Quantum Force in Superconductor

Transitions between states with continuous (called as classical state) and discrete (called as quantum state) spectrum of permitted momentum values is considered. The persistent current can exist along the ring circumference in the quantum state in contrast to the classical state. Therefore the average momentum can changes at the considered transitions. In order to describe the reiterated switching into and out the quantum state an additional term is introduced in the classical Boltzmann transport equation. The force inducing the momentum change at the appearance of the persistent current is called as quantum force. It is shown that dc potential difference is induced on ring segments by the reiterated switching if the dissipation force is not homogeneous along the ring circumference. The closing of the superconducting state in the ring is considered as real example of the transition from classical to quantum stateComment: 4 pages, RevTex, 0 figure

Magnetic Response in a Zigzag Carbon Nanotube

Magnetic response of interacting electrons in a zigzag carbon nanotube threaded by a magnetic flux is investigated within a Hartree-Fock mean field approach. Following the description of energy spectra for both non-interacting and interacting cases we analyze the behavior of persistent current in individual branches of a nanotube. Our present investigation leads to a possibility of getting a filling-dependent metal-insulator transition in a zigzag carbon nanotube.Comment: 9 pages, 14 figure

Diamagnetic Persistent Currents and Spontaneous Time-Reversal Symmetry Breaking in Mesoscopic Structures

Recently, new strongly interacting phases have been uncovered in mesoscopic systems with chaotic scattering at the boundaries by two of the present authors and R. Shankar. This analysis is reliable when the dimensionless conductance of the system is large, and is nonperturbative in both disorder and interactions. The new phases are the mesoscopic analogue of spontaneous distortions of the Fermi surface induced by interactions in bulk systems and can occur in any Fermi liquid channel with angular momentum $m$. Here we show that the phase with $m$ even has a diamagnetic persistent current (seen experimentally but mysterious theoretically), while that with $m$ odd can be driven through a transition which spontaneously breaks time-reversal symmetry by increasing the coupling to dissipative leads.Comment: 4 pages, three eps figure

A Solvable Regime of Disorder and Interactions in Ballistic Nanostructures, Part I: Consequences for Coulomb Blockade

We provide a framework for analyzing the problem of interacting electrons in a ballistic quantum dot with chaotic boundary conditions within an energy $E_T$ (the Thouless energy) of the Fermi energy. Within this window we show that the interactions can be characterized by Landau Fermi liquid parameters. When $g$, the dimensionless conductance of the dot, is large, we find that the disordered interacting problem can be solved in a saddle-point approximation which becomes exact as $g\to\infty$ (as in a large-N theory). The infinite $g$ theory shows a transition to a strong-coupling phase characterized by the same order parameter as in the Pomeranchuk transition in clean systems (a spontaneous interaction-induced Fermi surface distortion), but smeared and pinned by disorder. At finite $g$, the two phases and critical point evolve into three regimes in the $u_m-1/g$ plane -- weak- and strong-coupling regimes separated by crossover lines from a quantum-critical regime controlled by the quantum critical point. In the strong-coupling and quantum-critical regions, the quasiparticle acquires a width of the same order as the level spacing $\Delta$ within a few $\Delta$'s of the Fermi energy due to coupling to collective excitations. In the strong coupling regime if $m$ is odd, the dot will (if isolated) cross over from the orthogonal to unitary ensemble for an exponentially small external flux, or will (if strongly coupled to leads) break time-reversal symmetry spontaneously.Comment: 33 pages, 14 figures. Very minor changes. We have clarified that we are treating charge-channel instabilities in spinful systems, leaving spin-channel instabilities for future work. No substantive results are change

Distribution of persistent currents in a multi-arm mesoscopic ring

We propose an idea to investigate persistent current in individual arms of a multi-arm mesoscopic ring. Following a brief description of persistent current in a traditional Aharonov-Bohm (AB) ring, we examine the behavior of persistent currents in separate arms of a three-arm mesoscopic ring. Our analysis may be helpful in studying magnetic response of any complicated quantum network. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2011