Efficient photo-Nernst terahertz emission in single heavy-metal films

TL;DR

This paper demonstrates that standalone heavy-metal films like platinum can efficiently emit terahertz radiation via the photo-Nernst effect, challenging the traditional view of metals as passive components in spintronic THz emitters.

Contribution

It introduces the ultrafast photo-Nernst effect as a new mechanism for THz emission in single heavy-metal films, expanding the understanding of their active role in spintronic devices.

Findings

Pt nanofilms emit strong THz signals at cryogenic temperatures.

The THz emission polarity is controlled by the Nernst coefficient sign.

Scaling and alloying enhance emission to levels comparable with bilayer structures.

Abstract

State-of-the-art metallic terahertz (THz) emitters rely predominantly on spintronic heterostructures, where heavy metals serve as passive spin-to-charge converters. Here, we demonstrate efficient THz radiation from standalone Pt nanofilms at cryogenic temperatures and under external magnetic fields. The governing mechanism is identified as the ultrafast photo-Nernst effect, wherein a transient thermal gradient drives a transverse charge current. The THz emission polarity is directly dictated by the sign of the Nernst coefficient, as verified by the phase reversal observed between Pt and W or Ta. Remarkably, both thickness scaling and alloying-induced suppression of thermal conductivity independently amplify the single-layer emission to levels comparable with benchmark spintronic bilayers. These findings redefine the established role of heavy metals from passive spin-sinks to active THz emitters, uncovering a universal emission paradigm applicable across diverse spintronic and quantum materials.