arXiv subjects

Min-Chul Cha

Publications and source records attributed to Min-Chul Cha.

21 records · Page 2Linked to original sources

arXiv1994

Topological Defects, Orientational Order, and Depinning of the Electron Solid in a Random Potential

We report on the results of molecular dynamics simulation (MD) studies of the classical two-dimensional electron crystal in the presence disorder. Our study is motivated by recent experiments on this system in modulation doped semiconductor systems in very strong magnetic fields, where the magnetic length is much smaller than the average interelectron spacing $a_0$, as well as by recent studies of electrons on the surface of helium. We investigate the low temperature state of this system using a simulated annealing method. We find that the low temperature state of the system always has isolated dislocations, even at the weakest disorder levels investigated. We also find evidence for a transition from a hexatic glass to an isotropic glass as the disorder is increased. The former is characterized by quasi-long range orientational order, and the absence of disclination defects in the low temperature state, and the latter by short range orientational order and the presence of these defects. The threshold electric field is also studied as a function of the disorder strength, and is shown to have a characteristic signature of the transition. Finally, the qualitative behavior of the electron flow in the depinned state is shown to change continuously from an elastic flow to a channel-like, plastic flow as the disorder strength is increased.

cond-mat↗

arXiv1994

Orientational Order and Depinning of the Disordered Electron Solid

We study the ground state of two-dimensional classical electron solids under the influence of modulation-doped impurities by using a simulated annealing molecular dynamics method. By changing the setback distance as a parameter, we find that in the strong disorder limit the ground state configuration contains both isolated dislocations and disclinations, whereas in the weak disorder regime only dislocations are present. We show, via continuum elasticity theory, that the ground state of the lattice should be unstable against a proliferation of free disclinations above a critical dislocation density. Associated with this, the behavior of the threshold electric field as a function of the setback distance changes.

cond-mat↗

arXiv1993

Universal conductivity in the boson Hubbard model in a magnetic field

The universal conductivity at the zero-temperature superconductor-insulator transition of the two-dimensional boson Hubbard model is studied for cases both with and without magnetic field by Monte Carlo simulations of the (2+1)-dimensional classical $XY$-model with disorder represented by random bonds correlated along the imaginary time dimension. The effect of magnetic field is characterized by the frustration $f$. From the scaling behavior of the stiffness, we determine the quantum dynamical exponent $z$, the correlation length exponent $ν$, and the universal conductivity $σ^*$. For the disorder-free model with $f=1/2$, we obtain $z \approx 1$, $1/ν\approx 1.5$, and $σ^*/σ_Q =0.52 \pm 0.03 $ where $σ_Q$ is the quantum conductance. We also study the case with $f=1/3$, in which we find $σ^*/σ_Q = 0.83 \pm 0.06 $. The value of $σ^*$ is consistent with a theoretical estimate based on the Gaussian model. For the model with random interactions, we find $z=1.07 \pm 0.03$, $ν\approx 1$, and $σ^*/σ_Q= 0.27 \pm 0.04$ for the case $f=0$, and $z=1.14 \pm 0.03$, $ν\approx 1$, and $σ^*/σ_Q= 0.49 \pm 0.04$ for the case $f=1/2$.

cond-mat↗