45 research outputs found
Recipe for single-pair-Weyl-points phonons carrying the same chiral charges
Recently, Wang et al. [Phys. Rev. B, 106, 195129 (2022)] challenged a widely
held belief in the field of Weyl physics, demonstrating that
single-pair-Weyl-points (SP-WPs) can exist in nonmagnetic spinless systems,
contrary to previous assumptions that they could only exist in magnetic
systems. Wang et al. observed that the SP-WPs with opposite and even chiral
charges (i.e., |C| = 2 or 4) could also exist in nonmagnetic spinless systems.
In this Letter, we present a novel finding in which SP-WPs have a partner,
namely a charged nodal surface, in nonmagnetic spinless systems. In contrast to
previous observations, we show that the SP-WPs can have uneven chiral charges
(i.e., |C| = 1). We identify 6 (out of 230) space groups (SGs) that contain
such SP-WPs by searching the encyclopedia of emergent particles in
three-dimensional crystals. Our finds were confirmed through the phonon spectra
of two specific materials Zr3O (with SG 182) and NaPH2NO3 (with SG 173). This
discovery broadens the range of materials that can host SP-WPs and applies to
other nonmagnetic spinless crystals
Genuine Dirac half-metal: A 2D d0-type ferromagnet Mg4N4
When the spin-orbit coupling (SOC) is absent, almost all the proposed
half-metals with the twofold degenerate nodal points at the K (or K') in
two-dimensional (2D) materials are misclassified as "Dirac half-metals" owing
to the way graphene was utilized in the earliest studies. Actually, each band
crossing point at K or K' is described by a 2D Weyl Hamiltonian with definite
chirality; hence, it must be a Weyl point. To the best of our knowledge, there
have been no reports of a genuine (i.e., fourfold degenerate) Dirac point
half-metal in 2D yet. In this Letter, we proposed for the first time that the
2D d0-type ferromagnet Mg4N4 is a genuine Dirac half-metal with a fourfold
degenerate Dirac point at the S high-symmetry point, intrinsic magnetism, high
Curie temperature, 100% spin-polarization, robustness to the SOC and uniaxial
and biaxial strains, and 100% spin-polarized edge states. The work can be seen
as a starting point for future predictions of intrinsically magnetic materials
with genuine Dirac points, which will aid the frontier of topo-spintronics
researchers
CrX (X=Se, Te) monolayers as new platform to realize robust spin filter, spin diode and spin valve
Two-dimensional ferromagnetic (FM) half-metals are promising candidates for
advanced spintronic devices with small-size and high-capacity. Motivated by
recent report on controlling synthesis of FM CrTe nanosheet, herein, to
explore the potential application in spintronics, we designed spintronic
devices based on CrX (X=Se, Te) monolayers and investigated their spin
transport properties. We found that CrTe monolayer based device shows
spin filtering and dual spin diode effect when applying bias voltage, while
CrS monolayer is an excellent platform to realize a spin valve. The
different transport properties are primarily ascribed to the semiconducting
spin channel, which is close to and away from the Fermi level in CrTe
and CrSe monolayers, respectively. Interestingly, the current in
monolayer CrSe based device also displays a negative differential
resistance effect (NDRE) and a high magnetoresistance ratio (up to 2*10).
Moreover, we found thermally induced spin filtering effect and NDRE in
CrSe junction when applying temperature gradient instead of bias
voltage. These theoretical findings highlight the potential of CrX
(X=Se, Te) monolayers in spintronic applications and put forward realistic
materials to realize nanosale spintronic device