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

Magnetoresistance fluctuations in short quasiballistic Si/SiGe wire segment s have been investigated as a function of magnetic field and temperature. T he segments are measured in a four-probe geometry and the voltage probe dis tances 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 amp litude delta R and the correlation field B-c of both the symmetric and anti symmetric part of the resistance fluctuations have been studied Its a funct ion of probe distance and temperature. It is found that, despite the quasib allistic character of electron transport in our samples, the behavior of th e amplitude and correlation field with probe separation is in good qualitat ive agreement with expressions derived for the diffusive regime. The observ ed magnitude of B-c, however, is much larger than expected for the diffusiv e transport regime. A better agreement for B-c is obtained using an express ion adapted for the quasiballistic regime. The temperature dependence of th e correlation field cannot be explained by expressions appropriate for the diffusive or the quasiballistic transport regime.