Ideal Weyl semimetal induced by magnetic exchange

Abstract

We report theoretical and experimental evidence that EuCd2As2 in magnetic fields greater than 1.6 T applied along the c axis is a Weyl semimetal with a single pair of Weyl nodes. Ab initio electronic structure calculations, verified at zero field by angle-resolved photoemission spectra, predict Weyl nodes with wavevectors k = (0, 0, ±0.03) × 2π/c at the Fermi level when the Eu spins are fully aligned along the c axis. Shubnikov-de Haas oscillations measured in fields parallel to c reveal a cyclotron effective mass of m * c = 0.08 me and a Fermi surface of extremal area Aext = 0.24 nm −2 , corresponding to 0.1% of the area of the Brillouin zone. The small values of m * c and Aext are consistent with quasiparticles near a Weyl node. The identification of EuCd2As2 as a model Weyl semimetal opens the door to fundamental tests of Weyl physics.

Anomalous conductance scaling in strained Weyl semimetals

“…We are confident that the conductance scaling uncovered in this work can be observed in experiment, considering the recent efforts in manufacturing microstructured Weyl semimetals [38], creating strain-induced fields in type-II Weyl semimetals [39], and transport experiments in Dirac nanowires [40,41]. As our results rely on time-reversal symmetry-breaking materials, magneticexchange induced Weyl semimetals [42,43] are promising platforms for experiments. We have uncovered the conditions necessary to observe the unusual scaling of the conductivity: The sample's width needs to be larger than the magnetic length, and the sample's length in transport direction needs to be larger than the mean free path.…”

Detection of Fermi arcs in Weyl semimetals through surface negative refraction

“…The space-resolved peak structure of the nonlocal conductance which indicates the trajectory of negative refraction can serve as unique evidence of the Fermi arc states. Recent progress on Weyl semimetals with a single pair of Weyl nodes in MnBi 2 Te 4 [42] and EuCd 2 As 2 [43,44] paves the way for the realization of our proposal. Furthermore, the manipulation of the negative refraction process offers potential applications of a Weyl semimetal nanowire as a field-effect transistor [40].…”

“…In reality, there are only a few material candidates for Weyl semimetals with only two Weyl points [42][43][44]. Hence, we investigate negative refraction between the surface states of T -symmetric Weyl semimetals, which are more abundant [12][13][14][15][16].…”

“…As a result, part of the scattering channels at the Fermi energy level is absent, serving as a source for unique transport properties, including negative refraction between different surfaces [41]. In reality, the electronic transport signatures will depend on the material details and their specific termination, both of which affect the Fermi arcs' orientation, dispersion, and length [12][13][14][15][16][17][42][43][44]. Notably, however, stateof-the-art fabrication techniques allow for controlled surface shaping on the level of a single layer [16,18,45,46], making it possible to explore the broad breadth of surface transport phenomena.…”

Field-effect transistor based on surface negative refraction in Weyl nanowire

“…(iv) Finally, in many Weyl semimetals, the Fermi arcs' dispersion is complex, making these surface states not much different from 2D normal metals, which cannot be used for WEYLFETs. Consequently, the material candidate for the WEYLFET should contain short Fermi arcs with small curvature [43][44][45].…”