We have studied the ground state and excited state properties of solid He-4 on the basis of the variational shadow wave function technique (SWF), which allows for relaxation and delocalisation of vacancies. We have found that a finite concentration of vacancies, if present, induces Bose-Einstein condensation (BEC) of the atoms at density close to the T = 0 K melting where vacancies are delocalised. No BEC is present in a perfect crystal or in a defected solid at higher densities. We have extended this technique to study longitudinal phonons in solid He-4 and to study the vacancy excitation at a finite momentum; we have been able to compute for the first time the vacancy excitation spectrum in solid He-4 at density close to melting. Our results give a band width of about 8 K.
|Titolo:||Bose-Einstein condensation and excitations in solid He-4 with vacancies|
GALLI, DAVIDE EMILIO (Primo)
|Settore Scientifico Disciplinare:||Settore FIS/03 - Fisica della Materia|
|Data di pubblicazione:||2003|
|Digital Object Identifier (DOI):||10.1142/S0217979203020387|
|Appare nelle tipologie:||01 - Articolo su periodico|