Ultrafast ghost Hall states in a 2d altermagnet

TL;DR

This paper demonstrates that 2D altermagnets like Cr$_2$SO can be controlled with femtosecond laser pulses to generate highly spin-polarized valley currents and ultrafast ghost Hall states, revealing new spin and charge dynamics.

Contribution

It introduces the concept of ultrafast control of valley and spin states in 2D altermagnets using femtosecond laser pulses, a novel approach in the field.

Findings

Linearly polarized light excites charge at specific valleys depending on polarization.

Nearly 100% spin-polarized valley currents can be generated.

Ultrafast 'ghost Hall' states with orthogonal spin and charge currents are created.

Abstract

Two-dimensional materials that exhibit optically active spin and valley degrees of freedom represent one of the most fascinating -- and potentially most technologically useful -- platforms for the ultrafast interaction of light and matter. Here we show, via the example of Cr$_2$SO, that two dimensional altermagnets host valley states controllable by femtosecond laser light: linearly polarized light pulses excite charge at one of two inequivalent valleys, with which valley charge is excited at determined by the polarization vector direction. This underpins a rich spin and valley physics including: (i) valleytronics $-$ the generation of nearly 100$\%$ spin polarized valley currents, as well as (ii) a "ghost Hall" effect $-$ the ultrafast creation of states in which spin and charge currents are orthogonal without invoking Hall physics. Our findings establish 2d altermagents as a platform providing a new route for the control of spin- and charge currents at ultrafast times.