Emergence of high-mobility carriers in topological kagome bad metal Mn$_3$Sn by intense photoexcitation

TL;DR

Intense photoexcitation in Mn$_3$Sn induces high-mobility carriers with significantly lighter effective mass, revealing complex interplay between electronic correlations, band topology, and nonequilibrium transport in a topological kagome metal.

Contribution

This study demonstrates the emergence of high-mobility carriers in Mn$_3$Sn under intense photoexcitation, highlighting the role of electronic correlations and dielectric screening in nonequilibrium conditions.

Findings

Photoexcitation induces a cyclotron resonance indicating high-mobility carriers.

High-mobility carriers have 50 times lighter effective mass and longer lifetime.

Threshold behavior suggests correlation effects beyond hot carrier contributions.

Abstract

Kagome-lattice materials offer novel playgrounds of exploring topologically nontrivial states of electrons under influence of many-body interactions. A noncollinear kagome antiferromagnet Mn$_3$Sn has attracted particular interest for application in spintronics owing to the large anomalous Hall effect related to the Weyl dispersion near the Fermi energy. In addition, strong electronic correlation suggesting the Kondo physics has also been implied. However, the effect of correlation on the band topology and their interplay remains elusive. Here, we investigate nonequilibrium Hall transport in a photoexcited Mn$_3$Sn using time-resolved terahertz Faraday rotation spectroscopy. In equilibrium, Mn$_3$Sn is a bad metal close to the Mott-Ioffe-Regal limit with low carrier mobility, and thus only the anomalous Hall effect is discerned. By contrast, intense photoexcitation beyond an approximate threshold gives rise to a clear cyclotron resonance, namely the normal Hall effect, indicating the emergence of unusual carriers with 50 times lighter effective mass and 40 times less scattering. The lifetime of high-mobility carriers as long as a few tens of picoseconds and a threshold-like behavior for the pump fluence are hardly explained by contribution of photoexcited hot carriers. Instead, the emergence of unusual carriers may be accounted for by dielectric screening of the on-site Coulomb interaction by high-density delocalized photocarriers. A possible role of electronic correlation in equilibrium transport in Mn$_3$Sn beyond the single-particle picture is discussed.