J. Chowdhury

Enhancement of persistent current in mesoscopic rings and cylinders: shortest and next possible shortest higher-order hopping

We present a detailed study of persistent current and low-field magnetic susceptibility in single isolated normal metal mesoscopic rings and cylinders in the tight-binding model with higher-order hopping integral in the Hamiltonian. Our exact calculations show that order of magnitude enhancement of persistent current takes place even in the presence of disorder if we include the higher-order hopping integral in the Hamiltonian. In strictly one-channel mesoscopic rings the sign of the low-field currents can be predicted exactly even in the presence of impurity. We observe that perfect rings with both odd and even numbers of electrons support only diamagnetic currents. On the other hand in the disordered rings, irrespective of realization of the disordered configurations of the ring, we always get diamagnetic currents with odd numbers of electrons and paramagnetic currents with even numbers of electrons. In mesoscopic cylinders the sign of the low-field currents cannot be predicted exactly since it strongly depends on the total number of electrons, Ne, and also on the disordered configurations of the system. From the variation of persistent current amplitude with system size for constant electron density, we conclude that the enhancement of persistent current due to additional higher-order hopping integrals is visible only in the mesoscopic regime.

Strange behavior of persistent currents in small Hubbard rings

We show exactly that small Hubbard rings exhibit unusual kink-like structures giving anomalous oscillations in persistent current. Singular behavior of persistent current disappears in some cases. In half-filled systems mobility gradually drops to zero with interaction, while it converges to some finite value in non-half-filled cases.

On the role of electron correlation and disorder on persistent currents in isolated one-dimensional rings

Abstract To understand the role of electron correlation and disorder on persistent currents in isolated 1D rings threaded by magnetic flux ϕ , we study the behavior of persistent currents in aperiodic and ordered binary alloy rings. These systems may be regarded as disordered systems with well-defined long-range order so that we do not have to perform any configuration averaging of the physical quantities. We see that in the absence of interaction, disorder suppresses persistent currents by orders of magnitude and also removes its discontinuity as a function of ϕ . As we introduce electron correlation, we get enhancement of the currents in certain disordered rings. Quite interestingly we observe that in some cases, electron correlation produces kink-like structures in the persistent current as a function of ϕ . This may be considered as anomalous Aharonov–Bohm oscillations of the persistent current and recent experimental observations support such oscillations. We find that the persistent current converges with the size of the rings.

Physics of zero- and one-dimensional nanoscopic systems

From Dilute Magnetic Alloys to Confined Nanostructures: Evolution of the Kondo Effect.- The Two Channel Kondo Effect in Quantum Dots.- Kondo Physics in Artificial Molecules.- Low Temperature Decoherence and Relaxation in Charge Josephson Junction Qubits.- Low-Energy Physical Properties of Edge States in Nanographite Systems.- Thermoelectric Phenomena from Macro-Systems to Nano-Systems.- Coherence and Interactions in Diffusive Systems.- Transport and Persistent Currents in Mesoscopic Rings: Interplay Between Electron-Electron Interaction and Disorder.- Electron Transport Through Mesoscopic Closed Loops and Molecular Bridges.- 2D Disordered Electronic System in the Presence of Strong Magnetic Field.

Ground-state phase diagram and magnetoconductance of a one-dimensional Hubbard superlattice at half filling

We have studied a one-dimensional Hubbard superlattice with different Coulomb correlations at alternating sites for a half-filled band. Mean field calculations based on the Hartree-Fock approximation together with a real space renormalization group technique were used to study the ground state of the system. The phase diagrams obtained in these approaches agree with each other from the weak to the intermediate coupling regime. The mean field results show very quick convergence with system size. The renormalization group results indicate a spatial modulation of local moments that was identified in some previous work. Also we have studied the magnetoconductance of such superlattices which reveals several interesting points.