Nonergodicity and microscopic symmetry breaking of the conductance fluctuations in disordered mesoscopic graphene

Abstract

We show a dramatic deviation from ergodicity for the conductance fluctuations in graphene. In marked contrast to the ergodicity of dirty metals, fluctuations generated by varying magnetic field are shown to be much smaller than those obtained when sweeping Fermi energy. They also exhibit a strongly anisotropic response to the symmetry-breaking effects of a magnetic field, when applied perpendicular or parallel to the graphene plane. These results reveal a complex picture of quantum interference in graphene, whose description appears more challenging than for conventional mesoscopic systems.

Imaging coherent transport in a mesoscopic graphene ring

“…For example, the magnetic and electrostatic Aharonov-Bohm (AB) effects [18][19][20][21][22][23] have already been examined using conventional transport measurements. Moreover, a significant number of questions recently emerged about the physics of some-observed or predicted-peculiar phenomena such as the increase of the AB oscillation amplitude at high magnetic field [18], the stability of semiclassical orbits with respect to system boundaries [24], the possibility to observe "relativistic quantum scars" in the LDOS of mesoscopic graphene devices [25,26], and the nonergodicity of UCFs in disordered mesoscopic graphene [27]. Revisiting these questions using the SGM imaging technique would certainly help to understand the underlying physics.…”

Hot Carriers in CVD-Grown Graphene Device with a Top h-BN Layer

“…The conductance fluctuations are observed, and they decrease as L increase from L = 0.32 to 50 K, which are typical properties in disordered mesoscopic graphene [24][25][26][27]. at various driving currents from I = 20 nA to 30000 nA at a fixed L of 0.32 K, which reveals similar conductance fluctuation characteristics by current heating in the nonequilibrium regime due to the hot carrier effects in disordered two-dimensional systems [18,[28][29][30][31].…”

“…These results suggest that the carrier-phonon scattering is absent in the multilayer graphene and the h-BN/graphene. The extremely long energy relaxation times in both devices (at least two orders of magnitudes longer than those in pristine exfoliated graphene [27,28] and graphene on SiC [30,34]) can be advantageous for applications in graphene-based hot carrier transistors [41] since carriers can maintain their high kinetic energy (and hence the high effective temperature) with a relatively low driving current.…”

Reversing hot-carrier energy-relaxation in graphene with a magnetic field

“…Nonetheless, we observe reproducible CF that are suppressed with increasing T L due to increased decoherence. 41,42 For each magnetic field, we have indicated with a set of markers the gate voltages corresponding to complete filling of an integer number (N L ¼ nh/4eB, with the sheet density n provided by a parallel-plate capacitor expression) of Landau levels. While there is some correlation between these voltages and the presence of significant structure in the resistance, the correlation is not perfect.…”

“…31,41,42 Layer identification was performed through a combination of optical microscopy and Raman imaging, and the use of bilayer graphene was primarily driven by the relative ease with which manageable pieces of this material could be isolated. Nonetheless, there is a natural benefit to using this system for studies of this type, since the magnetic-field induced changes in the density of states near the DP are more pronounced than for monolayer graphene.…”