arXiv subjects

S. Gronin

Publications and source records attributed to S. Gronin.

12 recordsLinked to original sources

arXiv2026

Emergence of Bogoliubov Fermi Surfaces in hybrid Al/InAs heterostructures

We investigate the microwave electrodynamics of a proximitized two-dimensional electron gas in hybrid superconductor/semiconductor heterostructures. Using lumped-element resonators with inductor wires oriented relative to an in-plane magnetic field, we directly probe the superfluid stiffness via the kinetic inductance. As the field increases, the resonance frequency exhibits a non-monotonic and strongly anisotropic evolution that cannot be explained by orbital pair breaking alone. We show that this behavior is consistent with the emergence of Bogoliubov Fermi surfaces, which selectively suppress the supercurrent response depending on the direction of the magnetic field. Microscopic calculations of the stiffness tensor capture the observed anisotropy driven by the interplay of Zeeman and orbital Fulde-Ferrell effects. Our results establish microwave stiffness measurements as a sensitive probe of anisotropic gapless superconductivity in hybrid systems.

cond-mat.supr-con↗

arXiv2022

Local and Non-local Microwave Impedance of a Three-Terminal Hybrid Device

We report microwave impedance measurements of a superconductor-semiconductor hybrid nanowire device with three terminals (3T). Our technique makes use of transmission line resonators to acquire the nine complex scattering matrix parameters (S-parameters) of the device on fast timescales and across a spectrum of frequencies spanning 0.3 - 7 GHz. Via comparison with dc-transport measurements, we examine the utility of this technique for probing the local and non-local response of 3T devices where capacitive and inductive contributions can play a role. Such measurements require careful interpretation but may be of use in discerning true Majorana zero modes from trivial states arising from disorder.

cond-mat.mes-hall↗

arXiv2022

Gate-Tunable Transmon Using Selective-Area-Grown Superconductor-Semiconductor Hybrid Structures on Silicon

We present a gate-voltage tunable transmon qubit (gatemon) based on planar InAs nanowires that are selectively grown on a high resistivity silicon substrate using III-V buffer layers. We show that low loss superconducting resonators with an internal quality of $2\times 10^5$ can readily be realized using these substrates after the removal of buffer layers. We demonstrate coherent control and readout of a gatemon device with a relaxation time, $T_{1}\approx 700\,\mathrm{ns}$, and dephasing times, $T_2^{\ast}\approx 20\,\mathrm{ns}$ and $T_{\mathrm{2,echo}} \approx 1.3\,\mathrm{μs}$. Further, we infer a high junction transparency of $0.4 - 0.9$ from an analysis of the qubit anharmonicity.

cond-mat.mes-hall↗

arXiv2021

Spin-Relaxation Mechanisms in InAs Quantum Well Heterostructures

The spin-orbit interaction and spin-relaxation mechanisms of a shallow InAs quantum well heterostructure are investigated by magnetoconductance measurements as a function of an applied top-gate voltage. The data were fit using the Iordanskii--Lyanda-Geller--Pikus model and two distinct transport regimes were identified which correspond to the first and second sub-bands of the quantum well. The spin-orbit interaction splitting energy is extracted from the fits to the data, which also displays two distinct regimes. The different sub-band regimes exhibit different spin-scattering mechanisms, the identification of which, is of relevance for device platforms of reduced dimensionality which utilise the spin-orbit interaction.

cond-mat.mes-hall↗

arXiv2021

Spin-orbit Energies in Etch-Confined Superconductor-Semiconductor Nanowires

We report magneto-transport measurements of quasi-1-dimensional (1D) Al-InAs nanowires produced via etching of a hybrid superconductor-semiconductor two-dimensional electron gas (2DEG). Tunnel spectroscopy measurements above the superconducting gap provide a means of identifying the 1D sub-bands associated with the confined 1D region. Fitting the data to a model that includes the different components of the spin-orbit interaction (SOI) reveals their strength, of interest for evaluating the suitability of superconductor-semiconductor 2DEG for realizing Majorana qubits.

cond-mat.mes-hall↗

arXiv2021

Josephson Junctions Via Anodization of Epitaxial Al on an InAs Heterostructure

We combine electron beam lithography and masked anodization of epitaxial aluminium to define tunnel junctions via selective oxidation, alleviating the need for wet-etch processing or direct deposition of dielectric materials. Applying this technique to define Josephson junctions in proximity induced superconducting Al-InAs heterostructures, we observe multiple Andreev reflections in transport experiments, indicative of a high quality junction. We further compare the mobility and density of Hall-bars defined via wet etching and anodization. These results may find utility in uncovering new fabrication approaches to junction-based qubit platforms.

cond-mat.supr-con↗

arXiv2021

Electrical Properties of Selective-Area-Grown Superconductor-Semiconductor Hybrid Structures on Silicon

We present a superconductor-semiconductor material system that is both scalable and monolithically integrated on a silicon substrate. It uses selective area growth of Al-InAs hybrid structures on a planar III-V buffer layer, grown directly on a high resistivity silicon substrate. We characterized the electrical properties of this material system at millikelvin temperatures and observed a high average field-effect mobility of $μ\approx 3200\,\mathrm{cm^2/Vs}$ for the InAs channel, and a hard induced superconducting gap. Josephson junctions exhibited a high interface transmission, $\mathcal{T} \approx 0.75 $, gate voltage tunable switching current with a product of critical current and normal state resistance, $I_{\mathrm{C}}R_{\mathrm{N}} \approx 83\,\mathrm{μV}$, and signatures of multiple Andreev reflections. These results pave the way for scalable and high coherent gate voltage tunable transmon devices and other superconductor-semiconductor hybrids fabricated directly on silicon.

cond-mat.mes-hall↗

arXiv2021

Zeeman-driven parity transitions in an Andreev quantum dot

The Andreev spectrum of a quantum dot embedded in a hybrid semiconductor-superconductor interferometer can be modulated by electrostatic gating, magnetic flux through the interferometer, and Zeeman splitting from in-plane magnetic field. We demonstrate parity transitions in the embedded quantum dot system, and show that the Zeeman-driven transition is accompanied by a 0-π transition in the superconducting phase across the dot. We further demonstrate that flux through the interferometer modulates both dot parity and 0-π transitions.

cond-mat.mes-hall↗

arXiv2020

Coherent transport through a Majorana island in an Aharonov-Bohm interferometer

Majorana zero modes are leading candidates for topological quantum computation due to non-local qubit encoding and non-abelian exchange statistics. Spatially separated Majorana modes are expected to allow phase-coherent single-electron transport through a topological superconducting island via a mechanism referred to as teleportation. Here we experimentally investigate such a system by patterning an elongated epitaxial InAs-Al island embedded in an Aharonov-Bohm interferometer. With increasing parallel magnetic field, a discrete sub-gap state in the island is lowered to zero energy yielding persistent 1e-periodic Coulomb blockade conductance peaks (e is the elementary charge). In this condition, conductance through the interferometer is observed to oscillate in a perpendicular magnetic field with a flux period of h/e (h is Planck's constant), indicating coherent transport of single electrons through the islands, a signature of electron teleportation via Majorana modes, could also be observed, suggesting additional non-Majorana mechanisms for 1e transport through these moderately short wires.

cond-mat.mes-hall↗

arXiv2020

Closing of the Induced Gap in a Hybrid Superconductor-Semiconductor Nanowire

Hybrid superconductor-semiconductor nanowires are predicted to undergo a field-induced phase transition from a trivial to a topological superconductor, marked by the closure and re-opening of the excitation gap, followed by the emergence of Majorana bound states at the nanowire ends. Many local density-of-states measurements have reported signatures of the topological phase, however this interpretation has been challenged by alternative explanations. Here, by measuring nonlocal conductance, we identify the closure of the excitation gap in the bulk of the semiconductor before the emergence of zero-bias peaks. This observation is inconsistent with scenarios where zero-bias peaks occur due to end-states with a trivially gapped bulk, which have been extensively considered in the theoretical and experimental literature. We observe that after the gap closes, nonlocal signals fluctuate strongly and persist irrespective of the presence of local-conductance zero-bias peaks. Thus, our observations are also incompatible with a simple picture of clean topological superconductivity. This work presents a new experimental approach for probing the spatial extent of states in Majorana wires, and reveals the presence of a regime with a continuum of spatially extended states and uncorrelated zero-bias peaks.

cond-mat.mes-hall↗

arXiv2019

Repairing the Surface of InAs-based Topological Heterostructures

Candidate systems for topologically-protected qubits include two-dimensional electron gases (2DEGs) based on heterostructures exhibiting a strong spin-orbit interaction (SOI) and superconductivity via the proximity effect. For InAs- or InSb-based materials, the need to form shallow quantum wells to create a hard-gapped $p$-wave superconducting state often subjects them to fabrication-induced damage, limiting their mobility. Here we examine scattering mechanisms in processed InAs 2DEG quantum wells and demonstrate a means of increasing their mobility via repairing the semiconductor-dielectric interface. Passivation of charged impurity states with an argon-hydrogen plasma results in a significant increase in the measured mobility and reduction in its variance relative to untreated samples, up to 45300 cm$^2$/(V s) in a 10 nm deep quantum well.

cond-mat.mes-hall↗

arXiv2018

Hybridization of sub-gap states in one-dimensional superconductor/semiconductor Coulomb islands

We present measurements of one-dimensional superconductor-semiconductor Coulomb islands, fabricated by gate confinement of a two-dimensional InAs heterostructure with an epitaxial Al layer. When tuned via electrostatic side gates to regimes without sub-gap states, Coulomb blockade reveals Cooper-pair mediated transport. When sub-gap states are present, Coulomb peak positions and heights oscillate in a correlated way with magnetic field and gate voltage, as predicted theoretically, with (anti) crossings in (parallel) transverse magnetic field indicating Rashba-type spin-orbit coupling. Overall results are consistent with a picture of overlapping Majorana zero modes in finite wires.

cond-mat.mes-hall↗