Superconductivity in undoped T' cuprates with Tc over 30 K

TL;DR

This study reports the discovery of superconductivity in undoped T'-RE2CuO4 thin films with Tc over 30 K, achieved through a simple, cost-effective process involving low oxygen partial pressure and low-temperature reduction.

Contribution

It demonstrates that undoped T'-RE2CuO4 can be superconducting with high Tc, challenging the belief that doping is necessary for superconductivity in cuprates.

Findings

Superconductivity achieved in undoped T'-RE2CuO4 with Tc over 30 K.

Gd2CuO4 becomes superconducting with Tconset ~20 K.

Simple thin-film process enables high-Tc superconductivity in undoped cuprates.

Abstract

Undoped cuprates have long been considered to be antiferromagnetic insulators. In this article, however, we report that superconductivity is achieved in undoped T'-RE2CuO4 (RE = Pr, Nd, Sm, Eu, and Gd). Our discovery was performed by using metal-organic decomposition (MOD), an inexpensive and easy-to-implement thin-film process. The keys to prepare the superconducting films are firing with low partial-pressure of oxygen and reduction at low temperatures. The highest Tc of undoped T'-RE2CuO4 is over 30 K, substantially higher than "electron-doped" analogs. Remarkably, Gd2CuO4, even the derivatives of which have not shown superconductivity so far, gets superconducting with Tconset as high as ~ 20 K. The implication of our discovery is briefly discussed.