Quantum ballistic transport in constrictions ofn-PbTe

Conductance of submicron constrictions of PbTe:Bi was studied up to 8 T and between 4.2 K and 50 mK. The structures were fabricated by electron beam lithography and chemical etching of high-electron mobility films grown by molecular beam epitaxy on ${\mathrm{BaF}}_2.$ In the moderately strong magnetic fields perpendicular to the current, $B>~1$ T, the conductance shows accurate quantization in the units of ${1e}^2/h$ as a function of the side-gate voltage. In the absence of the field, a temperature-independent step structure, with an average step height of $\approx e^2/h,$ is observed. It is suggested that such a quantization may reflect the lifting of the Kramers degeneracy by the exchange interaction among the electrons, effective despite a large dielectric constant of bulk PbTe.