Unconventional Bose–Einstein Condensations from Spin-Orbit Coupling
WU Cong-Jun1**, Ian Mondragon-Shem1, 2, ZHOU Xiang-Fa3
1Department of Physics, University of California, San Diego, CA 92093 2Instituto de Física, Universidad de Antioquia, AA 1226, Medellín, Colombia 3Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei 230026
Unconventional Bose–Einstein Condensations from Spin-Orbit Coupling
WU Cong-Jun1**, Ian Mondragon-Shem1, 2, ZHOU Xiang-Fa3
1Department of Physics, University of California, San Diego, CA 92093 2Instituto de Física, Universidad de Antioquia, AA 1226, Medellín, Colombia 3Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei 230026
摘要According to the "no-node" theorem, the many-body ground state wavefunctions of conventional Bose–Einstein condensations (BEC) are positive-definite, thus time-reversal symmetry cannot be spontaneously broken. We find that multi-component bosons with spin-orbit coupling provide an unconventional type of BECs beyond this paradigm. We focus on a subtle case of isotropic Rashba spin-orbit coupling and the spin-independent interaction. In the limit of the weak confining potential, the condensate wavefunctions are frustrated at the Hartree–Fock level due to the degeneracy of the Rashba ring. Quantum zero-point energy selects the spin-spiral type condensate through the "order-from-disorder" mechanism. In a strong harmonic confining trap, the condensate spontaneously generates a half-quantum vortex combined with the skyrmion type of spin texture. In both cases, time-reversal symmetry is spontaneously broken. These phenomena can be realized in both cold atom systems with artificial spin-orbit couplings generated from atom-laser interactions and exciton condensates in semi-conductor systems.
Abstract：According to the "no-node" theorem, the many-body ground state wavefunctions of conventional Bose–Einstein condensations (BEC) are positive-definite, thus time-reversal symmetry cannot be spontaneously broken. We find that multi-component bosons with spin-orbit coupling provide an unconventional type of BECs beyond this paradigm. We focus on a subtle case of isotropic Rashba spin-orbit coupling and the spin-independent interaction. In the limit of the weak confining potential, the condensate wavefunctions are frustrated at the Hartree–Fock level due to the degeneracy of the Rashba ring. Quantum zero-point energy selects the spin-spiral type condensate through the "order-from-disorder" mechanism. In a strong harmonic confining trap, the condensate spontaneously generates a half-quantum vortex combined with the skyrmion type of spin texture. In both cases, time-reversal symmetry is spontaneously broken. These phenomena can be realized in both cold atom systems with artificial spin-orbit couplings generated from atom-laser interactions and exciton condensates in semi-conductor systems.
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2011, Vol. 28 
