arXiv subjects

Z. B. Huang

Publications and source records attributed to Z. B. Huang.

8 recordsLinked to original sources

arXiv2011

Strong enhancement of d-wave superconducting state in the three-band Hubbard model coupled to an apical oxygen phonon

We study the hole binding energy and pairing correlations in the three-band Hubbard model coupled to an apical oxygen phonon, by exact diagonalization and constrained-path Monte Carlo simulations. In the physically relevant charge-transfer regime, we find that the hole binding energy is strongly enhanced by the electron-phonon interaction, which is due to a novel potential-energy-driven pairing mechanism involving reduction of both electronic potential energy and phonon related energy. The enhancement of hole binding energy, in combination with a phonon-induced increase of quasiparticle weight, leads to a dramatic enhancement of the long-range part of d-wave pairing correlations. Our results indicate that the apical oxygen phonon plays a significant role in the superconductivity of high-$T_c$ cuprates.

cond-mat.str-el↗

arXiv2007

The superconducting gap in the Hubbard model and the two gap energy scales in high-Tc cuprates

Recent excperiments (ARPES, Raman) suggest the presence of two distinct energy gaps in high-Tc superconductors (HTSC), exhibiting different doping dependences. Results of a variational cluster approach to the superconducting state of the two-dimensional Hubbard model are presented which show that this model qualitatively describes this gap dichotomy: One gap (antinodal) increases with less doping, a behavior long considered as reflecting the general gap behavior of the HTSC. On the other hand, the near-nodal gap does even slightly decrease with underdoping. An explanation of this unexpected behavior is given which emphasizes the crucial role of spin fluctuations in the pairing mechanism.

cond-mat.str-el↗

arXiv2006

Renormalization of the electron-spin-fluctuation interaction in the t-t'-U Hubbard model

We study the renormalization of the electron-spin-fluctuation (el-sp) vertex in a two-dimensional Hubbard model with nearest-neighbor (t) and next-nearest-neighbor (t') hopping by a Quantum-Monte-Carlo calculation. Our results show that for t'=0, the renormalized el-sp vertex decreases quite generally with decreasing temperature at all spin-fluctuation momentum transfers. The suppression of the el-sp vertex results in a substantial reduction of the effective pairing interaction mediated by antiferromagnetic spin fluctuations in both the intermediate- and strong-correlation regimes. The inclusion of a finite t'/t<0, increases the Landau damping rate of spin fluctuations, especially in the overdoped region. The increased damping rate leads to smaller vertex corrections, in agreement with earlier diagrammatic calculations. Still, the vertex correction reduces the spin-fermion vertex, as at t'=0.

cond-mat.supr-con↗

arXiv2005

Role of vertex corrections in the spin-fluctuation mediated pairing mechanism

We study numerically and partly diagrammatically the renormalization of the electron-spin interaction or vertex in a two-dimensional one-band Hubbard model with spin-fluctuation momentum transfer ${\vv q}=(π,π)$. We find that the renormalized electron-spin vertex decreases quite generally with decreasing temperature at all doping densities. As a combination of two concurring effects, i.e. the decrease of the vertex and the increase of the spin susceptibility, the effective pairing interaction increases with lowering temperature in the intermediate-correlation regime, but {\it flattens off} in the strong-correlation regime. Our findings indicate that in the high-T$_c$ cuprates the pairing mediated by antiferromagnetic spin fluctuations is substantially reduced due to vertex corrections.

cond-mat.str-el↗

arXiv2004

Electron-phonon vertex in the two-dimensional one-band Hubbard model

Using quantum Monte Carlo techniques, we study the effects of electronic correlations on the effective electron-phonon (el-ph) coupling in a two-dimensional one-band Hubbard model. We consider a momentum-independent bare ionic el-ph coupling. In the weak- and intermediate-correlation regimes, we find that the on-site Coulomb interaction $U$ acts to effectively suppress the ionic el-ph coupling at all electron- and phonon- momenta. In this regime, our numerical simulations are in good agreement with the results of perturbation theory to order $U^2$. However, entering the strong-correlation regime, we find that the forward scattering process stops decreasing and begins to substantially increase as a function of $U$, leading to an effective el-ph coupling which is peaked in the forward direction. Whereas at weak and intermediate Coulomb interactions, screening is the dominant correlation effect suppressing the el-ph coupling, at larger $U$ values irreducible vertex corrections become more important and give rise to this increase. These vertex corrections depend crucially on the renormalized electronic structure of the strongly correlated system.

cond-mat.str-el↗

arXiv2003

Asymmetric electron-phonon interactions in the three-band Peierls-Hubbard model

Using the Quantum Monte Carlo (QMC) technique within frozen-phonon, we studied the effects of the half-breathing O$(π,0)$ phonon mode on the ground-state properties of the three-band Peierls-Hubbard model. Our simulations are performed for both ionic and covalent electron-phonon couplings. The effects of lattice displacements on the ground-state energies and charge fluctuations are similar in magnitude for both hole- and electron-doped cases. However, the effects of lattice displacements on the magnetic properties are rather different. In the hole-doped case, the normalized next-nearest-neighbor Cu-Cu spin correlations are dramatically modified by both ionic and covalent electron-phonon couplings. On the other hand, in the electron-doped case, much smaller effects are observed. The distinct spin-phonon couplings, in conjunction with the spin-bag picture of the quasiparticle, could explain a strong mass renormalization effect in the p-type cuprates and a weaker effect in the n-type cuprates.

cond-mat.str-el↗

arXiv2000

Pairing, Charge, and Spin Correlations in the Three-Band Hubbard Model

Using the Constrained Path Monte Carlo (CPMC) method, we simulated the two-dimensional, three-band Hubbard model to study pairing, charge, and spin correlations as a function of electron and hole doping and the Coulomb repulsion $V_{pd}$ between charges on neighboring Cu and O lattice sites. As a function of distance, both the $d_{x^2 - y^2}$-wave and extended s-wave pairing correlations decayed quickly. In the charge-transfer regime, increasing $V_{pd}$ decreased the long-range part of the correlation functions in both channels, while in the mixed-valent regime, it increased the long-range part of the s-wave behavior but decreased that of the d-wave behavior. Still the d-wave behavior dominated. At a given doping, increasing $V_{pd}$ increased the spin-spin correlations in the charge-transfer regime but decreased them in the mixed-valent regime. Also increasing $V_{pd}$ suppressed the charge-charge correlations between neighboring Cu and O sites. Electron and hole doping away from half-filling was accompanied by a rapid suppression of anti-ferromagnetic correlations.

cond-mat.str-el↗

arXiv2000

Charge dynamics in doped triangular antiferromagnets

Within the framework of the fermion-spin theory based on the charge-spin separation, the charge dynamics of the doped antiferromagnet on a triangular lattice is studied. The holon part is treated by using the loop expansion to the second order. It is shown that the charge dynamics is mainly caused by charged holons moving in the background of spinon excitations. The optical conductivity spectrum shows an unusual behavior at low energies and an anomalous midinfrared band, while the resistivity exhibits a nonlinearity in temperatures.

cond-mat.str-el↗