November 2013

Abstracts of the QSIT Lunch Seminar, November 7, 2013

Universal transport properties of graphene on substrate

Nuno Couto Guimarães, Quantm Electronics group, Université de Genève

The recent developments of graphene transfer techniques to use h-BN as substrate has led to a new generation of graphene transistors displaying extremely high quality and exibiting exciting new physical phenomena. Despite the advances in fabrication, achieving high quality devices reproducibly still remains a challenge. Here we discuss how, through a systematic effort to optimize the quality of graphene transistors on h-BN, we found that the behaviour of graphene-on-substrates exhibit an unexpected universality. Specifically, our data shows that the carrier mobility and the amplitude of the charge density fluctuations around the charge neutrality point originate from the same microscopic mechanism. By analysing weak localization data obtained in magnetoconductance measurements, we show that the potential responsible for both the limit to the carrier mobility and for the charge density fluctuations is long-ranged. We further found that graphene devices with different substrates (SiO2, h-BN and SrTiO3) with different chemical and physical properties exhibit the same universal behaviour, suggesting that this universality originates from the properties of graphene itself. We identify strain in graphene as the most likely candidate to explain these observations.

Using electrons to excite optical atennas

Palash Bharadwaj, Photonics Laboratory, ETH Zurich

Optical antennas have recently emerged as a novel technological tool to control light emission on the nanoscale.  In this talk, I will introduce the concept of optical antennas in the context of photoemission from single quantum emitters such as dye molecules and colloidal quantum dots.  I will then discuss the possibility of using single electrons to excite a transmitting optical antenna. Along these lines, I will present results that demonstrate plasmon-mediated energy transfer between inelastically tunneling electrons and photons in metal nanostructures.

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