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Colloquia & Guest Speakers


Optical signatures from 2D materials- charge, strain, real and pseudo magnetic field signatures

Dr. Anna Swan, Boston University

Monday, September 26, 2016
3:00 p.m.
Goergen Hall, Room 101


Van der Waals materials such as graphene, hBN and the transition metal dichalcogenides (TMDCs) have made physics in 2D possible, and has revealed a host of interesting phenomena. Optical methods are relatively fast and non-destructive methods. In addition, very little sample preparation is needed, compared to for example transport measurements. One of our goals is to be able to use optical methods to fully characterize a sample with
predictive power regarding for example charge mobility. We are also interested in the optical response to different external perturbations, such as strain, magnetic and electric fields, dielectric screening and charge. I will discuss two materials, single layer MoS2 and graphene in different environments. Our work on MoS2 showing unprecedented bandgap tuning with strain, and discuss the temperature dependence of trions (charged, three particle excitons). I will also discuss how Raman spectroscopy of graphene can be used to determine e.g., strain, charge, layer thickness, defect concentration etc.  Here we focus on pristine suspended graphene and graphene sandwiched in hBN and show that the Raman 2D peak split can be used as a good measure of very low charge density and dielectric screening.   We revisit the origin of the asymmetry in the 2D peak that is observed at low doping and screening effects on Fermi velocity and the TO phonon dispersion.

Location:Goergen 101

Refreshments will be served.