Superconducting and magnetic phase diagram of RbEuFe4As4 and CsEuFe4As4 at high pressure

TL;DR

This study investigates how high pressure affects superconductivity and ferromagnetism in RbEuFe4As4 and CsEuFe4As4, revealing suppression of superconductivity and enhancement of magnetic transition with a phase change at higher pressures.

Contribution

It provides the first detailed high-pressure phase diagram of (Rb,Cs)EuFe4As4, showing the interplay between superconductivity, magnetism, and structural phase transitions.

Findings

Superconductivity is suppressed with increasing pressure.

Magnetic transition temperature increases initially with pressure.

Structural transition from tetragonal to half collapsed-tetragonal phase occurs around 10-12 GPa.

Abstract

The recently discovered (Rb,Cs)EuFe4As4 compounds exhibit an unusual combination of superconductivity (Tc = 35 K) and ferromagnetism (Tm = 15 K). We have performed a series of x-ray diffraction, ac magnetic susceptibility, dc magnetization, and electrical resistivity measurements on both RbEuFe4As4 and CsEuFe4As4 to pressures as high as 30 GPa. We find that the superconductivity onset is suppressed monotonically by pressure while the magnetic transition is enhanced at initial rates of dTm/dP = 1.7 K/GPa and 1.5 K/GPa for RbEuFe4As4 and CsEuFe4As4, respectively. Near 7 GPa, Tc onset and Tm become comparable. At higher pressures, signatures of bulk superconductivity gradually disappear. Room temperature x-ray diffraction measurements suggest the onset of a transition from tetragonal (T) to a half collapsed-tetragonal (hcT) phase at 10 GPa (RbEuFe4As4) and 12 GPa (CsEuFe4As4). The ability to tune Tc and Tm into coincidence with relatively modest pressures highlights (Rb,Cs)EuFe4As4 compounds as ideal systems to study the interplay of superconductivity and ferromagnetism.