Nonreciprocal Goos-Hänchen shift in a Dirac semimetal based asymmetric photonic crystal structure.

The generation and control of the Goos-Hänchen (GH) shift is a vital step toward its realistic applications, but investigations have mainly been limited to the directional-dependent ones; i.e., the GH shift is reciprocal for two opposite propagating directions. Here, by designing the asymmetrical multilayered structure with three-dimensional bulky Dirac semimetal (BDS) films, we theoretically confirm the footprint of the pronounced directional-dependent GH shift, and that it can be switched by the Fermi energy of the BDS. In addition to this electric field induced switching, the period numbers of the unit cells in the asymmetrical structure can also modulate the directional-dependent GH shift. The asymmetrical feature of the multilayered structure dominantly causes the emergence of the directional-dependent GH shift. Our discovery related to the directional-dependent GH shift constitutes an important ingredient for directional-dependent optophotonic devices such as directional sensors, optical switches, and detectors.

Prediction of negative refraction in Dirac semimetal metamaterial.

Negative refraction materials are indispensable building blocks in the optoelectric devices for their unique functionalities of controlling the light propagations, such as, superlens and transformation optics. However, material realizations of negative refraction are still limited to the conventional metals, semiconductors as well as magnetic materials. Here, we show that three dimensional Dirac semimetals have the opportunity to enable the negative refraction, which can be achieved through alternatively stacking three dimensional Dirac semimetals and the dielectric layers together. It is found that the effective perpendicular and parallel permittivities in this multilayered stack display the respective negative and positive values over a certain frequency region, which enables its negative group refractive angle and it can be controlled by the Fermi energy of Dirac semimetals. The spectra of transmittance in the multilayered structure for transverse magnetic wave also reveals an incident angle-independent transmittance dip, which originates from the zero value of the real part of the effective perpendicular permittivity. Our findings unveil the essential role of three dimensional Dirac semimetals in producing the negative group refraction responses and promise their applications in the metamaterial-based devices.

Enhanced photonic spin Hall effect in Dirac semimetal metamaterial enabled by zero effective permittivity.

With the recent discovery of three dimensional Dirac semimetals, their integrations with the optoelectronic devices allow the novel optical effects and functionalities. Here, we theoretically report the photonic spin Hall effect in a periodic structure, where three dimensional Dirac semimetals and the dielectric materials are assembled into the stack. The incident angle and frequency dependent spin shift spectrum reveals that the spin shifts of the transmitted wave in this structure emerge the obvious peaks and valleys for the horizontal polarized wave and their magnitudes and positions display a distinct dependence on the incident angle around the specific frequency. These observations originate from its zero value of the effective perpendicular permittivity and its greatly reduced transmission in the multilayered structure, whose mechanism is different from those in the previous works. Moreover, both the peaks and valleys of the transmitted spin shift are significantly sensitive to the Fermi energy of three dimensional Dirac semimetals, whose magnitudes and positions can be tuned by varying it. Our results highlight the vital role of three dimensional Dirac semimetals in their applications of the spin photonic devices and pave the way to explore the tunable photonic spin Hall effect by engineering their Fermi energies.