arXiv subjects

Rulin Wang

Publications and source records attributed to Rulin Wang.

5 recordsLinked to original sources

arXiv2020

Tracking the electronic oscillation in molecule with tunneling microscopy

Visualizing and controlling electron dynamics over femtosecond timescale play a key role in the design of next-generation electronic devices. Using simulations, we demonstrate the electronic oscillation inside the naphthalene molecule can be tracked by means of the tuning of delay time between two identical femtosecond laser pulses. Both the frequency and decay time of the oscillation are detected by the tunneling charge through the junction of scanning tunneling microscopy. And the tunneling charge is sensitive to the carrier-envelope phase (CEP) for few-cycle long optical pulses. While this sensitivity to CEP will disappear with the increase of time-length of pulses. Our simulation results show that it is possible to visualize and control the electron dynamics inside the molecule by one or two femtosecond laser pulses.

quant-ph↗

arXiv2015

Quantum Mechanical Modeling of Nanoscale Light Emitting Diodes

Understanding of the electroluminescence (EL) mechanism in optoelectronic devices is important for further optimization of their efficiency and effectiveness. Here, a quantum mechanical approach is formulated for modeling EL processes in nanoscale light emitting diodes (LED). Based on nonequilibrium Green's function quantum transport equations, interactions with electromagnetic vacuum environment is included to describe electrically driven light emission in the devices. Numerical studies of a silicon nanowire LED device are presented. EL spectra of the nanowire device under different bias voltages are simulated and, more importantly, propagation and polarization of emitted photon can be determined using the current approach.

cond-mat.mtrl-sci↗

arXiv2014

Hierarchical equations of motion for impurity solver in dynamical mean-field theory

A nonperturbative quantum impurity solver is proposed based on a formally exact hierarchical equations of motion (HEOM) formalism for open quantum systems. It leads to quantitatively accurate evaluation of physical properties of strongly correlated electronic systems, in the framework of dynamical mean-field theory (DMFT). The HEOM method is also numerically convenient to achieve the same level of accuracy as that using the state-of-the-art numerical renormalization group impurity solver at finite temperatures. The practicality of the novel HEOM+DMFT method is demonstrated by its applications to the Hubbard models with Bethe and hypercubic lattice structures. We investigate the metal-insulator transition phenomena, and address the effects of temperature on the properties of strongly correlated lattice systems.

cond-mat.str-el↗

arXiv2013

Time-dependent density-functional theory for real-time electronic dynamics on material surfaces

The real-time electronic dynamics on material surfaces is critically important to a variety of applications. However, their simulations have remained challenging for conventional methods such as the time-dependent density-functional theory (TDDFT) for isolated and periodic systems. By extending the applicability of TDDFT to systems with open boundaries, we achieve accurate atomistic simulations of real-time electronic response to local perturbations on material surfaces. Two prototypical scenarios are exemplified: the relaxation of an excess electron on graphene surface, and the electron transfer across the molecule-graphene interface. Both the transient and long-time asymptotic dynamics are validated, which accentuates the fundamental importance and unique usefulness of an open-system TDDFT approach. The simulations also provide insights into the characteristic features of temporal electron evolution and dissipation on surfaces of bulk materials.

physics.chem-ph↗

arXiv2013

Thermopower of few-electron quantum dots with Kondo correlations

The thermopower of few-electron quantum dots with Kondo correlations is investigated via a hierarchial equations of motion approach. The thermopower is determined by the line shape of spectral function within a narrow energy window defined by temperature. Based on calculations and analyses on single-level and two-level Anderson impurity models, the underlying relations between thermopower and various types of electron correlations are elaborated. In particular, an unconventional sign reversal behavior is predicted for quantum dots with a suitable inter-level spacing. The new feature highlights the significance of multi-level effects and their interplay with Kondo correlations. Our finding and understanding may lead to novel thermoelectric applications of quantum dots.

cond-mat.str-el↗