QFS2016 Book of Abstracts

Abstracts

P1.20 PRESSURE EFFECT ON THE EINSTEIN-LIKE PHONON MODE IN SUPERCONDUCTING YB 6 Orend´aˇc Mat´uˇs(1,2), Gab´ani Slavom´ır(1), Gaˇzo Emil(1), Prist´aˇs Gabriel(1), Flachbart Karol(1), Mori Takao(3), Wang Shao(4), Kamenev Konstantin(4) (1) Institute of Experimental Physics, SAS, Watsonova 47, 04001 Koˇsice, Slovakia (2) Institute of Physics, Faculty of Science, P.J. Safarik University, Park Angelinum 9, 04154 Koˇsice, Slovakia (3) Advanced Materials Laboratory, National Institute for Materials Science, Namiki 1-1, 305 0044 Tsukuba, Japan (4) Centre for Science at Extreme Conditions, University of Edinburgh, Mayfield road, EH9 3JZ Edinburgh, United Kingdom YB6 is known as a conventional type-II BCS superconductor, in which the strong coupling superconductivity with 2∆ /k B T c ≈ 4 . 1 is mediated by the Einstein-like phonon mode of Y atoms located at ~ ωE ≈ 9 meV. We have investigated the pressure effect on ωE by Raman scattering up to 14 GPa. A linear increase of this phonon mode energy with pressure yields a value of the isothermal Gr¨uneisen coefficient γT = − ∂lnωE/∂lnV = 3 . 85. Moreover, the pressure effect on the electron-phonon interaction calculated from the McMillan-Allen-Dynes expression for the superconducting transition temperature was determined. P1.21 PRESSURE DEPENDENCE OF THE UPPER AND THIRD CRITICAL FIELD IN SUPERCONDUCTING YB 6 Gab´ani Slavom´ır(1), Kuˇsn´ır J´an(2), Orend´aˇc Mat´uˇs(1,2), Gaˇzo Emil(1), Prist´aˇs Gabriel(1), Mori Takao(3), Flachbart Karol(1) 1) Institute of Experimental Physics, SAS, Watsonova 47, 04001 Koˇsice, Slovakia 2) Institute of Physics, Faculty of Science, P.J. Safarik University, Park Angelinum 9, 04154 Koˇsice, Slovakia 3) Advanced Materials Laboratory, National Institute for Materials Science, Namiki 1-1, 305 0044 Tsukuba, Japan We present measurements of the superconducting critical temperature T c , the upper critical field H c 2 and the third critical field H c 3 as a function of pressure in BCS superconductor YB 6 ( T c = 7 . 5 K , H c 2 (0) = 280 mT and H c 3 (0) = 450 mT ) up to 3 GPa. The magnetic susceptibility and magnetoresistivity measurement down to 2 K have shown a negative pressure effect on Tc as well as on H c 2 and H c 3 with slopes dlnT c /dp = 6 ÷ 7 %/GPa, dlnH c 2 /dp = − 14 %/GPa and dlnH c 3 /dp = − 11% /GPa , respectively. The positive pressure effect on the coherence length, dξ (0) /dp = 2 nm/GPa , together with the zero pressure effect on the magnetic penetration depth, dλ (0) /dp ≈ 0, imply that the Ginzburg-Landau parameter κ (0) = λ (0) /ξ (0) decreases markedly with pressure, dκ (0) /dp = − 0 . 32 /GPa , and moves YB 6 to the type-I direction at p c ≈ 10 GPa .

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