Article

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

• ##### F. Ronning
New Journal of Physics (Impact Factor: 3.67). 01/2010; DOI: 10.1088/1367-2630/12/2/023006
Source: arXiv

ABSTRACT 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. Comment: New Journal of Physics in press, 10 pages, 5 figures

0 Bookmarks
·
82 Views
• ##### Article: Intra-inter band pairing, order parameter symmetry in Fe-based superconductors : A model study
[Hide abstract]
ABSTRACT: In the quest of why there should be a single transition temperature in a multi-gapped system like Fe-based materials we use two band model for simplicity. The model comprises of spin density wave (SDW), orbital density wave (ODW) arising due to nested pieces of the electron and hole like Fermi surfaces; together with superconductivity of different pairing symmetries around electron and hole like Fermi surfaces. We show that either only intra or only inter band pairing is insufficient to describe some of the experimental results like large to small gap ratio, thermal behaviour of electronic specific heat jump etc. It is shown that the inter-band pairing is essential in Fe-based materials having multiple gaps to produce a single global $T_c$. Some of our results in this scenario, matches with the earlier published work \cite{two-band-prb}, differences with it and origin of difference between the two are also pointed out. Combined intra-inter band pairing mechanism produces the specific heat jump to superconducting transition temperature ratio proportional to square of the transition temperature, both in the electron and hole doped regime, for sign changing s$^{\pm}$ wave symmetry which takes the d+s pairing symmetry form. Our work thus demonstrates the importance of combined intra-inter band pairing irrespective of the pairing mechanism.
04/2014;
• Source
##### Article: Phase diagram and calorimetric properties of NaFe1-xCoxAs
[Hide abstract]
ABSTRACT: We measured the resistivity and magnetic susceptibility to map out the phase diagram of single crystalline NaFe1-xCoxAs. Replacement of Fe by Co suppresses both the structural and magnetic transitions; however, it also enhances the superconducting transition temperature (Tc) and superconducting component fraction. Magnetic susceptibility exhibits temperature-linear dependence in high temperatures up to 500 K for all the superconducting samples, but such behavior suddenly breaks down for the nonsuperconducting overdoped crystal, suggesting that the superconductivity is closely related to the T-linear dependence of susceptibility. Analysis on the superconducting-state specific heat of the optimally doped crystal provides strong evidence for a two-band s-wave order parameter with gap amplitudes of Δ1(0)/kBTc=1.78 and Δ2(0)/kBTc=3.11, being consistent with the nodeless gap symmetry revealed by angle-resolved photoemission spectroscopy experiment.
Physical review. B, Condensed matter 06/2012; · 3.66 Impact Factor
• Source
##### Article: Specific heat of Ca$_{0.32}$Na$_{0.68}$Fe$_2$As$_2$ single crystals: unconventional s$_\pm$ multi-band superconductivity with intermediate repulsive interband coupling and sizable attractive intraband couplings
[Hide abstract]
ABSTRACT: We report a low-temperature specific heat study of high-quality single crystals of the heavily hole doped superconductor Ca$_{0.32}$Na$_{0.68}$Fe$_2$As$_2$. This compound exhibits bulk superconductivity with a transition temperature $T_c \approx 34$\,K, which is evident from the magnetization, transport, and specific heat measurements. The zero field data manifests a significant electronic specific heat in the normal state with a Sommerfeld coefficient $\gamma \approx 53$ mJ/mol K$^{2}$. Using a multi-band Eliashberg analysis, we demonstrate that the dependence of the zero field specific heat in the superconducting state is well described by a three-band model with an unconventional s$_\pm$ pairing symmetry and gap magnitudes $\Delta_i$ of approximately 2.35, 7.48, and -7.50 meV. Our analysis indicates a non-negligible attractive intraband coupling,which contributes significantly to the relatively high value of $T_c$. The Fermi surface averaged repulsive and attractive coupling strengths are of comparable size and outside the strong coupling limit frequently adopted for describing high-$T_c$ iron pnictide superconductors. We further infer a total mass renormalization of the order of five, including the effects of correlations and electron-boson interactions.
11/2013; 89(13).