Magnetic Dirac fermions and Chern insulator supported on pristine silicon surface

Abstract

Emergence of ferromagnetism in non-magnetic semiconductors is strongly desirable, especially in topological materials thanks to the possibility to achieve quantum anomalous Hall effect. Based on first-principles calculations, we propose that for Si thin film grown on metal substrate, the pristine Si(111)-surface with a spontaneous weak reconstruction has a strong tendency of ferromagnetism and nontrivial topological properties, characterized by spin polarized Dirac-fermion surface states. In contrast to conventional routes relying on introduction of alien charge carriers or specially patterned substrates, the spontaneous magnetic order and spin-orbit coupling on the pristine silicon surface together gives rise to quantized anomalous Hall effect with a finite Chern number . This work suggests exciting opportunities in silicon-based spintronics and quantum computing free from alien dopants or proximity effects.

All‐Silicon Switchable Magnetoelectric Effect through Interlayer Exchange Coupling

“…Therefore, the Si surface is like a low‐buckled silicene under the periodic potential of the bulk silicon substrate, which has a periodicity with respect to the bare monolayer Si(111) of 1×1 lattice . The atomic configuration for each Si surface is in agreement with our previous calculations …”

“…Figure b shows the magnetization charge density in the A‐type AFM state, where the spin‐polarized charge density for each spin channel is strongly localized on the Si B atoms of two surfaces, respectively. Similar to the previous case, the spin‐polarized Dirac fermion with one spin channel around the Fermi level and the other one unoccupied is induced by the exchange splitting on each Si surface in the FM state. The energy difference between the two spin‐polarized Dirac cones from the same Si surface is called intralayer exchange splitting energy Δ ex for either surface shown in Figure d. In contrast with the previous case, [19] however, the spin‐polarized Dirac cones at Fermi level with intralayer exchange coupling Δ ex stem from the spin‐down electrons (blue) of the 1 st BL (the topmost BL) and the spin‐up electrons (red) of the 5 th BL (the lowest BL) separately.…”

“…Although some complex oxide compounds in bulk form indeed display A‐type antiferromagnetic ordering, there are rare reports on single phase semiconducting materials with weak long‐range exchange coupling. Recently, we have found that the pristine silicon thin films, with atomic reconstruction of Si(111)‐ R30° (Si hereafter) surface structure, show the presence of spontaneous spin‐polarized Dirac fermions with half‐filling at the Fermi level . As both time‐reversal and inversion symmetry are absent, the removal of the four‐fold degeneracy (spin and sublattice pseudospin degree of freedom) satisfies the basic requirement of the linear magnetoelectric (LME) effect, making the reversal control of ME possible .…”

Screening Magnetic Two-Dimensional Atomic Crystals with Nontrivial Electronic Topology

“…Unfortunately, the state is only realized in 2D materials with non-intrinsic magnetism at extremely low temperature (e.g. 30 mK for Cr-doped (Bi,Sb) 2 Te 3 thin film) [16][17][18][19][20][21][22] , hampering its extensive applications. Therefore, discovery of 2D magnets at an elevated temperature is of great importance, providing optimal platforms to enable realistic spintronic and quantum devices, as well as to realize new electronic states.To date 2D magnetic materials are limited to marginal modifications to existing compounds, for instance by: (i) adsorbing hydrogen on graphene 23 ; (ii) reconstructing surface/edge [24][25] ; or (iii) creating defects in MoS 2 nanosheets 26 .…”

Surface magnetism of gallium arsenide nanofilms

“…In graphene, BN and other two-dimensional crystals, magnetism can be induced by defects, structure distortions [19][20][21] as well as edge states [12,22,23]. Recently, ferromagnetism on reconstructed Si<111> surfaces has been theoretically predicted, where the time-reversal symmetry is broken by the spontaneous surface reconstruction and magnetic instability [24]. Magnetic moments in metal oxides and perovskite materials caused by holes in oxygen p orbitals have also been widely predicted [25][26][27][28][29][30], and ferromagnetic ordering is obtained if the hole density is high enough [25,26,[30][31][32].…”