EFRI NewLAW: Magnetic Field Free Magneto-optics and Chiral Plasmonics with Dirac Materials

West Virginia University Research Corporation, Morgantown WV

Investigators

Abstract

Most natural phenomena obey "time-reversal symmetry", which states that if the direction of time is reversed, for example, the propagation of light waves is the same in both forward and backward directions. But optical transport that only lets light pass one-way, termed "non-reciprocal propagation", is vital for energy reduction and noise suppression in telecommunications. The generation of non-reciprocity requires breaking time-reversal symmetry, and typically can be realized in magneto-optical materials via the Faraday effect (where light passing through a material is subject to an external magnetic field, thus changing the light wave orientation). This fundamental requirement of an external magnetic field places significant limitations on device miniaturization and on-chip integration. This program researches a new material platform "gapped Dirac materials" whose intrinsic Berry curvature, a key and newly-recognized property of their energy band structure, can act as an effective magnetic field - thus giving rise to unique chiral edge plasmon resonances that can facilitate non-reciprocal light propagation. The outcome of this research will enable compact, magnetic-field-free (and thus lightweight and energy-efficient) tunable nonreciprocal devices for optical communications and quantum information processing. This project will train graduate and under-represented students in STEM in a multidisciplinary environment; provide outreach to the public through programs such as Research Experience for Teachers, "Science on Tap" public lectures, and "Broaden the Horizon" that focuses on middle school female students; and develop and distribute analysis tools and codes under open source licenses. This project explores a new frontier in magneto-optics and magnetic-field-free non-reciprocal light transport based on Dirac materials such as transition-metal dichalcogenide monolayers, where the breaking of inversion symmetry and large spin-orbit coupling lead to valley-spin locking. The intrinsic Berry curvature of these materials further acts as an effective magnetic field in momentum space, which under a valley imbalance can give rise to chiral plasmon modes that enable non-reciprocal light propagation at mid infrared and terahertz frequencies. Valley polarization in these gapped Dirac materials will be induced through three approaches: 1) doping with transition-metal impurities; 2) proximity to layered magnetic transition-metal phosphorous trichalcogenides; and 3) electrical spin injection. Electromagnetic modeling and calculations of the Berry curvature, magneto optical effects, and chiral plasmons in selected monolayers and heterostructures will provide guidance for material synthesis by molecular beam epitaxy and chemical vapor deposition, and atomic scale characterization with spin-resolved scanning tunneling microscopy/spectroscopy, angle-resolved photoemission spectroscopy, and polarization selective photoluminescence, as well as far-field optical characterization and near-field scanning optical microscopy imaging. Through an integrated experimental-theoretical approach, this project aims to demonstrate wave guiding chiral plasmons in the mid-infrared to terahertz range to enable magnetic-field-free optical devices such as non-reciprocal Faraday isolators and tunable optical circulators.