Kondo Effect in Defect-bound Quantum Dots Coupled to NbSe$_2$

TL;DR

This paper demonstrates a van der Waals device with a defect-bound quantum dot coupled to NbSe₂, revealing a coexistence of Kondo effect and superconductivity influenced by NbSe₂'s two-gap structure.

Contribution

It introduces a novel platform using van der Waals heterostructures to study the interplay of Kondo effect and superconductivity in NbSe₂.

Findings

Observation of zero-bias conductance peak splitting with magnetic field.

Coexistence of Kondo effect and superconducting gap in the device.

Suppression of the low-energy gap by magnetic field due to NbSe₂'s two-gap nature.

Abstract

We report the fabrication of a van der Waals tunneling device hosting a defect-bound quantum dot coupled to NbSe$_2$. We find that upon application of magnetic field, the device exhibits a zero-bias conductance peak. The peak, which splits at higher fields, is associated with a Kondo effect. At the same time, the junction retains conventional quasiparticle tunneling features at finite bias. Such coexistence of a superconducting gap and a Kondo effect are unusual, and are explained by noting the two-gap nature of the superconducting state of NbSe$_2$, where a magnetic field suppresses the low energy gap associated with the Se band. Our data shows that van der Waals architectures, and defect-bound dots in them, can serve as a novel and effective platform for investigating the interplay of Kondo screening and superconducting pairing in unconventional superconductors.