Spin Splitting Pada Sistem 1H-WSe2 Monolayer Dengan Sistem Point Defect : Kajian Komputasional Berbasis Density Functional Theory

Muhammad Oktavian Dharma Setyawan, Moh Adhib Ulil Absor, S.Si.,M.Sc.,Ph.D

2026 | Tesis | S2 Ilmu Fisika

Material transition metal dichalcogenides (TMDCs) monolayer memiliki karakteristik broken inversion symmetry, efek spin–orbit interaction (SOI) yang kuat, serta valley degree of freedom, sehingga berpotensi sebagai kandidat material untuk perangkat elektronik generasi lanjut. Penelitian ini mengkaji secara komputasional berbasis density functional theory (DFT) sifat elektronik dan spin pada monolayer 1H-WSe? dengan sistem point defect. Metode band unfolding diterapkan untuk mengidentifikasi defect states yang terbentuk di sekitar level Fermi. Analisis struktur geometri menunjukkan bahwa sistem dengan vacancy Se (V_Se) dan vacancy W (V_W) masing-masing memiliki simetri point group C_3v dan C₁, dengan energi formasi yang mengindikasikan V_Se lebih stabil dibandingkan V_W. Kemudian, akibat densitas muatan pada V_Se, terdapat dua defect states di atas level fermi pada sistem V_Se, apabila SOI diterapkan maka defect states tersebut akan mengalami splitting. Kontribusi dominan dari defect states sistem V_Se terdapat pada orbital NN W-d-out-of-plane<!--[if gte msEquation 12]>d3z2-r2+dxz+dyz<![endif]--><!--[if !msEquation]--> <!--[endif]--> dan NN W-d-in-plane<!--[if gte msEquation 12]>dx2-y2+dxy<![endif]--><!--[if !msEquation]--> <!--[endif]-->. Dengan adanya SOI, pada sistem V_Se pemisahan level energi pada splitting ?₁ menunjukkan nilai maksimum sebesar 0,13 eV dan splitting ?₂ sebesar 0,086 eV. Perhitungan spin-resolved band dan analisis Hamiltonian k.p menunjukkan sistem V_Se memiliki polarisasi spin kuat pada bidang out-of-plane sehingga fenomena spin-valley locking tetap terjaga.

Monolayer transition metal dichalcogenides (TMDCs) exhibit broken inversion symmetry, strong spin–orbit interaction (SOI), and a distinct valley degree of freedom, making them promising candidates for next-generation electronic devices. This study presents a computational investigation based on density functional theory (DFT) of the electronic and spin properties of monolayer 1H-WSe? with point defects. The band unfolding method is employed to identify defect states formed near the Fermi level. Geometric structure analysis reveals that systems with Se vacancy (V_Se) and W vacancy (V_W) possess C_3v and C₁ point-group symmetries, respectively, with formation energy calculations indicating that V_Se is more stable than V_W. Owing to charge density redistribution in the V_Se system, two defect states emerge above the Fermi level. When SOI is included, these states undergo energy splitting with the dominant contributions to the defect states in the VSe system originate from the d orbitals of nearest-neighbor W atoms, specifically the NN W-d-out-of-plane and NN W-d-in-plane orbitals. With the inclusion of SOI, the V_Se system shows maximum energy separations of 0.13 eV for splitting ?? and 0.086 eV for splitting ??. Furthermore, spin-resolved band structure calculations and k.p Hamiltonian analysis reveal a strong out-of-plane spin polarization in the V_Se system, indicating that the spin–valley locking phenomenon remains robust.

Kata Kunci : SOI, point defect, metode unfolding, spintronik, valleytronik, DFT