Marko Zivkovic

Quantum Transport in Graphene Nanoribbons with Realistic Edges

Due to their unique electrical properties, graphene nanoribbons (GNRs) show great promise as the building blocks of novel electronic devices. However, these properties are strongly dependent on the geometry of the edges of the graphene devices. Thus far, only zigzag and armchair edges have been extensively studied. However, several other self-passivating edge reconstructions are possible, and were experimentally observed. Here we utilize the nonequilibrium Green’s function (NEGF) technique in conjunction with tight binding methods to model quantum transport through armchair, zigzag, and several other self-passivated edge reconstructions. In addition, we consider the experimentally relevant cases of mixed edges, where random combinations of possible terminations exist on a given GNR boundary. We find that transport through GNRs with self-passivating edge reconstructions is governed by the sublattice structure of the edges, in a manner similar to their parent zigzag or armchair configurations. Furthermore, ...

Sagnac rotational phase shifts in a mesoscopic electron interferometer with spin-orbit interactions

The Sagnac effect is an important phase coherent effect in optical and atom interferometers where rotations of the interferometer with respect to an inertial reference frame result in a shift in the interference pattern proportional to the rotation rate. Here, we analyze the Sagnac effect in a mesoscopic semiconductor electron interferometer. We include in our analysis the Rashba spin-orbit interactions in the ring. Our results indicate that spin-orbit interactions increase the rotation-induced phase shift. We discuss the potential experimental observability of the Sagnac phase shift in such mesoscopic systems.

Sagnac effect in a chain of mesoscopic quantum rings

The ability to interferometrically detect inertial rotations via the Sagnac effect has been a strong stimulus for the development of atom interferometry because of the potential 10{sup 10} enhancement of the rotational phase shift in comparison to optical Sagnac gyroscopes. Here we analyze ballistic transport of matter waves in a one-dimensional chain of N coherently coupled quantum rings in the presence of a rotation of angular frequency {omega}. We show that the transmission probability, T, exhibits zero transmission stop gaps as a function of the rotation rate interspersed with regions of rapidly oscillating finite transmission. With increasing N, the transition from zero transmission to the oscillatory regime becomes an increasingly sharp function of {omega} with a slope {partial_derivative}T/{partial_derivative}{omega}{approx}N{sup 2}. The steepness of this slope dramatically enhances the response to rotations in comparison to conventional single ring interferometers such as the Mach-Zehnder interferometer and leads to a phase sensitivity well below the quantum shot-noise limit typical of atom interferometers.

Taking it to the next interface level: Advancing game design for higher education STEM applications

Despite the demand for science, technology, engineering, and math (STEM) professionals and their role in driving innovation and economic growth, literature consistently reports that less than forty percent of students in the United States starting out in a STEM college program complete their degree. One way to increase the pipeline of STEM professionals in the near-term is to increase the retention rates of students pursuing STEM degree programs. It is well-established that a key component of achievement in STEM-related curricula at every level (elementary, secondary, or post-secondary) is the students degree of engagement with the subject matter. This work details the development of a game platform that integrates undergraduate STEM content in a compelling and holistic fashion in which users can navigate the environment using natural gestures. Recognizing that the inclusion of games in educational contexts is a broad area of ongoing study, the authors confine the scope of this project to the development of advanced game systems for higher education STEM applications.

Quantum bistability and spin current shot noise of a single quantum dot coupled to an optical microcavity

Here we explore spin dependent quantum transport through a single quantum dot coupled to an optical microcavity. The spin current is generated by electron tunneling between a single doped reservoir and the dot combined with intradot spin flip transitions induced by a quantized cavity mode. In the limit of strong Coulomb blockade, this model is analogous to the Jaynes-Cummings model in quantum optics and generates a pure spin current in the absence of any charge current. Earlier research has shown that in the classical limit where a large number of such dots interact with the cavity field, the spin current exhibits bistability as a function of the laser amplitude that drives the cavity. We show that in the limit of a single quantum dot this bistability continues to be present in the intracavity photon statistics. Signatures of the bistable photon statistics manifest themselves in the frequency dependent shot noise of the spin current despite the fact that the quantum mechanical average spin current no longer exhibits bistability. Besides having significance for future quantum dot based optoelectronic devices, our results shed light on the relation between bistability, which is traditionally viewed as a classical effect, and quantum mechanics.