Theory of Josephson Phenomena in Superfluid 3He

Quite detailed theoretical description of superfluid 3He is possible on length scales that are much larger than the atomic scale. We discuss weak links between two bulk states of 3He-B. The current through the weak link is determined by the bound states at the link. The bound state energies are spin split depending on the order parameters in the bulk. As a result, unusual current-phase relations with pi state appear. For not too weak links, the order parameter in the bulk is modified because of the Josephson coupling. This leads to a stronger pi state and to an additional current at constant pressure bias. The theoretical results are compared with experiments.Comment: 6 pages, 9 figures, talk on LT-24, Orlando, Florid

Comment on "Ballistic SNS sandwich as a Josephson junction"

The old problem of supercurrent in a long ballistic SNS Josephson junction is interpreted using a simple picture of the fermion energy levels in the normal and superconducting regions. We argue that a recent paper on the topic by Sonin contains erroneous results.Comment: 5 pages, 1 figure, in version 2 an appendix containing mathematical details is adde

Stability of A-B phase boundary in a constriction

Abstract We report on a Ginzburg-Landau calculation of the stability of a boundary between A and B phases of superfluid 3 He in a two-dimensional constriction. In the macroscopic limit the stability follows a well-known relation, which depends on the surface tension s AB of the A-B boundary. In the narrow-constriction limit the surface tension is not well defined, but the interface is always stable, and a weak link between the A and B phases is obtained. Pinning of A-B interface Properties of the A-B interface in superfluid It is well known that in the macroscopic limit the pinning stability of the interface is determined only by its finite surface tension s AB where Df AB ¼ f A À f B is the difference in bulk condensation energy densities of the two phases. However, the macroscopic concept of surface tension is not well defined in the limit of small constrictions, and Eq. Numerical results Our computational method employs a standard minimization routine for the GL free energy functional

Bloch gain in dc-ac-driven semiconductor superlattices in the absence of electric domains

We theoretically study the feasibility of amplification and generation of terahertz radiation in dc-ac-driven semiconductor superlattices in the absence of electric domains. We find that if in addition to a dc bias a strong terahertz pump field is applied, a Bloch gain profile for a small terahertz signal can be achieved under the conditions of a positive static differential conductivity. Here, the positive differential conductivity arises, similarly to the case of a large-signal amplification scheme [H. Kroemer, arXiv:cond-mat/0009311 (unpublished)], due to modifications in dc current density caused by the application of a high-frequency ac field [ K. Unterrainer et al. Phys. Rev. Lett. 76 2973 (1996)]. Whereas the sign of absorption at low and zero frequencies is sensitive to the ac fields, the gain profile in the vicinity of the gain maximum is robust. We suggest to use this ac-induced effect in a starter for a terahertz Bloch oscillator. Our analysis demonstrates that the application of a short terahertz pulse to a superlattice allows the suppression of the undesirable formation of electric domains and the achievement of a sustained large-amplitude operation of the dc-biased Bloch oscillator

Terahertz Bloch oscillator with suppressed electric domains: Effect of elastic scattering

We theoretically consider the amplification of THz radiation in a superlattice Bloch oscillator. The main dilemma in the realization of THz Bloch oscillator is finding operational conditions which allow simultaneously to achieve gain at THz frequencies and to avoid destructive space-charge instabilities. A possible solution to this dilemma is the extended Limited Space-Charge Accumulation scheme of Kroemer (H. Kroemer, cond-mat/0009311). Within the semiclassical miniband transport approach we extend its range of applicability by considering a difference in the relaxation times for electron velocity and electron energy. The kinetics of electrons and fields establishing a stationary signal in the oscillator is also discussed.Comment: Submitted to proceedings of the summer school-conference of AQDJJ programme of ESF, Kiten, Bulgaria, 9-24 June 200