From weak- to strong-coupling superconductivity in the AlB 2 -type solid solution SrGa 1- x Al x Ge with honeycomb layers

• Published in: Journal of physics. Condensed matter 2024-11, Vol.37 (4)
• Main Authors: Walicka, Dorota I, Blacque, Olivier, Klimczuk, Tomasz, von Rohr, Fabian O
• Format: Article
• Language: English
• ISSN: 1361-648X

We report on the structure and the superconducting properties of 9-electron 111 compounds with honeycomb layers, namely SrGaGe, SrAlGe, and the SrGa1-xAl Ge solid solution. By means of single-crystal x-ray diffraction we show that, on one hand, SrGaGe crystallizes into the centrosymmetric 6/ space group ( = 4.2555(2) Å, = 4.7288(2) Å) with statistical disorder in the [GaGe]62-honeycomb layers. On the other hand, we confirm that SrAlGe crystallizes in a non-centrosymmetric space group, namely 6¯ ( = 4.2942(1) Å, = 4.7200(2) Å) with fully ordered [AlGe]62-honeycomb layers. By using magnetization and specific heat measurements, we show that the superconducting properties of SrGaGe and SrAlGe differ significantly from each other. SrGaGe is a superconductor with a critical temperature ofTc= 2.6 K falling into the weak coupling limit, while SrAlGe has aTc= 6.7 K and can be classified in the strong coupling limit. By realizing the SrGa1-xAl Ge solid solution, we were able to investigate the transition between the different crystal structures as well as the evolution of the electronic properties. We show that the transition from the weak-to strong-coupling superconductivity in this system is likely associated with the disorder-to-order transition of the honeycomb layer, along with the loss of the inversion center in the crystal structure.