Inorganic & Coordination Chemistry, Short talk
IC-025

Two-gap to single-gap superconducting transition in the Ca1-xSrxAlSi Solid Solution

D. I. Walicka1, Z. Guguchia2, J. Lago3, O. Blacque1, H. O. Jeschke1, K. Ma1, F. O. von Rohr1,4*
1Department of Chemistry, University of Zurich, CH-8057 Zurich, Switzerland, 2Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland, 3Departamento de Química Inorgánica, Universidad del País Vasco, UVP/EHU, E-48080, Bilbao, Spain, 4Department of Physics, University of Zurich, CH-8057 Zurich, Switzerland

The interest in compounds with AlB2 structure type raised significantly after the discovery of the superconductivity in the layered compound MgB2 with a critical temperature of Tc = 39 K [1].  CaAlSi and SrAlSi are ternary superconductors with the highest critical temperatures of Tc = 8 K, and 5 K, respectively, within this group [2]. They surprisingly differ in properties among each other, e.g. opposite pressure effect, although they have similar electronic and crystallographic structures [3].

 Within this work we have synthesized and characterized the continuous Ca1-xSrxAlSi solid solution. We present an improved structural model for the parent compound CaAlSi and we show an evidence for the structural instability in CaAlSi to enhance the superconductivity across the solid solution.  Furthermore, by means of muon-spin rotation experiments we prove that CaAlSi is a two-gap superconductor while SrAlSi is a single-gap superconductor, and that these two different electronic states are connected by a continuous transition.

[1] J. Nagamatsu, N. Nakagawa, T. Muranaka, Y. Zenitani, J. Akimitsu, Nature, 2001, 410, 63–64.
[2] M. J. Evans, Y. Wu,V.F Kranak, N. Newman, A. Reller, F.J. Garcia-Garcia, U. Häussermann, Physical Review B, 2009, 80, 064514.
[3] B. Lorenz, J. Cmaidalka, R.L. Meng, C.W. Chu, Physical Review B, 2003, 68(1), 014512.