Speakers: Romuald Lemański (Institute of Low Temperature and Structure Research Polish Academy of Sciences, Wrocław, Poland)
Place: Na Slovance, main lecture hall
Presented in English
Organisers:
Department of Condensed Matter Theory
Abstract:
We analyse the transformation from insulator to metal induced by thermal fluctuations within the Falicov-Kimball model. Using the Dynamic Mean Field Theory (DMFT) formalism on the Bethe lattice we find rigorously the temperature dependent Density of States (DOS) at half filling in the limit of high dimensions. At zero temperature (T=0) the system is ordered to form the checkerboard pattern and the DOS has the gap Δ at the Fermi level εF = 0, which is proportional to the interaction constant U. With an increase of T the DOS evolves in various ways that depend on U. For U > Ucr the gap persists and the system is always an insulator. However, if U < Ucr, two additional subbands develop inside the gap. They become wider with increasing T and at a certain U-dependent temperature TMI they merge at εF. defining a transition from insulator to metal. It appears, that TMI approaches the order-disorder phase transition temperature TO-DO when U is close to 0 or Ucr, but TMI is substantially lower than TO-DO for intermediate values of U. Moreover, we show analytically that TMI =0 at U = 2 < Ucr, hence we prove that a quantum critical point exists for the ordered metal at (T = 0, U = 2). Having calculated the temperature dependent DOS we study thermodynamic properties of the system. We show how the order parameter d and the gap Δ change with temperature and construct the phase diagram in T and U. We display regions of stability of four different phases: ordered insulator, ordered metal, disordered insulator and disordered metal (see Ref. [1]).
[1] R. Lemański and K. Ziegler, Phys Rev. B 89, 075104 (2014).
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