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arXiv:cond-mat/0512702 · Physical Review B

Insulator-metal-insulator transition and selective spectral-weight transfer in a disordered strongly correlated system

P. Lombardo, R. Hayn, G. I. Japaridze

Published Aug 28, 2006• 27 citations
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Abstract

We investigate the metal-insulator transitions at finite temperature for the Hubbard model with diagonal alloy disorder. We solve the dynamical mean-field-theory equations with the noncrossing approximation and we use the coherent potential approximation to handle disorder. The excitation spectrum is given for various correlation strength $U$ and disorder. Two successive metal-insulator transitions are observed at integer-filling values as $U$ is increased. An important selective transfer of spectral weight arises upon doping. The strong influence of the temperature on the low-energy dynamics is studied in detail.

DOI
10.1103/physrevb.74.085116

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We derive the disorder vs doping phase diagram of the doped Hubbard model via dynamical mean-field theory combined with typical medium theory, which allows the description of both Mott (correlation driven) and Anderson (disorder driven) metal-insulator transitions. We observe a transition from a metal to an Anderson-Mott insulator for increasing disorder strength at all interactions. In the weak correlation regime and rather small doping, the Anderson-Mott insulator displays properties which are similar to the ones found at half filling. In particular, this phase is characterized by the presence of empty sites. If we further increase either the doping or the correlation, however, an Anderson-Mott phase of a different kind arises for sharply weaker disorder strength. This phase occupies the largest part of the phase diagram in the strong-correlation regime and is characterized by the absence of the empty sites.
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The tight-binding diagonally disordered Anderson model with on-site Coulomb interaction is solved in the mean-field hopping approach. Phase diagrams of the metal-insulator transition are obtained from the free energy for the half-filled band and the binary-alloy distribution. For attractive interaction (U<0), the Coulomb term gives additional localizing effect and for some values of the microscopic parameters the temperature induced two transitions (insulator to metal to insulator). For U>0 two different types of behavior are distinguished. For small disorder (W\ensuremath{\le}U/2), the metallic phase can be induced by disorder, while for large W, the disorder always destroys the phase of extended states.
Disordered Hubbard model in d=∞d=\inftyd=∞
We investigate the effects of static, diagonal disorder in the d=∞d=\inftyd=∞ Hubbard model by treating the dynamical effects of local Hubbard correlations and disorder on an equal footing. This is achieved by a proper combination of the iterated perturbation theory and the coherent potential approximation. Within the paramagnetic phase, we find that the renormalized Fermi liquid metal phase of the pure Hubbard model is stable against disorder for small disorder strengths. With increasing disorder, strong resonant scattering effects destroy low-energy Fermi liquid coherence, leading to an {\it incoherent} metallic non-FL state off half-filling. Finally, for large enough disorder, a {\it continuous} transition to the Mott-Anderson insulating phase occurs. The nature of the non-FL metallic phase, as well as the effects of the low energy coherence (incoherence) on optical conductivity and electronic Raman spectra, are considered in detail.