Weyl Fermion magneto-electrodynamics and ultralow field quantum limit in TaAs

Infrared spectroscopy in high magnetic fields reveals the lowest quantum limit in a Weyl semimetal.

Crystalline chirality and interlocked double hourglass Weyl fermion in polyhedra-intercalated transition metal dichalcogenides

Introducing crystalline chirality into transition metal dichalcogenides (TMDs) has attracted much attention due to its modulation effect on optical properties and the potential to reveal new forms of electronic states. Here, we predict a number of chiral materials by intercalating polyhedra into TMD lattices, finding a type of double hourglass Weyl fermion interlocked with crystalline chirality. The best candidate RhV3S6 (P6322) possesses the largest hourglass energy window of ~380 meV, as well as strong optical circular dichroism (CD) in the infrared regime, both of which are tunable by external strains. The chirality is originally induced by the configuration of intercalated polyhedra and then reduced by the rotational atomic displacements triggered by intercalation, as indicated by CD calculations. Our study opens the way of designing chiral materials with spin-split double hourglass Weyl fermions via structural unit intercalation in achiral crystals for future chiral-functionalized optoelectronic and spintronic devices.

Momentum-space signatures of Berry flux monopoles in the Weyl semimetal TaAs

Since the early days of Dirac flux quantization, magnetic monopoles have been sought after as a potential corollary of quantized electric charge. As opposed to magnetic monopoles embedded into the theory of electromagnetism, Weyl semimetals (WSM) exhibit Berry flux monopoles in reciprocal parameter space. As a function of crystal momentum, such monopoles locate at the crossing point of spin-polarized bands forming the Weyl cone. Here, we report momentum-resolved spectroscopic signatures of Berry flux monopoles in TaAs as a paradigmatic WSM. We carried out angle-resolved photoelectron spectroscopy at bulk-sensitive soft X-ray energies (SX-ARPES) combined with photoelectron spin detection and circular dichroism. The experiments reveal large spin- and orbital-angular-momentum (SAM and OAM) polarizations of the Weyl-fermion states, resulting from the broken crystalline inversion symmetry in TaAs. Supported by first-principles calculations, our measurements image signatures of a topologically non-trivial winding of the OAM at the Weyl nodes and unveil a chirality-dependent SAM of the Weyl bands. Our results provide directly bulk-sensitive spectroscopic support for the non-trivial band topology in the WSM TaAs, promising to have profound implications for the study of quantum-geometric effects in solids.

Topological terms and anomaly matching in effective field theories on ℝ3 × 𝕊1. Part I. Abelian symmetries and intermediate scales

We explicitly calculate the topological terms that arise in IR effective field theories for SU(N) gauge theories on ℝ3 × 𝕊1 by integrating out all but the lightest modes. We then show how these terms match all global-symmetry ’t Hooft anomalies of the UV description. We limit our discussion to theories with abelian 0-form symmetries, namely those with one flavour of adjoint Weyl fermion and one or zero flavours of Dirac fermions. While anomaly matching holds as required, it takes a different form than previously thought. For example, cubic- and mixed-U(1) anomalies are matched by local background-field-dependent topological terms (background TQFTs) instead of chirallagrangian Wess-Zumino terms. We also describe the coupling of 0-form and 1-form symmetry backgrounds in the magnetic dual of super-Yang-Mills theory in a novel way, valid throughout the RG flow and consistent with the monopole-instanton ’t Hooft vertices. We use it to discuss the matching of the mixed chiral-center anomaly in the magnetic dual.

Symmetry Conservation of Dirac Fermion With Double Junction and Gauge Field of Weyl Fermion With Single Junction

Majorana fermion and Weyl fermion have matters and antimatters. But Majorana fermion has zero resistance and Weyl fermion has a resistance. It was confirmed that CP symmetry is preserved in the case of Dirac fermion because it only has spin current as the antimatter. Dirac fermion is supercurrent because CP symmetry is preserved by double schottky contact, but the Majorana fermion with ohmic contact has decreased current due to symmetry violation. Parity symmetry conservation was confirmed from the electrical properties of transistors, and charge symmetry conservation was confirmed in diode properties.

Coexistence of Rarita–Schwinger–Weyl fermion and spin-1 excitation in Bi4Ni6S4

In addition to Dirac and Weyl fermions, exotic massless fermions with non-zero Berry curvature fluxes may exist in condensed matter systems under the protection of crystal symmetry, for example, spin-1 excitations with threefold degeneracy and spin-3/2 Rarita–Schwinger–Weyl fermions with fourfold degeneracy. More recently, the theory of topological quantum chemistry has provided us with a convenient way to find the existence of these quasi-particles. Herein, we have found a space group (No. 199) that may have both spin-1 excitations and spin-3/2 Rarita–Schwinger–Weyl fermions near the Fermi level. By using the ab initio density functional theory, we show that these unconventional quasi-particles mentioned above coexist in Bi4Ni6S4 in space group [Formula: see text] (No. 199), when spin-orbit coupling is considered. Their non-trivial topology results in a series of Fermi arcs connecting the projection of these excitations on (001) surface.

Sensitivity of Dirac fermion and Weyl fermion by the Energy Conservation Law of Lenz

The law of Lenz as an energy conservation law between the electric field and the magnetic field allows the charge current and spin current generated by matters and antimatters to be symmetrical with each other. Thus, there is a Lenz plane of symmetry to the electromagnet energy. Phase isolators are charged current by electrons and spin current by spin. The charge current is Weyl fermion, and the spin current is Dirac fermion. The charge current and spin current are characterized by balancing each other, and the fermion, which has both particles and carriers, is Majorana fermion. The reaction was investigated when phase insulators in the state of Dirac fermion and Weyl fermion were exposed to CO2 gas. Although the sensitivity of the phase isolator has decreased as Weyl fermion makes spin current in the gas environment, the sensitivity of the phase isolator has increased as Dirac fermion makes charge current in the gas environment. The spin current of the Dirac fermion has a super current characteristic with a resistance of zero and quantum tunneling phenomenon has occurred. According to Lenz's energy conservation law, the electron sensor has an advantage of the phase insulator in the state of Dirac fermion, where the charge current increases.