113 research outputs found
The effects of non-linear electron-phonon interactions on superconductivity and charge-density-wave correlations
Determinant quantum Monte Carlo (DQMC) simulations are used to study
non-linear electron-phonon interactions in a two-dimensional Holstein-like
model on a square lattice. We examine the impact of non-linear electron-lattice
interactions on superconductivity and on Peierls charge-density-wave (CDW)
correlations at finite temperatures and carrier concentrations. We find that
the CDW correlations are dramatically suppressed with the inclusion of even a
small non-linear interaction. Conversely, the effect of the non-linearity on
superconductivity is found to be less dramatic at high temperatures; however,
we find evidence that the non-linearity is ultimately detrimental to
superconductivity. These effects are attributed to the combined hardening of
the phonon frequency and a renormalization of the effective linear
electron-phonon coupling towards weaker values. These results demonstrate the
importance of non-linear interactions at finite carrier concentrations when one
is addressing CDW and superconducting order and have implications for
experiments that drive the lattice far from equilibrium.Comment: 5 Pages, 5 Figure
Numerical study of the electron-phonon interaction in multiorbital materials
This thesis examines the electron-phonon (e-ph) interaction in multiorbital correlated systems using various numerical techniques, including determinant quantum Monte Carlo and dynamical mean field theory. First, I studied the non-linear e-ph coupling in a one band model and found that even a weak non-linear e-ph couplings can significantly shape both electronic and phononic properties. Second, I study the interplay between the e-ph and electron-electron (e-e) interactions in a multiorbital Hubbard-Holstein model in both one- and infinite-dimension. In both cases, I found that a weak e-ph interaction is enough to induce a phase transition from the Mott phase to the charge-density-wave phase. Moreover, I find that not only the e-e correlation but also the e-ph interaction can induce an orbital-selective phase. Our results imply that the e-ph interaction is significant in the multiorbital correlated materials, such as the iron-based superconductors. Last, I studied the offdiagonal e-ph interaction in a two-dimensional three-orbital model defined on a Lieb lattice. I consider an sp-type model, which is like a 2D analog of the barium bismuthate high temperature superconductors. I found a metal-to-insulator (MI) transition as decreasing temperature at half filling and identified a dimerized structure in the insulating phase. With hole doping, the ordered polarons and bipolarons correlations disappear but the short-range correlations are present, implying that polarons and bipolarons preform in the matellic phase and freeze into a periodic array in the insulating state. In sum, this thesis reveals the importance of the e-ph interaction in the multiorbital materials and gives an alarm to people when study these multiorbital materials
Static and dynamical magnetic properties of the extended Kitaev-Heisenberg model with spin vacancies
Motivated by the potential to suppress the antiferromagnetic long-range order
in favor of the long-sought-after Kitaev quantum spin liquid state, we study
the effect of spin vacancies in the extended Kitaev-Heisenberg model. In
particular, we focus on a realistic model obtained from fitting inelastic
neutron scattering on -RuCl. We observe that the long-range zigzag
magnetic ordered state only survives when the doping concentration is smaller
than 5\%. Upon further increasing the spin vacancy concentration, the ground
state becomes a short-range ordered state at low temperatures. Compared with
experiments, our classical solution over-stabilizes the zigzag correlation in
the presence of spin vacancies. Our theoretical results provide guidance toward
interpreting inelastic neutron scattering experiments on magnetically diluted
Kitaev candidate materials.Comment: 9 figure
Charge-Density Wave in Overdoped Cuprates Driven by Electron-Phonon Couplings
Recent resonant x-ray scattering (RXS) experiments revealed a novel charge
order in highly overdoped LaSrCuO (LSCO). The observed charge
order appears around the wavevector and remains robust from
cryogenic temperatures to room temperature. To investigate the origin of this
charge order in the overdoped region, we use determinant quantum Monte Carlo
(DQMC) simulations to examine models with various interactions. We demonstrate
that this CDW originates from remnant correlations in overdoped cuprates. The
doping-independent wavevector further reflects the presence of
nonlocal electron-phonon couplings. Our study reveals the importance of phonons
in the cuprates, which assist correlated electrons in the formation of exotic
phases.Comment: 7 pages, 4 figure
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