Model of the influence of an external magnetic field on the gain of terahertz radiation from semiconductor superlattices

We theoretically analyze the influence of magnetic field on small-signal absorption and gain in a superlattice. We predict a very large and tunable THz gain due to nonlinear cyclotron oscillations in crossed electric and magnetic fields. In contrast to Bloch gain, here the superlattice is in an electrically stable state. We also find that THz Bloch gain can be significantly enhanced with a perpendicular magnetic field. If the magnetic field is tilted with respect to the superlattice axis, the usually unstable Bloch gain profile becomes stable in the vicinity of Stark-cyclotron resonances

Terahertz Bloch oscillator with a modulated bias

Electrons performing Bloch oscillations in an energy band of a dc-biased superlattice in the presence of weak dissipation can potentially generate THz fields at room temperature. The realization of such Bloch oscillator is a long-standing problem due to the instability of a homogeneous electric field in conditions of negative differential conductivity. We establish the theoretical feasibility of stable THz gain in a long superlattice device in which the bias is quasistatically modulated by microwave fields. The modulation waveforms must have at least two harmonics in their spectra.Comment: 5 page

C∗-segal algebras with order unit, II

We continue the work begun in [12] on noncommutative C∗ -Segal algebras, with an emphasis on the order structure. We extend and improve the main results of [12], and characterize the C∗-Segal algebras with an order unitization.Keywords: Segal algebra, approximate ideal, multiplier module, C∗-Segal algebra, order unit, order unitizatio

Order structure, multipliers, and Gelfand representation of vector-valued function algebras

Abstract We continue the study begun by the third author of $C^*$-Segal algebra valued function algebras, with an emphasis on the order structure. Our main result is a characterization theorem for $C^*$-Segal algebra valued function algebras with an order unitization. As an intermediate step, we establish a function algebraic description of the multiplier module of arbitrary Segal algebra valued function algebras. We also consider Gelfand representation of these algebras in the commutative case