New superconduting cuprates with no effective doping: T'-(La3+)2-x(RE3+)xCuO4

TL;DR

This paper reports the synthesis of new superconducting cuprates with no effective doping, achieved through molecular beam epitaxy, high-quality film preparation, and impurity oxygen removal, resulting in superconductivity around 21-25 K.

Contribution

The study introduces a novel class of superconducting cuprates stabilized without doping by using isovalent substitution and advanced thin film techniques.

Findings

Superconductivity observed at ~21-25 K in new cuprates.

High-quality T' phase films achieved at low temperatures.

Effective removal of impurity oxygen enhances superconductivity.

Abstract

We report the synthesis of new superconducting cuprates T'-La2-xRExCuO4 (RE = Sm, Eu, Tb, Lu, and Y) using molecular beam epitaxy. The new superconductors have no effective dopant, at least nominally. The substitution of isovalent RE for La was essentially performed to stabilize the T' phase of La2CuO4 instead of the T phase. The maximum Tconset is ~ 25 K and Tczero is ~ 21 K. The keys to our discovery are (1) the preparation of high-crystalline-quality La-based T' films by low-temperature (~ 650C) thin film processes, and (2) more thorough removal of impurity oxygen at the apical site, which is achieved by the larger in-plane lattice constant (a0) of T'-La2-xRExCuO4 than other T'-Ln2CuO4 (Ln = Pr, Nd, Sm, Eu, Gd) with the aid of large surface-to-volume ratio of thin films.