1,491 research outputs found

### The Doped Two Chain Hubbard Model

The properties of the two-chain Hubbard Model doped away from half-filling
are investigated. The charge gap is found to vanish, but a finite spin gap
exists over a range of interchain hopping strength $t_\perp$. In this range,
there are modified $d_{x^2-y^2}$--like pairing correlations whose strength is
correlated with the size of the spin gap. It is found that the pair field
correlations are enhanced by the onsite Coulomb interaction U.Comment: 10 pages and 5 postscript figures, RevTeX 3.0, UCI-CMTHE-94-0

### Quantum information analysis of the phase diagram of the half-filled extended Hubbard model

We examine the phase diagram of the half-filled one-dimensional extended
Hubbard model using quantum information entropies within the density-matrix
renormalization group. It is well known that there is a charge-density-wave
phase at large nearest-neighbor and small on-site Coloumb repulsion and a
spin-density-wave at small nearest-neighbor and large on-site Coloumb
repulsion. At intermediate Coulomb interaction strength, we find an additional
narrow region of a bond-order phase between these two phases. The phase
transition line for the transition out of the charge-density-wave phase changes
from first-order at strong coupling to second-order in a parameter regime where
all three phases are present. We present evidence that the additional
phase-transition line between the spin-density-wave and bond-order phases is
infinite order. While these results are in agreement with recent numerical
work, our study provides an independent, unbiased means of determining the
phase boundaries by using quantum information analysis, yields values for the
location of some of the phase boundaries that differ from those previously
found, and provides insight into the limitations of numerical methods in
determining phase boundaries, especially those of infinite-order transitions.Comment: 8 pages, 7 figure

### Studying a relativistic field theory at finite chemical potential with the density matrix renormalization group

The density matrix renormalization group is applied to a relativistic complex
scalar field at finite chemical potential. The two-point function and various
bulk quantities are studied. It is seen that bulk quantities do not change with
the chemical potential until it is larger than the minimum excitation energy.
The technical limitations of the density matrix renormalization group for
treating bosons in relativistic field theories are discussed. Applications to
other relativistic models and to nontopological solitons are also suggested.Comment: 9 pages, 5 figures; v2: title changed; references added, conclusions
expanded, to be published in PR

### The Density Matrix Renormalization Group applied to single-particle Quantum Mechanics

A simplified version of White's Density Matrix Renormalization Group (DMRG)
algorithm has been used to find the ground state of the free particle on a
tight-binding lattice. We generalize this algorithm to treat the tight-binding
particle in an arbitrary potential and to find excited states. We thereby solve
a discretized version of the single-particle Schr\"odinger equation, which we
can then take to the continuum limit. This allows us to obtain very accurate
results for the lowest energy levels of the quantum harmonic oscillator,
anharmonic oscillator and double-well potential. We compare the DMRG results
thus obtained with those achieved by other methods.Comment: REVTEX file, 21 pages, 3 Tables, 4 eps Figure

### Numerical study of a superconductor-insulator transition in a half-filled Hubbard chain with distant transfers

The ground state of a one-dimensional Hubbard model having the next-nearest
neighbor hopping (t') as well as the nearest-neighbor one (t) is numerically
investigated at half-filling. A quantum Monte Carlo result shows a slowly
decaying pairing correlation for a sizeable interaction strength $(U \leq 2t)$,
while the system is shown to become insulating for yet larger $U>U_C\sim 3t$
from a direct evaluation of the charge gap with the density-matrix
renormalization group method. The results are consistent with Fabrizio's recent
weak-coupling theory which suggests a transition from a superconductor into an
insulator at a finite U.Comment: 4 pages, RevTeX, uses epsf.sty and multicol.st

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