Nuclear and electron spins in a quantum wire may spontaneously form an ordered state at very low temperatures, according to work recently carried out by an international team of physicists. The team was studying the conductance of gallium-arsenide quantum wires and discovered that, at temperatures of 0.1 K and lower, the conductance of the wires dropped below the universal quantized value. This reduced quantization is explained using a theoretical model that proposes that the nuclear and electron spins order themselves in a helical formation at these temperatures.
A quantum wire confines electrons to a single direction of movement. As a consequence, and unlike a regular wire, its conductance is quantized – the flow of current is not proportional to the voltage applied. The conductance takes discrete values in multiples of 2e2/h where e is the elementary charge and h is Planck's constant. The factor of two comes from the fact that the spin of electrons in an unordered state can take one of two values.
Dominik Zumbühl from the University of Basel in Switzerland, along with colleagues at Harvard and Princeton universities in the US, measured the conductance of gallium-arsenide quantum wires at temperatures ranging from 20 K to 0.01 K. They noted that, at the higher temperatures, the wires did indeed exhibit the universal quantized conductance in units of 2e2/h. At lower temperatures, however, they saw something new.To read more, click here.