Two Linear Regimes in Optical Conductivity of a Type-I Weyl Semimetal: The Case of Elemental Tellurium

Chiral phonons: circularly polarized Raman spectroscopy and ab initio calculations in a chiral crystal tellurium

Recently, phonons with chirality (chiral phonons) have attracted significant attention. Chiral phonons exhibit angular and pseudoangular momenta. In circularly polarized Raman spectroscopy, the peak split of the Γ 3 $$ {\Gamma}_3 $$ mode is detectable along the principal axis of the chiral crystal in the backscattering configuration. In addition, peak splitting occurs when the pseudoangular momenta of the incident and scattered circularly polarized light are reversed. Until now, chiral phonons in binary crystals have been observed, whereas those in unary crystals have not been observed. Here, we observe chiral phonons in a chiral unary crystal Te. The pseudoangular momentum of the phonon is obtained in Te by an ab initio calculation. From this calculation, we verified the conservation law of pseudoangular momentum in Raman scattering. From this conservation law, we determined the handedness of the chiral crystals. We also evaluated the true chirality of the phonons using a measure with symmetry similar to that of an electric toroidal monopole.

Real-space imaging and control of chiral anomaly induced current at room temperature in topological Dirac semimetal

Chiral fermions (CFs) in condensed matters, distinguished by right (+) or left (-) handedness, hold a promise for emergent quantum devices. Although a chiral anomaly induced current, J_chiral = J(+) - J(-), occurs in Weyl semimetals due to the charge imbalance of the CFs, monitoring spatial flow and temporal dynamics of J_chiral has not been demonstrated yet. Here, we report real-space imaging and control of J_chiral on the topological Dirac semimetal KZnBi at room temperature (RT) by near-field terahertz (THz) spectroscopy, establishing a relation for an electromagnetic control of J_chiral. In THz electric and external magnetic fields, we visualize a spatial flow of coherent J_chiral in macroscopic length scale and monitor its temporal dynamics in picosecond time scale, revealing its ultralong transport length around 100 micrometers. Such coherent J_chiral is further found to be controlled according to field directions, suggesting the feasibility of information science with topological Dirac semimetals at RT.

Optical Response of Chiral Multifold Semimetal PdGa

We present a theoretical study of the band structure and optical conductivity for the chiral multifold semimetal PdGa. We identify several characteristic features in the optical conductivity and provide their origins within the band structure. As experimental optical studies for the mentioned compound have not been reported, we contrast our results with the related compounds, RhSi and CoSi. We believe that the presented hallmarks will provide guidance to future experimental works.

Radial Spin Texture of the Weyl Fermions in Chiral Tellurium

Trigonal tellurium, a small-gap semiconductor with pronounced magneto-electric and magneto-optical responses, is among the simplest realizations of a chiral crystal. We have studied by spin- and angle-resolved photoelectron spectroscopy its unconventional electronic structure and unique spin texture. We identify Kramers-Weyl, composite, and accordionlike Weyl fermions, so far only predicted by theory, and show that the spin polarization is parallel to the wave vector along the lines in k space connecting high-symmetry points. Our results clarify the symmetries that enforce such spin texture in a chiral crystal, thus bringing new insight in the formation of a spin vectorial field more complex than the previously proposed hedgehog configuration. Our findings thus pave the way to a classification scheme for these exotic spin textures and their search in chiral crystals.