Probing the intrinsic shot noise of a Luttinger liquid through impedance matching

TL;DR

This paper demonstrates how impedance matching can reveal the intrinsic shot noise properties of a finite Luttinger liquid, allowing the extraction of fractional charge excitations and improving understanding of their experimental signatures.

Contribution

It introduces a method to analyze shot noise in Luttinger liquids through impedance matching, enabling the study of fractional charges without complex Keldysh techniques.

Findings

Impedance matching aligns shot noise properties of finite and infinite LLs.

Explicit expressions for AC shot noise depend on fractional charges.

Method applies to experimental setups with STM injection and impurity backscattering.

Abstract

We argue that a simple way to bypass reflections at the boundaries of a finite Luttinger liquid (LL) connected to electrodes is to match load and drain impedances to the characteristic impedance of the LL viewed as a mesoscopic transmission line. For an impedance matched LL, this implies that the AC and DC shot noise properties of a finite LL are identical to those of an infinite LL. Even for an impedance mismatched LL, we show by a careful analysis of reflections that the intrinsic infinite LL properties can still be extracted yielding possibly irrational charges for the LL elementary excitations. We improve on existing results for AC shot noise by deriving expressions with explicit dependence on the charges of the fractional states. Most notably these results can be established quite straightforwardly without resort to the Keldysh technique. We apply these arguments to two experimental setups which allow the observation of different sets of fractional quasiparticles: (i) injection of current by a STM tip in the bulk of a LL; (ii) backscattering of current by an impurity. An Appendix reviews pedagogically the 'fractional states picture' of the LL.