Phonon softening in Lu(Pt1−xPdx)2In close to a zero-temperature structural instability

The structural transition in Lu(Pt${}_{1\ensuremath{-}x}$Pd${}_{x}$)${}_{2}$In attracts special interest since it can be tuned to zero temperature with the appearance of a superconducting dome around structural quantum criticality. The authors combined inelastic neutron and x-ray scattering measurements to study this structural transition. They determined the low-energy phonon dispersions and detected the relevant phonon branch becoming soft. While theoretical calculations broadly agree with the measured dispersion, a clear non-mean-field behavior is demonstrated at this phase transition, which might be connected with quantum criticality and the superconducting dome.