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Springer eBooks

Consistent models of spin 0 and 1/2 extended particles scattering in external fields

S. Twareque Ali, Eduard Prugovečki

Published Apr 6, 2008• 1 citation
Publisher
DOI
10.1007/3-540-10023-7_114

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We consider the one-dimensional t-J model, which consists of spin-1/2 electrons on a lattice with nearest neighbor hopping t constrained by the excluded multiple occupancy of the lattice sites and spin-exchange J between neighboring sites. The model is integrable at the supersymmetric point, J=2t. We extend the model by introducing an impurity of arbitrary spin S that interacts with the electrons on the neighboring sites without destroying the integrability. The lattice model is defined by the scattering matrices via the quantum inverse scattering method. The interaction Hamiltonian between the impurity and the itinerant electrons is only explicitly constructed in the continuum limit. The discrete Bethe ansatz equations diagonalizing the model are derived and the solutions are classified according to the string hypothesis. The thermodynamic Bethe ansatz equations are derived and the impurity free energy is obtained for arbitrary bandfilling as a function of temperature and external magnetic field. The properties of the impurity depend on one coupling parameter. The impurity can localize up to one itinerant electron and has in general mixed valent properties. The integer valent low T small H fixed point of the impurity corresponds to an asymptotically free spin S, while if either T or H (or both) become large the impurity behaves like an asymptotically free spin (S+).
We investigate two-component boson systems consisting of atoms and binary bound molecules of the same atoms. We assume that a coherent superposition of atomic and molecular Bose?Einstein condensates is formed in a non-stationary state leading to oscillations between the two condensates. To facilitate the formulation, we first give analogies in neutrino oscillations applicable for two states of one particle. We then extend to many non-interacting particles in an external field treated in the mean-field approximation as for collective motion of finite systems. We then go beyond the mean field and provide a framework for interacting particles and correlated wavefunctions. The atom?molecule oscillation frequency is dominated by the molecular binding energy when the atom?atom scattering length is substantially smaller than the oscillator trap length. Comparable scattering lengths can completely change the oscillation frequency. The damping time of the oscillations decreases with atom number and scattering lengths, although a large increase can occur for special combinations of the different interactions.
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