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Quantum Monte Carlo studies of soft Bosonic systems and Minimum Energy Pathways

Sebastiano Saccani

SDL, 2013

Abstract

In this thesis, we make use of Monte Carlo techniques to address two rather different subjects in condensed matter physics. The first study deals with the characterization of a relatively novel and elusive phase of matter, the so-called supersolid, in which crystalline order and dissipationless flow coexist. While supersolidity is a well studied phenomenology in lattice models, we will be working here in continuous space, where much fewer results are available. Specifically, we study a soft core Bosonic system, quantum analog of thoroughly studied classical models, which displays an unambiguous supersolid phenomenology. In this system such a behavior is not obtained through Bose Condensation of lattice defects, but rather it is mean field in character. By computer simulations we characterize many properties of the system: of these, the most prominent are the phase diagram of the system and its excitation spectrum. This study is loosely related to the ultracold atom experimental field, as it is speculated that interparticle potential pertaining to the same class of the one employed here may be realized in this context. After the recent (and apparently definitive) ruling out of supersolidity effects in ^4He, it seems fair to state that ultracold atoms are the most promising candidate for the observation of this phenomenology. In this section we employ our own implementation of the worm algorithm on the continuum. The second part of this thesis is instead related to electronic…

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