Photo-Nernst current in graphene

TL;DR

This paper introduces the photo-Nernst effect in graphene, demonstrating how laser-induced electron heating in a magnetic field generates a measurable photocurrent along the edges, revealing new insights into gapless material optoelectronics.

Contribution

The study identifies and characterizes the photo-Nernst effect in graphene, expanding understanding of thermoelectric photocurrent mechanisms in two-dimensional materials.

Findings

Photocurrent is generated uniformly along graphene edges with opposite signs at each edge.

The signal exhibits antisymmetry in magnetic field and peaks at the neutrality point.

Quantum oscillations are observed at higher magnetic fields.

Abstract

Photocurrent measurements provide a powerful means of studying the spatially resolved optoelectronic and electrical properties of a material or device. Generally speaking there are two classes of mechanism for photocurrent generation: those involving separation of electrons and holes, and thermoelectric effects driven by electron temperature gradients. Here we introduce a new member in the latter class: the photo-Nernst effect. In graphene devices in a perpendicular magnetic field we observe photocurrent generated uniformly along the free edges, with opposite sign at opposite edges. The signal is antisymmetric in field, shows a peak versus gate voltage at the neutrality point flanked by wings of opposite sign at low fields, and exhibits quantum oscillations at higher fields. These features are all explained by the Nernst effect associated with laser-induced electron heating. This photo-Nernst current provides a simple and clear demonstration of the Shockley-Ramo nature of long-range photocurrent generation in a gapless material.