Gap structure in the electron-doped Iron-Arsenide Superconductor Ba(Fe0.92Co0.08)2As2: low-temperature specific heat study

New Journal of Physics (Impact Factor: 3.56). 01/2010; 12(2). DOI: 10.1088/1367-2630/12/2/023006
Source: arXiv


We report the field and temperature dependence of the low-temperature
specific heat down to 400 mK and in magnetic fields up to 9 T of the
electron-doped Ba(Fe0.92Co0.08)2As2 superconductor. Using the phonon specific
heat obtained from pure BaFe2As2 we find the normal state Sommerfeld
coefficient to be 18 mJ/mol.K^2 and a condensation energy of 1.27 J/mol. The
temperature dependence of the electronic specific heat clearly indicate the
presence of the low-energy excitations in the system. The magnetic field
variation of field-induced specific heat cannot be described by single clean s-
or d-wave models. Rather, the data require an anisotropic gap scenario which
may or may not have nodes. We discuss the implications of these results.

Download full-text


Available from: Krzysztof Gofryk,
18 Reads
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report a doping, magnetic field, and low-temperature-dependent study of the specific heat of the iron-arsenide Ba(Fe1-xCox)2As2 at underdoped (x=0.045) , optimal-doped (x=0.08) and overdoped ( x=0.103 and 0.105) regimes. By subtracting the lattice specific heat the temperature and magnetic field dependence of the electronic specific heat has been studied. The temperature and field dependencies of the superconducting part of Cp exhibit similar behavior for all doping concentrations. The temperature variation in the electronic specific heat as well as its field dependence cannot be described by a single isotropic s -wave gap, pointing to a complex gap structure in the system. The lack of doping dependence indicates that the gap structure does not change significantly as a function of doping. We also observe a significant residual linear term of unknown origin in the specific heat of Ba(Fe1-xCox)2As2 which suggests that inhomogeneity may be an important factor in Co-doped BaFe2As2 .
    Physical Review B 05/2010; 81(18). DOI:10.1103/PhysRevB.81.184518 · 3.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report on the effect of annealing on the temperature and field dependencies of the low temperature specific heat of the electron-doped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ for under-(x = 0.045), optimal- (x = 0.08) and over-doped (x = 0.105 and 0.14) regimes. We observed that annealing significantly improves some superconducting characteristics in Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$. It considerably increases $T_{c}$, decreases $\gamma_{0}$ in the superconducting state and suppresses the Schottky-like contribution at very low temperatures. The improved sample quality allows for a better identification of the superconducting gap structure of these materials. We examine the effects of doping and annealing within a self-consistent framework for an extended s-wave pairing scenario. At optimal doping our data indicates the sample is fully gapped, while for both under and overdoped samples significant low-energy excitations possibly consistent with a nodal structure remain. The difference of sample quality offers a natural explanation for the variation in low temperature power laws observed by many techniques.
    Physical review. B, Condensed matter 09/2010; 83(6). DOI:10.1103/PhysRevB.83.064513 · 3.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The three-dimensional band structure and superconducting gap of Ba0.6K0.4Fe2As2 are studied with angle-resolved photoemission spectroscopy. In contrast with previous results, we have identified three holelike Fermi surface sheets near the zone center with sizable out-of-plane or kz dispersion. The superconducting gap on certain Fermi surface sheets shows significant kz dependence. Moreover, the superconducting gap sizes are different at the same Fermi momentum for two bands with different spatial symmetries (one odd, one even). Our results further reveal the three-dimensional and orbital-dependent structure of the superconducting gap in iron pnictides, which facilitates the understanding of momentum-integrated measurements and provides a distinct test for theories.
    Physical Review Letters 09/2010; 105(11):117003. DOI:10.1103/PhysRevLett.105.117003 · 7.51 Impact Factor
Show more