Abstract:

We discuss supersolidity as a consequence of off-diagonal long-range order (ODLRO) in an interacting Bose system. For a class of variational wavefunctions used for solid helium, there is no ODLRO or supersolidity, even though there exist zero-point motion and exchange effect. In particular, we consider the presence of vacancies, and study the Hartree-Fock wave function built up from localized wave functions of single atoms, with nearest neighboring overlap. The zero-momentum particle number is expressed in terms of permanents of matrices. It is found that the condensate fraction is proportional to and of the same order of magnitude as that of the vacancy concentration, hence there is ODLRO when the number of vacancies is a finite fraction of the number of the lattice sites.
 
 
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