Second-order Structural Transition in Superconductor La${}_3$Co${}_4$Sn${}_{13}$

Abstract

The quasi-skutterudite superconductor La${}_3$Co${}_4$Sn${}_{13}$ undergoes a phase transition at $T^{\ast }=152$ K. By measuring the temperature dependence of heat capacity, electrical resistivity, and the superlattice reflection intensity using X-ray, we explore the character of the phase transition at $T^{\ast }$. Our lattice dynamic calculations found imaginary phonon frequencies around the $\mathbf{M}$ point, when the high temperature structure is used in the calculations, indicating that the structure is unstable at the zero temperature limit. The combined experimental and computational results establish that $T^{\ast }$ is associated with a second-order structural transition with $\mathbf{q}$=(0.5, 0.5, 0) (or the $\mathbf{M}$ point). Further electronic bandstructure calculations reveal Fermi surface sheets with low curvature segments, which allow us to draw qualitative comparison with both Sr${}_3$Ir${}_4$Sn${}_{13}$ and Sr${}_3$Rh${}_4$Sn${}_{13}$ in which similar physics has been discussed recently.

6 pages, 4 figures, accepted for publication in Phys. Rev. B (Rapid Com)