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37

Sep 20, 2013
09/13

by
N. K. Kuzmenko; V. M. Mikhajlov

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A practical version of the polynomial canonical formalism is developed for normal mesoscopic systems consisting of N independent electrons. Drastic simplification of calculations is attained by means of proper ordering excited states of the system. In consequence the exact canonical partition function can be represented as a series in which the first term corresponds to the ground state whereas successive groups of terms belong to many particle-hole excitations (one particle-hole two...

Source: http://arxiv.org/abs/cond-mat/0404299v1

63
63

Sep 18, 2013
09/13

by
N. K. Kuzmenko; V. M. Mikhajlov

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Oscillating behaviour of the susceptibility and heat capacity is considered for normal and superconducting mesoscopic systems (nanoclusters and quantum dots). It is proved that at low temperature an increasing magnetic field applied to a mesoscopic system generates local extrema of the susceptibility and heat capacity. A maximum for the susceptibility and a minimum for heat capacity simultaneously arise in those points of the field where crossings of quantum levels of the normal and...

Source: http://arxiv.org/abs/cond-mat/0401468v1

32
32

Sep 22, 2013
09/13

by
N. K. Kuzmenko; V. M. Mikhajlov

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The heat capacity (C) of a mesoscopic nonsuperconducting fermion system treated as a canonical ensemble of independent particles is studied in a wide range of particle numbers and temperatures which vary from values close to zero up to the Fermi energy. The temperature evolution of C is naturally divided into four stages. On the first one the heat capacity exponentially increases with temperature and at a resonance temperature reaches either a local maximum or an irregularity in its growth....

Source: http://arxiv.org/abs/0811.2078v1

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39

Sep 22, 2013
09/13

by
N. K. Kuzmenko; V. M. Mikhajlov

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Temperature variations of the heat capacity (C) are studied in a low temperature regime for 2D-, and 3D-systems with N~100-10000 treated as a canonical ensemble of N-noninteracting fermions. The analysis of C is performed by introducing function q, the spectral distribution of C, that gives the contribution of each single-particle state to C. This function has two peaks divided by the energy interval ~(2-5)T. If at some temperature Tres there takes place a resonance i.e. the positions of these...

Source: http://arxiv.org/abs/0811.4771v1

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29

Sep 18, 2013
09/13

by
N. K. Kuzmenko; V. M. Mikhajlov

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The theoretical investigation of the cluster de Haas - van Alphen (dHvA) oscillations in three-dimensional systems performed for the first time. Applying a three-dimensional oscillator model to systems with electron numbers $10 < N \leq 10^5$ we predict distinctive size effects: the dHvA oscillations can be observed only within a certain temperature range determined by $N$; the lower size limit for $N$ is $\approx 20$; the amount of the dHvA oscillations is reduced with decreasing $N$ which...

Source: http://arxiv.org/abs/cond-mat/0401652v1

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34

Sep 22, 2013
09/13

by
N. K. Kuzmenko; V. M. Mikhajlov; S. Frauendorf

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Paircorrelations and the magnetic susceptibility of electrons in a spherical cavity are studied both for grand canonical and the canonical ensemble. The coupling constant of the $BCS$ Hamiltonian is adjusted to experimental values of the gap parameter. The gap parameter is found to increase for small grains as a consequence of the pronounced shell structure in the spectrum of the spherical cavity. The sharp phase transition at $T_c$ is smeared out for the canonical ensemble. The strong...

Source: http://arxiv.org/abs/cond-mat/9807011v2

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45

Sep 18, 2013
09/13

by
N. K. Kuzmenko; V. M. Mikhajlov; S. Frauendorf

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The response of $nm$-size spherical superconducting clusters to a magnetic field is studied for the canonical ensemble of electrons in a single degenerate shell. For temperatures close to zero, the discreteness of the electronic states causes a step like destruction of the pair correlations with increasing field strength, which shows up as peaks in the susceptibility and heat capacity. At higher temperatures the transition becomes smoothed out and extends to field strengths where the pair...

Source: http://arxiv.org/abs/cond-mat/0002030v1

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34

Sep 20, 2013
09/13

by
S. Frauendorf; N. K. Kuzmenko; V. M. Mikhajlov; J. Sheikh

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The pair correlations in mesoscopic systems such as $nm$-size superconducting clusters and nuclei are studied at finite temperature for the canonical ensemble of fermions in model spaces with a fixed particle number: i) a degenerate spherical shell (strong coupling limit), ii) an equidistantly spaced deformed shell (weak coupling limit). It is shown that after the destruction of the pair correlations at T=0 by a strong magnetic field or rapid rotation, heating can bring them back. This...

Source: http://arxiv.org/abs/physics/0301036v1

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49

Sep 24, 2013
09/13

by
A. D. Efimov; A. A. Pasternak; D. N. Doinikov; V. M. Mikhajlov; J. Srebrny

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Interpretation of the B(E2) values at energies higher the first backbending indicates that the maximum boson of IBM has to increase with energy and spin.

Source: http://arxiv.org/abs/nucl-th/0103074v1

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33

Sep 21, 2013
09/13

by
A. A. Pasternak; A. D. Efimov; E. O. Podsvirova; V. M. Mikhajlov; J. Srebrny; T. Morek; Ch. Droste; Y. Sasaki; M. Oshima; S. Juutinen; G. B. Hagemann

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Lifetimes of the yrast states in 120Xe and ground state band below and above band crossing in 118Te have been measured by DSAM in the 111Cd(12C,3n) reaction and by DSAM and RDM in the 109Ag(13C,p3n) reaction, respectively. The results are compared with E2 transition probabilities in 119I and 128Ba. The experimental data are compared with calculation done in the framework of the IBM1 model in the O(6) and SU(5) limits.

Source: http://arxiv.org/abs/nucl-ex/0104008v1