It is shown that within the Feng-Lee-Stone theory of low-frequency noise in dirty metals [Phys. Rev. Lett. 56, 1960, 2772(E) (1986)], the application of a relatively weak magnetic field reduces the noise power by precisely a factor of 2. The field scale for the relative noise power to approach the value of (1/2 is $B_c$=A(h/e)/$L_{\mathrm{in}{}^2}$ in two dimensions, where $L_{\mathrm{in}}$ is the inelastic length and A is a constant of order unity. This result holds in all systems to which the theory applies, even in the presence of spin-orbit and impurity spin interactions; however in the absence of spin-orbit interaction there will be an additional factor-of-2 reduction at fields such that the Zeeman splitting exceeds hD/$L_{\mathrm{in}{}^2}$ (where D is the diffusion constant). This prediction provides an unambiguous experimental test of the theory, independent of the microscopic origin of the noise. The universal reduction factors are related to basic symmetry properties of the orthogonal, unitary, and symplectic random-matrix ensembles.

• Received 18 November 1988

DOI:https://doi.org/10.1103/PhysRevB.39.10736