Novel quantum magnetism and Mott physics with Sp(2N) and SU(2N) symmetries - large spin ultra-cold fermions are different

Speaker: 
CongJun Wu (UCSD)
Event Date and Time: 
Mon, 2015-11-16 12:00 - 13:00
Location: 
Hennings 318
Local Contact: 
Fei ZHou
Intended Audience: 
Graduate
The large spin ultra-cold fermionic systems provide a whole new opportu-nity to investigate large symmetries, say, Sp(2N) and SU(2N), which are often studied in high energy physics. In our early works, we proved an exact and generic Sp(4), or, iso-morphically SO(5) symmetry in the hyperfine spin-3/2 systems without fine-tuning. This symmetry provides a unified framework to understand the competition between quantum magnetism, charge-density-wave, and superconductivity. For the recent experimental sys-tem of Yb atoms with the SU(6) symmetry, its quantum magnetic fluctuations are much stronger than that of spin-1/2 electrons in solids. We employ the determinant projector quantum Monte-Carlo method to investigate the ground state magnetic properties in the Mott insulating states in the half-filled 2D square lattice, which is free of the sign problem. Long-range Néel orders are found for at small and intermediate values of U, and exhibit non-monotonic behavior with respect to U, which first grow and then drop as U increases. This result is fundamentally different from the SU(2) case in which the Néel moments in-crease monotonically and saturate. A transition to the columnar dimer phase is found in the strong interaction regime. Ref. 1. D. Wang, Y. Li, Z. Cai, Z. Zhou, Y. Wang, C. Wu, Phys. Rev. Lett. 112, 156403 (2014). 2. Z. Cai, H. Hung, L. Wang, D. Zheng, C. Wu, Phys. Rev. Lett. 110, 220401 (2013). 3. C. Wu, Mod. Phys. Lett. B 20, 1707 (2006) (brief review). 4. C. Wu, Phys. Rev. Lett. 95, 266404 (2005). 5. C. Wu, J. P. Hu, and S. C. Zhang, Phys. Rev. Lett. 91, 186402 (2003).
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