Ultrafast Momentum-resolved Hot Electron Dynamics in the Two-dimensional Topological Insulator Bismuthene

TL;DR

This study investigates hot electron dynamics in room-temperature two-dimensional topological insulator bismuthene using time-resolved photoemission, revealing rapid carrier relaxation and potential for optical control of quantum spin Hall effects.

Contribution

It provides the first detailed mapping of hot electron relaxation pathways in bismuthene at room temperature, highlighting the role of topological in-gap states.

Findings

Photocarrier lifetimes are significantly shorter than in conventional semiconductors.

Spectral signatures confirm the presence of topological in-gap states.

Large band gap enables potential optical control of QSH functionalities.

Abstract

Two-dimensional quantum spin Hall (QSH) insulators are a promising material class for spintronic applications based on topologically-protected spin currents in their edges. Yet, they have not lived up to their technological potential, as experimental realizations are scarce and limited to cryogenic temperatures. These constraints have also severely restricted characterization of their dynamical properties. Here, we report on the electron dynamics of the novel room-temperature QSH candidate bismuthene after photoexcitation using time- and angle-resolved photoemission spectroscopy. We map the transiently occupied conduction band and track the full relaxation pathway of hot photocarriers. Intriguingly, we observe photocarrier lifetimes much shorter than in \red{conventional} semiconductors. This is ascribed to the presence of topological in-gap states already established by local probes. Indeed, we find spectral signatures consistent with these earlier findings. Demonstration of the large band gap and the view into photoelectron dynamics mark a critical step toward optical control of QSH functionalities.