Prediction of Near-Room-Temperature Quantum Anomalous Hall Effect on Honeycomb Materials

Abstract

Recently, this long-sought quantum anomalous Hall effect was realized in the magnetic topological insulator. However, the requirement of an extremely low temperature (approximately 30 mK) hinders realistic applications. Based on ab-initio band structure calculations, we propose a quantum anomalous Hall platform with a large energy gap of 0.34 and 0.06 eV on honeycomb lattices comprised of Sn and Ge, respectively. The ferromagnetic order forms in one sublattice of the honeycomb structure by controlling the surface functionalization rather than dilute magnetic doping, which is expected to be visualized by spin polarized STM in experiment. Strong coupling between the inherent quantum spin Hall state and ferromagnetism results in considerable exchange splitting and consequently an ferromagnetic insulator with a large energy gap. The estimated mean-field Curie temperature is 243 and 509 K for Sn and Ge lattices, respectively. The large energy gap and high Curie temperature indicate the feasibility of the quantum anomalous Hall effect in the near-room-temperature and even room-temperature regions.PACS numbers: 71.70. Ej,73.43.Cd, The quantum anomalous Hall (QAH) effect is a topologically nontrivial phase characterized by a finite Chern number and chiral edge states inside the bulk band gap, which leads to the quantized Hall effect without a magnetic field [1]. The chiral edge states carry dissipationless electric current owing to robustness against backscattering [2] and are therefore attractive for applications in low-power-consumption electronics. Recently, this long-sought QAH effect was realized chromium-doped (Bi,Sb) 2 Te 3 (ref.[3]), the magnetic topological insulator [4,5]. However, the requirement of an extremely low temperature (approximately 30 mK) hinders realistic applications, which is fundamentally limited by the bulk energy-gap and the ferromagnetic Curie temperature [3]. Thus, novel materials are in high demand for future applications of the QAH effect.In a quantum spin Hall (QSH) system [6][7][8], the topological band structure is identified by a band inversion in both spin channels that are time-reversal (TR) conjugates of each other. A pair of counter-propagating edge states with opposite spins exists, i.e., two copies of quantum anomalous Hall (QAH) edge states. If the ferromagnetic (FM) order suppresses one of the spin channels, it can lead to the QAH effect [9][10][11]. The band inversion in a single spin channel, which is characterized by a finite Chern number, originates from the gapless edge state inside the bulk energy-gap. Therefore, the following transition-metal-doped topological insulators were proposed to realize the QAH effects: the aforementioned chromium-doped Bi 2 Te 3 (ref.[11]), manganesedoped HgTe quantum wells (QWs) [10,12], and other magnetically doped QWs [13,14]. The bulk energy-gap of these 2D QSH insulators are usually of the order of 1 or 10 meV. It is believed that the ferromagnetism of a magnetic QSH insulator can be enhanced owing to the band edge singularity of such an ...

Band gap opening in stanene induced by patterned B–N doping

“…5,16 Thus, stanene has a great potential for photo-related applications than graphene. 87 Moreover, achieving ultra-low 21 work function in graphene is very important for electronics and electron emission devices. [89][90][91] As stanene and doped stanene have lower work function than graphene, they can be promising for electronic device technologies.…”

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Prediction of high-temperature quantum anomalous Hall effect in two-dimensional transition-metal oxides

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Large-gap quantum spin Hall states in decorated stanene grown on a substrate

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