NMR study of superconductivity and spin fluctuations in hole-doped superconductor Ca1-xNaxFe2As2 (Tc =32 K)

TL;DR

This study uses NMR techniques to investigate the superconducting and magnetic properties of hole-doped Ca1-xNaxFe2As2, revealing unconventional pairing and strong antiferromagnetic spin fluctuations linked to superconductivity.

Contribution

First NMR analysis of Ca1-xNaxFe2As2 showing evidence of unconventional pairing and magnetic fluctuations in this compound.

Findings

Superconductivity is of singlet type with a sharp Knight shift drop below Tc.

Absence of coherence peak in 1/T1 suggests unconventional pairing symmetry.

Strong low-energy antiferromagnetic spin fluctuations are present, supporting a magnetic pairing mechanism.

Abstract

We report both 23Na and 75As NMR studies on hole-doped Ca1-xNaxFe2As2 superconducting single crystals (x\approx 0.67) with Tc =32 K. Singlet superconductivity is suggested by a sharp drop of the Knight shift 75K below Tc. The spin-lattice relaxation rate 1/T1 does not show the Slichter-Hebel coherence peak, which suggests an unconventional pairing. The penetration depth is estimated to be 0.24 {\mu}m at T=2 K. 1/75T1T shows an anisotropic behavior and a prominent low-temperature upturn, which indicates strong low-energy antiferromagnetic spin fluctuations and supports a magnetic origin of superconductivity.