Magnetoresistance fluctuations in short n-type Si/SiGe heterostructure wires

Magnetoresistance fluctuations in short quasiballistic Si/SiGe wire segments have been investigated as a function of magnetic field and temperature. The segments are measured in a four-probe geometry and the voltage probe distances L are taken smaller or larger than the phase coherence length l(phi) (approximate to 1.5 mu m at T =0.1 K) and the electron mean free path l(e) (approximate to 0.8 mu m). At magnetic fields smaller than B= 1 T, the amplitude delta R and the correlation field B-c of both the symmetric and antisymmetric part of the resistance fluctuations have been studied Its a function of probe distance and temperature. It is found that, despite the quasiballistic character of electron transport in our samples, the behavior of the amplitude and correlation field with probe separation is in good qualitative agreement with expressions derived for the diffusive regime. The observed magnitude of B-c, however, is much larger than expected for the diffusive transport regime. A better agreement for B-c is obtained using an expression adapted for the quasiballistic regime. The temperature dependence of the correlation field cannot be explained by expressions appropriate for the diffusive or the quasiballistic transport regime.