Temperature Dependence and Magnetic Field Dependence of Quantum Point Contacts in Si-Inversion Layers

The conductance of ballistic point contacts in high-mobility Si-inversion layers has been studied at several temperatures between 75 and 600 mK both without and in a magnetic field (up to 12T). When the width of constrictionis varied in zero magnetic field, step-like features at multiples of 4e2/h are observed in the conductance that are independent of temperature. In the presence of a magnetic field, the spin and valley degeneracies are lifted and the conductance is quantized at multiples of e2/h. The transition from zero-field quantized conduction to the quantum Hall effectprovides a direct demonstration of the magnetic depopulation of one-dimensional subbands in the constriction.