arXiv subjects

Alejandro Muramatsu

Publications and source records attributed to Alejandro Muramatsu.

22 records · Page 2Linked to original sources

arXiv2000

Single hole dynamics in the t-J model on a square lattice

We present quantum Monte Carlo (QMC) simulations for a single hole in a t-J model from J=0.4t to J=4t on square lattices with up to 24 x 24 sites. The lower edge of the spectrum is directly extracted from the imaginary time Green's function. In agreement with earlier calculations, we find flat bands around $(0,\pmπ)$, $(\pmπ,0)$ and the minimum of the dispersion at $(\pmπ/2,\pmπ/2)$. For small J both self-consistent Born approximation and series expansions give a bandwidth for the lower edge of the spectrum in agreement with the simulations, whereas for J/t > 1, only series expansions agree quantitatively with our QMC results. This band corresponds to a coherent quasiparticle. This is shown by a finite size scaling of the quasiparticle weight $Z(\vec k)$ that leads to a finite result in the thermodynamic limit for the considered values of $J/t$. The spectral function $A(\vec k, ω)$ is obtained from the imaginary time Green's function via the maximum entropy method. Resonances above the lowest edge of the spectrum are identified, whose J-dependence is quantitatively described by string excitations up to J/t=2.

cond-mat.str-el↗

arXiv1999

Single hole dynamics in the one dimensional t-J model

We present a new finite-temperature quantum Monte Carlo algorithm to compute imaginary-time Green functions for a single hole in the t-J model on non-frustrated lattices. Spectral functions are then obtained with the Maximum Entropy method. Simulations of the one-dimensional case show that a simple charge-spin separation Ansatz is able to describe the overall features of the spectral function over the whole energy range for values of J/t from 1/3 to 4. This includes the bandwidth W \sim 4t + J and the compact support of the spectral function. The quasiparticle weight Z_k is computed on lattices up to L=96 sites, and scales as Z_k\propto L^{-1/2}.

cond-mat.str-el↗

arXiv1997

Quantum Monte Carlo simulations of infinitely strongly correlated fermions

Numerical simulations of the two-dimensional t-J model in the limit $J/t \ll 1$ are performed for rather large systems (up to $N = 12 \times 12$) using a world-line loop-algorithm. It is shown that in the one-hole case with J=0, where no minus signs appear, very low temperatures ($βt \sim 3000$) are necessary in order to reach Nagaoka's state. $J/t \ltsim 0.05$ leads to the formation of partially polarized systems, whereas $J/t \gtsim 0.05 $ corresponds to minimal spin. The two-hole case shows enhanced total spin up to the lowest attainable temperatures ($βt = 150$).

cond-mat.str-el↗

arXiv1996

SO(3) nonlinear $σ$ model for a doped quantum helimagnet

A field theory describing the low-energy, long-wavelength sector of an incommensurate, spiral magnetic phase is derived from a spin-fermion model that is commonly used as a microscopic model for high-temperature superconductors. After integrating out the fermions in a path-integral representation, a gradient expansion of the fermionic determinant is performed. This leads to an O(3)$\otimes$O(2)-symmetric quantum nonlinear $σ$ model, where the doping dependence is explicitly given by generalized fermionic susceptibilities which enter into the coupling constants of the $σ$ model and contain the fermionic band-structure that results from the spiral background. A stability condition of the field theory self-consistently determines the spiral wavevector as a function of the doping concentration. Furthermore, terms of topological nature like the $θ$-vacuum term in (1+1)-dimensional nonlinear $σ$ models are obtained for the plane of the spiral.

cond-mat↗