Dynamic nonlinear behavior is reported at high currents in the quantum Hall regime of GaAs heterostructures, resulting from breakdown of the dissipationless current flow. It is demonstrated that this breakdown is spatially localized and transient switching is observed on microsecond time scales among a set of distinct dissipative states. A simple macroscopic picture is proposed to account for these novel phenomena.PACS numbers: 73.40.Lq, 72.20.Ht, 72.20.My, 72.70. + m The quantum Hall effect 1 ' 2 is of great import for both many-body physics and fundamental metrology. The extreme accuracy with which the Hall resistance is quantized, despite the presence of disorder in the inversion-layer devices, is now fairly well understood as being due to the nearly complete freedom from dissipation in the quantized Hall regime. However, the nature of the localized states in a high magnetic field, the role of finite electric fields, and the nature of various dissipative effects remain poorly understood. Ebert etal. 3 have recently discovered that there is a critical current density above which the dissipation suddenly rises by several orders of magnitude. We report in this Letter unexpected new phenomena associated with this breakdown. We show that the breakdown is spatially localized and exhibits a rich time-dependent structure. In addition to a strong background of broadband noise we observe transient switching on a microsecond time scale among a discrete set of distinct dissipative states. Our observations demonstrate the significance of this breakdown phenomenon and provide a deeper understanding of the novel transport properties associated with the quantum Hall effect.Two high-quality GaAs-Ga^Al^As (# = 0.29) heterojunction devices [hereafter referred to as GaAs(7) and GaAs (8)] were used in this study. Both devices have zero-magnetic-field mobilities in excess of 10 5 cm 2 /(V s) at 4.2 K, and at 1.1 K yield excellent 6453.2-£2 (i =4) Hall steps that are flat and reproducible to at least 0.02 ppm. Figure 1 gives the sample geometry and displays the current dependence of the Hall resistance R H = (V 3 -V 4 )// SD and the dissipative voltage V x = V 2 -V 4 (at its minimum) for GaAs (7). Table I shows that V x changes by 7 orders of magnitude between / SD =25 and 370 juA and becomes as large as one-tenth of the Hall voltage V H while (as shown in Fig. 1) the value of JR H decreases by only 0.1 ppm! Similarly the other Hall-probe resistance R H f = (^I-^ASD decreases by only 0.6 ppm. These changes in R u are -0.01% of what is expected from the mixing of V x into V H due to the known misalignment of the Hall probes (3 rel-1374

The InAs/GaSb materials system, with different species for both cations and anions, allows one to envision the construction of heterojunctions with either InSb- or GaAs-like interfaces. As a result, this system provides a unique opportunity to explore the limits of interfacial control that can be achieved at the monolayer level by vapor phase growth techniques. Using migration-enhanced epitaxial techniques, we have prepared a series of InAs/GaSb superlattices with both types of interfaces. The large differences in bond lengths and vibrational properties of InSb and GaAs interfaces allow x-ray diffraction and Raman spectroscopy to be sensitive probes of interfacial structure. The x-ray and Raman measurements reveal that it is possible to grow superlattices with almost pure InSb-like or GaAs-like interfaces.

We have performed optical transmission measurements on radiatively heated GaAs substrates as a function of molecular beam epitaxial growth of InAs, GaSb, AlSb, and GaAs films. The energy gap of the GaAs substrate is observed to decrease strongly in energy when materials with band gaps smaller than GaAs are deposited. This decrease in energy gap is a consequence of a substantial increase in growth temperature induced by the deposition of the film. We have observed increases in temperature of over 150 °C from the temperature measured before film growth. Because the thermocouple is weakly coupled to the radiatively heated substrate, conventional temperature controllers are ineffective at measuring or accounting for this change in temperature.

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The effect of interface pond configuration on the structural and optical properties of short-period ( ~5 0 A) GaSb/lnAs superlattices has been examined. Structures consisting of eight monolayers of GaSb and seven monolayers of lnAs with either 'GaAs-like' or 'InSb-like' interface bonds were grown by MBE. Evidence for differences in the Structural properties, vibrational properties and band srrucrure or me two rypes 01 mareriai was omaineo usiny x-ray uimraciiuri, Raman scattering, interband magneto-absorption and ohotoconductivitv measurements.