Sandia National Laboratories
Proposed more than 80 years ago, research on Bloch oscillations (BO) has gained a renewed interest, as a Bloch oscillator can be utilized as a solid-state, electrically biased, frequency-tunable terahertz source and detector. So far, work on BO has mainly been carried out in vertical quantum well superlattice structures. On the other hand, a surface superlattice patterned in a two-dimensional electron system (2DES) has long been proposed as an alternative device structure to generate BO. A surface superlattice has three-dimensional quantization, as opposite to the conventional vertical quantum well superlattice. As a result, gaps exist in all three dimensions in the energy spectrum, which can lead to BO at relatively moderate electric field. It has also been shown that, in surface superlattices, the electron-optical phonon scattering, one of the limiting mechanisms in achieving BO in the terahertz range in vertical superlattice, can be completely suppressed, and, thus, electrically generated BO can become possible. Furthermore, compared to a vertical superlattice, a surface superlattice offers other various advantages, for example, easy device fabrication and multiple fundamental frequencies. It can also fully utilize the benefit of long coherent transport time achieved in high mobility 2DES. To date, however, very few studies of BO in surface superlattices have been reported.
I will report here the experimental evidence of BO in two-dimensional antidot arrays. First, negative differential conductance (NDC), one of the signatures of BO, was observed. In one sample, several current jumps were observed in the NDC region. Our theoretical modeling yields reasonable agreement with the experimental data. More measurements have been carried out to examine the so-called reversed Bloch oscillations and magneto-transport. In particular, in magneto-transport measurements, evidence of the Bloch oscillations induced edge magneto-plasmon resonance was observed.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000
For other physics colloquia, please visit www.utdallas.edu/physics/lectures