Transition metal dimers on GAAS(110) surface: a DFT study

Abstract

Dilute magnetic semiconductors (DMSs) have gained appreciable interest in the past two decades. This is due to the perspectives of both fundamental physics and novel applications. They are useful in the context of single dopants (solotronics) because studying individual dopants and their interactions with the host pro-vides rich physics. Here we carry out density functional theory calculations for transition metal element dimer dopants on GaAs(110) surface using Quantum Espresso software by employing ultra-soft pseudopotentials (USPP) and report properties such as exchange energy, spin-resolved density of states, spin-resolved projected density of states, structural and magnetic relaxations, and STM images of surface with dimers. We model the GaAs(110) surface with the BURAI software package, and we study 4 transition metal dimers on near and far configurations on the surface, Fe, Cr, V, and Co. Since the dopants are magnetic, we consider both the ferromagnetic and antiferromagnetic alignments. We show that magnetic configurations greatly alter the relaxed positions of dopants. We also report the exchange energy between ferromagnetic (triplet) and antiferromagnetic (singlet) states for near and far configurations. At the end of our calculations, we found the relationship between exchange energy and distance and reported a dramatic change in the magnitude of the exchange energy as a function of dimer separation. We also observe that except for the Co dimers, Fe, Cr, and V dimers have a reasonable exchange energy between ferromagnetic and antiferromagnetic alignments. This is due to nonzero magnetic moments on these transition metal dopants. For less than two percent of dopant ratio, we observed a metallic system for Fe dimer, a semiconducting system for Cr, and a half-metallic system for V dimers. Electronic structure calculations such as DOS and PDOS projections are in parallel with the expectations of ferromagnetic and antiferromagnetic alignments. We also study scanning tunneling microscopic images of these dimers on the surface showing a large contrast under a bias voltage of 1V. Semiconducting surfaces such as GaAs hosting transition metal dopants with d-orbitals in this thesis have the potential to be excellent platforms for novel quantum applications such as fast-switching qubits. Also, reported spin-resolved density of states (DOS) and spin-resolved projected density of states can be used to understand the hybridization of bands, exchange splitting on orbitals, and design materials for future spintronic and optical applications.