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Seminars & Lectures

* TITLE

Unconventional quantum phase transitions of bosons in optical lattices: Anomalous hysteresis and quantum tricriticality

* SPEAKERS

Name	Affiliation	E-mail
Ippei Danshita	Yukawa Inst. For Theoretical Physics, Kyoto Univ.	dapei2005(at)gmail.com

* HOST(Applicant)

Name	Affiliation	E-mail
Gentaro Watanabe	APCTP	gentaro_watanabe(at)apctp.org

* DATE / TIME

2013-11-26, 16:00

* PLACE

503 Conference Room

* ABSTRACT

Systems of optical lattices loaded with ultracold gases have provided unique opportunities for the studies of quantum phase transitions (QPTs). Extraordinary controllability and cleanness of optical-lattice systems make it possible to theoretically predict and experimentally discover novel QPTs. In this talk, we consider the two specific systems to predict unconventional QPTs: a) dipolar bosons in triangular optical lattices and b) two-component bosons in hypercubic optical lattices.
In the former case, we apply the cluster-mean-field theory combined with cluster-size scaling (CMF+S) to the hardcore Bose-Hubbard model on a triangular lattice, and map out the ground-state phase diagram [1,2]. CMF+S allows us to access even the region where the hopping energy J is negative so that geometrical frustration forbids quantum Monte Carlo (QMC) simulations. We especially focus on unconventional hysteresis behaviors accompanying the first-order QPT between the superfluid and the solid with one third filling.
In the latter case, we use a QMC method to solve the two-component Bose-Hubbard model and obtain its ground-state phase diagram [3]. We show that the superfluid-insulator QPT can be of first order in contrast to the single-component case, and that there are associated tricritial points in the phase diagram. We find that the QPT through the tricritical points belongs to a universality class different from that for the standard vacuum-superfluid QPT.

[1] D. Yamamoto, I. Danshita, and C. A. R. Sa de Melo, Phys. Rev. A 85, 021601(R) (2012)
[2] D. Yamamoto, G. Marmorini, and I. Danshita, arXiv:1309.0086 (2013).
[3] Y. Kato, D. Yamamoto, and I. Danshita, arXiv:1311.2145 (2013).

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