Condensed Matter & Surface Sciences

COLLOQUIUM

 

 

MARC BOCKRATH

The Ohio State University

 

 

Electronics and Straintronics in Graphene

 

 

We will discuss a number of our ongoing research projects aimed at understanding the properties of low-dimensional systems such as graphene and two-dimensional material heterostructures.  First, we have measured the quantum transport properties of individual nanoscale folds in graphene.  We find that they act as quantum dots, indicating quantum confinement of electrons.  Our data can be understood as confinement resulting from synthetic gauge fields due to the strain caused by the folds. These folds are theoretically predicted to transmit electrons with different valley index with different probability, opening the door to the realization of straintronic valley filters.  In addition, recently several research groups have demonstrated placing graphene on hexagonal BN (hBN) with crystallographic alignment.  This not only creates a protected environment yielding high-mobility devices, but also due to the resulting superlattice formed in these heterostructures, an energy gap, secondary Dirac Points, and Hofstadter quantization in a magnetic field have been observed.  In these systems, we observe a p Berry’s phase shift in the magneto-oscillations when tuning the Fermi level past the secondary Dirac points, originating from a change in topological pseudospin winding number from odd to even when the Fermi-surface electron orbit begins to enclose the secondary Dirac points. Finally, we study the properties of additional graphene/hBN layer electrostatically gated structures such as twisted trilayers that are comprised of AB-stacked bilayer graphene contacting a graphene monolayer through a twist angle, and hBN-encapsulated graphene bilayers with large applied perpendicular electric field.  In the twisted trilayers, which couple the massive bilayer spectrum to that of the massless monolayer spectrum, the interlayer interactions and screening produce a nonlinear monolayer graphene gate capacitance and renormalize the layers’ band structure. In the encapsulated bilayers, we perform Landau level spectroscopy, measure the layer polarizability of the electrons, and observe easy-axis quantum Hall ferromagnetism.

 

 

 

Thursday, October 19, 2017

4:10 p.m. -- Walter Lecture Hall 245