Effect on Conductance of an Isomer State in a Quantum Point Contact

摘要

We describe a novel phenomenological model for transmission through an adiabatic 1-dimensional constriction, where the electronic configuration around the middle of a quantum point contact can be in two configurations: the usual ground state with spin neutrality (S=0) and a higher (virtual) isomer with an uncompensated electronic spin (S=1/2), which modifies the conductance at higher temperatures, where it is thermally populated, giving rise to the so-called 0.7 structure. Bias spectroscopy reveals the energy difference between the two isomers. The isomer reflects the charge/spin separation in the middle of the constriction. The high energy isomer is a spin 1/2 state (but not magnetically ordered), and will not directly contribute to the transmission unless temperature is high or biasing allow a Kondo-like resonant transmission. The resonant transmission represents a reduction in conduction from the fully quantized value, 2e2/h.