Two-dimensional superconductor-insulator quantum phase transitions in an electron-doped cuprate

TL;DR

This study demonstrates a two-dimensional superconductor-insulator transition in an electron-doped cuprate using electric and magnetic fields, revealing quantum critical behavior and differences from hole-doped systems.

Contribution

It provides the first detailed analysis of electric and magnetic field-induced SITs in electron-doped cuprates, highlighting unique critical resistance values and transition mechanisms.

Findings

SITs are quantum phase transitions governed by percolation effects.

Critical sheet resistances are much lower than the pair quantum resistance.

Fermionic excitations may exist at finite temperature near SITs.

Abstract

We use ionic liquid-assisted electric field effect to tune the carrier density in an electron-doped cuprate ultrathin film and cause a two-dimensional superconductor-insulator transition (SIT). The low upper critical field in this system allows us to perform magnetic field (B)-induced SIT in the liquid-gated superconducting film. Finite-size scaling analysis indicates that SITs induced both by electric and magnetic field are quantum phase transitions and the transitions are governed by percolation effects - quantum mechanical in the former and classical in the latter case. Compared to the hole-doped cuprates, the SITs in electron-doped system occur at critical sheet resistances (Rc) much lower than the pair quantum resistance RQ=h/(2e)2=6.45 k{\Omega}, suggesting the possible existence of fermionic excitations at finite temperature at the insulating phase near SITs.