future events

Collective modes in a quantum solid

TYPECondensed Matter Seminar
Speaker:Daniel Podolsky
Location:Lidow Nathan Rosen (300)

We provide a theoretical explanation for the optical modes observed  in inelastic neutron scattering (INS) on the BCC solid phase of helium-4  [T. Markovich, E. Polturak, J. Bossy, and E. Farhi, Phys. Rev. Lett. 88, 195301 (2002)].  We argue that these excitations are amplitude (Higgs) modes associated with fluctuations of the crystal order parameter  within the unit cell. We present an analysis of the modes based on an effective Ginzburg-Landau model, classify them according to their symmetry properties, and compute their signature in INS experiments. In addition, we calculate the dynamical structure factor by means of an ab-intio quantum Monte Carlo simulation and find a finite frequency excitation at zero relative momentum.