Shot noise reduction in quantum wires with the 0.7 structure

Shot noise reduction in quantum wires is interpreted within the model for the 0.7 structure in the conductance of near perfect quantum wires [T. Rejec, A. Ramšak, and J. H. Jefferson, Phys. Rev. B 62, 12985 (2000)]. It is shown how the Fano factor structure is related to the specific structure of the conductance as a consequence of the singlet-triplet nature of the resonances with the probability ratio $1:3$. An additional feature in the Fano factor, related to the 0.25 structure in conductance, is predicted.

Figure 1

(Color online) (a) A weak negative potential fluctuation binds one electron (electron density shown with dashed line) with the energy below first channel minimum, ${ϵ}_b<0$ (dotted line) and chemical potential ${\mu }_L\sim {\mu }_R$. (b) Finite conduction with electron energy, $ϵ>0$, and linear regime, ${\mu }_L\gtrsim {\mu }_R$. The two-electron scattering (quasibound) state is singlet or triplet. $V_{\mathit{eff}}$ is an effective double barrier tunneling potential for the scattered electron. (c) A larger source-drain voltage where the triplet $\left({ϵ}_1\right)$ resonance becomes overdamped with a broader, more robust, singlet $\left({ϵ}_0\right)$ becoming visible in transport.

Figure 2

(Color online) Panels $\left({\mathrm{a}}_1\right)$ and $\left({\mathrm{b}}_1\right)$: Singlet and triplet transmission probabilities as a function of Fermi energy $\mu$ measured relative to the bottom of the first channel. Results for cylindrical quantum wires with a symmetric bulge for all parameters as in Figs. 3(b) and 3(c) of Ref. 13. In panels $\left({\mathrm{a}}_2\right)$ and $\left({\mathrm{b}}_2\right)$ the conductance (full lines) and the Fano factor are presented. Panels $\left({\mathrm{a}}_3\right)$ and $\left({\mathrm{b}}_3\right)$: The Fano factor as a function of $G$ (full line) and unitarity limits (dotted line). $\left({\mathrm{c}}_1\right)$ Transmission probabilities as would arise, e.g., for a left-right asymmetric confining potential (in resonance $T_S<1$). The corresponding energy dependence of the Fano factor and conductance, $\left({\mathrm{c}}_2\right)$, and Fano factor as a function of conductance, $\left({\mathrm{c}}_3\right)$. The energy and temperature scale is here in the units of single-triplet energy difference $J$.

Figure 3

(Color online) (a) Inset: Experimental values from Ref. 12 for $F\left(G\right)$ for $B=0$ (bullets) and two different interpolating (fitting) forms of $F$. Main figure: Conductance for $T=515\mathrm{mK}$ and $B=0$ (dashed line), singlet (full line), and triplet (dotted) transmission probabilities extracted from experimental values of $G\left(\mu \right)$ vs $\mu$ and using two interpolating forms for $F$. The shaded area corresponds to the shaded area in the inset. (b) As in (a), for $T=273\mathrm{mK}$.