Graphene

Paving the Way Towards 1D Helical Conductors with Fractional Quantum Statistics

  • By Aude Marjolin
  • 22 February 2017

In a letter published in the February 2017 issue of Nature Nanotechnology, Ben Hunt and his collaborators at the Massachusetts Institute of Technology, the University of California Santa Barbara, and the National Institute for Materials Science in Tsukuba, Japan describe how they engineered a graphene electron–hole bilayer device into a helical 1-dimensional (1D) conductor and characterized its transport properties. In a helical 1D conductor, electrons moving in opposite directions also have opposite spin polarizations, and such helical states can be obtained by combining two quantum Hall (QH) edge states with opposite spins and opposite momenta relative to the magnetic field (i.e. opposite chiralities).

My colleagues at MIT came up with this ingenious way of producing helical edge states from two decoupled graphene layers, and then they proved their idea worked with a series of powerful transport experiments,” says Hunt. “I was thrilled to be able to make a contribution to the experiment by using capacitance measurements to help prove that the unique helical states they observe really are edge states.”

Whispering Galleries and Berry Phase Switches in Circular Graphene Resonators

Speaker(s): 
Joseph Stroscio
Dates: 
Thursday, January 12, 2017 -
4:00pm to 5:00pm

Ballistic propagation and the light-like dispersion of graphene charge carriers make graphene an attractive platform for optics-inspired graphene electronics where gate tunable potentials can control electron refraction and transmission. In analogy to optical wave propagation in lenses, mirrors and metamaterials, gate potentials can be used to create Fabry-Pérot interferometers and a negative index of refraction for Veselago lensing. In circular geometries, gate potentials caninduce whispering gallery modes (WGM), similar to optical and acoustic whispering galleries [1,2...

Whispering Galleries and Berry Phase Switches in Circular Graphene Resonators

Speaker(s): 
Joseph Stroscio
Dates: 
Tuesday, January 12, 2016 -
4:00pm to 5:00pm

Ballistic propagation and the light-like dispersion of graphene charge carriers make graphene an attractive platform for optics-inspired graphene electronics where gate tunable potentials can control electron refraction and transmission. In analogy to optical wave propagation in lenses, mirrors and metamaterials, gate potentials can be used to create Fabry-Pérot interferometers and a negative index of refraction for Veselago lensing. In circular geometries, gate potentials caninduce whispering gallery modes (WGM), similar to optical and acoustic whispering...

Modelling Carbon Materials from Pencil and Paper to High-throughput Screening

Speaker(s): 
Johan Carlsson
Dates: 
Thursday, October 20, 2016 -
4:00pm to 5:00pm

Carbon materials have extraordinary properties, but utilizing these properties in applications requires a deep understanding of the materials. Modelling and simulations can here be a very useful complement to experiments and even be used to predict properties ahead of the experiments. This is particularly relevant for graphene, which was investigated theoretically in great detail long before it was possible to perform any experiments. The first investigations were performed on ideal sheets using pencil and paper, but as grown grown graphene sheets are often...

Massive Dirac Fermions and Hofstadter Butterfly in a van der Waals Heterostructure

  • By Aude Marjolin
  • 21 June 2013

The remarkable transport properties of graphene, such as the high electron mobility, make it a promising material for electronics. However, unlike semiconductors such as silicon, graphene's electronic structure lacks a band gap, and a transistor made out of graphene would not have an “off” state. Ben Hunt and his colleagues modulated the electronic properties of graphene by building a heterostructure consisting of a graphene flake resting on hexagonal boron nitride (hBN), which has the same honeycomb structure as graphene, but consists of alternating boron and nitrogen atoms instead of carbons. The natural mismatch between the graphene and hBN lattices led to a moire pattern with a large wavelength, causing the opening of a band gap, the formation of an elusive fractional quantum Hall state, and, at high magnetic fields, a fractal phenomenon in the electronic structure called the Hofstadter butterfly.