Current-voltage spectroscopy of the subband structure of strongly pinched-off quantum point contacts

We demonstrate current-voltage spectroscopy of the one-dimensional subband structure of pinched-off quantum point contacts (QPCs). This technique yields the full subband structure and effective barrier of the QPC, without the need to perform an undesirable average over a range of gate voltage. Our measurements reveal strong asymmetry in the potential drop across the QPC, and a significantly enhanced subband spacing, in the pinch-off regime.