Konstantin N. Nesterov, Y. Alhassid
We study the mesoscopic fluctuations of thermodynamic observables in nano-sized metallic grains whose single-particle dynamics is chaotic and whose dimensionless Thouless conductance is large. Such a grain is modeled by the universal Hamiltonian describing the competition between exchange and pairing correlations. The exchange term is taken into account exactly by a spin projection method, and the pairing term is treated in the static-path approximation together with small-amplitude quantal fluctuations around each static fluctuation of the pairing field. Odd-even particle-number effects induced by pairing correlations are taken into account using a number-parity projection. We find that the exchange interaction shifts the number-parity effects in the heat capacity and spin susceptibility to lower temperatures, and may suppress the re-entrant behavior of the spin susceptibility for an odd number of electrons in the grain. If the exchange coupling constant is sufficiently large and the pairing gap is similar to or smaller than the single-particle mean level spacing, the number-parity effects are suppressed by mesoscopic fluctuations and the fluctuations of the spin susceptibility may be particularly large.
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http://arxiv.org/abs/1204.5738
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