Superfluid density of the ±s-wave state for the iron-based superconductors

Yunkyu Bang

doi:10.1209/0295-5075/86/47001

All issues

Volume 86 / No 4 (May 2009)

EPL, 86 4 (2009) 47001

Abstract

Issue		EPL Volume 86, Number 4, May 2009


Article Number		47001
Number of page(s)		6
Section		Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
DOI		https://doi.org/10.1209/0295-5075/86/47001
Published online		26 May 2009

EPL, 86 (2009) 47001

Superfluid density of the ±s-wave state for the iron-based superconductors

Yunkyu Bang

Department of Physics, Chonnam National University - Kwangju 500-757, Korea and Asia Pacific Center for Theoretical Physics - Pohang 790-784, Korea

Corresponding author: ykbang@jnu.ac.kr

Received: 14 April 2009
Accepted: 29 April 2009

Abstract

We study the superfluid density of the ±s-wave state of the minimal two-band model for the Fe-based superconductors and its evolution with impurity concentration. We show that the impurity scattering of the strong-coupling limit induces the self-energy of a generic form ${\rm Im}\Sigma _{imp}(\omega )\approx i\gamma +i\beta \omega$ beyond a critical impurity concentration $\Gamma _{imp} > \Gamma _{crit}$ . This form of ${\rm Im}\Sigma _{imp}(\omega)$ causes the temperature dependence of the superfluid density $[\rho _{s}(T)-\rho _{s}(0)]\approx -\gamma T^{2}-\beta T^{3}$ . Combined with the full gap behavior of $\rho _{s}(T)$ for lower impurity concentration $\Gamma _{imp} < \Gamma _{crit}$ , the ±s-wave state produces a continuous evolution of $\Delta \lambda (T)$ : exponentially flat $\rightarrow T^{3}\rightarrow T^{2}$ with increasing impurity concentration that is consistent with the measurements of the Fe pnictide superconductors such as M-1111 (M = La, Nd, Sm, Pr) and Ba-122 with various dopings, except LaFePO which shows $\Delta \lambda (T)\propto T^{1.2}$ at low temperatures by a recent experiment. Our results also demonstrate that the density of states (DOS) measured by thermodynamic properties and the DOS measured by transport properties can in general be different.

PACS: 74.20.-z – Theories and models of superconducting state / 74.20.Rp – Pairing symmetries (other than s-wave) / 74.25.Nf – Response to electromagnetic fields (nuclear magnetic resonance, surface impedance, etc.)

© EPLA, 2009

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