Imaging Transport Resonances in the QHE

This webpage includes high resolution images and movies related to our recent work imaging transport resonances in the quantum Hall effect. We have also posted some of our simuation results and PDF versions of talks that we have presented.

This work has recently appeared in Physical review letters: "Imaging Transport Resonances in the Quantum Hall Effect", Physical Review Letters 95 136804 (2005) (link). (Preprint available on cond-mat/0506347)

High resolution Images

Click on the thumbnails to enlarge the images.

	A 9x9 um hole bubble image showing the in-phase charging signal. The image is taken at 5.0T (nu = 1.26) with a tip voltage of +1.75V. This is a zoomed portion of the image shown in figure 4(c) of our paper.
	A 9x9 um hole bubble image showing the lagging-phase charging signal.

Presentations

Presentations are in PDF format or in Powerpoint 2003 format.

Note that animations in a Powerpoint 2003 presentation will not display properly in Powerpoint versions earlier than Powerpoint 2002. If you do not have a compatible copy of Powerpoint, a free Powerpoint 2003 viewer can be downloaded from Microsoft from this website.

• Contributed Talk presented by G. A. Steele at EP2DS-16 in Albuquerque, NM, July 2005. This presentation has several extra slides at the end, including data at different filling factors and an alternative explanation of our earlier results on topographic mapping of the quantum Hall liquid using a few-electron bubble
• A short talk presented by G. A. Steele at the APS March Meeting in L.A. in 2005
• A long talk presented by R. C. Ashoori at a conference at the University of Minnesota

Movies

The following are in uncompressed avi format.

		Movies showing the evolution of 5x5 um in-phase and lagging-phase scans with bias voltage at 4.8T. Tip voltage is stepped from -0.25 to 1.55V in steps of 0.2V. At a critical voltage, the hole bubble forms, and then continues to grow as the voltage is increased.
		More hole-bubble movies showing the evolution of a 10x10 um in-phase and lagging-phase scan with bias voltage at 5.5T. Tip voltage is stepped from -0.35 to 1.65V in steps of 0.1V.
		Electron-bubble movies showing the evolution of a 5x5 in-phase and lagging-phase scan with bias voltage at 8T. Tip voltage is stepped from -3.25 to +1.25V in steps of 0.2V.

Simulations

A movie showing the evolution of the density profile as the tip is scanned, as calculated in our simulations. The bulk filling factor is 0.8 and the tip bias is chosen to produce a local filling factor of 1.3 under the tip. The blue color scale represent local densities of nu < 1, the green represent incompressible regions of nu = 1, and the pink color scale are local densities of nu > 1. The simulation includes an approximate model of donor correlations from Efros, Pikus, and Samsonidze, Phys. Rev. B 41 8295 (1990). We have used the non-equilibrium model with a Ceff of 1.5e10 e/cm^2.

5x5um images showing the density profile of the 2DES at integer filling showing a typical network of incompressible strips. The disorder model is the same as used above. The first image shows the actual density profile, while the second is threasholded so that nu < 1 regions are blue, the nu = 1 incompressible regions are white, and nu > 1 regions are pink. Several instances are shown where small islands lie inside incompressible strips that separate larger compressible regions. Click on thumbnails to enlarge.