The Unusual Superconducting State at 49 K in Electron-Doped CaFe2As2 at Ambient

TL;DR

This study reports the discovery of an unusual superconducting phase at 49 K in electron-doped CaFe2As2, which exhibits distinct properties from previously known doping-induced superconductivity in similar compounds.

Contribution

It presents the first observation of a high-temperature superconducting phase at 49 K in electron-doped CaFe2As2, contrasting with prior hole-doping and pressurization results.

Findings

Superconductivity at 49 K with low critical field ~4 Oe

Coexistence of a second phase at 21 K with higher critical field >5 T

Unusual superconducting behavior contrasting previous doping methods

Abstract

We report the detection of unusual superconductivity up to 49 K in single crystalline CaFe2As2 via electron-doping by partial replacement of Ca by rare-earth. The superconducting transition observed suggests the possible existence of two phases: one starting at ~ 49 K, which has a low critical field ~ 4 Oe, and the other at ~ 21 K, with a much higher critical field > 5 T. Our observations are in strong contrast to previous reports of doping or pressurizing layered compounds AeFe2As2 (or Ae122), where Ae = Ca, Sr or Ba. In Ae122, hole-doping has been previously observed to generate superconductivity with a transition temperature (Tc) only up to 38 K and pressurization has been reported to produce superconductivity with a Tc up to 30 K. The unusual 49 K phase detected will be discussed.