Spintronic THz emitters based on transition metals and semi-metals/Pt multilayers

TL;DR

This paper explores advanced material and interface engineering strategies in spintronic THz emitters, achieving significant enhancements in THz emission by optimizing multilayer structures, using semi-metals, and reducing optical absorption effects.

Contribution

It introduces novel multilayer and semi-metal configurations for spintronic THz emitters, improving emission efficiency through material and interface optimization.

Findings

Enhanced THz emission with multilayer structures

Correlation between spin diffusion length and THz emission

Distinction between self and interface spin-to-charge conversion

Abstract

Spintronic terahertz (THz) emitters (STE) based on the inverse spin Hall effect in ferromagnetic/heavy metal (FM/HM) heterostructures have become important sources for THz pulse generation. The design, materials and control of these interfaces at the nanometer level has become vital to engineer their THz emission properties.In this work, we present studies of the optimization of such structures through a multi-pronged approach, taking advantage of material and interface engineering to enhance the THz spintronic emission. This includes: the application of multi-stacks of HM/FM junctions and their application to trilayer structures, the use of spin-sinks to simultaneously enhance the THz emitted fields and reduce the use of thick Pt layers to reduce optical absorption, and the use of semi-metals to increase the spin polarization and thus the THz emission. Through these approaches, significant enhancements of the THz field can be achieved. Importantly, taking into account the optical absorption permits to elucidate novel phenomena such as the relation between the spin diffusion length and the spin-sink using THz spectroscopy, as well as possibly distinguishing between self and interface spin-to-charge conversion in semi-metals.