arXiv subjects

H. Grabert

Publications and source records attributed to H. Grabert.

22 records · Page 2Linked to original sources

arXiv1999

Crossover from Fermi liquid to Wigner molecule behavior in quantum dots

The crossover from weak to strong correlations in parabolic quantum dots at zero magnetic field is studied by numerically exact path-integral Monte Carlo simulations for up to eight electrons. By the use of a multilevel blocking algorithm, the simulations are carried out free of the fermion sign problem. We obtain a universal crossover only governed by the density parameter $r_s$. For $r_s>r_c$, the data are consistent with a Wigner molecule description, while for $r_s<r_c$, Fermi liquid behavior is recovered. The crossover value $r_c \approx 4$ is surprisingly small.

cond-mat.str-el↗

arXiv1998

Effect of the Tunneling Conductance on the Coulomb Staircase

Quantum fluctuations of the charge in the single electron box are investigated. The rounding of the Coulomb staircase caused by virtual electron tunneling is determined by perturbation theory up to third order in the tunneling conductance and compared with precise Monte Carlo data computed with a new algorithm. The remarkable agreement for large conductance indicates that presently available experimental data on Coulomb charging effects in metallic nanostructures can be well explained by finite order perturbative results.

cond-mat.mes-hall↗

arXiv1997

Is the direct observation of electronic coherence in electron transfer reactions possible?

The observability of electronic coherence in electron transfer reactions is discussed. We show that under appropriate circumstances large-amplitude oscillations can be found in the electronic occupation probabilities. The initial preparation of the system is of crucial importance for this effect, and we discuss conditions under which experiments detecting electronic coherence should be feasible. The Feynman-Vernon influence functional formalism is extended to examine more general and experimentally relevant initial preparations. Analytical expressions and path integral quantum dynamics simulations were developed to study the effects of various initial preparations on the observability of electronic coherence.

cond-mat↗

arXiv1995

Semiclassical Density Matrix Near the Top of a Barrier

Employing the path integral approach, we calculate the semiclassical equilibrium density matrix of a particle moving in a nonlinear potential field for coordinates near the top of a potential barrier. As the temperature is decreased, near a critical temperature $T_c$ the harmonic approximation for the fluctuation path integral fails. This is due to a caustic arising at a bifurcation point of the classical paths. We provide a selfconsistent scheme to treat the large quantum fluctuations leading to a nonlinear fluctuation potential. The procedure differs from methods used near caustics of the real time propagator. The semiclassical density matrix is determined explicitly for the case of asymmetric barriers from high temperatures down to temperatures somewhat below $T_c$. Pacs: 03.65.Sq, 05.30.-d

quant-ph↗