Hanbury-Brown and Twiss exchange and non-equilibrium-induced correlations in disordered, four-terminal graphene-ribbon conductor

Abstract

We have investigated current-current correlations in a cross-shaped conductor made of graphene. The mean free path of charge carriers is on the order of the ribbon width which leads to a hybrid conductor where there is diffusive transport in the device arms while the central connection region displays near ballistic transport. Our data on auto and cross correlations deviate from the predictions of Landauer-Büttiker theory, and agreement can be obtained only by taking into account contributions from non-thermal electron distributions at the inlets to the semiballistic center, in which the partition noise becomes strongly modified. The experimental results display distinct Hanbury – Brown and Twiss (HBT) exchange correlations, the strength of which is boosted by the non-equilibrium occupation-number fluctuations internal to this hybrid conductor. Our work demonstrates that variation in electron coherence along atomically-thin, two-dimensional conductors has significant implications on their noise and cross correlation properties.

Hanbury Brown and Twiss exchange correlations in a graphene box

“…This model is in fact quite close to the model employed in Ref. 13 . Such a model, lacking voltage variation over the graphene box, was not able to match all the measured quantities G ij , S 11 , S 33 , S 13 properly.…”

“…Closest to the present work is our previous experiment with a graphene cross sample with 50 nm nanoribbon arms 13 . In that graphene cross the HBT effect was characterized by occupation number noise in the nearly ballistic central region and regular diffusive noise in the ribbon arms.…”

“…To our knowledge, only one experiment has so far addressed HBT exchange effects in diffusive conductors. Cross correlations and HBT exchange were measured in a cross-shaped graphene conductor in which the charge carrier density, and thereby the screening of impurities, could be tuned by the back gate voltage 13 . According to the theory, in a diffusive conductor with cross geometry the paths of scattering electrons are quite restricted, and the HBT exchange effect should disappear 11,12 .…”

Low-noise correlation measurements based on software-defined-radio receivers and cooled microwave amplifiers

“…1 was used successfully in a dry dilution refrigerator to collect shot noise data from a graphene sample mounted on the mixing chamber plate at 50 mK. 32 A few sweeps of cross-and autocorrelation data from this experiment have been plotted in Fig. 5 for reference.…”

Shot Noise in Mesoscopic Systems: from Single Particles to Quantum Liquids

“…On the other hand, Oliver et al measured the crosscorrelation between the two outputs of a beam splitter in the time domain [68]. While these HBT experiments were performed using GaAs/AlGaAs semiconductor devices, similar experiments were later conducted using graphene [158,159] and free electrons in a vacuum [160]. Another well-known example of a fermion-quantum-optics experiment is Mach-Zehnder interferometry using QH edge channels [163].…”