Electronic phase separation in the slightly underdoped iron pnictide superconductor Ba(1-x)K(x)Fe(2)As(2)

TL;DR

This study reveals that in slightly underdoped Ba(1-x)K(x)Fe(2)As(2), electronic phase separation occurs intrinsically, leading to coexistence of magnetic and superconducting regions on a nanometer scale, as shown by multiple experimental techniques.

Contribution

It provides direct evidence of intrinsic mesoscopic electronic phase separation in a specific iron pnictide superconductor using combined experimental methods.

Findings

Magnetic order appears below ~70 K.

Coexistence of magnetic and non-magnetic states below Tc.

Phase separation occurs on a scale of tens of nanometers.

Abstract

Here we present a combined study of the slightly underdoped novel pnictide superconductor Ba(1-x)K(x)Fe(2)As(2) by means of X-ray powder diffraction, neutron scattering, muon spin rotation (muSR), and magnetic force microscopy (MFM). Commensurate static magnetic order sets in below Tm ~ 70 K as inferred from the emergence of the magnetic (1 0 -3) reflection in the neutron scattering data and from the observation of damped oscillations in the zero-field-muSR asymmetry. Transverse-field muSR below Tc shows a coexistence of magnetically ordered and non-magnetic states, which is also confirmed by MFM imaging. We explain such coexistence by electronic phase separation into antiferromagnetic and superconducting/normal state regions on a lateral scale of several tens of nanometers. Our findings indicate that such mesoscopic phase separation can be considered an intrinsic property of some iron pnictide superconductors.