Hydrostatic pressure study of the structural phase transitions and superconductivity in single crystals of (Ba1-xKx)Fe2As2 (x = 0 and 0.45) and CaFe2As2

TL;DR

This study investigates how hydrostatic pressure influences structural phase transitions and superconductivity in iron arsenide single crystals, revealing pressure-induced superconductivity and phase transformations with detailed resistivity measurements.

Contribution

It provides new insights into pressure effects on phase transitions and superconductivity in (Ba,K)Fe2As2 and CaFe2As2, including the rapid induction of superconductivity in CaFe2As2.

Findings

Pressure suppresses structural transitions in BaFe2As2 and shifts superconducting onset in (Ba,K)Fe2As2.

Superconductivity in CaFe2As2 is induced rapidly under pressure and confined to a narrow pressure range.

Pressure alters the resistivity and phase behavior, revealing complex phase diagrams.

Abstract

We studied the effect of hydrostatic pressure (P) on the structural phase transitions and superconductivity in the ternary and pseudo-ternary iron arsenides CaFe2As2, BaFe2As2, and (Ba0.55K0.45)Fe2As2, by means of measurements of electrical resistivity (rho) in the 1.8 - 300 K temperature (T) range, pressures up to 20 kbar, and magnetic fields up to 9 T. CaFe2As2 and BaFe2As2 (lightly doped with Sn) display structural phase transitions near 170 K and 85 K, respectively, and do not exhibit superconductivity in ambient pressure, while K-doped (Ba0.55K0.45)Fe2As2 is superconducting for T < 30 K. The effect of pressure on BaFe2As2 is to shift the onset of the crystallographic transformation down in temperature at the rate of about -1.04 K/kbar, while shifting the whole rho(T) curves downward, whereas its effect on superconducting (Ba0.55K0.45)Fe2As2 is to shift the onset of superconductivity to lower temperatures at the rate of about -0.21 K/kbar. The effect of pressure on CaFe2As2 is first to suppress the crystallographic transformation and induce superconductivity with onset near 12 K very rapidly, i.e., for P < 5 kbar. However, higher pressures bring about another phase transformation characterized by reduced resistivity, and the suppression of superconductivity, confining superconductivity to a narrow pressure dome centered near 5 kbar. Upper critical field (Hc2) data in (Ba0.55K0.45)Fe2As2 and CaFe2As2 are discussed.