An ab initio approach to anisotropic alloying into the Si(001) surface

Employing density functional theory calculations we explore initial stage of competitive alloying of co-deposited silver and indium atoms into a silicon surface. Particularly, we identify respective adsorption positions and activation barriers governing their diffusion on the dimer-reconstructed silicon surface. Further, we develop a growth model that properly describes diffusion mechanisms and silicon morphology with the account of silicon dimerization and the presence of C-type defects. Based on the surface kinetic Monte Carlo simulations we examine dynamics of bimetallic adsorption and elaborate on the temperature effects on the submonolayer growth of Ag-In alloy. A close inspection of adatom migration clearly indicates effective nucleation of Ag and In atoms, followed by the formation of orthogonal atomic chains. We show that the epitaxial bimetal growth might potentially lead to exotic ordering of adatoms in the form of anisotropic two-dimensional lattices via orthogonal oriented single-metal rows. We argue that this scenario becomes favorable provided above room temperature, while our numerical results are shown to be in agreement with experimental findings.Comment: 8 pages, 5 figure

Skyrmion-driven topological Hall effect in a Shastry-Sutherland magnet

The Shastry-Sutherland model and its generalizations have been shown to capture emergent complex magnetic properties from geometric frustration in several quasi-two-dimensional quantum magnets. Using an $sd$ exchange model, we show here that metallic Shastry-Sutherland magnets can exhibit a topological Hall effect driven by magnetic skyrmions under realistic conditions. The magnetic properties are modeled with competing symmetric Heisenberg and asymmetric Dzyaloshinskii-Moriya exchange interactions, while a coupling between the spins of the itinerant electrons and the localized moments describes the magnetotransport behavior. Our results, employing complementary Monte Carlo simulations and a novel machine learning analysis to investigate the magnetic phases, provide evidence for field-driven skyrmion crystal formation for an extended range of Hamiltonian parameters. By constructing an effective tight-binding model of conduction electrons coupled to the skyrmion lattice, we clearly demonstrate the appearance of the topological Hall effect. We further elaborate on the effects of finite temperatures on both magnetic and magnetotransport properties.Ministry of Education (MOE)Published versionThe work of A.A.P. was supported by the Russian Science Foundation Project No. 20-72-00044. P.S. acknowledges support from the Ministry of Education (MOE), Singapore, in the form of AcRF Tier 2 Grant No. MOE2019-T2-2-119