Avik Ghosh: Electronic switching using Tunable Dirac fermion optics

posted 27 May 2019, 12:14 by info admin   [ updated 12 Aug 2019, 02:41 ]
Charles Brown Dept of Electrical and Computing Engineering and the Dept of Physics at the University of Virginia

The unconventional flow of electrons in 2D Dirac cone systems provides unique opportunities to realize nontrivial optical analogues of their electronic counterparts. Using quantum simulations of electron flow as well as careful junction fabrication [1] and transport experiments from our collaborators - we can now demonstrate the ability to steer electrons using the negative index Veselago effect [2], collimate them at junctions using Klein tunneling [3] and rotate their transmission lobes to demonstrate the analogue of Malus' law for polarizer-analyzers [4]. Other examples such as antiKlein tunneling and electronic Brewster angles still remain to be seen experimentally. In all these examples, as well as analogous transport studies of Neel skyrmions along racetracks, the key underlying physics is driven by the conservation of topological charge carried by the spins and pseudospins. These symmetry effects give us additional degrees of tunability that are quite unconventional for electronic switching. For instance, the ability to collimate electron flow can be used to engineer a gate-tunable transport gap in bulk graphene [6], which is necessary to beat the fundamental Boltzmann limit on electronic switching. Such a gap also helps us tune the junction resistance over 3 orders of magnitude, pushing it well beyond typical contact resistances, making the output current saturate and giving us a high RF f_max power gain [6]. A PN junction on a 3D topological insulator can help polarize the transmitted spins and control the intrinsic charge-to-spin current ratio through spin-momentum locking [7].

[1] ACS Nano article ASAP 2019.
[2] Science, vol. 353 :6307 , pp. 1522-1525, 2016
[3] PNAS 2019, in press
[4] Physical Review B, vol. 86 , pp. 155412, 2012
[5] ACS Nano, vol. 7 :11 , pp. 9808-9813, 2013
[6] Nature Scientific Reports 7, 9714, 2017.
[7] Physical Review Letters, vol. 114 , pp. 176801, 2015

Avik Ghosh is Professor at the Charles Brown Dept of Electrical and Computing Engineering and the Dept of Physics at the University of Virginia. He did his PhD in condensed matter theory at the Ohio State University, and a postdoctoral fellowship in Electrical Engineering at Purdue University. He is the UVA site-director of the NSF-Industry University Cooperative Center on Multifunctional Integrated Systems Technology (MIST). Ghosh has authored 125+ refereed papers and a book (“Nanoelectronics – a Molecular View”, World Scientific 2016) in the area of computational nano-materials and devices. He has given over 125 invited lectures worldwide. He is Fellow of the Institute of Physics (IOP), senior member of the IEEE, and has received the IBM Faculty Award, the NSF CAREER Award, a 2006 best paper award from the Army Research Office, and UVA’s All University Teaching Award. His group’s work with Columbia University on negative refractive index behavior in graphene was voted by the editors of Physics World as one of the top 10 research breakthroughs of 2016.