Correlation-Induced Conductance Suppression at Level Degeneracy in a Quantum Dot

The large, level-dependent $g$ factors in an InSb nanowire quantum dot allow for the occurrence of a variety of level crossings in the dot. While we observe the standard conductance enhancement in the Coulomb blockade region for aligned levels with different spins due to the Kondo effect, a vanishing of the conductance is found at the alignment of levels with equal spins. This conductance suppression appears as a canyon cutting through the web of direct tunneling lines and an enclosed Coulomb blockade region. In the center of the Coulomb blockade region, we observe the predicted correlation-induced resonance. Our findings are supported by numerical and analytical calculations.

Figure 1

(a) SEM image of a fabricated InSb nanowire quantum-dot device. (b) Conductance in gray scale measured at a source-drain bias of $V_{\mathrm{sd}}=0.5\mathrm{mV}$. (c) Schematic for the evolution of the single-particle levels 4 and 5 with magnetic field (neglecting the level interaction and Coulomb charging). Letters $A$, $B$, and $C$ mark the three single-particle level degenerate points investigated in this work. (d) Conductance along line cut $A$ in (b) showing a conventional spin-$1/2$ Kondo peak at $B=0$. (e) Conductance along line cut $B$ showing an integer-spin Kondo-like conductance enhancement at $B\approx 1.5\mathrm{T}$.

Figure 2

Details of the conductance suppression. (a) Enlarged section of Fig. 1b. (b)–(f) Conductance plots along line cuts C1-C5 (at backgate voltages of 848, 822, 762, 708, and 690 mV) of (a), respectively.

Figure 3

Conductance where interaction is of minor importance. (a) Experimental data (crosses) for $V_{\mathrm{bg}}=690\mathrm{mV}$ together with calculated results using the noninteracting Green’s function (GF) model with $V_{\mathrm{sd}}=0.5\mathrm{mV}$ (black solid line) and the Breit-Wigner (BW) formula of Eq. (3) (black dashed line). Corresponding 2vN results, including interactions, are given in thin orange lines for two temperatures. (b) Conductance from the GF model in its region of validity, together with the positions of the minimal conductance from the experiment (red dots) and the 2vN model (blue crosses).

Figure 4

Calculations by the 2vN approach at $k_{B}T=0.2\mathrm{meV}$, $V_{\mathrm{sd}}=0.5\mathrm{mV}$, and $\Omega =0$ unless stated otherwise. (a) Canyon of conductance suppression. (b) Conductance for different interlevel couplings $\Omega$ together with the experimental data. (c) Conductance for different bias values of $V_{\mathrm{sd}}$.