Electronic structure of unidirectional superlattices in crossed electric and magnetic fields and related terahertz oscillations

We have studied Bloch electrons in a perfect unidirectional superlattice subject to crossed electric and magnetic fields, where the magnetic field is oriented ``in-plane'', i.e. in parallel to the sample plane. Two orientation of the electric field are considered. It is shown that the magnetic field suppresses the intersubband tunneling of the Zener type, but does not change the frequency of Bloch oscillations, if the electric field is oriented perpendicularly to both the sample plane and the magnetic field. The electric field applied in-plane (but perpendicularly to the magnetic field) yields the step-like electron energy spectrum, corresponding to the magnetic-field-tunable oscillations alternative to the Bloch ones.Comment: 7 pages, 1 figure, accepted for publication in Phys. Rev.

Weak-field Hall effect and static polarizability of Bloch electrons

A theory of the weak field Hall effect of Bloch electrons based on the analysis of the forces acting on electrons is presented. It is argued that the electric current is composed of two contributions, that driven by the electric field along current flow and the non-dissipative contribution originated in demagnetization currents. The Hall resistance as a function of the electron concentration for the tight-binding model of a crystal with square lattice and body-centered cubic lattice is described in detail. For comparison the effect of strong magnetic fields is also discussed

Amplification of electromagnetic radiation in a superlattice placed in a tilted magnetic field

The interaction of electrons in a superlattice with electromagnetic radiation in presence of static electric and magnetic fields is investigated. The electric field is directed along the superlattice axis while the magnetic field is inclined at an arbitrary angle to the axis of superlattice. It is shown that the dependence of current in the superlattice on electric field in the general case can have several maxima. In some regions of electric and magnetic field values, the absorption coefficient for high frequency electromagnetic radiation can be negative that means the electromagnetic wave will be amplified. We note that negative absorption in the system is possible at some conditions at the region of positive differential conductivity in contrast to classical Bloch oscillator in which amplification takes place in case of negative differential conductivity only. This phenomenon can be used for the design of a teraherz amplifier and generator based on the superlattice