Two types of superconducting domes in unconventional superconductors

TL;DR

This study reveals that unconventional superconductors often exhibit two distinct superconducting domes with different normal state properties, suggesting NFL physics as a common route to higher Tc, and challenges the QCP-based explanation.

Contribution

The paper provides a comprehensive analysis across multiple superconductor families, identifying two types of superconducting domes and clarifying their origins and relation to NFL phases.

Findings

Two types of SC domes with distinct properties

Higher Tc dome linked to NFL or strange metal phase

QCP is unlikely the main driver for NFL in these materials

Abstract

Uncovering the origin of unconventional superconductivity is often plagued by the overwhelming material diversity with varying normal and superconducting (SC) properties. In this article, we deliver a comprehensive study of the SC properties and phase diagrams using multiple tunings (such as disorder, pressure or magnetic field in addition to doping and vice versa) across several families of unconventional superconductors, including the copper-oxides, heavy-fermions, organics and the recently discovered iron-pnictides, iron-chalcogenides, and oxybismuthides. We discover that all these families often possess two types of SC domes, with lower and higher superconducting transition temperatures Tc, both unconventional but with distinct SC and normal states properties. The lower Tc dome arises with or without a quantum critical point (QCP), and not always associated with a non-Fermi liquid (NFL) background. On the contrary, the higher-Tc dome clearly stems from a NFL or strange metal phase, without an apparent intervening phase transition or a QCP. The two domes appear either fully separated in the phase diagram, or merged into one, or arise independently owing to their respective normal state characteristics. Our findings suggest that a QCP-related mechanism is an unlikely scenario for the NFL phase in these materials, and thereby narrows the possibility towards short-range fluctuations of various degrees of freedom in the momentum and frequency space. We also find that NFL physics may be a generic route to higher-Tc superconductivity.