The Superconducting Plateau

TL;DR

This paper examines the phenomenon of a superconducting plateau in lightly doped strontium titanate, analyzing experimental data to understand the underlying mechanisms and constraints on theoretical models.

Contribution

It introduces the concept of a density exponent and discusses the role of a quantum critical point in the formation of the superconducting plateau.

Findings

Superconducting critical temperature remains constant over a wide doping range.

Low critical current and high critical field are linked to small carrier momentum.

Theoretical models must account for the observed plateau phenomenon.

Abstract

Two recent experiments in lightly doped strontium titanate have shown that the superconducting critical temperature remains constant in a range of carrier concentrations covering almost three orders of magnitude. The importance of this phenomenon, hereby dubbed a superconducting plateau, is comparable to the celebrated superconducting dome. The dramatic empirical evidence impose severe constraints on any proposal for a superconducting mechanism at low doping. We analyze the experimental results to see what type of theoretical models can be suitable in this regime. We show that the low critical current, absence of diamagnetic screening and the high critical field are all related to the small momentum of the carriers, which is expected at low densities. We quantify the dependency of the critical temperature on density by introducing the "density exponent". We discuss the role of a quantum critical point in the formation of a plateau and comment on the need for more experimental data.