Fano Factor Reduction on the 0.7 Conductance Structure of a Ballistic One-Dimensional Wire

We have measured the nonequilibrium current noise in a ballistic one-dimensional wire which exhibits an additional conductance plateau at $0.7\times 2e^2/h$. The Fano factor shows a clear reduction on the 0.7 structure, and eventually vanishes upon applying a strong parallel magnetic field. These results provide experimental evidence that the 0.7 structure is associated with two conduction channels that have different transmission probabilities.

Figure 1

(a) Conductance characteristics $G(V_g)$ at $T=273$, 360, 515, 666, and 779 mK. With increasing temperature the resonance at $0.9\times 2G_0$ disappears, whereas the 0.7 structure (in this case close to $0.65\times 2G_0$) becomes more pronounced. (b) $G(V_g)$ at $T=560\mathrm{m}\mathrm{K}$ in parallel fields $B=0$ to 8 T, in steps of 1 T. With increasing $B$, the 0.7 structure evolves into the spin-split plateau at $G_0$.

Figure 2

Typical current noise power spectrum variation as a function of the frequency for $I=10\mathrm{n}\mathrm{A}$. The solid line is a fit of white noise plus $1/f$ noise. The inset shows the ratio $S_{1/f}(I)/S_{I\mathrm{P}\mathrm{o}\mathrm{i}\mathrm{s}\mathrm{s}}$ as a function of the zero bias conductance.

Figure 3

Excess noise without (○) and with (●) thermal corrections, as a function of the Poissonian noise at $T=460\mathrm{m}\mathrm{K}$ with $G(0)=0.71\times 2G_0$. The dotted line fit to the uncorrected data $\Delta S_I$ gives an overestimated $F^{+}=0.28$. The dashed line fit to $\Delta S_{I\mathrm{C}\mathrm{o}\mathrm{r}\mathrm{r}}$ gives $F^{+}=0.17$, an upper bound closer to $F$. The inset shows $G$ as a function of $V$.

Figure 4

Upper bound of the Fano factor at $T=460\mathrm{m}\mathrm{K}$ without thermal corrections (○), plotted versus the zero bias conductance. The solid circles (●) show the same measurements as the open circles, but with thermal corrections applied. Squares (□) show the Fano factor with thermal corrections at $T=610\mathrm{m}\mathrm{K}$ and $B=3\mathrm{T}$, and the triangles (▲) are similarly corrected data at $T=580\mathrm{m}\mathrm{K}$ and $B=8\mathrm{T}$.