Tunable strong photo-mixing in Weyl semimetals

Twist dependent magneto-optical response in twisted bilayer graphene

“…An expression for general E and B has been derived and agrees with (58) in [57]. Although a Floquet approach is much more compatible with circular polarisations, we expect the B 2 response to increase in both planar directions with magnitudes approximately equal to the addition of the corresponding linear field components, i.e.…”

“…It has been shown that the linear optical conductivity reduces by a factor of 0.5 for T = 0 to T = 300 K under a monochromatic driving field of ω = 1 THz [49]. This is in contrast other topological materials where, using similar semiclassical modelling, a nonzero temperature can lead to nonuniform thermal enhancement of current density by up to a factor of 3 over T = 0 K to T = 600 K for monochromatic fields of ω = 1 THz [58]. Considering that thermal enhancement of current density has been attributed to low energy carrier transitioning between topologically distinct points, a nonzero temperature could potentially enhance interlayer magneto-optical current in TBG.…”

“…To study the magneto-optical response and its dependence on both twist angle and Fermi level we adopt a semiclassical formalism to derive a general expression for the low-energy magneto-optical response of TBG including effects from both the Berry curvature and the magnetic moment [57]. In the low field region where the linear electric field response dominates [11,12,49,[58][59][60] we employ a linearised Boltzmann equation to isolate the transverse and longitudinal conductivities up to the second order in magnetic field and up to the linear order in electric field. The crux of this method lies in approximating electronic quantities from the system with B = 0 : H B =0 (k)|ũ s,r (k) = ˜ s,r |ũ s,r (k) by explicitly computable quantities from the system with B = 0 : H(k)|u s,r (k) = s,r |u s,r (k) .…”

Broadband strong optical dichroism in topological Dirac semimetals with Fermi velocity anisotropy*

“…We found that the optical conductivity exhibits strong anisotropy with the universal scaling law, Λ i j = (v i /v j ) 2 , independent of temperature, Fermi level, and scattering effects, and is broadly applicable to the sub-THZ to at least 50 THz frequency window. Recently, the optical properties of topological semimetals with nodal topology beyond Dirac semimetal, such as Weyl semimetal [74] and nodal loop semimetal, [75][76][77][78] have been extensively studied. We expect this ever-expanding family of topological semimetals, [79] in which the optical and electronic properties are highly anisotropic along different crystal directions, to continually offer interesting platforms for the uncovering of exotic anisotropic optics and optoelectronic phenomena critical for the design of next-generation novel devices.…”