Striped quantum Hall phases

Recent experiments seem to confirm predictions that interactions lead to charge density wave ground states in higher Landau levels. These new ``correlated'' ground states of the quantum Hall system manifest themselves for example in a strongly anisotropic resistivity tensor. We give a brief introduction and overview of this new and emerging field.Comment: 10 pages, 1 figure, updated reference to experimental wor

Plasma Instability and Amplified Mode Switching Effect in THz Field Effect Transistors with Grating Gate

We developed a theory of collective plasma oscillations in a dc current-biased field effect transistor with interdigitated dual grating gate and demonstrated a new mechanism of electron plasma instability in this structure. The instability in the plasmonic crystal formed in the transistor channel develops due to conversion of the kinetic energy carried by the drifting plasmons into electromagnetic energy. The conversion happens at the opposite sides of the gate fingers due to the asymmetry produced by the current flow and occurs through the gate finger fringing capacitances. The key feature of the proposed instability mechanism is the behavior of the plasma frequency peak and its width as functions of the dc current bias. At a certain critical value of the current, the plasma resonant peak with small instability increment experiencing redshift with increasing current changes to the blue shifting peak with large instability increment. This amplified mode switching (AMS) effect has been recently observed in graphene-interdigitated structures (S. Boubanga-Tombet et al., Phys. Rev. X 10, 031004 (2020)). The obtained theoretical results are in very good qualitative agreement with these experiments and can be used in future designs of the compact sources of THz EM radiation.Comment: 15 pages, 6 figure

Terahertz-Frequency Plasmonic-Crystal Instability in Field-Effect Transistors with Asymmetric Gate Arrays

We present a theory for plasmonic crystal instability in a semiconductor field-effect transistor with a dual grating gate, designed with strong asymmetry in the crystal elementary cell. Under the action of a dc current bias, we demonstrate that Bloch plasma waves in the resulting plasmonic crystal, formed in this transistor, develop the Dyakonov-Shur instability across the entire Brillouin zone. By calculating the energy spectrum of the plasmonic crystal and its instability increments, we analyze the dependence of the latter on the electron drift velocity and the extent of the structural asymmetry. Our results point to the possibility of exciting radiating steady-state plasma oscillations at room temperature, in transistors with asymmetric gate arrays that should be readily implementable via standard nanofabrication techniques. Long-range coherence of the unstable plasma oscillations, generated in the elementary cells of the crystal, should dramatically increase the radiated THz electromagnetic power, making this approach a promising pathway to the generation of THz signals.Comment: 17 pages, 3 figure

Coulomb effects on the quantum transport of a two-dimensional electron system in periodic electric and magnetic fields

The magnetoresistivity tensor of an interacting two-dimensional electron system with a lateral and unidirectional electric or magnetic modulation, in a perpendicular quantizing magnetic field, is calculated within the Kubo formalism. The influence of the spin splitting of the Landau bands and of the density of states (DOS) on the internal structure of the Shubnikov-de Haas oscillations is analyzed. The Coulomb electron - electron interaction is responsible for strong screening and exchange effects and is taken into account in a screened Hartree-Fock approximation, in which the exchange contribution is calculated self-consistently with the DOS at the Fermi level. This approximation describes both the exchange enhancement of the spin splitting and the formation of compressible edge strips, unlike the simpler Hartree and Hartree-Fock approximations, which yield either the one or the other.Comment: 20 pages, revtex, 7 ps figures, to appear in Phys. Rev.

Grating-Gate Tunable Plasmon Absorption In Inp And Gan Based Hemts

Gate-voltage tunable plasmon resonances in the two dimensional electron gas of high electron mobility transistors (HEMT) fabricated from the InGaAs/InP and AlGaN/GaN materials systems are reported. Gates were in the form of a grating to couple normally incident THz radiation into 2D plasmons. Narrow-band resonant absorption of THz radiation was observed in transmission for both systems in the frequency range 10 - 100 cm-1. The fundamental and harmonic resonances shift toward lower frequencies with negative gate bias. Calculated spectra based on the theory developed for MOSFETs by Schaich, Zheng, and McDonald (1990) agree well with the GaN results, but significant differences for the InGaAs/InP device suggest that modification of the theory may be required for HEMTs in some circumstances. © 2009 SPIE