CPM Seminar

Graphene Quantum Strain Transistors

Alexandre Champagne

Department of Physics
Concordia University

Applying a mechanical strain to graphene is nearly equivalent to imposing a magnetic field, and can modify the path of electrons. A ballistic graphene transport device under the correct strain and electric field is expected to have zero conductivity due to total internal reflection of its Dirac carriers at the contact-channel interface. If this were realized experimentally, it would create graphene transistors for ballistic (quantum) circuits. Despite a large number of idealized theoretical work on transport in strained graphene, little progress has been made on experiments and in connecting the theoretical expectations to the data. We present both a simple theoretical model and advanced experimental work aimed at demonstrating quantum strain transistors in graphene.

We first present an applied model for ballistic transport in uniaxially strained graphene. This model combines theoretical transport with realistic experimental limitations originating from our suspended device design, materials, and instrumentation. In this model, we consider first order strain effects which deform the Dirac cones, and shift the energy and momentum positions of the Dirac points. At sufficient strain and gate voltage, the transmission probability of carriers changes dramatically resulting in a high on/off ratio transistor effect. We clarify how this theoretical model could be used to extract the applied strain, crystal chirality, and contact doping of a device from experimental data.

We then describe the building of the experimental platform (instrumentation and devices) necessary to demonstrate graphene quantum strain transistors. We observe ballistic transport in suspended graphene transistors, and show that their electrodes (source, drain) are themselves ballistic. We present a home-built uniaxial strain assembly which operates at 0.3 K, and transport data confirming its precise calibration.

Finally, we report transport data in uniaxially strained graphene channels. We clearly observe the theoretically predicted behavior of quantum strain transistors: a strain-controlled decrease in conductivity and strain-tunable work function in graphene. More experimental work is needed to achieve the sought after high on/off ratio transistors.