Efek Strain Terhadap Spin Splitting dan Spin Textures Timah Selenium (SnSe) Monolayer: Kajian Komputasional Berbasis Density Functional Theory

MUHAMMAD ANSHORY, Dr. Moh. Adhib Ulil Absor, M.Sc.

2020 | Tesis | MAGISTER FISIKA

Telah dilakukan kajian komputasi berbasis density functional theory (DFT) untuk mengamati struktur elektronik material Timah Selenium (SnSe) monolayer pada zona Brillouin pertama akibat pemberian efek strain. Penelitian ini menunjukkan adanya fenomena spin-splitting di sekitar titik Y dan telah dianalisis menggunakan teori gangguan k.p dan grup simetri sehingga diperoleh parameter kekuatan interaksi spin-orbit (SOI) untuk sistem SnSe monolayer. Berdasarkan hasil perhitungan spin textures di sekitar titik Y pada pita konduksi dan pita valensi diperoleh arah orientasi polarisasi spin yang seragam ke arah out-of-plane. Selain itu, efek strain dapat menyebabkan perubahan ferroelectric distortion akibat polarisasi listrik internal sehingga mempengaruhi besarnya parameter SOI. Pemberian uniaxial strain searah sumbu- x terbukti efektif dalam meningkatkan parameter SOI yaitu mencapai 1.48 eVA pada pita konduksi akibat tensile 8%. Hasil penelitian ini menegaskan bahwa kontrol parameter SOI dapat dilakukan dengan strain tanpa mengubah arah polarisasi spin yang out-of-plane menjadikan sistem SnSe monolayer sebagai kandidat material persistent spin helix (PSH) yang menjanjikan untuk piranti spintronik.

A computational research based on density functional theory (DFT) has been carried out to observe the electronic structure of the Tin Selenide (SnSe) monolayer material in the first Brillouin zone under strain effect. This research shows the emerged spin-splitting phenomenon around the Y point, which has been analyzed using the k.p perturbation theory and symmetry group to obtain the spin-orbit interaction (SOI) parameter for the SnSe monolayer system. Based on the calculation of spin textures on the conduction and valence band around Y point, a uniform spin polarization orientation has been accomplished in the out-of-plane direction. In addition, the strain effect shifts the value of in-plane ferroelectric distortion, which changes the magnitude of internal electric polarization; thus, it affects the magnitude of the SOI parameter. Furthermore, applying uniaxial strain in the x-axis direction is proved effective in increasing the SOI parameter, which reached 1.48 eVA in the conduction band due to 8% tensile strength. In conclusion, the results of this research confirm that control of the SOI parameter can be carried out by giving strain without changing the direction of out-of-plane spin polarization; therefore it leads the SnSe monolayer system to be a promising candidate of a persistent spin helix (PSH) material for spintronic devices.

Kata Kunci : DFT, PSH, SnSe, spin splitting, spin textures, strain