arXiv subjects

T. K. Lee

Publications and source records attributed to T. K. Lee.

45 records · Page 3Linked to original sources

arXiv1998

Phase diagram of the two-chain Hubbard model

We have calculated the charge gap and spin gap for the two-chain Hubbard model as a function of the on-site Coulomb interaction and the interchain hopping amplitude. We used the density matrix renormalization group method and developed a method to calculate separately the gaps numerically for the symmetric and antisymmetric modes with respect to the exchange of the chain indices. We have found very different behaviors for the weak and strong interaction cases. Our calculated phase diagram is compared to the one obtained by Balents and Fisher using the weak coupling renormalization group technique.

cond-mat.str-el↗

arXiv1998

d-Wave Pairing Correlation in the Two-Dimensional t-J Model

The pair-pair correlation function of the two-dimensional t-J model is studied by using the power-Lanczos method and an assumption of monotonic behavior. In comparison with the results of the ideal Fermi gas, we conclude that the 2D t-J model does not have long range d-wave superconducting correlation in the interesting parameter range of $J/t \leq 0.5$. Implications of this result will also be discussed.

cond-mat.supr-con↗

arXiv1997

Phase Separation of the Two-Dimensional t-J model

The boundary of phase separation of the two-dimensional t-J model is investigated by the power-Lanczos method and Maxwell construction. The method is similar to a variational approach and it determines the lower bound of the phase separation boundary with $J_c/t=0.6\pm 0.1$ in the limit $n_e\sim 1$. In the physical interesting regime of high T_c superconductors where $0.3<J/t<0.5$ there is no phase separation.

cond-mat.str-el↗

arXiv1996

Dispersion of a single hole in the t-J model

The dispersion of a single hole in the t-J model obtained by the exact result of 32 sites and the results obtained by self-consistent Born approximation and the Green function Monte Carlo method can be simply derived by a mean-field theory with d-RVB and antiferromagnetic order parameters. In addition, it offers a simple explanation for the difference observed between those results. The presence of the extended van Hove region at (pi,0) is a consequence of the d-RVB pairing independenct of the antiferromagnetic order. Results including t' and t" are also presented and explained consistently in a similar way.

cond-mat↗

arXiv1996

Low energy excitations of the t-J model in 1D and 2D

We present an exact diagonalization study of the low energy singlet and triplet states for both 1D and 2D t-J model. A scan of the parameter ratio J/t shows that for nearly all low energy states in both 1D and 2D the excitation energy takes the linear form E(t,J) = a t + b J. In 1D this is the natural consequence of the factorization of the low energy wave functions, i.e. spin-charge separation. Examination of the low energy eigenstates in 2D shows that in the singlet sector the lowest states are collective modes, which for larger J correspond to `dynamical hole columns', i.e. a periodic modulation of the hole density. This modulation is well reproduced by treating holes as hard-core Bosons with an attractive interaction.

cond-mat↗

arXiv1996

Variational Study of the Spin-Gap Phase of the One-Dimensional t-J Model

We propose a correlated spin-singlet-pairs wave function to describe the spin-gap phase of the one-dimensional $t-J$ model at low density. Adding a Jastrow factor with a variational parameter, $ν$, first introduced by Hellberg and Mele, is shown to correctly describe the long-range behavior expected for the Luther-Emery phase. Using the variational Monte Carlo method we establish a relation between $ν$ and the Luttinger exponent $K_ρ$, $K_ρ=\frac{1}{2ν}$.

cond-mat↗

arXiv1994

t-J model Studied by the New Lanczos-Power Method

The initial trial wave function used in a simple ground-state projection method, the power method, is systematically improved by using Lanczos algorithm. Much faster convergence to the ground state achieved by using these wave functions significantly reduces the effect of the fermion sign problem. The energy, spin and charge correlation functions are calculated for the ground states of the two-dimensional $t-J$ model. Results for an $8\times8$ cluster with 42 and 26 electrons are presented. The density correlation function for the $t-J$ model at small J shows a surprisingly good agreement with that of a system of non-interacting hard-core bosons.

cond-mat↗

arXiv1994

Is there spin-charge separation in the 2D Hubbard and t-J models at low electronic densities?

The spin and density correlation functions of the two-dimensional Hubbard model at low electronic density $ $ are calculated in the ground state by using the power method, and at finite temperatures by using the quantum Monte Carlo technique. Both approaches produce similar results, which are in close agreement with numerical and high temperature expansion results for the two-dimensional ${\rm t-J}$ model. Using perturbative approximations, we show that the examination of the density correlation function alone is not enough to support recent claims in the literature that suggested spin and charge separation in the low electronic density regime of the ${\rm t-J}$ model.

cond-mat↗

arXiv1994

Non-Fermi-Liquid-Like Behavior in The Two-Dimensional t-J Model

The spin, charge and pairing correlation functions for the ground state of two-dimensional $t-J$ model are calculated by using the power method which projects out the ground state from a variational wave function. ``Exact'' results are obtained for $10\times10$ and $8\times8$ lattices with low particle densities. The results are surprisingly similar to that of one-dimensional $t-J$ model. The phenomenology is almost perfectly correlated with the concept of Tomonaga-Luttinger liquid and it is incompatible with traditional Fermi liquid theory.

cond-mat↗