Enhancement of Superconducting Transition Temperature due to the strong Antiferromagnetic Spin Fluctuations in Non-centrosymmetric Heavy-fermion Superconductor CeIrSi3 :A 29Si-NMR Study under Pressure

TL;DR

This study reveals that strong antiferromagnetic spin fluctuations in CeIrSi3 under pressure promote unconventional superconductivity with line nodes, contributing to its relatively high transition temperature among Ce-based heavy-fermion superconductors.

Contribution

It provides the first detailed 29Si-NMR evidence linking antiferromagnetic spin fluctuations to enhanced superconductivity in non-centrosymmetric CeIrSi3.

Findings

Superconductivity appears at 2.7-2.8 GPa with line nodes in the gap.

Normal state shows non-Fermi liquid behavior due to AFM spin fluctuations.

Strong AFM fluctuations likely cause the high Tc in CeIrSi3.

Abstract

We report a 29Si-NMR study on the pressure-induced superconductivity (SC) in an antiferromagnetic (AFM) heavy-fermion compound CeIrSi3 without inversion symmetry. In the SC state at P=2.7-2.8 GPa, the temperature dependence of the nuclear-spin lattice relaxation rate 1/T_1 below Tc exhibits a T^3 behavior without any coherence peak just below Tc, revealing the presence of line nodes in the SC gap. In the normal state, 1/T_1 follows a \sqrt{T}-like behavior, suggesting that the SC emerges under the non-Fermi liquid state dominated by AFM spin fluctuations enhanced around quantum critical point (QCP). The reason why the maximum Tc in CeIrSi3 is relatively high among the Ce-based heavy-fermion superconductors may be the existence of the strong AFM spin fluctuations. We discuss the comparison with the other Ce-based heavy-fermion superconductors.