Condensed-Matter Physics & Materials Science Seminar

"Unconventional multi-band feature and pairing symmetry in Ba122 system superconductors as revealed by optical spectroscopy"

Presented by Yaomin Dai, Chinese Academy of Sciences, China

Thursday, January 5, 2012, 1:30 pm — Small Seminar Room, Bldg. 510

The newly discovered iron-based superconductors break a new path to the mechanism of high temperature superconductivity besides the copper oxide superconductors. A crucial issue for this new family of superconductors is the symmetry of the electron pairs, which is directly related to the mechanism of superconductivity.

We investigated the optical response of the hole [Ba1-xKxFe2As2] and electron [Ba(Fe1-xCox)2As2] doped Ba122 system iron-based superconductors. For the optimally doped Ba1-xKxFe2As2 (x = 0.4) sample, the normal state optical response reveals two electronic subsystems which exhibit strikingly different temperature dependence. Below Tc, the optical conductivity vanishes below an absorption edge, and no residual conductivity appears at low frequencies in the superconducting state, strongly indicating a superconducting gap with s-wave symmetry. However, for the optimally doped Ba(Fe1-xCox)2As2 (x = 0.08) sample, large residual optical conductivity is observed at low frequencies in the superconducting state, implying the existence of unpaired quasiparticles. This low frequency optical response does not favor the s-wave pairing symmetry. The remarkable difference in low frequency optical response between the K and Co doped samples, combined with the pair-breaking mechanism in an s± gap, provides strong evidence for an s± pairing symmetry in Ba122 system iron-based superconductors.

Hosted by: Christopher Homes

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