Crystal structure and phonon softening in Ca3Ir4Sn13

Abstract

We investigated the crystal structure and lattice excitations of the ternary intermetallic stannide Ca3Ir4Sn13 using neutron and x-ray scattering techniques. For T > T* ~ 38 K the x-ray diffraction data can be satisfactorily refined using the space group Pm-3n. Below T* the crystal structure is modulated with a propagation vector of q = (1/2, 1/2, 0). This may arise from a merohedral twinning in which three tetragonal domains overlap to mimic a higher symmetry, or from a doubling of the cubic unit cell. Neutron diffraction and neutron spectroscopy results show that the structural transition at T* is of a second-order, and that it is well described by mean-field theory. Inelastic neutron scattering data point towards a displacive structural transition at T* arising from the softening of a low-energy phonon mode with an energy gap of Delta(120 K) = 1.05 meV. Using density functional theory the soft phonon mode is identified as a 'breathing' mode of the Sn12 icosahedra and is consistent with the thermal ellipsoids of the Sn2 atoms found by single crystal diffraction data.

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• Ca${}_3$Ir${}_4$Sn${}_{13}$: A weakly correlated nodeless superconductor
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• Microscopic studies of the normal and superconducting state of Ca3Ir4Sn13
• Superconducting and magnetic properties of Sr3Ir4Sn13
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• A neutron scattering study of the mixed state of Yb${}_3$Rh${}_4$Sn${}_{13}$

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• Strong enhancement of conventional superconductivity near a quantum critical point of (Ca,Sr)_3Ir_4Sn_13
• Evidence of a structural quantum critical point in (Ca${}_x$Sr${}_{1-x}$)${}_3$Rh${}_4$Sn${}_{13}$ from a lattice dynamics study
• Second-order Structural Transition in Superconductor La${}_3$Co${}_4$Sn${}_{13}$
• Soft phonon modes in the vicinity of the structural quantum critical point
• Possible unconventional pairing in $(\text{Ca,Sr}{)}_3(\text{Ir,Rh}{)}_4{\text{Sn}}_{13}$ superconductors revealed by controlling disorder
• The effective increase in atomic scale disorder by doping and superconductivity in Ca${}_3$Rh${}_4$Sn${}_{13}$
• Optical spectroscopy study of charge density wave order in Sr${}_3$Rh${}_4$Sn${}_{13}$ and (Sr${}_{0.5}$Ca${}_{0.5}$)${}_3$Rh${}_4$Sn${}_{13}$
• Pressure effects on the structural and superconducting transitions in La3Co4Sn13
• Structural phase transition, precursory electronic anomaly and strong-coupling superconductivity in quasi-skutterudite (Sr${}_{1-x}$Ca${}_x$)${}_3$Ir${}_4$Sn${}_{13}$ and Ca${}_3$Rh${}_4$Sn${}_{13}$
• Unveiling charge density wave quantum phase transitions by x-ray diffraction
• Experimental Determination of the Fermi Surface of Sr3Ir4Sn13
• Possible quantum fluctuations in the vicinity of the quantum critical point of $(\mathbf{Sr},\mathbf{Ca}{)}_3\mathbf{I}{\mathbf{r}}_4\mathbf{S}{\mathbf{n}}_{13}$ revealed by high-energy X-ray diffraction study
• Robust superconductivity and the suppression of charge-density wave in ${\text{Ca}}_3({\text{Ir}}_{1-x}{\text{Rh}}_x{)}_4{\text{Sn}}_{13}$ single crystals at ambient pressure
• Magnetostructural Coupling at the Néel point in YNiO3 Single Crystals