where G 0 ≡ 2e 2 h is the conductance quantum (≈77.6 µS), e is the elementary charge, and h is the Planck constant. T is the probability of an electron or hole to tunnel across the junction under an applied bias voltage, V . Since we study the low-bias conductance of junctions that exhibit coherent hole transport, T is modeled as the hole tunneling probability across a trapezoidal barrier (Fig. ):