Spin Dynamics in Iron-based Layered Superconductor (La_{0.87}Ca_{0.13})FePO Revealed by ^{31}P and ^{139}La NMR Studies

TL;DR

This study uses NMR techniques to investigate the spin dynamics and electronic structure of the iron-based superconductor (La_{0.87}Ca_{0.13})FePO, revealing Fermi-liquid behavior, quasi-two-dimensionality, and unusual spin fluctuations in the superconducting state.

Contribution

It provides new insights into the spin dynamics and electronic structure of (La_{0.87}Ca_{0.13})FePO, highlighting the presence of ferromagnetic fluctuations and low-energy spin dynamics in the superconductor.

Findings

Fermi-liquid state with moderate ferromagnetic fluctuations below 30K

Quasi-two-dimensional electronic structure with more conductive FeP layer

An increase in 1/T_1T below T_c indicating novel spin dynamics

Abstract

We report ^{31}P and ^{139}La NMR studies of (La_{0.87}Ca_{0.13})FePO, which is a family member of the recently discovered superconductor LaFeAs(O_{1-x}F_x). In the normal state, Knight shift and $1/T_1T$ show that a Fermi-liquid state with moderate ferromagnetic fluctuations emerges below 30K. From 1/T_1T of ^{31}P and ^{139}La, quasi-two dimensional electronic structure is suggested, in which the FeP layer is more conductive than the LaO layer. In the superconducting (SC) state, although a clear Meissner signal was observed, 1/T_1T increases below T_c, in contrast to a decrease of 1/T_1T due to the opening of a SC gap, suggesting that novel low-energy spin dynamics develop in the SC state.