London's limit for the lattice superconductor

A stability problem for the current state of the strong coupling superconductor has been considered within the lattice Ginzburg-Landau model. The critical current problem for a thin superconductor film is solved within the London limit taking into account the crystal lattice symmetry. The current dependence on the order parameter modulus is computed for the superconductor film for various coupling parameter magnitudes. The field penetration problem is shown to be described in this case by the one-dimensional sine-Gordon equation. The field distribution around the vortex is described at the same time by the two-dimensional elliptic sine-Gordon equation.Comment: 7 pages, 3 figures, Revtex4, mostly technical correction; extended abstrac

Two mini-band model for self-sustained oscillations of the current through resonant tunneling semiconductor superlattices

A two miniband model for electron transport in semiconductor superlattices that includes scattering and interminiband tunnelling is proposed. The model is formulated in terms of Wigner functions in a basis spanned by Pauli matrices, includes electron-electron scattering in the Hartree approximation and modified Bhatnagar-Gross-Krook collision tems. For strong applied fields, balance equations for the electric field and the miniband populations are derived using a Chapman-Enskog perturbation technique. These equations are then solved numerically for a dc voltage biased superlattice. Results include self-sustained current oscillations due to repeated nucleation of electric field pulses at the injecting contact region and their motion towards the collector. Numerical reconstruction of the Wigner functions shows that the miniband with higher energy is empty during most of the oscillation period: it becomes populated only when the local electric field (corresponding to the passing pulse) is sufficiently large to trigger resonant tunneling.Comment: 26 pages, 3 figures, to appear in Phys. Rev.

Unraveling of free carrier absorption for terahertz radiation in heterostructures

The relation between free carrier absorption and intersubband transitions in semiconductor heterostructures is resolved by comparing a sequence of structures. Our numerical and analytical results show how free carrier absorption evolves from the intersubband transitions in the limit of an infinite number of wells with vanishing barrier width. It is explicitly shown that the integral of the absorption over frequency matches the value obtained by the f-sum rule. This shows that a proper treatment of intersubband transitions is fully sufficient to simulate the entire electronic absorption in heterostructure THz devices.Comment: 6 pages, accepted by Physical Review

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