Electron pinball and commensurate orbits in a periodic array of scatterers

We have introduced an artificial array of scatterers into a macroscopic two-dimensional conductor nearly devoid of intrinsic defects. This generates pronounced structure in the magnetoresistance, anomalous low-field Hall plateaus, and a quenching of the Hall effect about B = 0. Our calculations show that the predominant features in the data arise from commensurate classical orbits impaled upon small groups of the imposed scatterers

Fabrication and Characterization of Deep Mesa Echted "Anti"-dot Superlattices in GaAs-AlGaAs Heterostructures

By etching a periodic array of holes through a ;mobility two-dimensional electron gas we define high-a lateral, ``anti\'\'-dot-type superlattice with periods a=200 and a=300 nm, much smaller than the electron mean free path in the unpatterned material. The devices are fabricated using electron beam lithography and reactive ion etching techniques, and characterized by magnetotransport experiments. Commensurability effects and the observed quenching of the Hall effect indicate that the electron gas between the etched holes essentially maintains its initial high electron mobility. Applied Physics Letters is copyrighted by The American Institute of Physics

Microablation with ultrashort laser pulses

This paper reports the micro machining results of different materials (AI, Si, InP and fused silica) using a Ti:sapphire laser at the wavelength of 800 and 267 nm with variable pulse lengths in the range from 100 fs to lo ps. The hole arrays with a diameter up to a few µm through microdrilling are presented. We discussed how an effective suppression of the thermal diffusion inside the ablated materials and an effective microablation could be realized. If the laser fluence is taken only slightly above the threshold, a hole array can be drilled with diameters even smaller than the wavelength of the laser. Some examples are presented in the paper

Magnetoresistance in a Grid-Type Lateral Superlattice: The Role of Disorder

The magnetoresistance of a two-dimensional electron gas (2DEG) subjected to a weak two- dimensional (2D) lateral superlattice potential is expected to reflect the peculiar self-similar energy spectrum of Bloch electrons in a magnetic field, i.e., the splitting of Landau levels (LL\'s) into sublevels. One experimentally established effect of a periodic potential is that the discrete LL\'s are transformed into Landau bands and cause magnetoresistance oscillations due to an extra band- conductivity contribution. Theoretically, this band-conductivity contribution is expected to be suppressed if the splitting of the Landau bands is resolved. We study the suppression of the band-conductivity as a function of the electron mobility at millikelvin temperatures. Microfabricated gates, defined on top of high mobility GaAs/AlGaAs heterojunctions. are used to electrostatically impose a 2D-periodic potential with 150 nm period upon the 2DEG. By applying a positive bias the electron mobility is increased and we find the band- conductivity effectively suppressed if the mobility is well above 1 × 106 cm2/Vs