Abstract
Dirac cones in a two-dimensional environment have attracted much attention not only because of the massless Dirac fermions but also due to their capability to lock the spin direction with the momentum. Here we demonstrate that the Rashba effect within a single layer of a binary alloy composed of heavy atoms, Pb and Au, can be driven by and even tweaked with the adjacent top and bottom layers to yield cone-like structures and further enhance the Rashba coupling strength. Two cones are observed at the surface zone center with giant Rashba parameters 1.53 and 4.45 eVÅ; an anisotropic giant Rashba splitting at the surface zone boundary has a great value, 6.26 eVÅ, inferring the critical role of p-d hybridization between Pb and Au. Our results reveal not only an interesting natural phenomenon but also a feasible method of tweaking the Rashba effect of a two-dimensional system.
Highlights
Spin–orbit coupling (SOC) is an atomic property caused by the electric field exerted on an electron from a nucleus
We discovered a binary-alloy film composed of dual heavy atoms, Au and Pb, which unfolds a large Rashba effect, yielding two cones at Γ0 and two giant Rashba splittings at M
Calculations of the electronic structure indicate that such a Rashba effect can be produced only via a special buckling configuration induced by squeezing from the top Au and bottom Pb layers
Summary
Spin–orbit coupling (SOC) is an atomic property caused by the electric field exerted on an electron from a nucleus. SOC is proportional to the square of the charge, Z2, of a nucleus; a surface terminated on a heavy-element solid is expected to exhibit a Rashba effect via splitting of two-dimensional (2D) surface states [2,3,4] Another way to produce the Rashba effect is to form an ultra-thin layer of a heavy element on a semiconductor surface [5,6,7,8,9]. First-principles calculations on both alloys attributed the enhancement of the Rashba effect to the strong distortion of the surface-state wave function [12] Both alloy films comprise heavy and light atoms to produce the in-plane electric field; more accurately, it is more related to how electrons are distributed in vicinity of atomic cores of heavy atoms than to types of atoms involved.
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