Electromagnetic scattering laws in Weyl systems

Abstract

Wavelength determines the length scale of the cross section when electromagnetic waves are scattered by an electrically small object. The cross section diverges for resonant scattering, and diminishes for non-resonant scattering, when wavelength approaches infinity. This scattering law explains the colour of the sky as well as the strength of a mobile phone signal. We show that such wavelength scaling comes from the conical dispersion of free space at zero frequency. Emerging Weyl systems, offering similar dispersion at non-zero frequencies, lead to new laws of electromagnetic scattering that allow cross sections to be decoupled from the wavelength limit. Diverging and diminishing cross sections can be realized at any target wavelength in a Weyl system, providing the ability to tailor the strength of wave–matter interactions for radiofrequency and optical applications.

Observation of Hourglass Nodal Lines in Photonics

“…Also, the HNL can support negative refraction [41], which usually requires simultaneously well-designed negative effective permittivity and permeability in overlapped frequency range. Other photonic applications that arise from the unique density of states of the nodal line include black-body radiation [42], spontaneous emission and resonant scattering [43]. With introduction of pseudo-magnetic field (synthetic vector potential), anomalous quantum oscillation may also be observed in the HNL [44].…”

Generating Weyl nodes in non-centrosymmetric cubic crystal structures

“…The associated non-trivial topological properties of Weyl semimetals have led to a variety of unusual physical phenomena such as the Adler-Bell-Jackiw chiral anomaly on a lattice [7][8][9][10] and the anomalous quantum Hall effect [11][12][13]. Similarly, artificially created bosonic platforms, such as nanophotonic systems [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] and cold atoms in optical lattices [30][31][32][33], can be tailored to host Weyl excitations and display unique phenomena such as robust photonic surface states, tunable axial gauge fields or long-range interactions between quantum emitters. Remarkably, fermionic and bosonic Weyl systems can often be described with a common physical picture, which has lead to a significant cross-fertilization between the two areas.…”

Soft self-assembly of Weyl materials for light and sound

“…Excitations following the Weyl equation [7][8][9] have been experimentally observed in electronic condensed matter in the so-called Weyl semi-metal TaAs [22][23][24][25][26], as well as in photonic [27][28][29][30][31][32], phononic, and acoustic [33][34][35][36] crystals, and in homogeneous magnetized plasma [37]. Beyond their fundamental importance, such discoveries may pave the way towards multiple applications enabled by the peculiar properties of Weyl points, such as their angular and frequency selective response and the existence of topologically protected arc surface states (called Fermi arcs in the electronic context) that appear at the boundary of finite samples, even when time-reversal invariance is not broken [38][39][40][41][42][43]. This is in sharp contrast with gapped topological materials where the existence of one-way channels requires to break time-reversal invariance in some way, such as with external drives [44][45][46][47], magnetic or rotation fields [48][49][50][51] or active materials [52,53].…”