Terahertz spin- and valleytronics

• Applicant: Professorin Sangeeta Sharma, Ph.D.
• Subject Area: Theoretical Condensed Matter Physics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 522036409

Spin and valley indices represent the key quantum labels of quasi-particles in a wide class of two dimensional materials, and form the foundational elements of the fields of spintronics and valleytronics. While it is well established that ultrafast light pulses can control the charge state of a valley, robust protocols for control over the magnitude and direction of valley and spin-currents remains a sought for goal. By employing tailored hybrid light pulses combining THz modulating envelopes with charge excitation pulses we aim to demonstrate light control over the generation of spin and valley currents in a wide range of materials: spin currents in the 2d magnets CrI3 and Fe3GeTe2 and valley currents heterostructures of hexagonal BN (hBN) and single layer graphene. The latter system will provide a platform for probing moire effects in coherent current generation, while heterostructures of the 2d magnet CrI3 and TMDCs will be investigated as a system for which the layer freedom in a few layer stack can be selectively excited by tuning pulse parameters. The work is divided into three work packages :(WP) WP1: Establish how hybrid light pulses of (THz) pilot and excitation components can generate controlled spin photocurrents in 2d magnets. Two magnets of current experimental interest will be considered: CrI3 and Fe3GeTe2. In this work-package methodologies for the rest of the project will be established and tested, most importantly the accuracy of a Wannierized tight-binding as compared to ab-initio time-dependent density functional theory (TD-DFT) will be established. WP2: Generation of valley photocurrents in moires of hexagonal Boron Nitride and graphene, building on preliminary work establishing a photocurrent response in minimally gapped ideal graphene. A key question is the determination of moire effects on valley currents induced by light: what is the imprint of the moire on the photocurrent? WP3: Tailoring pulses for the generation of spin and valley photocurrents in heterostructures of 2d magnets and TMDC. The central question here will be how pulse parameters can be tuned to control both interlayer and intralayer current in the distinct layers of the heterostructure.

• DFG Programme: Research Grants