[{"type":"speech","title":"Soft-mode behavior in superconducting MgB\u2082-like ternary silicides MAlSi (M=Ca,Sr,Ba)","issued":{"date-parts":[["2006"]]},"author":[{"family":"Heid","given":"R."},{"family":"Bohnen","given":"K. P."},{"family":"Renker","given":"B."},{"family":"Adelmann","given":"P."},{"family":"Ernst","given":"D."},{"family":"Schober","given":"H."}],"note":"DPG Spring Meeting of the Divison Condensed Matter, 21st General Conf.of the Condensed Matter Division of the European Physical Society, Dresden, March 26-31, 2006 Verhandlungen der Deutschen Physikalischen Gesellschaft, R.6, B.41(2006) TT 18.6","abstract":"Low Temperature Physics\nSectional Programme Overview\nTT 18 Superconductivity: Borides, Borocarbides, Carbides, ...\nTime: Tuesday 15:00\u201318:30\nTT 18.1 Tue 15:00 HSZ 02\nThree-Dimensional MgB2 -Type Superconductivity in HoleDoped Diamond \u2014 \u2022Jens Kortus1 , Lilia Boeri2 , and Ole\nGermany \u2014 2 MPI FKF Stuttgart, Germany\nWe substantiate by numerical and analytical calculations that the recently discovered superconductivity in boron-doped diamond is caused\nby electron-phonon coupling of the same type as in MgB2 , albeit in\nthree dimensions. Using \ufb01rst-principles linear response methods based\non density functional theory we obtain the phonon dispersion and the\nelectron-phonon coupling strength as function of hole doping. As revealed by these calculations, holes at the top of the zone-centered, degenerate sigma-bonding valence-band couple strongly to the optical bondstretching phonon modes. This mechanism shows several very similar\naspects to the one which drives the superconductivity in MgB2 . However, the increase from two dimensions in MgB2 to three dimensions in\ndiamond reduces the phonon mode softening crucial for the high Tc of\n40 K in MgB2 . Even if diamond had the same bare coupling constant as\nMgB2 , which could be achieved with higher doping, Tc would be limited\nto only 25 K. Using the same theoretical methods we also investigate\nthe possibility of superconductivity in the isostructural and isoelectronic\nsemiconductors Si and Ge. Superconductivity above 1 K in Si (Ge) requires hole doping beyond 5% (10%).\n(2004)\nTT 18.2 Tue 15:15 HSZ 02\nSuperconductivity and electron phonon coupling in doped\nMgB2 compounds \u2014 \u2022Vivien Petzold1 and Helge Rosner2 \u2014\n1\nTU Dresden \u2014 2 MPI for Chemical Physics of Solids Dresden\nRecently, substitutions on the metallic site in MgB2 , e.g. Mg1\u2212x Scx B2\n[1], Mg1\u2212x (AlLi)x B2 [2] and Nb1\u2212x B2 [3] were investigated intensively.\nFor the achievable doping levels (x=0.12...0.27) in Mg1\u2212x Scx B2 , the compound shows only very small structural changes, allowing the separation\nof lattice and doping e\ufb00ects. On the other hand Mg1\u2212x (AlLi)x B2 is isoelectronical to MgB2 , but varies in lattice constants depending on x. In\norder to investigate the in\ufb02uence of the degree of substitution on the electronic properties, we present band structure calculations using di\ufb00erent\nlevels of approximation: rigid band and virtual crystal approach as well\nas supercell calculations and coherent potential approximation. We show\nthat the latter two approaches lead to consistent results with respect to\nlattice expansion and electronic properties (density of states, Fermi surfaces). We demonstrate that in the transition metal (T) diborides the\ndoping dependent changes in the electronic structure are strongly in\ufb02uenced by the sp2 (B)-d(T) hybridization. The in\ufb02uence of the doping on\nthe electron phonon coupling is discussed.\n[1] Agrestini et al. Phys. Rev. B 70 134514 (2004).\n[2] Monni et al. cond-mat 0506162 (2005).\n[3] Yamamoto et al. Physica C 383 (2002) 197-206.\nTT 18.3 Tue 15:30 HSZ 02\nDensity functional theory for superconductors: Applications to\nMgB2 and Pb \u2014 \u2022A. Floris1 , N. Lathiotakis1 , A. Sanna2 , C.\nFranchini2 , M. Marques3 , M. Lueders4 , G. Profeta5 , A. Continenza5 , S. Massidda2 , and E.K.U. Gross1 \u2014 1 Freie Universitaet\nBerlin, Arnimallee 14, D-14195 Berlin, Germany \u2014 2 INFM SLACS and\nDipartimento di Scienze Fisiche, Universita\u2019 degli Studi di Cagliari, Italy\n\u2014 3 Institut de Min\u00b4ralogie et de Physique des Milieux Condens\u00b4s, Unie\nversit\u00b4 Pierre et Marie Curie - Paris VI, France \u2014 4 Daresbury Laboe\nratory, Warrington WA4 4AD, United Kingdom \u2014 5 C.A.S.T.I. - INFM\nand Dipartimento di Fisica, Universita\u2019 degli studi dell\u2019Aquila, Italy\nPredicting the properties of superconductors is of both fundamental\nand technological importance. The discovery of superconductivity in\nMgB2 (Tc =39.5 K), with a clear presence of two gaps, has renewed the\ninterest in conventional superconductivity. Here we present two applications of a novel approach to superconductivity that allows one to calculate material-speci\ufb01c properties without using any adjustable parameters. Within this approach, we have obtained the critical temperature\nand the two gaps of MgB2 in good agreement with experiment, taking\ninto account the strong anisotropy of both the electron-phonon and the\nCoulomb interactions. Moreover, in a fully k-resolved formalism, we \ufb01nd\nRoom: HSZ 02\ntwo di\ufb00erent gaps also in Pb, and we relate this fact to the di\ufb00erence in\nstrength of the electron-phonon coupling associated with the two bands\ncrossing the Fermi level. This calculation shows how our formalism is\nable to capture, in absence of any ad-hoc model, the features of multigap superconductors.\nTT 18.4 Tue 15:45 HSZ 02\nSpeci\ufb01c heat of Mg(B1\u2212x Cx )2 : Two Superconducting Gaps \u2014\nWilliam E. Mickelson1 , and Alex Zettl1 \u2014 1 University of California, Berkeley, CA, USA \u2014 2 Max Planck Institute for Chemical Physics\nof Solids, Dresden, Germany\nWe present speci\ufb01c heat data of polycrystalline Mg(B1\u2212x Cx )2 with\nx = 0.1 and 0.2 from 1K to 35K in magnetic \ufb01elds up to 9T.\nRecently, MgB2 was identi\ufb01ed as a phonon-mediated two-gap superconductor with remarkably high transition temperature of 39K. The small\ngap and the large gap open at the same temperature due to interband coupling. Substituting carbon on the boron site has the e\ufb00ect of electron \ufb01lling and inducing disorder. The superconducting transition temperature\ndecreases monotonically from 39K for MgB2 to 20K for Mg(B0.8 C0.2 )2 .\nThe speci\ufb01c heat of both samples can be accurately \ufb01tted with two superconducting energy gaps using the extended \u03b1 model. The amplitudes\nof the gaps are found to be larger than the BCS value for the large gap\nand smaller than the BCS value for the small gap. However, it is observed that the size of both gaps decreases upon increasing the carbon\ncontent.\nThe evolution of the gap sizes, the normal-state Sommerfeld coe\ufb03cients,\nthe Debye temperatures and the critical \ufb01elds are compared to those of\nMgB2 .\nTT 18.5 Tue 16:00 HSZ 02\nSuperconducting properties of the 13 K rare earth carbide superconductor, La2 C3 \u2014 \u2022Jun Sung Kim, Reinhard K. Kremer,\nVolodymyr Babizhetskyy, Ove Jepsen, and Arndt Simon \u2014\nMPI-FKF, 70569 Stuttgart\nSuperconductivity in rare earth carbides has attracted interest again\nafter the recent discovery of the 18 K superconductor Y2 C3 .[1] We have\nsuccessfully synthesized the related La system, La2 C3 , and after a careful\ncontrol of the carbon content and the annealing procedures, optimized\nthe superconducting properties reaching at sharp transition temperature\nTc \u223c 13.2 K. The superconducting properties have been investigated by\nheat capacity measurements in magnetic \ufb01elds up to H= 9 T, resistivity\nand magnetization measurements up to H = 30 T. The characteristic\nspeci\ufb01c heat anomaly is compared to the predictions of the BCS and\nthe \u03b1 model, and a quantitative estimate of the electron-phonon coupling strength and the logarithmic average phonon frequency is made.\nFrom a detailed analysis including full potential electronic structure calculations based on the re\ufb01ned structure gained from the re\ufb01nement of\nlow-temperature neutron powder di\ufb00raction experiments, La2 C3 is found\nto be in the strong electron-phonon coupling regime. The upper critical\n\ufb01elds show a clear enhancement with respect to the Werthamer-HelfandHohenberg prediction and amount to \u223c 20 T at 0 K.\n[1] G. Amano, S. Akutagawa, T. Muranaka, Y. Zenitani, and J.\nAkimutsu, J. Phys. Soc. Jpn. 73, 530 (2004).\n\u2014 15 min. break \u2014\nTT 18.6 Tue 16:30 HSZ 02\nSoft-mode behavior in superconducting MgB2 -like ternary\nsilicides MAlSi (M=Ca,Sr,Ba) \u2014 \u2022R. Heid1 , K.-P. Bohnen1 ,\nB. Renker1 , P. Adelmann1 , D. Ernst1 , and H. Schober2\n2\nThe discovery of","kit-publication-id":"230063975"}]