Figure 4 : Successive splittings of the ZBA.

From: Wigner and Kondo physics in quantum point contacts revealed by scanning gate microscopy

Figure 4

The figure analyses the low bias source-drain spectroscopy when the tip is scanned along the orange line 3 indicated in Fig. 3a. (a) Differential conductance G versus source-drain bias at a fixed gate voltage Vgate=−1 V for different tip positions from 0 to 450 nm. Successive curves are shifted upwards by 0.0075 × 2e2/h. Conductance peaks are visible at zero and finite bias on red and blue curves, respectively. (b) Colour plot of the same data as in a after subtraction of a smooth background to suppress the main gating effect of the tip. Peak positions are indicated by dots. The successive ZBA splittings give a checkerboard pattern. The asymmetry results from the bias-induced change of the QPC position. (c) Schematic of the QPC potential with one (top) and two (bottom) localized electrons, corresponding, respectively, to a S=1/2 ground state with a zero-bias Kondo peak and to a S=0 ground state with finite-bias Kondo peaks involving the excited state S=1 with singlet-triplet energy splitting J. The expected conductance G versus bias V is shown on the right for each state. (d) Schematic of the QPC potential with an increasing number of electrons localized by Coulomb interactions. The antiferromagnetic spin coupling in this small 1D Wigner crystal gives either a S=1/2 ground state (ZBA) or a S=0 ground state (splitting of the ZBA), depending on the parity (respectively odd or even).