Pseudogap of Superconducting correlation origin in iron-pnictide superconductor Ba0.6+{\delta}K0.4-{\delta}Fe2As2

TL;DR

This study identifies a pseudogap in an iron-pnictide superconductor, Ba0.6+δK0.4−δFe2As2, attributing it to superconducting correlations rather than magnetic origins, supported by optical conductivity measurements and theoretical modeling.

Contribution

It provides evidence that the pseudogap in this iron-pnictide is due to superconducting correlations, distinguished from magnetic effects, using optical data and preformed Cooper pair theory.

Findings

Pseudogap observed in optical conductivity above Tc up to 100 K.

Pseudogap attributed to superconducting correlations, not magnetic.

Theoretical model matches temperature evolution of optical data.

Abstract

Pseudogap (PG), a phenomenon of opening of gap like features above superconducting (SC) transition temperature (Tc), has been universally observed in the high-Tc cuprates (HTC) (1,2), some heavy fermion superconductors (3), and iron pnictides (4-7). Here, we report the observation of PG behavior in optical conductivity in an underdoped Ba0.6+{\delta}K0.4-{\delta}Fe2As2 (Tconset =36 K) single crystal far above Tc, up to 100 K (~ 3Tc). Unique scale separation in Ba0.6+{\delta}K0.4-{\delta}Fe2As2 compound - magnetic and SC correlation energy scales being widely separated - enabled us to establish that the PG structures observed in the range of 50 cm-1 - 150 cm-1 in optical conductivity is caused by the SC correlation and the magnetic correlation origin is ruled out. Theoretical calculations, based on the preformed Cooper pair model (8), provided an excellent description to the temperature evolution of the optical conductivity data from below to above Tc.