Topological semimetals have recently emerged as an important frontier of condensed matter physics. In these materials, the crossing points of electronic energy levels are topologically protected. It has been predicted that the electrons around these crossing points should display fascinating unconventional behavior in response to external perturbations such as passing an electrical current or shining light. The goal of this project is to experimentally investigate optical properties of topological semimetals. The realization of novel optical and optoelectronic phenomena in topological semimetals may lead to useful technological applications. Students and postdocs with expertise both in topological physics and time resolved optical techniques will be trained as the next generation of scientists in these fields. A crucial part of the educational component of this program is to contribute to improving the quality of K-12 math and science education especially in socio-economically impacted regions.

Technical Abstract

Weyl semimetal is a new topological phase of matter predicted to display fascinating properties. While the electronic band structure and transport have been systematically studied using angle resolved photoemission spectroscopy, scanning tunneling microscopy and electrical transport, optical properties of these materials remain largely unexplored despite predictions of many unconventional optical behaviors. The goal of this research program is to investigate the novel optical properties of chiral Weyl fermions in topological semimetals. In particular, it has been predicted that, in the presence of parallel electric and magnetic fields, Weyl fermions with different chiralities should intermix and give rise to a magnetic field dependent conductivity. It has been difficult to conclusively observe this phenomenon, known as the chiral anomaly, solely based on transport measurements. In this project, time-resolved photocurrent microscopy, transient grating spectroscopy and terahertz spectroscopy will be used to optically detect signatures of the chiral anomaly in Weyl semimetals. Additionally, photocurrent response of a Weyl semimetal will be used to map out the quantum geometry of its electronic wavefunction. This will allow detection of the Berry curvature monopoles and dipoles that arise from a Weyl node. The realization of the novel optical and optoelectronic phenomena in topological semimetals may allow us to control the Weyl fermions and their associated quantum anomalies by optical means, leading to useful optical and optoelectronic applications.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Agency
National Science Foundation (NSF)
Institute
Division of Materials Research (DMR)
Type
Standard Grant (Standard)
Application #
1809815
Program Officer
Tomasz Durakiewicz
Project Start
Project End
Budget Start
2018-06-01
Budget End
2021-05-31
Support Year
Fiscal Year
2018
Total Cost
$523,067
Indirect Cost
Name
Massachusetts Institute of Technology
Department
Type
DUNS #
City
Cambridge
State
MA
Country
United States
Zip Code
02139