Structural Phase Transition and Superconductivity in 2H-BaGaGe with Buckled Honeycomb Layers

Abstract

We report on the structural and superconducting properties of the intermetallic compound BaGaGe. We find that this material undergoes a structural second-order phase transition from the distorted AlB${}_2$-type structure (1H, $a$ = 4.3254(2) Å, $c$ = 5.1078(3) Å, P6/mmm) into the CaIn${}_2$-type structure (2H, $a$ = 4.3087(3) Å, $c$ = 10.2117(6) Å, P6${}_3$/mmc) at a transition temperature of $T_{\mathrm{S}}$ = 253 K. We find that the structural phase-transition corresponds to a coherent buckling of the honeycomb layers, which we can interpret as a disorder-to-order transition of the atoms located within this layer. We show that the 2H-BaGaGe phase becomes superconducting at a critical temperature of $T_{\mathrm{c}}$ = 2.1 K. The bulk nature of the superconductivity in 2H-BaGaGe is confirmed by means of specific heat measurements, where we determine a value of $\Delta C$/$\gamma T_{\mathrm{c}}$ = 1.59, which is close to the expected BCS value in the weak coupling limit.

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