Spin splitting, Kondo correlation and singlet-doublet quantum phase transition in a superconductor-coupled InSb nanosheet quantum dot

TL;DR

This paper demonstrates a superconductor-coupled InSb nanosheet quantum dot exhibiting spin splitting, Kondo effects, and a quantum phase transition, advancing understanding of topological superconductivity in 2D materials.

Contribution

It introduces a novel InSb nanosheet quantum dot device with tunable coupling, revealing complex quantum phenomena like Kondo effects and singlet-doublet transitions.

Findings

Observation of Kondo signatures with zero-bias peaks

Detection of a singlet-doublet quantum phase transition

Confirmation of strong spin-orbit coupling effects

Abstract

We realize a superconductor-coupled quantum dot (QD) in an InSb nanosheet, a 2D platform promising for studies of topological superconductivity. The device consists of a superconductor-QD-superconductor junction, where a bottom bilayer gate defines the QD and allows tuning of its coupling to the superconducting leads. The QD exhibits large $g$-factors and strong spin-orbit coupling. Transport measurements reveal Coulomb diamond-shaped differential conductance features with even-odd alternating sizes and pronounced conductance lines associated with the superconducting gap, confirming a few-electron, superconductor-coupled regime. At an odd electron occupation, Kondo signatures emerge, including a zero-bias peak that splits with magnetic field and is logarithmically suppressed at elevated temperatures. We further observe a doublet-singlet quantum phase transition, manifested by a clear change of Andreev bound states from crossing to anticrossing as the coupling strength increases. These results underscore the rich physics of InSb nanosheet QDs and their promise for topological quantum devices.