Microscopic coexistence of antiferromagnetic order and superconductivity in Ba$_{0.77}$K$_{0.23}$Fe$_{2}$As$_{2}$

TL;DR

This study uses NMR to demonstrate that antiferromagnetic order and superconductivity coexist microscopically in underdoped Ba0.77K0.23Fe2As2, revealing an unusual superconducting state with coexisting magnetism.

Contribution

First direct NMR evidence showing microscopic coexistence of antiferromagnetism and superconductivity in this compound.

Findings

Antiferromagnetic order develops below 46 K.

Superconductivity appears below 16.5 K.

Magnetic order and superconductivity coexist at the microscopic level.

Abstract

We report ^{75}As nuclear magnetic resonance studies on an underdoped single-crystal Ba0.77K0.23Fe2As2 with Tc = 16.5 K. Below T_N = 46 K, the NMR peaks for H//c split and those for H //a shift to higher frequencies, which indicates that an internal magnetic field along the c axis develops below T_N. The spin-lattice relaxation rate 1/T_1 measured at the shifted peak with H//a, which experiences the internal field, shows a distinct decrease below Tc({\mu}_0H = 12 T) = 16 K, following a T^3 relation at low temperatures. Our results show unambiguously that antiferromagnetic order and superconductivity coexist microscopically. The unusual superconducting state with the coexisting magnetism is highlighted.