Gapless metallic charge-density-wave phase driven by strong electron correlations

Abstract

We analyze 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 $\Delta$ at the Fermi level ${\epsilon }_F=0$, which is proportional to the interaction constant $U$. With an increase of $T$ the $DOS$ evolves in various ways that depend on $U$. For $U>U_{cr}$ the gap persists for any $T$ (then $\Delta >0$), so the system is always an insulator. However, if $U<U_{cr}$, two additional subbands develop inside the gap. They become wider with increasing $T$ and at a certain $U$-dependent temperature $T_{MI}$ they join with each other at ${\epsilon }_F$. Since above $T_{MI}$ the $DOS$ is positive at ${\epsilon }_F$, we interpret $T_{MI}$ as the transformation temperature from insulator to metal. It appears, that $T_{MI}$ approaches the order-disorder phase transition temperature $T_{O-DO}$ when $U$ is close to 0 or $U_{cr}$, but $T_{MI}$ is substantially lower than $T_{O-DO}$ for intermediate values of $U$. Having calculated the temperature dependent $DOS$ we study thermodynamic properties of the system starting from its free energy $F$. Then we find how the order parameter $d$ and the gap $\Delta$ change with $T$ and we construct the phase diagram in the variables $T$ and $U$, where we display regions of stability of four different phases: ordered insulator, ordered metal, disordered insulator and disordered metal. Finally, we use a low temperature expansion to demonstrate the existence of a nonzero DOS at a characteristic value of U on a general bipartite lattice.

19 pages, 9 figures; submitted to Physical Review B

References in corpus (4)

• Competition between Anderson localization and antiferromagnetism in correlated lattice fermion systems with disorder
• Quantum phases in mixtures of fermionic atoms
• Optical and dc transport properties of a strongly correlated charge density wave system: exact solution in the ordered phase of the spinless Falicov-Kimball model with dynamical mean-field theory
• Spectral properties in the charge density wave phase of the half-filled Falicov-Kimball Model

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