Nonlocality and Loss in Nonreciprocal Photonics Enabled by Weyl Semimetals

Engineering new nonreciprocal optical devices is an important initiative in current photonics research. There is a desire to engineer new, nonreciprocal integrated photonic devices to replace the current standard of magneto-optic materials, which require bulky external magnets incompatible with many chip-scale device architectures [1]. Much research has been dedicated to modeling and designing nonreciprocal devices made from Weyl semimetals (WSMs) for next generation isolators and enhanced near-field radiative heat transfer devices [2]. However, as has been recently discussed [3], the impacts of nonlocality and loss on the proposed nonreciprocal Weyl devices close the window of one-way transport and render the realistic structures less useful than those initially proposed in the lossless, local regime. While loss and nonlocality are inherent to plasmonic devices, nonreciprocal Weyl devices with large figures of merit can be engineered by judicious combinations of external symmetry-breaking stimuli. To date, the qualitative impacts of loss and nonlocality have been mostly investigated in intrinsic time reversal-breaking WSM [4]. Here, we expand this analysis to time reversal- and inversion symmetry-breaking WSMs under a variety of <i>in situ</i> and <i>ex situ</i> stimuli, which either induce or enhance nonreciprocity. These stimuli include inhomogeneous strain and Fizeau drag via DC current bias. By evaluating the effect of various external stimuli that induce nonreciprocity in WSMs – as well as their combinations – we aim to identify a breadth of useful regimes for nonreciprocal and tunable WSM devices operation when realistic loss and nonlocality are accounted for.<br/><br/>[1] S.V. Boriskina, M. Blevins, S. Pajovic, There and Back Again: the nonreciprocal adventures of light, Opt. Photon. News, Sept. 2022.<br/>[2] S. Pajovic, et al, Intrinsic nonreciprocal reflection and violation of Kirchhoff’s law of radiation in planar type-I magnetic Weyl semimetal surfaces, Phys. Rev. B 102(16), 165417, 2020.<br/>[3] Monticone and Gangaraj, Do Truly Unidirectional Surface Plasmon-Polaritons Exist?, Optica Vol. 6, Issue 9, pp. 1158-1165 (2019)<br/>[4] Buddhiraju et al., Absence of Unidirectionally Propagating Surface Plasmon-Polaritons in Nonreciprocal Plasmonics., Nat. Comm. (2020) 11:674<br/><br/>This research has been supported by the Army Research Office (W911NF-13-D-0001), Lincoln Laboratory, Massachusetts Institute of Technology (ACC-777), and a Draper Fellowship to M.B.