Superconducting Dome and Quantum Criticality in Two-Dimensional NbO2 Triangular Lattice

TL;DR

This study reports a new two-dimensional, strongly correlated superconductor Li1-xNbO2 with a triangular lattice, revealing a superconducting dome linked to quantum criticality and non-Fermi liquid behavior.

Contribution

It introduces Li1-xNbO2 as a novel strongly correlated superconductor with a triangular lattice and explores its electronic phase diagram under hole doping.

Findings

Superconductivity emerges near a quantum critical point.

The phase diagram shows a transition from Fermi-liquid to non-Fermi liquid states.

Superconductivity is associated with suppression of Kondo-singlet formation.

Abstract

The emergence of superconductivity with strong correlation is one of the most attracted issues in condensed-matter physics, as seen in various unconventional superconductors. Here we show a new strongly correlated superconductor Li1-xNbO2 with rich characteristics such as two-dimensional, geometrically frustrated, and triangular NbO2 lattice and correlated flat-band-like electronic states. We revealed the electronic phase diagram by implementing Li-ion electrochemical cells with LiNbO2 epitaxial films. The Li-ion deintercalation increased the hole-doping level in NbO2 layer, along which a band insulator LiNbO2 underwent to a Fermi-liquid (FL) metal and superconductor associated with non-Fermi liquid (NFL) characters. The evolution of the NFL state coincided with the suppression of the Kondo-singlet formation near the superconducting dome, which linked superconductivity with quantum criticality. The obtained phase diagram involves general aspects of strongly correlated superconductors and bridges the gap between various systems.