Study of 0-$\pi$ phase transition in hybrid superconductor-InSb nanowire quantum dot devices

TL;DR

This study investigates the 0-$$ phase transition in hybrid superconductor-InSb nanowire quantum dot devices, revealing gate-tunable Andreev bound states and their evolution near the quantum phase transition.

Contribution

It demonstrates continuous gate control of ABSs and explores the coexistence and transition between 0 and  states in hybrid nanowire quantum dots.

Findings

Gate-tunable ABSs with 0 and  levels were realized.

Coexistence of 0-type and -type ABSs in the same charge state.

Temperature and magnetic field measurements confirmed the phase transition scenario.

Abstract

Hybrid superconductor-semiconducting nanowire devices provide an ideal platform to investigating novel intragap bound states, such as the Andreev bound states (ABSs), Yu-Shiba-Rusinov (YSR) states, and the Majorana bound states. The competition between Kondo correlations and superconductivity in Josephson quantum dot (QD) devices results in two different ground states and the occurrence of a 0-$\pi$ quantum phase transition. Here we report on transport measurements on hybrid superconductor-InSb nanowire QD devices with different device geometries. We demonstrate a realization of continuous gate-tunable ABSs with both 0-type levels and $\pi$-type levels. This allow us to manipulate the transition between 0 and $\pi$ junction and explore charge transport and spectrum in the vicinity of the quantum phase transition regime. Furthermore, we find a coexistence of 0-type ABS and $\pi$-type ABS in the same charge state. By measuring temperature and magnetic field evolution of the ABSs, the different natures of the two sets of ABSs are verified, being consistent with the scenario of phase transition between the singlet and doublet ground state. Our study provides insights into Andreev transport properties of hybrid superconductor-QD devices and sheds light on the crossover behavior of the subgap spectrum in the vicinity of 0-$\pi$ transition.