Specific Heat To Hc2: Evidence for Nodes or Deep Minima in the Superconducting Gap of Under- and Overdoped Ba(Fe1-xCox)2As2

Abstract

Low temperature specific heat, C, in magnetic fields up to Hc2 is reported for underdoped Ba(Fe0.955Co0.045)2As2 (Tc=8 K) and for three overdoped samples Ba(Fe1-xCox)2As2 (x=0.103, 0.13, and 0.15, Tc=17.2, 16.5, and 11.7 K respectively). Previous measurements of thermal conductivity (as a function of temperature and field) and penetration depth on comparable composition samples gave some disagreement as to whether there was fully gapped/nodal behavior in the under-/overdoped materials respectively. The present work shows that the measured behavior of the specific heat gamma (proportional to C/T as T->0, i. e. a measure of the electronic density of states at the Fermi energy) as a function of field approximately obeys gamma proportional to H**(0.5 +- 0.1), similar to the Volovik effect for nodal superconductors, for both the underdoped and the most overdoped Co samples. However, for the two overdoped compositions x=0.103 and 0.13, the low field (H < 10 T) data show a Volovik-like behavior of gamma proportional to H**(0.3-0.4), followed by an inflection point, followed at higher fields by gamma proportional to H**1. We argue that within the 2-band theory of superconductivity, an inflection point may occur if the interband coupling is dominant.

arXiv commentaccepted for publication in Physical Review B

References in corpus (18)

• Superconductivity in Iron Compounds
• Superconductivity at 22 K in Co-doped BaFe2As2 Crystals
• Nodal Structure of Unconventional Superconductors Probed by the Angle Resolved Thermal Transport Measurements
• Nodes in the gap structure of the iron-arsenide superconductor Ba(Fe_{1-x}Co_x)_2As_2 from c-axis heat transport measurements
• Doping dependence of heat transport in the iron-arsenide superconductor Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$: from isotropic to strongly $k$-dependent gap structure
• Superfluid density and specific heat within self-consistent scheme for two-band superconductor
• Properties of the superconducting state in a two-band model
• Local measurement of the penetration depth in the pnictide superconductor Ba(Fe${}_{0.95}$Co${}_{0.05}$)${}_2$As${}_2$
• Interband superconductivity: contrasts between BCS and Eliashberg theory
• Field dependence of the zero energy density of states around vortices in an anisotropic gap superconductor
• Volovik effect in the $\pm$s-wave state for the iron-based superconductors
• Spectrum of low energy excitations in the vortex state: comparison of Doppler shift method to quasiclassical approach
• Effect of annealing on the specific heat of Ba(Fe1-xCox)2As2
• Theory of thermal conductivity in extended-$s$ state superconductors: application to ferropnictides
• Volovik effect in a highly anisotropic multiband superconductor: experiment and theory
• Calorimetric Evidence for Nodes in the Overdoped Ba(Fe${}_{0.9}$Co${}_{0.1}$)${}_2$As${}_2$
• Evidence for line nodes in the energy gap of the overdoped Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$ from low-temperature specific heat measurements
• A Field-directional Specific Heat Study on the Gap Structure of Overdoped Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$

Cited by in corpus (11)

• Superconducting Properties of the $s^{\pm }$-wave state: Fe-based superconductors
• Lower critical field and SNS-Andreev spectroscopy of 122-arsenides: Evidence of nodeless superconducting gap
• Nodeless superconductivity in the presence of spin-density wave in pnictide superconductors: The case of BaFe${}_{2-x}$Ni${}_x$As${}_2$
• Specific Heat Discontinuity DeltaC vs Tc in Annealed Ba(Fe1-xCox)2As2
• Angular-dependent upper critical field of overdoped Ba(Fe${}_{1-x}$Ni${}_x$)${}_2$As${}_2$
• Evolution of London penetration depth with scattering in single crystals of K${}_{1-x}$Na${}_x$Fe${}_2$As${}_2$
• Nodal superconductivity in isovalently substituted SrFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$ pnictide superconductor at the optimal doping, $x=$0.35
• Unconventional bulk superconductivity in YFe${}_2$Ge${}_2$ single crystals
• Superconducting gap evolution in overdoped BaFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$ single crystals through nanocalorimetry
• Specific Heat vs Field of LiFe1-xCuxAs
• Anomalous Superconducting-Gap Structure of Slightly Overdoped Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$