Do the quantum corrections to the soliton mass vanish?

The one-loop quantum corrections to the soliton mass are found to vanish for a large class of two-dimensional supersymmetric models and the three-dimensional supersymmetric CPⁿ model. This was achieved by quantizing in a box with supersymmetric boundary conditions.     

Heat conductivity in small quantum systems: Kubo formula in Liouville space

We consider chains consisting of several identical subsystems weakly coupled by various types of next neighbor interactions. At both ends the chain is coupled to a respective heat bath with different temperature modeled by a Lindblad formalism. The temperature gradient introduced by this environment is then treated as an external perturbation. We propose a method to evaluate the heat current and the local temperature profile of the resulting stationary state as well as the heat conductivity in such systems. This method is similar to Kubo techniques used e.g. for electrical transport but extended here to the Liouville space.     

Kubo Hall conductivity on a finite cylinder and the integer quantum hall effect

An additive disordered electron system on a finite cylinder with perpendicular magnetic field is considered. The inequivalent representations of the aximuthal translational group are used to derive conductivity expressions from the Kubo formula and to formulate a phenomenological criterion for localization. These conductivity expressions are shown to be equivalent to the Steda, formula and applied to find spectral conditions for the integer quantum Hall effect to occur on a finite cylinder. The confinement does not give rise to corrections to the quantized values in and, order in the ratio magnetic length/system length. The present approach to the integer quantum Hall effect is compared with several others developed so far.     

solitons in quantum Hall systems

We present here an elementary pedagogical introduction to CP_N solitons in quantum Hall systems. We begin with a brief introduction to both CP_N models and to quantum Hall (QH) physics. We then focus on spin and layer-spin degrees of freedom in QH systems and point out that these are in fact CP_N fields for N = 1 and N = 3. Excitations in these degrees of freedom will be shown to be topologically non-trivial soliton solutions of the corresponding CP_N field equations. We conclude with a brief summary of our own recent work in this area, done with Sankalpa Ghosh. Received 17 November 2001 Published online 2 October 2002 RID="a" ID="a"e-mail: doug0700@mail.jnu.ac.in     

Radiative corrections and quantum gates in molecular systems

We propose a method for quantum information processing using molecules coupled to an external laser field. This utilizes molecular interactions, control of the external field, and an effective energy shift of the doubly excited state of two coupled molecules. Such a level shift has been seen in the two-photon resonance experiments recently reported by Hettich et al. Here we show that this can be explained in terms of the QED Lamb shift. We quantify the performance of the proposed quantum logic gates in the presence of dissipative mechanisms. The unitary transformations required for performing one- and two-qubit operations can be implemented with present day molecular technology. The proposed techniques can also be applied to coupled quantum dot and biomolecular systems.     

Electron spin transitions in quantum Hall systems

A system of two-dimensional electron gas in a strong magnetic field exhibits a remarkable phenomenon known as the fractional quantum Hall effect. Rapid advances in experimental techniques and intense theoretical work for well over a decade have significantly contributed to our understanding of the mechanism behind the effect. It is now a well established fact that electron correlations are largely responsible for the occurrence of this phenomenon. In recent years, theoretical and experimental investigations have revealed that those electron correlations, which are responsible for the quantum Hall effect, are also the reason for various spin transitions in the system. In this review, we systematically follow the theoretical studies of the role spin degree of freedom play in the quantum Hall effect regime and also describe several ingenious experiments reported in recent years which are in good agreement with the emerging theoretical picture.     

Interlayer transport in bilayer quantum Hall systems

Bilayer quantum Hall systems have a broken symmetry ground state at a filling factor which can be viewed either as an excitonic superfluid or as a pseudospin ferromagnet. We present a theory of interlayer transport in quantum Hall bilayers that highlights remarkable similarities and critical differences between transport in Josephson junction and ferromagnetic metal spin-transfer devices. Our theory is able to explain the size of the large but finite low-bias interlayer conductance and the voltage width of this collective transport anomaly.     

Higher order corrections to the Grimus-Stockinger formula

For the Grimus-Stockinger formula the same dimensionless parameter of asymptotic expansion is found by several ways of calculations. This parameter strongly depends on the width of wave packet.     

Weak localization corrections to the anomalous Hall effect

We calculate localization corrections to the anomalous Hall conductivity in the framework of side-jump and skew scattering mechanisms. In contrast to the ordinary Hall effect, there exists a nonvanishing localization correction to the anomalous Hall resistivity. The correction to the anomalous Hall conductivity vanishes in case of side-jump mechanism, but is nonzero for the skew scattering.     

Metal insulator transition in modulated quantum Hall systems

The quantum Hall effect is studied numerically in modulated two-dimensional electron systems in the presence of disorder. Based on the scaling property of the Hall conductivity as well as the localization length, the critical energies where the states are extended are identified. We find that the critical energies, which are distributed to each of the subbands, combine into one when the disorder becomes strong, in the way depending on the symmetry of the disorder and/or the periodic potential.     

Anisotropic multicomponent terahertz photoconductivity in quantum Hall systems

The decay times of the terahertz photoconductivity signal are studied for samples in the quantum Hall regime. The photoconductivity signal has both the longitudinal components caused by the photoinduced change in the longitudinal resistance and the transverse components due to the photoinduced transverse current. The signal kinetics are qualitatively different for samples with relatively low (500 000 cm²/Vs and lower) and relatively high (900 000 cm²/Vs and higher) charge-carrier mobilities.