation into a unipolar regime, in which the supercurrent flows strictly in one direction. We introduce a signed unipolarity factor $\eta_u$, with $|\eta_u|>0.5$ defining the unipolar regime, and establish its quantitative relationship to the conventional diode efficiency $\eta$. The unipolarity proves robust against variations of the
quantum-dot level,
spin polarization, and Majorana hybridization, is enhanced by stronger Majorana coupling and Rashba
spin-orbit interaction, and persists at realistic temperatures and under quasiparticle poisoning. We further propose a topological diode figure of merit $\mathcal{Z}_{\rm TD}$, defined from the
Fourier spectrum of $\eta_u$, whose nonzero value provides a model-independent signature of the $4\pi$-periodic Majorana channel and distinguishes topological from trivial rectification mechanisms. Our findings establish the
quantum-dot–Majorana interferometer as a promising route toward high-performance topological superconducting diodes with clear experimental signatures accessible via standard dc transport measurements.
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All authors Jia Liu, Hao-Yuan Yang, Yuan Hong, Li Ma, Feng Chi, Zi-Chuan Yi, Li-Ming Liu, Zhen-Guo Fu
Mesoscale and Nanoscale Physics
Disorder-robust trivial Majorana-like states from smooth confinement in chiral superconducting nanowires
Eslam Ahmed, Jorge Cayao and Yukio Tanaka
Near-zero-energy states in Majorana nanowires can arise from topologically trivial mechanisms such as smooth spatial inhomogeneity and disorder, making zero-energy pinning alone insufficient evidence of bulk
topology. Here we identify a real-space mechanism governing their robustness to
symmetry-preserving disorder. For a chiral-symmetric Bogoliubov-de Gennes
Hamiltonian, we decompose a low-energy state into two normalized components of opposite chirality and show that disorder-induced splitting is bounded by their spatial overlap. We demonstrate this result in a finite Rashba nanowire with smooth chemical potential and pairing profiles. Below the bulk topological transition, smooth confinement produces partially separated chiral components with exponentially small overlap, yielding globally trivial Majorana-like Andreev bound states that remain near zero energy even under strong scalar, nonmagnetic disorder. The chiral overlap therefore provides a direct diagnostic of the protection of low-energy states against local perturbations, independent of the bulk topological invariant.
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Mesoscale and Nanoscale Physics
Probing crystal-field modulations with magnetic adatoms on the incipient charge-density-wave superconductor $2H$-NbS$_2$
Werner M.J. van Weerdenburg, Margarete Huisinga, Constantin Flommersfeld et al. (+2 more)
The interplay between multiple
quantum phases in layered materials may lead to incipient
quantum behavior, where the material's ground state is close to a phase transition and sensitive to local disorder. The transition metal dichalcogenide material $2H$-NbS$_2$ exhibits incipient charge-density-wave behavior along with a well-developed superconducting state, creating a scenario where the local
lattice instabilities play a crucial role. Here we present how an individual
magnetic atom on $2H$-NbS$_2$ can be applied as a local sensor to reveal hidden
crystal-field modulations. By manipulating the adatom across the surface with the tip of a scanning tunneling microscope, we measure variations in the Yu-Shiba-Rusinov (YSR) excitation spectra and map the local environment around an intrinsic point defect. We find that while the superconducting state is spatially uniform, the YSR excitation energy strongly depends on the position of the atom. We determine that the main contribution to this effect originates from variations in the local
crystal-field environment. These results establish a new approach to investigate
crystal-field modulations at the atomic scale and reveal how defects and
lattice instabilities shape the atomic landscape of an incipient charge-density-wave material.
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All authors Werner M.J. van Weerdenburg, Margarete Huisinga, Constantin Flommersfeld, Lisa M. Rütten, Katharina J. Franke
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.supr-con
Revealing Hidden Unconventional Pairing through Nonreciprocal Transport
Wen-Bo Dai, Ming Gong, Xianxin Wu et al. (+2 more)
Identifying the pairing
symmetry of Cooper pairs is a fundamental step toward understanding the microscopic mechanisms of unconventional
superconductors. However, experimental identification remains a formidable challenge, particularly when unconventional pairing is obscured by a dominant $s$-wave component that masks its spectroscopic signatures. Here, we develop a
symmetry-resolved framework to identify superconducting pairing
symmetry through nonreciprocal conductance upon exchanging source and detector terminals in multiterminal devices. We show that nonreciprocal transport arises from
symmetry-breaking components of the superconducting order parameter and exhibits a characteristic angular dependence that encodes the momentum-space structure of the pairing gap. In particular, time-reversal-breaking singlet pairing induces nonreciprocal charge transport, while
spin-triplet pairing generates nonreciprocal
spin responses, providing distinct transport fingerprints of the underlying order. We demonstrate this mechanism using representative models of iron-based and noncentrosymmetric
superconductors and outline experimental protocols for multiterminal measurements. Our results advance the theoretical understanding of nonreciprocal transport in
superconductors, and establish it as a
symmetry-selective probe for identifying hidden unconventional pairing in a wide range of superconducting materials.
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All authors Wen-Bo Dai, Ming Gong, Xianxin Wu, Chui-Zhen Chen, X. C. Xie
Mesoscale and Nanoscale Physics
Symmetry Breaking by Interfacial Dead Layers: Observation of Forbidden Self-Induced Spin-Orbit Torque in Symmetric Ferromagnets
Athira Ravindran K, Raghvendra Posti, Manish Kumar Mohanta et al. (+8 more)
Conventionally,
spin-orbit torques (SOTs) in ferromagnets require heavy-metal layers or engineered structural asymmetry to break inversion
symmetry. In this work, we report the observation of robust, self-generated SOTs in a nominally symmetric, heavy-metal-free MgO/NiFe/MgO trilayer - a geometry where such torques are theoretically forbidden. By combining harmonic Hall measurements with SQUID magnetometry and X-ray photoelectron spectroscopy, we identify the
symmetry-breaking origin: a 1.8 nm
magnetic dead layer at the bottom interface. Crucially, we demonstrate a quantitative agreement between our data and the drift-
diffusion theory predicted by Kim and Lee, yielding a theoretically extracted dead-layer thickness (1.2 nm) which matches structural characterization. Furthermore, density-functional calculations confirm that NiFe possesses sufficient intrinsic
spin Hall conductivity to support the observed
spin currents. These results reframe the parasitic dead layer as a functional spintronic component, establishing a universal, all-ferromagnetic route to SOTs in standard
magnetic heterostructures.
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All authors Athira Ravindran K, Raghvendra Posti, Manish Kumar Mohanta, Abhishek Kumar, Damanpreet Kaur, Alberto Anadón, Sebastien Petit-Watelot, Juan-Carlos Rojas-Sánchez, Michel Hehn, Puru Jena, Debangsu Roy
Mesoscale and Nanoscale Physics
Buried germanium quantum well proximitised by magnetic field-resilient superconducting platinum iridium germanosilicide
Praveen Viswanathan, Erik Lemmens Sjöstrand, Davide Costa et al. (+8 more)
Hybrid
superconductor-
semiconductor systems provide a versatile platform for
quantum technologies, ranging from superconducting-
spin interfaces to topological
quantum devices. Progress toward scalable implementations requires
superconductors that exhibit high critical fields ($>1$T) at accessible temperatures integrated with low-disorder
semiconductor heterostructures. Here we demonstrate a superconducting platinum iridium germanosilicide (PtIrSiGe), with critical out-of-plane
magnetic field up to $B_{\perp} = 1.9$T and critical temperature of $T_c\sim 1.85$K, integrated with planar germanium with mobility $\mu = 1.3\times 10^6$cm$^{2}$/Vs via top-down lithography fabrication. We show that the integrity of the germanium
quantum well and mobility and density of the 2D hole gas are preserved despite annealing at $500\deg$C, a temperature comparable to that used for strained germanium epitaxy. We further demonstrate proximitisation of a buried germanium
quantum well in a gate-defined Josephson junction/SQUID on a Ge/SiGe
heterostructure.
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All authors Praveen Viswanathan, Erik Lemmens Sjöstrand, Davide Costa, Marinus Fischer, Athique Ahmed, Sara Martí-Sánchez, Lucas E. A. Stehouwer, Jordi Arbiol, Anasua Chatterjee, Giordano Scappucci, Karina L. Hudson
Mesoscale and Nanoscale Physics
Long-range exchange interaction controls the fine structure of excited trion states in semiconductor quantum dots
M.M. Glazov and E.L. Ivchenko
We develop a microscopic theory of the long-range electron-hole exchange interaction in charged
excitons (trions) confined in
semiconductor quantum dots. While the ground-state singlet trion remains degenerate in the
spin component of unpaired charge carrier by time-reversal
symmetry, excited trion states exhibit a rich fine structure resulting from the interplay of electron-electron and electron-hole exchange interactions. We derive the effective long-range exchange
Hamiltonian for both the
spin-$3/2$ heavy-hole and a simple
spin-$1/2$ valence band models. The long-range exchange interaction mixes singlet and triplet trion configurations, giving rise to anisotropic fine-structure splittings and related polarization-dependent optical spectra determined by the
quantum-dot shape. Analytical expressions are obtained for the long-range exchange parameters. The developed theory establishes a unified microscopic description of the fine structure of excited trions in
semiconductor quantum dots and provides a framework for interpreting polarization-resolved optical spectroscopy of charged excitonic complexes.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el
Spin Polarization of a Two-Dimensional Electron Liquid
G. A. Nikolaev, M. E. Sergeev, I. V. Kukushkin et al. (+1 more)
We show experimentally that the longitudinal resistance of a strongly correlated two-dimensional electron system provides a quantitative measure of its
spin polarization. Using electrically detected electron
spin resonance to independently calibrate the
spin state, we establish a parameter-free relation between magnetotransport and
spin polarization, allowing the latter to be determined from transport alone. This approach enables the
magnetic state of the electron
liquid to be mapped across a broad range of carrier densities and
magnetic fields.
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All authors G. A. Nikolaev, M. E. Sergeev, I. V. Kukushkin, A. V. Shchepetilnikov
Mesoscale and Nanoscale Physics
Quantum sensing composite excitations in an anisotropic ferromagnet via a qubit
Amey S. Rodge, Tarek Moussa, Akashdeep Kamra et al. (+1 more)
Ordered magnets harbor intrinsically squeezed ground states and magnonic excitations characterized by
entanglement between
spins and nonclassical
magnon number composition. A pathway to detecting the superpositions of noneigenmode
magnon number states underlying these nonclassical
magnetic ground states has recently been demonstrated by utilizing a
qubit coupled to the
magnon mode via a direct dispersive interaction. Here, we theoretically develop this
qubit spectroscopy further delineating the capabilities and limitations of this
qubit spectroscopy for sensing the
quantum superpositions that underlie the excited states. We demonstrate that the spectroscopy lends itself naturally to unraveling the superpositions that underlie the various quantized squeezed-
magnon number states. However, excited states comprising superpositions of multiple squeezed Fock states become increasingly hard due to the large number of possible transitions, and resulting peaks, in the
qubit spectroscopy thereby requiring
qubits with narrower linewidths. Along the same lines, we theoretically demonstrate the
qubit spectroscopy of a low amplitude coherent squeezed-
magnon state analyzing the tradeoff between frequency crowding due to multiple transitions and peak linewidths. Our work lays the groundwork and design equations for deploying high-quality
qubits towards sensing the composite nature of
spin excitations in
magnetic systems.
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All authors Amey S. Rodge, Tarek Moussa, Akashdeep Kamra, Bashab Dey
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Time-resolved study of carbonization and growth of ultrathin 3C-SiC on Si(111) under ultra-high vacuum
Pranjali Jadhao, Mojdeh Fallahpour, Josef Polčák et al. (+6 more)
The early-stage formation of silicon carbide (SiC) on Si(111) by ethylene exposure under ultra-high
vacuum (UHV) was investigated to resolve the time-dependent chemical and morphological
evolution of an ultrathin layer. Clean Si(111) substrates were exposed to C$_2$H$_4$ at 800 {\deg}C for 2 min to 4 h, and the surfaces followed by in-situ X-ray photoelectron spectroscopy (XPS) and ex-situ AFM, SEM, AES, SIMS and TEM. Si 2p and C 1s peak analysis shows the progressive conversion of elemental silicon into a carbidic Si-C phase, the SiC fraction overtaking the elemental component between 120 and 160 min and saturating near 80-81% beyond 180 min, leaving about 19-20% residual elemental silicon. Correlative SEM and AFM reveal a parallel morphological progression, from sparse isolated islands to a coalesced, near-continuous layer. AES depth profiling confirms carbon incorporated into the near-surface region rather than weakly adsorbed as contamination, assigning the islands to early SiC
nuclei. TEM confirms the zinc-blende
lattice and the presence of cubic silicon carbide (3C-SiC). Together, these results provide a time-resolved picture of SiC nucleation, coalescence and layer growth on Si(111), relevant to 3C-SiC heteroepitaxy, and can be utilized in the optimization of SiC/Si(111) templates for growth of III-nitride and other carbide systems on silicon (e.g. Mo$_2$C).
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All authors Pranjali Jadhao, Mojdeh Fallahpour, Josef Polčák, Eva Kolíbalová, Michal Horák, Jan Michalička, Petr Bábor, Stanislav Voborný, Tomáš Šikola
Mesoscale and Nanoscale Physics
Noisy Braiding of Majorana Modes: A Comparison of Nanowire Trijunction and Quantum-Dot-Assisted Architectures
Dibyajyoti Sahu and Suhas Gangadharaiah
Majorana zero modes have emerged as one of the most promising platforms for topological
quantum computation, since their non-Abelian braiding statistics allow
quantum information to be encoded nonlocally and manipulated through braiding operations that are, in principle, protected against local perturbations. In practice, however, a braid is only as robust as its physical implementation: finite-time operation, residual couplings, and environmental noise can all convert local excitations into logical errors during the exchange process. Here, we address this question through a microscopic comparison of two representative braiding architectures, a nanowire trijunction and a
quantum-dot-assisted setup, simulating the full time-dependent Bogoliubov–de Gennes dynamics under both noiseless and noisy conditions. We show that the dot-assisted architecture consistently achieves a lower error over a shorter timescale than the trijunction, owing to its more localized exchange mechanism. This advantage persists in the presence of noise, and a spatially resolved analysis further reveals that, in the dot-assisted geometry, fast noise localized on the dot produces a smaller error than equivalent noise on the wires, whereas slow, quasi-static noise on the dot becomes the dominant limitation. Taken together, these findings link the different error contributions directly to device geometry, pointing to concrete design principles for noise-resilient Majorana-based
quantum gates.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el
Geometrical approach and topological electron density in the $p_x + ip_y$ superconductor
Karyn Le Hur, Kabir Narayanan and Óscar Mañas Chambert
We present an analysis on the geometrical and physical nature of the $p_x + ip_y$
superconductor on the square
lattice, with an emphasis on the topological phase transition at half-filling. We develop a local topological marker from specific Dirac points within the Brillouin zone, which is introduced via the addition of two one-dimensional (1D) $\mathbb{Z}$ $(\mathbb{Z}_2$) invariants defined on the Bloch sphere. We relate this topological marker to the electron spectral function integrated on frequency through the local momentum-resolved electron density, which may be measured via Angle Resolved Photoemission Spectroscopy (ARPES), and show that it remains well-protected including temperature effects. Integrating on a small area around a specific point in momentum space associated to the measure uncertainty, this also reveals the Van Hove logarithmic profile of the density of states in the derivative of the local marker while preserving the topological information. Topological transitions correspond to a protected semi-metal. We analyse the real space representation of this topological marker from correlation functions. We present physical responses such as the topological superfluid density.
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Mesoscale and Nanoscale Physics
Parity-Resolved Quantum Capacitance and Quantum Inductance in Topological, Trivial, and Normal Nanowire Interferometers
Viktoriia Pinchenkova, Valerii K. Kozin, Maximilian Hünenberger et al. (+2 more)
Quantum-capacitance measurements convert the
curvature of a
quantum-dot energy in a flux-threaded nanowire loop into fast parity-sensitive signals and, therefore, have become a promising readout tool for Majorana devices. However, Majorana-like
quantum-capacitance responses can also arise from topologically trivial Andreev bound states, making capacitance alone insufficient to identify a topological phase. To analyze this problem, we consider a
quantum dot coupled to both ends of four nanowire realizations: a topological nanowire hosting Majorana bound states, non-topological superconducting nanowires hosting one or two Andreev bound states, and a fully normal nanowire. Motivated by proposals to use
quantum inductance as an additional phase-sensitive probe, we compute both the parity-resolved
quantum capacitance $C_\mathrm{Q}$ and inverse
quantum inductance $L_\mathrm{Q}^{-1}$ as functions of the
magnetic flux by exact diagonalization. We show that signatures associated with zero-energy Majorana bound states, such as $h/e$ periodicity and an $h/(2e)$ flux shift between even and odd parity sectors in $C_\mathrm{Q}$ and $L_\mathrm{Q}^{-1}$, are not sufficient indicators of topological superconductivity. In certain realistic parameter regimes, similar Majorana-like behavior can arise from a trivial Andreev bound state and even from a purely normal nanowire. By contrast, two nearly zero-energy Andreev bound states can generate a pronounced $h/(2 e)$-periodic component associated with charge-$2e$ transfer, providing a clear non-Majorana signature. A low-energy projection shows that the Majorana, single-Andreev-state, and normal cases can be mapped onto the same minimal low-energy model explaining their similar flux-dependent responses despite their different physical origins.
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All authors Viktoriia Pinchenkova, Valerii K. Kozin, Maximilian Hünenberger, Daniel Loss, Jelena Klinovaja
Mesoscale and Nanoscale Physics
Magnetically induced Circular Photogalvanic Effect in Symmetric Two-dimensional Materials
Peng Liu, Fanhao Jia, Ruixue Li et al. (+3 more)
Photocurrents that depend on the helicity of the incident light can be generated in both bulk and low-dimensional materials lacking inversion
symmetry, known as the circular photogalvanic effect (CPGE). We propose that by employing a
magnetic effect, the limitation on the inversion
symmetry broken materials can be overcome, such that helicity-dependent photocurrent can be generated in a symmetric material, i.e., a magneto-circular photogalvanic effect (MCPGE). As a proof of principle, we elucidate the mechanism of such an MCPGE through an effective
Hamiltonian of a monolayer SbH on a
magnetic substrate with an adjustable magnetization. Moreover, the associated response in optical absorption is analyzed, both single-particle and excitonic, through a Bethe-Salpeter equation to describe the Coulomb interaction in
excitons. Our result broadens the mechanism of CPGE and opens new opportunities for optoelectronic devices.
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All authors Peng Liu, Fanhao Jia, Ruixue Li, Yuan Li, Igor Zutic, Gaofeng Xu
Mesoscale and Nanoscale Physics
Polarization engineered all 2D Graphene/Ferroelectric hybrid for persistence-free photoresponse
Navkiranjot Kaur Gill, Shaili Sett, Saloni Kakkar et al. (+3 more)
Graphene-based van der Waals hybrid photodetectors typically work on trap-mediated photogating mechanism, exhibiting high sensitivity, but under-perform in the fast detection of repetitive optical signals. Designing photodetectors that are simultaneously fast and highly sensitive has therefore remained difficult. In this work, we realize both attributes by integrating atomically thin sliding ferroelectrics in the design architecture, thereby uniting semiconducting properties with intrinsic polarization fields capable of efficiently governing interfacial photocarrier dynamics. We report a bilayer
graphene-bilayer MoS2 (with MoS2 in a rhombohedrally stacked (3R) configuration) van der Waals photodetector with edge-contacted dual-gated field-effect transistor architecture. The photo-induced modulation in spontaneous out-of-plane polarization of 3R-MoS2 and selective confinement of charge carriers in bilayer
graphene under an out-of-plane displacement field results in a tunable persistence-free photoresponse. Here, the photoinduced polarization change in 3R-MoS2 produces an optically controlled gating effect that alters the electrostatic environment of bilayer
graphene, resulting in a temperature-independent photoresponse with rapid response times of the order of 10's of milliseconds (limited by the measurement instrument). We demonstrate reproducible detection of optical signals and examine the
photon-counting resolution of this structure in high-sensitivity regimes, where we determine its internal
quantum efficiency to be 10 percent with minimum detectable
photon number of 31 in single shot measurements. This work highlights the functionality of 3R-MoS2 in manipulating the interfacial charge dynamics and establishes the hybrid of
graphene and ferroelectric 3R-MoS2 as a promising platform for ultra-sensitive optoelectronic devices.
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All authors Navkiranjot Kaur Gill, Shaili Sett, Saloni Kakkar, Kenji Watanabe, Takashi Taniguchi, Arindam Ghosh
Mesoscale and Nanoscale Physics
Size-Dependent Band-Tail Localization in Oxide Semiconductors Revealed by Direct Density-of-States Mapping
Chang Niu, Kisoo Nam, Aravindh Shankar et al. (+5 more)
Disorder-induced localization is expected to become increasingly important as amorphous oxide
semiconductor transistors are scaled toward low-dimensional channels, yet the electronic states responsible for this transport regime remain difficult to resolve experimentally. Here, we use a lock-in-based electric-field penetration technique to directly map the effective density of states (DOS) in In-based oxide
semiconductor thin-film transistors (TFTs). The extracted
quantum capacitance, carrier density, and chemical potential reveal a disorder-dominated transport regime in which band-tail states are not merely passive traps, but become screening-active and partially transport-active. Geometry-dependent DOS mapping shows an exponential suppression of the effective DOS with channel length, demonstrating size-dependent band-tail localization and providing a microscopic origin for a distinct localization-induced threshold-voltage roll-off mechanism. Temperature-dependent measurements show that the disorder-dominated DOS is strongly suppressed at low temperatures, while extended diffusive states remain nearly unchanged, confirming the localization origin. By tuning film thickness, O2 annealing, and In/Ga/Zn composition, we further demonstrate systematic suppression of disorder and effective-DOS localization. This work establishes direct DOS mapping as a device-level probe of localization physics and provides a pathway for engineering disorder in low-dimensional oxide
semiconductor electronics.
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All authors Chang Niu, Kisoo Nam, Aravindh Shankar, Jian-Yu Lin, Sanjeev Khare, Sumi Lee, Pramey Upadhyaya, Peide D. Ye
Mesoscale and Nanoscale Physics
Gradient-based optimization of non-Abelian fractional quantum states in patterned superlattices
Yifei Guan, Lichen Yu, Zizhuang Liu et al. (+2 more)
The realization of fractional Chern
insulator (FCI) states in moiré
heterostructures has attracted intense interest in the study of correlated topological states. So far, most experimentally realized FCI states may be interpreted as
lattice analogues of Abelian fractional
quantum Hall (FQH) states. Realizing non-Abelian FCI states is an important challenge in the field. Patterned dielectric superlattices provide a versatile platform for engineering topological flat bands. Such systems offer substantial structural flexibility and tunability, because their
lattice patterns, periods, and other structural parameters can all be designed and fabricated. Here, we provide a gradient-based optimization workflow to design non-Abelian fractional states in patterned bilayer
graphene superlattices. The experimentally relevant structural parameters of the superlattice devices are gradient-optimized to favor a flat Chern band with
quantum-
geometric properties reminiscent of those of the first excited Landau level. Exact diagonalization calculations at 1/2 filling of the optimized Chern band naturally yield non-Abelian FCIs. We apply this workflow to triangular, honeycomb, and kagome patterned superlattices and find robust non-Abelian FCIs over a large region of the parameter space spanned by superlattice constant and vertical potential drop. Our work thus establishes an experimentally feasible framework for exploring non-Abelian FCIs in realistic patterned-superlattice devices.
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All authors Yifei Guan, Lichen Yu, Zizhuang Liu, Xin Lu, Jianpeng Liu
Mesoscale and Nanoscale Physics
Phonon-assisted transport and hole-phonon coupling in GaAs double quantum dots
Jin Leng, Wei-Zhu Liao, Hao-Tian Jiang et al. (+5 more)
Hole-
phonon interactions play an important role in transport and decoherence processes in
semiconductor quantum dots. Here we investigate hole-
phonon coupling in a gate-defined GaAs double
quantum dot integrated with a
quantum point contact charge sensor. Under finite source-drain bias, pronounced oscillatory stripe patterns appear near specific charge transition regions in the charge stability diagram. We attribute these oscillations to
phonon emission during inelastic interdot tunneling. A theoretical model including piezoelectric hole-
phonon coupling reproduces the observed patterns. Furthermore, our analysis shows that the oscillations emerge only in particular charge configurations. Our results provide direct insight into
phonon-assisted transport and coherent hole-
phonon interactions in
semiconductor quantum dots.
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All authors Jin Leng, Wei-Zhu Liao, Hao-Tian Jiang, Di Liu, Bao-Chuan Wang, Gang Cao, Hai-Ou Li, Guo-Ping Guo