Pressure-induced unconventional superconductivity near a quantum critical point in CaFe2As2

TL;DR

This study reveals pressure-induced unconventional, gapless superconductivity near a quantum critical point in CaFe2As2, emphasizing the role of electron correlations in pairing mechanisms.

Contribution

It provides the first detailed NMR/NQR investigation of pressure-induced superconductivity and quantum criticality in CaFe2As2, highlighting the evolution of gap structure and electron correlations.

Findings

Superconductivity appears near a quantum critical point under pressure.

Superconducting gap structure evolves from gapless to multiple gaps with pressure.

Electron correlations are crucial for Cooper pair formation in CaFe2As2.

Abstract

75As-zero-field nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements are performed on CaFe2As2 under pressure. At P = 4.7 and 10.8 kbar, the temperature dependences of nuclear-spin-lattice relaxation rate (1/T1) measured in the tetragonal phase show no coherence peak just below Tc(P) and decrease with decreasing temperature. The superconductivity is gapless at P = 4.7 kbar but evolves to that with multiple gaps at P = 10.8 kbar. We find that the superconductivity appears near a quantum critical point under pressures in the range 4.7 kbar < P < 10.8 kbar. Both electron correlation and superconductivity disappear in the collapsed tetragonal phase. A systematic study under pressure indicates that electron correlations play a vital role in forming Cooper pairs in this compound.