Asymptotically exact trial wave functions for yrast states of rotating Bose gases

We revisit the composite fermion (CF) construction of the lowest angular momentum yrast states of rotating Bose gases with weak short range interaction. For angular momenta at and below the single vortex, $L \leq N$, the overlaps between these trial wave functions and the corresponding exact solutions {\it increase} with increasing system size and appear to approach unity in the thermodynamic limit. In the special case $L=N$, this remarkable behaviour was previously observed numerically. Here we present methods to address this point analytically, and find strongly suggestive evidence in favour of similar behaviour for all $L \leq N$. While not constituting a fully conclusive proof of the converging overlaps, our results do demonstrate a striking similarity between the analytic structure of the exact ground state wave functions at $L \leq N$, and that of their CF counterparts. Results are given for two different projection methods commonly used in the CF approach

Few-electron artificial molecules formed by laterally coupled quantum rings

We study the artificial molecular states formed in laterally coupled double semiconductor nanorings by systems containing one, two and three electrons. An interplay of the interring tunneling and the electron-electron interaction is described and its consequences for the magnetization and charging properties of the system are determined. It is shown that both the magnetic dipole moment generated by the double ring structure and the chemical potential of the system as function of the external magnetic field strongly depend on the number of electrons and the interring barrier thickness. Both the magnetization and chemical potentials exhibit cusps at the magnetic fields inducing ground-state parity and / or spin transformations. The symmetry transformations are discussed for various tunnel coupling strengths: from rings coupled only electrostatically to the limit of coalesced rings. We find that in the ground-states for rings of different radii the magnetic field transfers the electron charge from one ring to the other. The calculations are performed with the configuration interaction method based on an approach of Gaussian functions centered on a rectangular array of points covering the studied structure. Electron-electron correlation is also discussed

Few-electron eigenstates of concentric double quantum rings

Few-electron eigenstates confined in coupled concentric double quantum rings are studied by the exact diagonalization technique. We show that the magnetic field suppresses the tunnel coupling between the rings localizing the single-electron states in the internal ring, and the few-electron states in the external ring. The magnetic fields inducing the ground-state angular momentum transitions are determined by the distribution of the electron charge between the rings. The charge redistribution is translated into modifications of the fractional Aharonov-Bohm period. We demonstrate that the electron distribution can be deduced from the cusp pattern of the chemical potentials governing the single-electron charging properties of the system. The evolution of the electron-electron correlations to the high field limit of a classical Wigner molecule is discussed.Comment: to appear in Physical Review

A Carbon Nanotube Based Nanorelay

We investigate the operational characteristics of a nanorelay based on a conducting carbon nanotube placed on a terrace in a silicon substrate. The nanorelay is a three terminal device that acts as a switch in the GHz regime. Potential applications include logic devices, memory elements, pulse generators, and current or voltage amplifiers.Comment: 4 pages, 3 figure

Quantum Hall Physics - hierarchies and CFT techniques

The fractional quantum Hall effect, being one of the most studied phenomena in condensed matter physics during the past thirty years, has generated many groundbreaking new ideas and concepts. Very early on it was realized that the zoo of emerging states of matter would need to be understood in a systematic manner. The first attempts to do this, by Haldane and Halperin, set an agenda for further work which has continued to this day. Since that time the idea of hierarchies of quasiparticles condensing to form new states has been a pillar of our understanding of fractional quantum Hall physics. In the thirty years that have passed since then, a number of new directions of thought have advanced our understanding of fractional quantum Hall states, and have extended it in new and unexpected ways. Among these directions is the extensive use of topological quantum field theories and conformal field theories, the application of the ideas of composite bosons and fermions, and the study of nonabelian quantum Hall liquids. This article aims to present a comprehensive overview of this field, including the most recent developments.Comment: added section on experimental status, 59 pages+references, 3 figure

Electron spin and charge switching in a coupled quantum dot quantum ring system

Few-electron systems confined in a quantum dot laterally coupled to a surrounding quantum ring in the presence of an external magnetic field are studied by exact diagonalization. The distribution of electrons between the dot and the ring is influenced by the relative strength of the dot and ring confinement, the gate voltage and the magnetic field which induces transitions of electrons between the two parts of the system. These transitions are accompanied by changes in the periodicity of the Aharonov-Bohm oscillations of the ground-state angular momentum. The singlet-triplet splitting for a two electron system with one electron confined in the dot and the other in the ring exhibits piecewise linear dependence on the external field due to the Aharonov-Bohm effect for the ring-confined electron, in contrast to smooth oscillatory dependence of the exchange energy for laterally coupled dots in the side-by-side geometry.Comment: to appear in PRB in August 200

Laser-controlled local magnetic field with semiconductor quantum rings

We analize theoretically the dynamics of N electrons localized in a semiconductor quantum ring under a train of phase-locked infrared laser pulses. The pulse sequence is designed to control the total angular momentum of the electrons. The quantum ring can be put in states characterized by strong currents. The local magnetic field created by these currents can be used for a selective quantum control of single spins in semiconductor systems