Quantum well states and amplified spin-dependent Friedel oscillations in thin films

TL;DR

This paper demonstrates how quantum well states in ferromagnetic Fe thin films on W(001) induce giant, anisotropic, spin-filtered Friedel oscillations around impurities, controllable by film thickness, affecting material properties.

Contribution

It reveals the control of anisotropic Friedel oscillations via quantum well states in ferromagnetic thin films, highlighting their impact on impurity detection and spin-dependent phenomena.

Findings

Giant anisotropic charge density oscillations observed

Oscillations can be detected at distances up to 50 nm

Control of oscillations achieved by varying film thickness

Abstract

Electrons mediate many of the interactions between atoms in a solid. Their propagation in a material determines its thermal, electrical, optical, magnetic and transport properties. Therefore, the constant energy contours characterizing the electrons, in particular the Fermi surface, have a prime impact on the behavior of materials. If anisotropic, the contours induce strong directional dependence at the nanoscale in the Friedel oscillations surrounding impurities. Here we report on giant anisotropic charge density oscillations focused along specific directions with strong spin-filtering after scattering at an oxygen impurity embedded in the surface of a ferromagnetic thin film of Fe grown on W(001). Utilizing density functional theory, we demonstrate that by changing the thickness of the Fe films, we control quantum well states confined to two dimensions that manifest as multiple flat energy contours, impinging and tuning the strength of the induced charge oscillations which allow to detect the oxygen impurity at large distances ($\approx$ 50nm).