SGM 4

Tuning of quantum interference in top gated graphene

The chiral nature of quasiparticles in graphene gives rise to a number of peculiar magnetotransport phenomena such as a nonzero Berry phase resulting in half-integer quantum Hall effect and negative magnetoresistance. Quantum interference effects in graphene are nowadays theoretically well understood, based on the interplay between different chirality-breaking scattering mechanisms and dephasing time. From an experimental point of view, in high quality graphene, the low density of short-range scatterers allows the Berry phase to manifest as a Weak Antilocalization (WAL) dip in the magnetoresistance. As the pi-phase contribution is averaged out by chirality breaking scattering, enhanced backscattering results in the usual Weak Localization (WL) correction. Essential in driving the transition between WAL and WL regimes is the possibility of tuning the charge density in the graphene monolayer.

The quest for monolithic integration of devices recently moved the interest towards Epitaxial Graphene (EG) on SiC, which has reached high mobility and uniformity on the wafer scale. Despite such interest, the interplay between localization and chirality is still rather unexplored for EG grown on the Si face, where only positive magnetoresistance due to electron localization has been observed so far.

WL-pic
Figure 1: (a) Longitudinal resistance R_xx as a function of top gate voltage V_TG, showing a maximum at the charge neutrality point. The values of V_TG selected for magnetoresistance measurements are indicated. (b) The amplitude of the WL peak decreases as the temperature is increased (point II), evolving into a WAL dip for sufficiently low charge density (point IV).

We performed quantum-interference measurements in top-gated Hall bars of monolayer graphene epitaxially grown on the Si face of SiC, in which the transition from the Weak Localization to Weak Anti Localization regime was achieved varying temperature and charge density. We perform a systematic study of the quantum corrections to the magnetoresistance due to quantum interference of quasiparticles and electron-electron interaction. We analyze the contribution of the different scattering mechanisms affecting the magnetotransport in the -2.0 x 10^10 cm^-2 to 3.75 x 10^11 cm^-2 density region and find a significant influence of the charge density on the intravalley scattering time. Furthermore, we observe a modulation of the electron-electron interaction with charge density not accounted for by present theory. Our results stress the role of SiC-based devices as a promising technology for graphene coherent electronics.

Publications:

  1. Andrea Iagallo, Shinichi Tanabe, Stefano Roddaro, Makoto Takamura, Hiroki Hibino, and Stefan Heun: Tuning of quantum interference in top-gated graphene on SiC, arXiv:1311.7276 [cond-mat.mes-hall].
  2. Andrea Iagallo, Shinichi Tanabe, Stefano Roddaro, Makoto Takamura, Hiroki Hibino, and Stefan Heun: Tuning of quantum interference in top-gated graphene on SiC, Phys. Rev. B 88, 235406 (2013).

Presented at:

  1. A. Iagallo, S. Tanabe, S. Roddaro , M. Takamura, H. Hibino, S. Heun, and F. Beltram: Tuning of quantum interference in top gated graphene, 20th International Conference on Electronic Properties of Two-Dimensional Systems (EP2DS-20), Wroclaw, Poland, 1 – 5 July 2013 (poster). [Abstract] [Poster].