Kajian Komputasional Valley Splitting pada Sistem Heterointerface WSe2/CoO Berbasis Density Functional Theory

Yalesveva Rashwan Mushafa, Moh. Adhib Ulil Absor, S.Si., M.Sc., Ph.D.

2025 | Skripsi | FISIKA

Kajian komputasional valley splitting pada sistem heterointerface WSe2/CoO dilaksanakan menggunakan metode density functional theory (DFT) dengan fungsional exchange-correlation Perdew-Burke-Ernzerhof (PBE). Penelitian dimulai dengan mengoptimasi fungsi gelombang Kohn-Sham dengan kriteria konvergensi 2,7x10^-8 eV, dilanjutkan dengan optimasi geometri WSe2 dan CoO heksagonal dengan kriteria gaya 5x10^-3 eV/A. Sistem heterointerface yang dikonstruksi terdiri dari 1 lapis monolayer WSe2 dan 3 lapis CoO heksagonal. Geometri struktur heterointerface dioptimasi dengan kriteria gaya yang sama sehingga kestabilan kisi tercapai dengan energi ikat kisi senilai -18,353 eV. Untuk meninjau valley splitting pada heterointerface, kalkulasi struktur elektronik melibatkan 2 titik simetri tinggi dalam zona Brillouin pertama yaitu K dan K'. Sifat magnetik CoO berpengaruh terhadap keadaan elektronik WSe2 sehingga memicu pemecahan simetri time-reversal yang menyebabkan pemecahan Zeeman pada titik-titik tersebut. Interaksi spin-orbit yang kuat dalam WSe2 juga berkontribusi pada pemecahan ini. Analisis spin texture menunjukkan terjadinya pemecahan valley antara titik Q dan Q' senilai 137 meV. Penelitian ini menunjukkan bahwa valley dalam monolayer WSe2 dapat dikendalikan dengan substrat magnetik sehingga cocok untuk aplikasi valleytronic.

A first-principles study to investigate valley splitting in WSe2/CoO heterointerface system was conducted using Density Functional Theory (DFT) method. In this work, the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional was employed. The calculation began with optimizing the Kohn-Sham wavefunction up to a convergence criteria of 2.7x10^-8 eV, followed by structural relaxation of WSe2 and hexagonal CoO using a force convergence criterion of 5x10^-3 eV/A. The heterointerface system, consisting of a single WSe2 layer and 3 hexagonal CoO layers, were also structurally optimized. The system exhibited structural stability with a lattice binding energy of -18.353 eV. To investigate the valley splitting within the heterointerface, high symmetry points within the first Brillouin zone (K and K') were considered during the electronic structure calculation. The magnetic nature of CoO affected the electronic states of WSe2, breaking the time-reversal symmetry, then inducing Zeeman splittings on the valleys’ k-points. Such splittings were also contributed by the strong spin-orbit coupling within WSe2. Spin texture analysis revealed a 137 meV of splitting was obtained between the Q and Q' valleys. This work suggests that valleys in WSe2 monolayer can be manipulated using magnetic substrate, making this system a promising candidate for valleytronic applications.

Kata Kunci : Density Functional Theory, heterointerface, valley splitting