Single-electron tunneling in a quantum dot — Coulomb diamonds in the (V_gate, V_bias) plane
Coulomb blockade occurs when the charging energy E_C = e²/2C exceeds thermal energy kT. Current is suppressed unless V_bias or V_gate is tuned to allow a single electron on/off the island. The diamond-shaped blockade regions arise from the electrostatic energy landscape; vertices of adjacent diamonds correspond to charge degeneracy points where conductance peaks occur.