Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2019 / Paper 2 / Section B / 21 / v / Solution 2026-10-20
View more
With ballistic conductance quantization, as a gate opens the channel, conductance plateaux at appear; successive transverse modes add one quantum, approximately per spin-degenerate subband. Their appearance is the key low-temperature electrical signature.
Figure 1.
Ideal conductance plateaux sharpen as thermal and disorder broadening become small compared with subband spacing
. Source. Details.
Require transverse confinement with separated subbands, and measurement-bias energy well below the subband spacing, a mean free path exceeding the channel length, and smooth low-reflection coupling to reservoirs. Correct for appreciable external series resistance. Phase coherence is needed for additional interference oscillations, but perfect phase coherence across an entire macroscopic circuit is not a separate requirement for the basic mode-counting result. A field that resolves spin splitting can produce increments.[ref]
Read the full article