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Journal of Physical Studies 9(1), 52–65 (2005)
DOI: https://doi.org/10.30970/jps.09.52 THERMODYNAMIC PROPERTIES OF PSEUDOSPIN-ELECTRON MODEL IN THE GAUSSIAN FLUCTUATION APPROXIMATIONK. V. Tabunshchyk
Institute for Condensed Matter Physics of the
National Academy of Sciences of Ukraine, |
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We investigate the thermodynamics of phase transitions in pseudospin-electron model with strong coupling, and focus on the role of fluctuation effects in the vicinity of transitions. We analyze the behaviour of grand canonical potential, and find the mean value of physical quantities as well as root-mean-square fluctuations of an internal field within the generalized random phase approximation (GRPA), the Onyszkiewicz type approximation, and self-consistent gaussian fluctuation approximation. Within all of these approximations we obtain the possibility of first order phase transitions with a jump of pseudospin mean value and reconstruction of electron spectrum. The final results are presented in the form of phase diagrams in plane temperature-longitudinal field $T_{\rm c}-h$, and we find that the fluctuation effects cause quantitative and, in some special cases, qualitative changes on the phase diagrams near a critical point. We show that taking the fluctuations into account may also lead to narrowing the temperature range where modulated (chessboard) phase can be found.
PACS number(s): 63.20.Ry, 71.10.Fd, 77.80.Bh