Revealing electron-lattice decoupling by Peltier thermometry and nanoscale thermal imaging in graphene

TL;DR

This paper introduces a novel nanoscale imaging technique that simultaneously maps electron and lattice temperatures in graphene at cryogenic conditions, revealing significant electron-phonon decoupling and new electron cooling pathways.

Contribution

The study presents the first spatially resolved cryogenic imaging method for electron and lattice temperatures in graphene, enabling detailed analysis of non-equilibrium energy dissipation.

Findings

Electron temperature increases nearly three orders of magnitude more than lattice temperature.

Strong electron-phonon decoupling observed under modest current bias.

Method applicable to various van der Waals heterostructures.

Abstract

Electrical currents in low-dimensional quantum materials can drive electrons far from equilibrium, creating stark imbalance between electron and lattice temperatures. Yet, no existing methods enable simultaneous nanoscale mapping of both temperatures at cryogenic conditions. Here, we introduce a scanning probe technique that images the local lattice temperature and extracts electron temperature at gate-defined p-n junctions in graphene. By applying an alternating electrical current and analyzing first- and second-harmonic responses, we disentangle Joule heating from the Peltier effect-the latter encoding the local electron temperature. This enables the first spatially resolved cryogenic imaging of both phenomena in graphene. Even under modest current bias, the electron temperature increases by nearly three orders of magnitude more than the lattice temperature, revealing strong electron-phonon decoupling and indicating a previously unrecognized electron cooling pathway. Our minimally invasive method is broadly applicable to van der Waals heterostructures and opens new avenues for probing energy dissipation and non-equilibrium transport in correlated and hydrodynamic electron systems.