Current Noise in InAs/GaInSb Quantum Well Interfaces

We report preliminary shot noise measurements in InAs/GaInSb quantum well interfaces. The band structure of these composite quantum wells is inverted, and the electron and hole densities are equal at the cross point of the valence and conduction bands. The holes in the strained GaInSb layer couple strongly to the electrons in the InAs layer, opening a gap in the spectrum of the 2d bulk. When gated into the appropriate regime, this allows only topologically-protected 1d helical edge states to contribute to charge transport. Using a back gate to tune the Fermi level, we can sweep into the hybridized bulk gap, recognized by a peak in the longitudinal resistance. If the helical edge length is within the coherence length of the sample, only ballistic transport should occur along the edge, and one would expect the shot noise to be dominated by the resistance of the contacts. We will compare current noise measurements of samples in the nominal Quantum Spin Hall Insulator state and in the lower-resistance, bulk transport state.