Our next 2D & Physics and Mathematics Seminar Series will occur on Wednesday, 19 April. We welcome Dr. Gopal Dixit from the Indian Institute of Technology (IIT) Bombay.

Title: Valleytronics and Valley-transistor in Two-dimensional Materials

 

Abstract: Analogues to spin, electrons in two-dimensional (2D) materials endow an additional quantum attribute: valley pseudospin, which is associated with the valleys in the energy landscape of these materials. There are two degenerate valleys situated at the corners of the Brillouin zone in 2D materials. Similar to 0 and 1, two valleys can be seen as two units of operations. Not only that, operations in between the two units, i.e., the superposition of 1 and 0, can also be realized using

two valleys. The superposition principle is an essential ingredient for quantum technology. Therefore, these valleys have the potential to encode, process, and store quantum information, opening the field of valleytronics at room temperature – A holy grail for quantum computing. Moreover, coherent switching of electronic excitation from one valley to another on a timescale faster than the valley decoherence is quintessential for valleytronics-based emerging quantum technologies at ambient conditions.

In this talk, I will discuss how valley-selective excitation in graphene with zero bandgaps can be achieved by an all-optical means. Ultrashort laser pulses are employed to obtain the desired control over valley polarization. By tailoring the waveforms of the laser pulses to the symmetry of the graphene’s sub-lattice, first I will demonstrate that it is possible to induce and read valley polarization in 2D materials including graphene — a medium where light-driven valleytronics was thought to be impossible. In the later part of this talk, I will show a coherent protocol to initiate valley-selective excitation, de-excitation, and switch the excitation to another valley within tens of femtoseconds — timescale faster than any valley decoherence time. Our coherent control protocol consists of three time-separated linear pulses, polarised along the same direction. A laser pulse can cause electrons to wiggle several hundred trillion times a second. This means valleytronics at petahertz rates is possible, which exceeds modern computational speeds by a million times.

[1] Mrudul M. S., Jimenez-Galan A., Ivanov M., and Dixit G.: “Light-Induced Valleytronics in Pristine Graphene” Optica 8, 422 (2021).

[2] Mrudul M. S., and Dixit G.: “Controlling Valley Polarisation in Graphene via Tailored Light Pulses” J. Phys. B 54, 224001 (2021). (Invited article for Emerging Leader 2021)

[3] Rana N. and Dixit G.: “All-Optical Ultrafast Valley-Switch in Two-Dimensional Materials” Phys. Rev. Applied 19, 034056 (2023).

 

About Speaker: After receiving a doctoral degree from the Indian Institute of Technology (IIT) Kharagpur, Dr. Gopal Dixit joined the Center for Free-Electron Laser Science (CFEL), Hamburg Germany as a scientist. In 2013, he moved from Hamburg to Max-Born Institute (MBI) in Berlin Germany. He spent around eight years as a guest scientist in different German institutions, before joining IIT Bombay, Mumbai in 2015. He has received several prestigious fellowships, such as Marie-Curie, Ramanujan, Early Career Research Award, and DAAD Research Ambassador award.

Currently, he is an Associate Professor at IIT Bombay. He is also visiting scientist at MBI Berlin and MPI-PKS Dresden Germany. His research group at the Ultrafast Lab focuses on probing ultrafast processes in nature at the attosecond and femtosecond timescales.

 TEAMS link: Link

Schedule: April 19, 2023, 11:00 AM to 12:00 PM