Microscopic Theory of a System of Interacting Bosons: A Unifying New Approach

摘要

This paper reports an entirely new approach to the microscopic understanding of the behavior of a system of interacting bosons such as liquid ~4He. It reveals that each particle in the system represents a (q,-q) pair (SMW pair) moving with a center of mass momentum K. An energetically weak effect, resulting from inter-particle attraction and the overlap of wave packets, locks these particles in phase (φ) space at Δφ = 2nπ (with n = 1,2,3,…) and leads them to acquire a kind of collective binding. The entire system below λ-point behaves like a single macroscopic molecule. The binding is identified as an energy gap between the superfluid and normal states of the system. The λ-transition, resulting from inter-particle quantum correlations, is the onset of an order-disorder of particles in their φ-space and their Bose Einstein condensation (BEC) in the ground state of the system defined by q = π/d and K = 0. The fractional density of condensed particles (n_(k=0)(T)) varies monotonically from n_(k=0)(T_λ) = 0 to n_(k=0) = 1.0. The λ-transition represents the occurrence of twin phenomena of broken gauge symmetry and phase coherence. In variance with the conventional belief, it is concluded that the system can not have p = 0 condensate. In addition to the well known modes of collective motions such as phonons, rotons, maxons, etc., the superfluid state also exhibits a new kind of quantum quasi-particle, omon, characterized by a phononlike wave of the oscillations of momentum coordinates of the particles. The theory explains the properties of He-II, including the origin of quantized vortices, critical velocities, logarithmic singularity of specific heat and related properties, etc., at the quantitative level. It conforms to the excluded volume condition, microscopic and macroscopic uncertainty, and vindicates the two fluid theory of Landau, an idea of macroscopic wave function envisaged by London, etc. As discussed elsewhere in this journal, the framework of this theory can also help in unifying the physics of widely different systems of interacting bosons and fermions.