Journal of Physics Conference Series

Impurity induced insulator-to-metal transitions in half-filled Mott insulators

Hisatoshi Yokoyama, Ryo Sato, Kenji Kobayashi

Published Sep 1, 2019• 0 citations

Abstract

Abstract In view of cuprate superconductors, effects of point-type impurity potential (V) on half-filled antiferromagnetic and paramagnetic states are studied for a strongly correlated square-lattice Hubbard model (U/t = 12) with a diagonal transfer (t′), using a variational Monte Carlo method. In the trial states, we introduce a Rice-Brinkman-type one-body projector for V, which enables us to treat the whole range of V (− ∞ < V/t < ∞) with small statistical errors. Filling-control-type Mott (insulator-to-metal) transitions are found to occur at <?CDATA $V=V_{U}^{\left( \pm \right)}$?> V = V U ( ± ) (∼ ±U). In the metallic states <?CDATA $\left( \left| V \right|>\left| V_{U}^{\left( \pm \right)} \right| \right)$?> ( | V | > | V U ( ± ) | ) , charge carriers are holes (electrons) in the case of attractive (repulsive) potential. The mechanism of the transitions is intuitively understood.

DOI: 10.1088/1742-6596/1293/1/012024

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Journal of Physics Conference Series

Impurity induced insulator-to-metal transitions in half-filled Mott insulators

Hisatoshi Yokoyama, Ryo Sato, Kenji Kobayashi

Published Sep 1, 2019• 0 citations

Publisher

Abstract

DOI: 10.1088/1742-6596/1293/1/012024

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V={V}_{U}^{(\pm )}\sim \pm U

?> V = V U ( ± ) ∼ ± U . The phase realized for <?CDATA

V\lt {V}_{U}^{(-)}

?> V < V U ( − ) is robust d-SC and the charge carriers are holes, whereas for <?CDATA

V\gt {V}_{U}^{(+)}

?> V > V U ( + ) a metallic (or weak d-SC) state appears with charge carriers of electrons. For a partially-filled case where the impurity density is equal to the doping rate, a d-SC-to-insulator transition arises at V ≡ V M ∼ 4t. In the weak-|V| phases, the impurity effects in the electron distribution are smeared out by the screening effect, whereas in the strong-|V| phases, the electron distribution directly depend on the impurity configurations.

A(ω, k)

show formation of two Hubbard bands and their antiferromagnetic shadows separated by a Mott gap in the plane of energy

ω

and momentum

k

with lowering temperatures. These four bands produce splitting to two low-energy narrow bands and two SDW-like bands in the dispersion. Near half filling, the low-energy narrow band persists at low temperatures. This narrow band has a particularly weak dispersion and large weights around

(π, 0)

and

(0, π)

momenta. The velocity of these low-energy excitations is shown to vanish towards the MIT, indicating the mass divergence as in the Brinkman-Rice picture, but most prominently around

(π,0)

and

(0,π)

with strong momentum dependence. This reflects the suppression of the coherence near the MIT. Main structures in

A(ω, k)

show remarkable similarities to quantum Monte-Carlo results in two dimensions as well as in the one-dimensional Hubbard model. The charge compressibility appears to diverge with decreasing doping concentration in both one and two dimensions in agreement with the exact and quantum Monte-Carlo results. We also discuss implications of the flat dispersion formed near the Fermi level to the observations in high-$\Tc$ cuprate superconductors.