arXiv subjects

Liang Chen

Publications and source records attributed to Liang Chen.

509 records · Page 29Linked to original sources

arXiv1995

Numerical renormalization group study of the 1D t-J model

The one-dimensional (1D) $t-J$ model is investigated using the density matrix renormalization group (DMRG) method. We report for the first time a generalization of the DMRG method to the case of arbitrary band filling and prove a theorem with respect to the reduced density matrix that accelerates the numerical computation. Lastly, using the extended DMRG method, we present the ground state electron momentum distribution, spin and charge correlation functions. The $3k_F$ anomaly of the momentum distribution function first discussed by Ogata and Shiba is shown to disappear as $J$ increases. We also argue that there exists a density-independent $J_c$ beyond which the system becomes an electron solid.

cond-mat↗

arXiv1995

Magnetic and pair correlations of the Hubbard model with next-nearest-neighbor hopping

A combination of analytical approaches and quantum Monte Carlo simulations is used to study both magnetic and pairing correlations for a version of the Hubbard model that includes second-neighbor hopping $t^{\prime }=-0.35t$ as a model for high-temperature superconductors. Magnetic properties are analyzed using the Two-Particle Self-Consistent approach. The maximum in magnetic susceptibility as a function of doping appears both at finite $% t^{\prime }$ and at $t^{\prime }=0$ but for two totally different physical reasons. When $t^{\prime }=0$, it is induced by antiferromagnetic correlations while at $t^{\prime }=-0.35t$ it is a band structure effect amplified by interactions. Finally, pairing fluctuations are compared with $% T $-matrix results to disentangle the effects of van Hove singularity and of nesting on superconducting correlations. The addition of antiferromagnetic fluctuations increases slightly the $d$-wave superconducting correlations despite the presence of a van Hove singularity which tends to decrease them in the repulsive model. Some aspects of the phase diagram and some subtleties of finite-size scaling in Monte Carlo simulations, such as inverted finite-size dependence, are also discussed.

cond-mat↗

arXiv1994

Calculation of the singlet-triplet gap of the antiferromagnetic Heisenberg Model on the ladder

The ground state energy and the singlet-triplet energy gap of the antiferromagnetic Heisenberg model on a ladder is investigated using a mean field theory and the density matrix renormalization group. Spin wave theory shows that the corrections to the local magnetization are infinite. This indicates that no long range order occurs in this system. A flux-phase state is used to calculate the energy gap as a function of the transverse coupling, $J_\perp$, in the ladder. It is found that the gap is linear in $J_\perp$ for $J_\perp\gg 1$ and goes to zero for $J_\perp\to 0$. The mean field theory agrees well with the numerical results.

cond-mat↗

arXiv1993

Theory of spin and charge fluctuations in the Hubbard model

A self-consistent theory of both spin and charge fluctuations in the Hubbard model is presented. It is in quantitative agreement with Monte Carlo data at least up to intermediate coupling $(U\sim 8t)$. It includes both short-wavelength quantum renormalization effects, and long-wavelength thermal fluctuations which can destroy long-range order in two dimensions. This last effect leads to a small energy scale, as often observed in high temperature superconductors. The theory is conserving, satisfies the Pauli principle and includes three-particle correlations necessary to account for the incipient Mott transition.

cond-mat↗

arXiv1993

Comment on ``Magnetic Susceptibility of the two-dimensional Hubbard model ''

The observed magnetic spin susceptibility of high-temperature superconductors such as La$_{2- x}$Sr$_x$CuO$_4$ increases when $x$ increases from zero, i.e. as one dopes away from half-filling. Recent Monte Carlo simulations of A. Moreo (Phys. Rev. B {\bf 48}, 3380 (1993)) suggest that this behavior can be reproduced by the two-dimensional Hubbard model only at large coupling, namely, $U/t$ of order $10$. Using longer runs, our Monte Carlo simulations show that the same behavior as for $U/t=10$ is obtained even in the intermediate coupling regime ($U/t=4$), as long as the temperature is low enough ($T=t/6$) that strong antiferromagnetic correlations are building up at half-filling. These results are consistent with the fact that in two-dimensions, the GRPA should fail in the parameter range where it predicts a magnetic phase transition.

cond-mat↗