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Giant proximity exchange and valley splitting in transition metal dichalcogenide/hBN/(Co, Ni) heterostructures
Physical Review B ( IF 3.7 ) Pub Date : 
Klaus Zollner, Paulo E. Faria Junior, and Jaroslav Fabian

We investigate the proximity-induced exchange coupling in transition-metal dichalcogenides (TMDCs), originating from spin injector geometries composed of hexagonal boron-nitride (hBN) and ferromagnetic (FM) cobalt (Co) or nickel (Ni), from first-principles. We employ a minimal tight-binding Hamiltonian that captures the low energy bands of the TMDCs around K and K’ valleys, to extract orbital, spin-orbit, and exchange parameters. The TMDC/hBN/FM heterostructure calculations show that due to the hBN buffer layer, the band structure of the TMDC is preserved, with an additional proximity-induced exchange splitting in the bands. We extract proximity exchange parameters in the 1–10 meV range, depending on the FM. The combination of proximity-induced exchange and intrinsic spin-orbit coupling (SOC) of the TMDCs, leads to a valley polarization, translating into magnetic exchange fields of tens of Tesla. The extracted parameters are useful for subsequent exciton calculations of TMDCs in the presence of a hBN/FM spin injector. Our calculated absorption spectra show large splittings for the exciton peaks; in the case of MoS2/hBN/Co we find a value of about 8 meV, corresponding to about 50 Tesla external magnetic field in bare TMDCs. The reason lies in the band structure, where a hybridization with Co d orbitals causes a giant valence band exchange splitting of more than 10~meV. Structures with Ni do not show any d level hybridization features, but still sizeable proximity exchange and exciton peak splittings of around 2~meV are present in the TMDCs.

中文翻译:

过渡金属二硫化氢/ hBN /(Co,Ni)异质结构中的巨大邻近交换和峰谷分裂

我们从第一原理出发,研究了由六方氮化硼(hBN)和铁磁(FM)钴(Co)或镍(Ni)组成的自旋注射器几何结构中过渡金属二硫化氢(TMDCs)中的邻近感应交换耦合。我们采用最小紧束缚哈密顿量,它捕获了K和K'谷周围TMDC的低能带,以提取轨道,自旋轨道和交换参数。TMDC / hBN / FM异质结构计算表明,由于hBN缓冲层的存在,TMDC的能带结构得以保留,并在该带中进行了额外的邻近感应交换。根据FM,我们提取1–10 meV范围内的邻近交换参数。TMDC的邻近感应交换和固有自旋轨道耦合(SOC)的组合会导致波谷极化,转换成数十特斯拉的磁场。在存在hBN / FM自旋注入器的情况下,提取的参数可用于TMDC的后续激子计算。我们计算出的吸收光谱显示出激子峰的大分裂;对于MoS2/ hBN / Co,我们发现大约为8 meV,相当于裸露的TMDC中大约50特斯拉外部磁场。原因在于能带结构,其中与Co杂交d轨道导致大于10meV的巨大价带交换分裂。含镍的结构未显示任何d 分子杂交技术具有高水平的杂交特征,但在TMDC中仍存在相当大的邻近交换和约2meV的激子峰分裂。
更新日期:2020-01-24
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