Tunable effective $g$ factor in InAs nanowire quantum dots

We report tunneling spectroscopy measurements of the Zeeman spin splitting in InAs few-electron quantum dots. The dots are formed between two InP barriers in InAs nanowires with a wurtzite crystal structure grown using chemical beam epitaxy. The values of the electron $g$ factors of the first few electrons entering the dot are found to strongly depend on dot size. They range from close to the InAs bulk value in large dots $\mid g^{*}\mid =13$ down to $\mid g^{*}\mid =2.3$ for the smallest dots.

Figure 1

(Color) (a) STEM image of a nanowire and schematic of the InAs QD. (b) High-resolution STEM image of a QD from the same growth as S#4 and S#6. $L=12\mathrm{nm}$ is defined as the length of the InAs segment (bright) between two InP barriers (dark) with widths $w_1$ and $w_2$. (c) CB oscillations in $I_{SD}$ as a function of $V_g$ at $B=0\mathrm{T}$ for S#4. (d) $I_{SD}$ as a function of magnetic field and gate voltage. The peaks shift as a function of $B$ because of the Zeeman effect and small orbital shifts. (e) Peak separations $\Delta V_G$ as a function of $B$ showing the Zeeman splitting for the first electrons added to the dot with $g^{*}=4.4$, 2.3, 8.9 for S#4, S#1, S#7, respectively.

Figure 2

(a) Differential conductance as a function of gate voltage and applied bias for S#3 at $B=10\mathrm{T}$. The Zeeman split excited states are seen as lines running parallel to the diamond edges as indicated by the arrows. (b) Differential conductance at a gate voltage of 620 mV as a function of bias and magnetic field where the linear Zeeman splitting is directly observed.

Figure 3

Dependence of dot length on the effective $g$ factor. The top curve is the theoretical values obtained from Eq. (1) and hard wall confinement.