Drude and superfluid weights in extended systems: The role of discontinuities and δ-peaks in the oneand two-body momentum densities
Please cite this item using this persistent URLhttp://hdl.handle.net/11693/21608
Journal of the Physical Society of Japan
- Research Paper 
The question of conductivity is revisited. Using the total momentum shift operator to construct the perturbed many-body Hamiltonian and ground state wave function the second derivative of the ground state energy with respect to the perturbing field is expressed in terms of the one and two-body momentum densities. The distinction between the adiabatic and envelope function derivatives, hence that between the Drude and superfluid weights, can be introduced in a straightforward manner. It is shown that a discontinuity in the momentum density leads to a contribution to the Drude weight, but not the superfluid weight, however a δ-function contribution in the two-body momentum density (such as in the BCS wave-funtion) contributes to both quantities. The connection between the discontinuity in the momentum density and localization is also demonstrated. © 2012 The Physical Society of Japan.