SUBSURFACE CHARGE ACCUMULATION IMAGING OF A QUANTUM HALL LIQUID

The unusual properties of two-dimensional electron systems that give r ise to the quantum Hall effect have prompted the development of new mi croscopic models for electrical conduction(1-6). The bulk properties o f the quantum Hall effect have also been studied experimentally using a variety of probes including transport(7,8), photoluminescence(9,10), magnetization(11) and capacitance(12,13) measurements. However, the f act that two-dimensional electron systems typically exist some distanc e (about 1,000 Angstrom) beneath the surface of the host semiconductor has presented an important obstacle to more direct measurements of mi croscopic electronic structure in the quantum Hall regime. Here we int roduce a cryogenic scanning-probe technique-'subsurface charge accumul ation' imaging-that permits very high resolution examination of system s of mobile electrons inside materials. We use this technique to image directly the nanometre-scale electronic structures that exist in the quantum Hall regime.