Condensed Matter Physics Seminar

Prof. Issai Shlimak, Bar-Ilan University, Israel

Monday 16 February 2015, 1100-1200
Physics Department

In A13 (theory office/meeting room), Physics:

Localization of charge carriers in monolayer graphene gradually disordered by ion irradiation

Raman scattering (RS) and film resistance R were measured in six series of samples fabricated by electron-beam lithography on the surface of a large size (5x5 mm) monolayer graphene film. Samples were irradiated by different doses of C ions. It was observed that in highly irradiated samples, the RS lines disappear which is accompanied by the exponential increase of R and strongly non-linear current-voltage characteristics. These facts are interpreted as the evidence that graphene film ceases to be a continuous and splits into small-size fragments. Comparison of irradiation with light C ions and heavy Xe ions showed that degree of disorder is not determined by the dose, but the density of structural defects ND induced by irradiation.

Measurements of the temperature dependence R(T) and magnetoresistance reveal the gradual transition of conductivity with increase of ND: from metallic conductivity in initial samples through the weak localization and antilocalization regime at small degree of disorder to the variable-range-hopping conductivity for strongly localized carriers. Fitting the theoretical curves with experimental data allows to determine several important parameters like the maximal dephasing length in the weak localization regime and radius of localization for the case of strong disorder.

It is suggested that the strengthening of localization with increase of ND could be explained by assuming that the structural defects in graphene are of amphoteric nature, i.e. they can be either donors or acceptors and compensate each other.

Reference:

[1] I. Shlimak et al., Phys. Rev. B 91, 045414 (2015);

[2 ] E. Zion et al., arXiv: 1501.04581v1 (2015), submitted to PRL.