Mean field theory for the domain formation in a spin-1 condensate

Wenxian Zhang, D. L. Zhou, Long You

Qiang Zhao, Hongyan Liu

Wenxian Zhang, D. L. Zhou, M.-S. Chang +2 more

We interpret the recently observed spatial domain formation in spin-1 atomic condensates as a result of dynamical instability. Within the mean field theory, a homogeneous condensate is dynamically unstable (stable) for ferromagnetic (antiferromagnetic) atomic interactions. We find that this dynamical instability naturally leads to spontaneous domain formation as observed in several recent experiments for condensates with rather small numbers of atoms. For trapped condensates, our numerical simulations compare quantitatively to the experimental results, thus largely confirming the physical insight from our analysis of the homogeneous case.

Andrew J. Robertson, Hong Yuan Ling, David E. Grochowski

Bao Cheng-guang

The spin structures of small spin-1 condensates ( N ⩽ 1000) under a magnetic field B have been studied beyond the mean field theory. Instead of the spinors, the many body spin eigenstates have been obtained. We have defined and calculated the spin correlative probabilities to extract information from these eigenstates. The correlation coefficients and the fidelity susceptibility have also been calculated. Thereby, the details of the spin structures responding to the variation of B can be better understood. In particular, from the correlation coefficients, which are the ratio of the two-body probability to the product of two one-body probabilities, strong correlation domains of B are found. The emphasis is placed on the sensitivity of the condensates toward B . No phase transitions in spin structures are found. However, abrupt changes in the derivatives of observables (correlative probabilities) are found in some particular domains of B . In these domains, the condensates are highly sensitive to B . The effect of temperature is considered. The probabilities defined in the paper can work as a bridge to relate theories and experiments. Therefore, they can be used to discriminate various spin structures and refine the interactions.

Subhasree Pradhan, A. Taraphder

Exciton formation and condensation in a two band correlated model is studied using slave rotor mean field (SRMF) theory. In the SRMF theory, charge and spin degrees are treated as independent degrees of freedom. Using this, we capture the effective many body scales beyond conventional mean-field theory. While the formation of exciton is favoured by the hybridization, it is strongy influenced by the Coulomb repulsion between electrons in the two bands. Beyond a critical value of hybridization, there is complete coheherence among the electrons and holes signalling a condensation of excitons.