MICROSCOPIC CALCULATIONS OF QUANTUM PHASE TRANSITIONS IN FRUSTRATED MAGNETIC LATTICES

Abstract

It is nowadays acknowledged that the coupled cluster method (CCM) provides one of the most powerful and most widely used of all ab initio techniques of microscopic quantum many-body theory. It has been applied to a broad range of both finite and extended physical systems defined on a spatial continuum, where it has generally yielded numerical results which are among the most accurate available. This widespread success has spurred many recent applications to quantum systems defined on a lattice. We discuss here a typical example of a two-dimensional spin-half Heisenberg magnet with two kinds of competing nearest-neighbour bonds. We show how the CCM can successfully describe the influence of strong quantum fluctuations on the zero-temperature phases and their quantum phase transitions. The model shows how the CCM can successfully describe the effects of competition between magnetic bonds with and without the presence of frustration. The frustrated case is particulary important since many other methods, including quantum Monte Carlo simulations, typically fail in this regime.