Why a magnetized quantum wire can act as an optical amplifier: A short survey

Abstract

This article reviews the fundamental issues associated with the magnetoplasmon excitations investigated in a semiconducting quantum wire characterized by a harmonic confining potential and subjected to an applied (perpendicular) magnetic field. We embark on the charge-density excitations in a two-subband model within the framework of Bohm-Pines's random-phase approximation. The problem involves two length scales: $l_0=\sqrt{\hslash /m^{\ast }{\omega }_0}$ and $l_c=\sqrt{\hslash /m^{\ast }{\omega }_c}$, which characterize the strengths of the confinement and the magnetic field ($B$). Essentially, we focus on the device aspects of the intersubband collective (magnetoroton) excitation, which observes a negative group velocity between maxon and roton. Consequently, it leads to tachyon-like (superluminal) behavior without one's having to introduce the negative energies. Existence of the negative group velocity is a clear manifestation of a medium with population inversion brought about due to a metastable state caused by the magnetic field that satisfies the condition $B>B_{th}$; $B_{th}$ being the threshold value below which the magnetoroton does not exist. The interest in negative group velocity is based on anomalous dispersion in a medium with inverted population, so that gain instead of absorption occurs at the frequencies of interest. A medium with an inverted population has the remarkable ability of amplifying a small optical signal of definite wavelength, i.e., it can serve as an {\em active} laser medium. An extensive scrutiny of the gain coefficient suggests an interesting and important application: the electronic device designed on the basis of such magnetoroton modes can act as an optical amplifier. Examining the magnetic-field dependence of the life-time of magnetorotons leads us to infer that relatively smaller magnetic fields are optimal.

arXiv commentarXiv admin note: substantial text overlap with arXiv:1012.5422, arXiv:1306.3597

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Cited by in corpus (2)

• The Quantum Pinch Effect in Semiconducting Quantum Wires: A Bird's-Eye View
• The fundamentals of harnessing the magneto-optics of quantum wires for designing optical amplifiers: Formalism