Ultrafast THz probing of nonlocal orbital current in transverse multilayer metallic heterostructures

TL;DR

This paper demonstrates ultrafast THz probing of orbital-to-charge current conversion in metallic heterostructures, revealing the dominant orbital effects and their temperature dependence, with significant enhancement observed in W-inserted structures.

Contribution

First experimental demonstration of orbital-to-charge current conversion in metallic heterostructures using THz emission detection, distinguishing orbital and spin contributions through temperature dependence.

Findings

NiFe/Nb exhibits the strongest inverse orbital Hall effect.

CoFeB/Pt shows maximum inverse spin Hall effect contribution.

W-insertion in CoFeB/W/Ta enhances THz emission tenfold due to orbital transport.

Abstract

THz generation from femtosecond photoexcited spintronic heterostructures has recently become a versatile tool for investigating ultrafast spin-transport and transient charge-current in a non-contact and non-invasive manner. The same from the orbital effects is still in the primitive stage. Here, we experimentally demonstrate orbital-to-charge current conversion in metallic heterostructures, consisting of a ferromagnetic layer adjacent to either a light or a heavy metal layer, through detection of the emitted THz pulses. Temperature-dependent experiments help to disentangle the orbital and spin components that are manifested in the respective Hall-conductivities, contributing to THz emission. NiFe/Nb shows the strongest inverse orbital Hall effect with an experimentally extracted value of effective Hall-conductivity, \sigma_SOH^int^eff ~ 195 {\Omega}^(-1){cm}^(-1), while CoFeB/Pt shows maximum contribution from the inverse spin Hall effect. In addition, we observe nearly ten-fold enhancement in the THz emission due to pronounced orbital-transport in W-insertion heavy metal layer in CoFeB/W/Ta heterostructure as compared to the CoFeB/Ta bilayer counterpart.