Suchergebnisse

A characteristic feature of the electronic structure of iron-based supercon-ductors is the shift of experimental electronic bands in comparison to the results of calculations. The temperature dependence of the band structure for FeSe can manifest the mechanism of such shifts, but different studies give opposite directions for these shifts in the centre of the Brillouin zone. In this paper, we report downward shift of both dxz and dyz bands in Z point within the temperature range 20160 K. Together with the results of evolution of the electronic structure in A point, such shifts should lead to a break of parity between electron and hole charge carriers that can be interpreted as an increase of electron-carrier density with increasing temperature. © 2018 G.V. Kurdyumov Institute for Metal Physics of N.A.S. of Ukraine. All rights reserved. ; This study was supported by the Ukrainian–German grant from the MES of Ukraine (Project M/20-2017) and RFBR grant No. 16-05-00938 supported crystal growth experiments. ; The work of D.A.Ch. was supported by the program 211 of the Russian Federation Government (agreement No. 02.A03.21.0006) and by the Russian Government Program of Competitive Growth of Kazan Federal University.

The electronic structure of SrPd2Ge2 single crystals is studied by angle-resolved photoemission spectroscopy (ARPES), scanning tunneling spectroscopy (STS), and band structure calculations within the local-density approximation (LDA). The STS measurements show a single s-wave superconducting energy gap (0) = 0.5 meV. The photon-energy dependence of the observed Fermi surface reveals a strongly three-dimensional character of the corresponding electronic bands. By comparing the experimentally measured and calculated Fermi velocities a renormalization factor of 0.95 is obtained, which is much smaller than typical values reported in Fe-based superconductors. We ascribe such an unusually low band renormalization to the different orbital character of the conduction electrons and, using ARPES and STS data, argue that SrPd2Ge2 is likely to be a conventional superconductor, which makes it clearly distinct from isostructural iron pnictide superconductors of the "122" family ; This work was supported by the DFG priority program SPP1458, Grants No. KN393/4, BO1912/2-1, and No. BO3537/1-1 (D.S.I. and J.T.P.); by the Slovak Research and Development Agency under Contract No. VVCE-0058-07, Slovak VEGA Grants No. 0148/10 and No. 1/0138/10, and the 7th FP MNT-ERA.Net II. ESO (T.S., P.S., J.G.R, and P.S.); by the Spanish MEC under projects Consolider Ingenio Molecular Nanoscience CSD2007-00010 and FIS2008-00454 (J.G.R.); and by the Korean government (MEST) Grants No. R15-2008-006-01002-0 and 2011-0028736 (N.H.S., B.K.C.)