title: Fractional Mott insulator-to-superfluid transition of Bose-Hubbard model in a trimerized Kagomé optical lattice.
abstract: By generalizing the traditional single-site strong coupling expansion approach to a cluster one, we study the zero-temperature phase diagram of bosonic atoms in a trimerized Kagomé optical lattice. Some new features are present in this system. Due to the strong intra-trimer hopping interaction, there will be a new Mott insulator (MI), which is by definition incompressible but with a fractional filling per trimer. This is different from the traditional MI, which has an integral filling and originates only from the repulsive interaction between particles. We investigate the MI-to-superfluid transition and the nature of the fractional MI by calculating the critical exponents of phase transitions and the low-lying energy excitation spectra of quasiparticles (quasihole). We will show how the low-energy properties of this system can be understood qualitatively as a Bose-Hubbard model in triangular lattice from the point of view of the cluster strong coupling expansion. We also discuss how our results are related to experiment by studying the Bragg spectroscopy.
authors.affiliation: Key Laboratory of Advanced Technologies of Materials (Ministry of Education of China). Superconductivity R&D Center (SRDC), Mail Stop 165#, Southwest Jiaotong University, Chengdu, Sichuan 610031, People's Republic of China. Institute of Advanced Studies, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.
authors.forename: Qi-Hui
authors.initials: QH
authors.lastname: Chen
authors.forename: Peng
authors.initials: P
authors.lastname: Li
authors.forename: Haibin
authors.initials: H
authors.lastname: Su