Fractional Shot Noise in the Kondo Regime

Transport through quantum dots in the Kondo regime obeys an effective low-temperature theory in terms of weakly interacting quasiparticles. Despite the weakness of the interaction, we find that the backscattering current and hence the shot noise are dominated by two-quasiparticle scattering. We show that the simultaneous presence of one- and two-quasiparticle scattering results in a universal average charge $5/3e$ as measured by shot-noise experiments. An experimental verification of our prediction would constitute a most stringent test of the low-energy theory of the Kondo effect.

Figure 1

Transport processes near the unitary limit. (a) In the unitary limit an electron incident from the source is almost totally transmitted into the drain, a process describing the free motion of a R mover. Weak backscattering between R movers and L movers is denoted by the wavy line. (b) Elastic backscattering of 1 R mover with energy $ϵ$ relative to $E_F=({\mu }_s+{\mu }_d)/2$. The energy dependence of this amplitude $\propto \alpha ϵ/T_K$ corresponds to scattering off a resonant level of width $\propto T_K/\alpha$, centered at $E_F$. (c) Inelastic backscattering of 1 R mover accompanied by creation of a particle-hole pair within one reservoir. (d) Inelastic backscattering of 2 R movers with opposite spins $\sigma$ and $\overline{\sigma }$. The amplitudes of processes (c), (d) are proportional to $\beta$, see Eq. (3).

Figure 2

Effective charge $e^{*}$ vs voltage for broken LR tunneling symmetry $\delta ={\delta }_{\theta }=1/20$. The crossover from $e^{*}/e=1$ to $e^{*}/e\approx 5/3$ occurs when $V/T_K$ exceeds $\delta$.