High-temperature superconductivity stabilized by electron-hole interband coupling in collapsed tetragonal phase of KFe2As2 under high pressure

TL;DR

This study reveals that high-pressure-induced structural changes in KFe2As2 enhance its superconductivity, driven by electron-hole interband coupling and Fermi surface reconstruction, leading to a new high-temperature superconducting phase.

Contribution

It demonstrates the stabilization of high-temperature superconductivity in KFe2As2 through electron-hole interband coupling in the collapsed tetragonal phase under high pressure.

Findings

Superconducting T_c peaks near 2 GPa and then diminishes with pressure.

A drastic T_c increase occurs at the structural phase transition above 13 GPa.

Fermi surface reconstruction involves a switch from hole- to electron-like charge carriers.

Abstract

We report a high-pressure study of simultaneous low-temperature electrical resistivity and Hall effect measurements on high quality single-crystalline KFe2As2 using designer diamond anvil cell techniques with applied pressures up to 33 GPa. In the low pressure regime, we show that the superconducting transition temperature T_c finds a maximum onset value of 7 K near 2 GPa, in contrast to previous reports that find a minimum T_c and reversal of pressure dependence at this pressure. Upon applying higher pressures, this T_c is diminished until a sudden drastic enhancement occurs coincident with a first-order structural phase transition into a collapsed tetragonal phase. The appearance of a distinct superconducting phase above 13 GPa is also accompanied by a sudden reversal of dominant charge carrier sign, from hole- to electron-like, which agrees with our band calculations predicting the emergence of an electron pocket and diminishment of hole pockets upon Fermi surface reconstruction. Our results suggest the high-temperature superconducting phase in KFe2As2 is substantially enhanced by the presence of nested electron and hole pockets, providing the key ingredient of high-T_c superconductivity in iron pnictide superconductors.