We have studied universal conductance fluctuations in the nonlocal magnetoresistance of ${\mathit{n}}^{+}$-GaAs wires. The Lee-Stone correlation field Δ${\mathit{B}}_{\mathit{c}}$ increases by a factor of 5 as the magnetic field increases from 0 to 12 T but the amplitude of the fluctuations does not change. It is possible to explain the increase of Δ${\mathit{B}}_{\mathit{c}}$ quantitatively in terms of a variation of the size of the phase coherence length. However, this should also give rise to a large change in the fluctuation amplitude, which is not observed. This implies that the universal scaling of the conductance fluctuations is not valid in high magnetic fields.

• Received 13 December 1991

DOI:https://doi.org/10.1103/PhysRevLett.69.1248