Probing Fermi surface topology by ultrafast pump pulse dynamics

TL;DR

This paper introduces a dynamical method using ultrafast pump pulses to detect Fermi surface topology changes, specifically Lifshitz transitions, by analyzing persistent oscillatory currents in a two-band model.

Contribution

It demonstrates a novel approach to identify topological Lifshitz transitions through resonant light coupling and post-pulse current analysis in a two-band system.

Findings

Resonant light induces persistent oscillatory currents at Lifshitz transitions.

The amplitude ratio of oscillatory currents signals the Fermi energy crossing saddle points.

The method provides a robust dynamical signature for topological Fermi surface changes.

Abstract

We present a dynamical approach to detect changes in Fermi surface topology in a two-band model. Specifically, we show that the system's response to a low intensity light pulse can precisely identify topological Lifshitz transitions. At a suitable frequency, the light resonantly couples valence and conduction electrons, leading to an oscillation in the interband coherence term. This, in turn, generate a persistent oscillatory current which survives even after the end of the pulse. Notably, the relative amplitude of the oscillatory current during the pulse with that of the post-pulse reaches a minimum when the Fermi energy aligns with the saddle point, providing a robust framework for dynamically identifying Lifshitz transitions.