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Anisotropic Superconducting Gap of Alkaline-earth Intercalated Graphites: $CaC_6$ and $SrC_6$  

Kim, Young-Wook (Department of Physics, Pohang University of Science and Technology)
Kremer, Reinhard K. (Max-Planck-Institut fuer Festkoerperforschung)
Kim, Jun-Sung (Department of Physics, Pohang University of Science and Technology)
Publication Information
Progress in Superconductivity / v.12, no.2, 2011 , pp. 104-109 More about this Journal
Abstract
We have investigated the anisotropy of the superconducting properties for $CaC_6$ and $SrC_6$ using upper critical fields ($H_{c2}$) and specific heat ($C_p$). From the upper critical fields of $CaC_6$ at different magnetic field orientations, H//c and H// ab, the anisotropy is found to be ~ 5 at low temperatures, much larger than that of $SrC_6$. These results are in contrast to the stronger anisotropy in the electronic structure for $SrC_6$ than for $CaC_6$ indicating a stronger anisotropy in the superconducting gap in $CaC_6$. The findings are confirmed by the temperature dependence of the superconducting specific heat below $T_c$ for $CaC_6$ and $SrC_6$, suggesting the important role of anisotropic electron-phonon coupling in superconducting intercalated graphites.
Keywords
intercalated graphite; upper critical fields; specific heat; anisotropic superconductivity;
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1 M. Thinkham, "Introduction to Superconductivity", 2ed, McGraw-Hill (1996).
2 G. Lamura, et al., "Experimental Evidence of s-Wave Superconductivity in Bulk $CaC_{6}$", Phys. Rev. Lett. 96, 107008 (2006).   DOI
3 N. Bergeal, et al., "Scanning Tunneling Spectroscopy on the Novel Superconductor $CaC_{6}$", Phys. Rev. Lett. 97, 077003 (2006).   DOI
4 A. Gauzzi et al., "Enhancement of Superconductivity and Evidence of Structural Instability in Intercalated Graphite $CaC_{6}$ under High Pressure", Phys. Rev. Lett. 98, 067002 (2007).   DOI
5 A. Sanna, et al., "Anisotropic gap of superconducting $CaC_{6}$: A first-principles density functional calculation", Phys. Rev. B 75, 020511(R) (2007).   DOI
6 J. S. Kim, et al., "Superconductivity in Heavy Alkaline-Earth Intercalated Graphites", Phys. Rev. Lett. 99, 027001 (2007).   DOI
7 R.S. Gonnelli, et al., "Evidence for gap anisotropy in $CaC_{6}$ from directional point-contact spectroscopy", Phys. Rev. Lett. 100, 207004 (2008).   DOI
8 K. Sugawara et al., "Fermi-surface-dependent superconducting gap in $C_{6}Ca$", Nat. Phys. 5, 40 (2009).   DOI   ScienceOn
9 N. R. Werthammer, E. Helfand, and P. C. Hohenberg, "Temperature and Purity Dependence of the Superconducting Critical Field, $H_{c2}$. III. Electron Spin and Spin-Orbit Effects", Phys. Rev. 147, 295 (1966).   DOI
10 T. E. Weller, et al., "Superconductivity in the intercalated graphite compounds$ C_{6}Yb $and $C_{6}Ca$" , Nat. Phys. 1, 39 (2005).   DOI   ScienceOn
11 G. Csanyi, et al., "The role of the interlayer state in the electronic structure of superconducting graphite intercalated compounds", Nat. Phys. 1, 42 (2005).   DOI   ScienceOn
12 N. Emery, et al., "Superconductivity of Bulk $CaC_{6}$", Phys. Rev. Lett. 95, 087003 (2005).   DOI
13 I. I. Mazin, "Intercalant-Driven Superconductivity in $YbC_{6}$ and $CaC_{6}$", Phys. Rev. Lett. 95, 227001 (2005).   DOI
14 M. Calandra and F. Mauri, "Theoretical Explanation of Superconductivity in $C_{6}Ca$", Phys. Rev. Lett. 95, 237002 (2005).   DOI
15 J. S. Kim et al., "Specific Heat of the Ca-Intercalated Graphite Superconductor $CaC_{6}$", Phys. Rev. Lett. 96, 217002 (2006).   DOI
16 J. S. Kim, et al., "Effect of pressure on superconducting Ca-intercalated graphite $CaC_{6}$", Phys. Rev. B. 74, 214513 (2006).   DOI
17 For a review, M. S. Dresselhaus and G. Dresselhaus, "Intercalation compounds of graphite", Adv. Phys. 51, 1 (2002).   DOI   ScienceOn
18 N. B. Hannay et al., "Superconductivity in Graphitic Compounds", Phys. Rev. Lett. 14, 225 (1965).   DOI