Isotope effects in the Hubbard-Holstein model within dynamical mean-field theory

Details Isotope effects in the Hubbard-Holstein model within dynamical mean-field theory Isotope effects in the Hubbard-Holstein model within dynamical mean-field theory

2006-09-25

arxiv.org/abs/cond-mat/0609630v1

Phys. Rev. B 74, 205108 (2006)

Physics

Condensed Matter

Strongly Correlated Electrons

10 pages, 8 figures. The paper has been already accepted on Phys. Rev. B

Scientific paper

10.1103/PhysRevB.74.205108

We study the isotope effects arising from the coupling of correlated electrons with dispersionless phonons by considering the Hubbard-Holstein model at half-filling within the dynamical mean-field theory. In particular we calculate the isotope effects on the quasi-particle spectral weight $Z$, the renormalized phonon frequency, and the static charge and spin susceptibilities. In the weakly correlated regime $U/t \lesssim 1.5$, where $U$ is the Hubbard repulsion and $t$ is the bare electron half-bandwidth, the physical properties are qualitatively similar to those characterizing the Holstein model in the absence of Coulomb repulsion, where the bipolaronic binding takes place at large electron-phonon coupling, and it reflects in divergent isotope responses. On the contrary in the strongly correlated regime $U/t \gtrsim 1.5$, where the bipolaronic metal-insulator transition becomes of first order, the isotope effects are bounded, suggesting that the first order transition is likely driven by an electronic mechanism, rather then by a lattice instability. These results point out how the isotope responses are extremely sensitive to phase boundaries and they may be used to characterize the competition between the electron-phonon coupling and the Hubbard repulsion.

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