Possible Evidence for Helical Nuclear Spin Order in GaAs Quantum Wires

We present transport measurements of cleaved edge overgrowth GaAs quantum wires. The conductance of the first mode reaches 2e(2)/h at high temperatures T greater than or similar to 10 K, as expected. As T is lowered, the conductance is gradually reduced to 1e(2)/h, becoming T independent at T less than or similar to 0.1 K, while the device cools far below 0.1 K. This behavior is seen in several wires, is independent of density, and not altered by moderate magnetic fields B. The conductance reduction by a factor of 2 suggests lifting of the electron spin degeneracy in the absence of B. Our results are consistent with theoretical predictions for helical nuclear magnetism in the Luttinger liquid regime.