Finite conductivity in mesoscopic Hall bars of inverted InAs/GaSb quantum wells

We have studied experimentally the low-temperature conductivity of mesoscopic size InAs/GaSb quantum well Hall bar devices in the inverted regime. Using a pair of electrostatic gates we move the Fermi level into the electron-hole hybridization state, observing a mini gap and Van Hove singularity at its edge. Temperature dependence of the conductivity in the gap shows a residual conductivity, which can be consistently explained by the contributions from the free as well as the hybridized carriers in the presence of impurity scattering, as proposed by Naveh and Laikhtman, [Europhys. Lett. 55, 545 (2001)]. Experimental implications for the stability of proposed quantum spin Hall helical edge states will be discussed.