Direct observation of hidden spin polarization in 2H−MoTe2

Abstract

Centrosymmetric (CS) nonmagnetic materials with hidden spin polarization induced by non-CS site symmetries and spin-orbit coupling are promising candidates for spintronic applications, in light of the zero net spin polarization and modulatable spin effects hidden in the local structures. There is, however, an open issue regarding the possible spin splitting induced by broken inversion symmetry at the sample surface. Here, we performed combinatorial experimental and theoretical studies on the potentially hidden spin polarization in 2H-MoTe 2 and its mechanism. A large spin splitting of 236 meV and opposite spin polarizations up to 80% along out-of-plane direction (z axis) in K and K valleys were observed from both spin-and angle-resolved photoemission spectroscopy (spin-ARPES) and density functional theory (DFT). We further found from the DFT calculations that a medium dipole field mimicked the surface symmetry breaking in ARPES measurements induces negligible variation of spin polarization. Our study demonstrates the existence of the intrinsic hidden spin effects in 2H-MoTe 2 and opens a way of utilizing these effects in spintronic devices.

Spin-layer locking induced second-order nonlinear effect in centrosymmetric crystals

“…We thus investigate the back-gate dependence of the polarization-resolved photocurrents with gate voltages from -80 V to 80 V ( Figure 1g). If the DC-related SONE observed in bilayer MoS2 is just an interface effect, it will fade to null at a certain gate voltage which can completely cancel the interface effect, akin to the recent valley Hall effect measurements 29 decoupled nature in bilayer transition-metal dichalcogenides (TMDCs) has recently been confirmed by intrinsic circular dichroism [27][28][29][30] , unconventional Ising superconductivity [47][48][49][50] and spin-orbitronics [20][21][22][23][24][25] .…”

“…Since both S and E(ω) are polar vectors and reverse the sign under the operation of inversion symmetry, SONE without higher-order photon wave vector effects is generally expected to vanish in centrosymmetric crystals with inversion symmetry of global crystal space group (see Supplementary Information) 12, 13 . However, being akin to recent studies of spatially localized spin polarization [17][18][19][20][21][22][23][24][25] , Berry Curvature 26 and circular dichroism [27][28][29][30][31][32] , one can imagine that for layered centrosymmetric crystal formed by two separated non-centrosymmetric constituent structural units, nonvanishing SONE can occur in each inversion-partner layer. Remarkably, if SONE from the two separated inversion asymmetric units are the same, their superposition will produce a nonzero net response, making the observation possible.…”

Transverse Rashba effect and unconventional magnetocrystalline anisotropy in graphene-nanoribbon-based centrosymmetric antiferromagnet

“…In fact, if a centrosymmetric crystal structure can be divided into two sectors associated with the inversion symmetry and there is a local dipole field in each sector, the Rashba effect will emerge and generate local spins opposite in direction in the two sectors. It should be noted that the local spins compensate each other and the total spin vanishes, as required by the inversion symmetry [9][10][11][12][13][14][15]. This implies that the Rashba effect may appear in antiferromagnets with inversion symmetry as an inverse effect of the R-2 type spin polarization in centrosymmetric nonmagnetic crystals, in the sense that the compensated spin polarization of antiferromagnet accommodates the Rashba effect.…”

Phonon-induced renormalization of electron wave functions

“…Still, local spin polarization can exist at atoms that are not located at an inversion center. Such local spin polarization is termed "hidden spin polarization" 45 and has been experimentally measured [46][47][48][49][50][51] . Figure 3 shows the normalized hidden spin polarization of one of the two selenium atoms in the unit cell (Se1) 38 .…”

“…Still, local spin polarization can exist at atoms that are not located at an inversion center. Such local spin polarization is termed "hidden spin polarization" 45 and has been experimentally measured [46][47][48][49][50][51] .…”