231 research outputs found
Shot Noise in Mesoscopic Transport Through Localised States
We show that shot noise can be used for studies of hopping and resonant
tunnelling between localised electron states. In hopping via several states,
shot noise is seen to be suppressed compared with its classical Poisson value
( is the average current) and the suppression depends on the
distribution of the barriers between the localised states. In resonant
tunnelling through a single impurity an enhancement of shot noise is observed.
It has been established, both theoretically and experimentally, that a
considerable increase of noise occurs due to Coulomb interaction between two
resonant tunnelling channels.Comment: 7 pages, 5 figures; Proceedings of the 10th Conference on Hopping and
Related Phenomena (Trieste 2003); requires Wiley style files (included
High-performance operation of single-mode terahertz quantum cascade lasers with metallic gratings
A periodic array of thin slits opened on a metallic surface can act as a one-dimensional photonic crystal for the propagation of surface-plasmon waves. We have used such structure for the implementation of distributed feedback resonators in quantum cascade lasers emitting near 2.5 THz. Single-mode emission, stable at all injection currents and operating temperatures, was achieved both in pulsed and continuous wave. The devices exhibited output powers of several milliwatts with low threshold current densities of ∼100 A cm2
Tunneling Between Two-Dimensional Electron Gases in a Strong Magnetic Field
We have measured the tunneling between two two-dimensional electron gases at
high magnetic fields , when the carrier densities of the two electron layers
are matched. For filling factors , there is a gap in the current-voltage
characteristics centered about , followed by a tunneling peak at ~mV. Both features have been observed before and have been attributed to
electron-electron interactions within a layer. We have measured high field
tunneling peak positions and fitted gap parameters that are proportional to
, and independent of the carrier densities of the two layers. This suggests
a different origin for the gap to that proposed by current theories, which
predict a dependence.Comment: 9 pages, cond-mat/yymmnn
Room temperature strong light-matter coupling in three dimensional terahertz meta-atoms
We demonstrate strong light-matter coupling in three dimensional terahertz meta-atoms at room temperature. The intersubband transition of semiconductor quantum wells with a parabolic energy potential is strongly coupled to the confined circuital mode of three-dimensional split-ring metal-semiconductor-metal resonators that have an extreme sub-wavelength volume (λ/10). The frequency of these lumped-element resonators is controlled by the size and shape of the external antenna, while the interaction volume remains constant. This allows the resonance frequency to be swept across the intersubband transition and the anti-crossing characteristic of the strong light-matter coupling regime to be observed. The Rabi splitting, which is twice the Rabi frequency (2ΩRabi), amounts to 20% of the bare transition at room temperature, and it increases to 28% at low-temperatur
Coupled-cavity terahertz quantum cascade lasers for single mode operation
We demonstrate the operation of coupled-cavity terahertz frequency quantum-cascade lasers composed of two sub-cavities separated by an air gap realized by optical lithography and dry etching. This geometry allows stable, single mode operation with typical side mode suppression ratios in the 30-40 dB range. We employ a transfer matrix method to model the mode selection mechanism. The obtained results are in good agreement with the measurements and allow prediction of the operating frequency
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