# Revisiting the Photon-Drag Effect in Metal Films

## TL;DR

This paper investigates the photon-drag effect in gold, revealing that surface molecules influence the signal and that the intrinsic effect's sign contradicts previous models, offering new insights into radiation pressure mechanisms.

## Contribution

It demonstrates the impact of adsorbed molecules on photon-drag measurements and challenges the conventional understanding of momentum transfer in metals.

## Key findings

- Adsorbed molecules alter the photon-drag signal in sign and magnitude.
- The intrinsic photon-drag effect's sign is opposite to the traditional model.
- Reinterpretation of previous measurements is necessary due to surface effects.

## Abstract

The photon-drag effect, the rectified current in a medium induced by conservation of momentum of absorbed or redirected light, is a unique probe of the detailed mechanisms underlying radiation pressure. We revisit this effect in gold, a canonical Drude metal. We discover that the signal for p-polarized illumination in ambient air is affected in both sign and magnitude by adsorbed molecules, opening previous measurements for reinterpretation. Further, we show that the intrinsic sign of the photon-drag effect is contrary to the prevailing intuitive model of direct momentum transfer to free electrons.