Exotic Phases and Excitations of Bosons in Optical Lattices: A Cluster Mean Field Study at Zero and Finite Temperatures

Malakar, Manali (2023) Exotic Phases and Excitations of Bosons in Optical Lattices: A Cluster Mean Field Study at Zero and Finite Temperatures. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Manali Malakar (18RS028)) 18RS028.pdf - Submitted Version Restricted to Repository staff only Download (39MB)

Abstract

Quantum simulation with ultracold atomic gases provides a unique opportunity to realize the strongly correlated novel phases of quantum many-body systems which are typically not observed in usual solid state materials. In this thesis, we study the formation of various exotic phases of lattice bosonic systems and examine their stability both under the effect of quantum as well as thermal fluctuations. We investigate the formation of different density structures in supersolids with co-existing superfluidity under the influence of long-range interactions as well as geometric frustration. Moreover, we discuss the formation of superfluid and supersolid phases of bosonic pairs due to the presence of a pair hopping term in such systems. Signature of various phases as well as their transitions can also be probed by studying the characteristic features of the low-lying excitations, which we calculate by using the time-dependent variational methods under the mean field framework, both at zero and finite temperatures. Furthermore, to understand such systems beyond the simple mean field analysis, we incorporate the inter-site correlations systematically by implementing the Cluster Mean Field (CMF) approach. Thermodynamic properties and the phase diagrams are also obtained by extending the CMF method at finite temperatures. We also analyze the melting process of supersolids, which reveals intriguing behavior due to the coexistence of two competing orders. Moreover, the CMF method at finite temperatures can also be used to study the formation and melting of supersolids due to the effect of lattice frustration. Finally, we discuss the results of our analyses and its relevance in the context of ongoing theoretical and experimental research in cold atomic systems.

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