Topological insulators in transition-metal intercalated graphene: The role ofdelectrons in significantly increasing the spin-orbit gap

Abstract

We study the effect of transition metal intercalation of graphene on the formation of twodimensional topological insulator with experimentally measurable edge states. Our first-principles calculations reveal that the spin-orbit coupling (SOC) gap in Re-intercalated graphene on SiC(0001) substrate can be as large as 100 meV. This value is five orders of magnitude larger than that of pristine graphene. Similar effect should also exist in Mn-or Tc-intercalated graphene. A tight-binding model Hamiltonian analysis establishes the role of orbital coupling between graphene p states and transition metal d states on the formation of the SOC gap. Remarkably, the gap can be larger than atomic SOC, as is the case for Mn. This finding opens the possibility of designing topological insulators comprised of only relatively light elements. Our study also reveals that the presence of the substrate should induce a splitting between the K and K' valleys with the potential to integrate spintronics with valleytronics.

Variation of the character of spin-orbit interaction by Pt intercalation underneath graphene on Ir(111)

“…In accordance with a number of works [17][18][19] a QSH phase in graphene was predicted to be formed due to deposition of certain heavy adatoms on graphene induced by enhanced SO coupling strength. Moreover, it has been predicted that the topological phase can be developed in transition metals (Re [19] and Mn [40]) intercalated graphene with formation of the increased SO gap due to orbital coupling between the graphene π states and transition metal d states.…”

“…Moreover, it has been predicted that the topological phase can be developed in transition metals (Re [19] and Mn [40]) intercalated graphene with formation of the increased SO gap due to orbital coupling between the graphene π states and transition metal d states. For the Pbintercalated graphene on Ir(111) [21] the most important factor for formation of the topological phase (and corresponding generation of a pseudomagnetic field resulting in the formation of Landau-like levels) was a spatial gradient of SOI along the surface formed by a c(4 × 2) superstructure.…”

“…The second method relies on the hybridization of the graphene states in the region of the Dirac point with the 5d impurity states near the Fermi level. Moreover, it was shown [19] that the intercalation of 5d metals underneath graphene can also induce an appearance of the spin-orbit gap and topological insulator phase. Recently, we had observed similar effects in graphene on Pt(111) [20].…”

Nontrivial spin structure of graphene on Pt(111) at the Fermi level due to spin-dependent hybridization

“…The appearance of a spin-orbit gap in graphene is intensively discussed, for instance, under the influence of heavy impurity atoms on graphene [43] or for transition-metal intercalated graphene [44]. It was shown that hybridization of the d states of heavy atoms with the π states can lead to a topological spin-orbit gap in the electronic structure.…”

Charge and Spin Transport in Disordered Graphene-Based Materials

“…Recent proposals to induce a topological phase in graphene include functionalization with heavy adatoms [29,268], covalent functionalization of the edges [269], proximity effect with other topological insulators [270,271,272], or intercalation and functionalization with 5d transition metals [273,274]. In particular, the seminal theoretical study [29] by Weeks and co-workers has revealed that graphene endowed with modest coverage of heavy adatoms (such as indium and thallium) could exhibit a substantial band gap and QSHE fingerprints (detectable in transport or spectroscopic measurements).…”