Ultrafast Generation of Pseudo-magnetic Field for Valley Excitons in WSe2 Monolayers

TL;DR

This paper demonstrates that circularly polarized femtosecond pulses can generate an ultrafast, ultrahigh valley pseudomagnetic field in monolayer WSe2, enabling coherent control of valley excitons for valleytronics and quantum information.

Contribution

It introduces a method to produce a strong, ultrafast pseudomagnetic field in monolayer WSe2 using optical Stark effect, advancing valley pseudospin manipulation techniques.

Findings

Achieved energy splitting >10 meV between valley excitons

Corresponds to an effective pseudomagnetic field over 170 Tesla

Demonstrated ultrafast, valley-selective optical control

Abstract

A new degree of freedom, the valley pseudospin, emerges in atomically thin two-dimensional transition metal dichalcogenides (MX2) and has attracted great scientific interest. The capability to manipulate the valley pseudospin, in analogy to the control of spin in spintronics, can open up exciting opportunities in valleytronics. Here we demonstrate that an ultrafast and ultrahigh valley pseudomagnetic field can be generated using circularly polarized femtosecond pulses to selectively control the valley degree of freedom in monolayer MX2. Employing ultrafast pump-probe spectroscopy, we observed a pure and valley-selective optical Stark effect in WSe2 monolayers from the non-resonant pump, which instantaneously lift the degeneracy of valley exciton transitions without any dissipation. The strength of the optical Stark effect scales linearly with both the pump intensity and the inverse of pump detuning. An energy splitting more than 10 meV between the K and K_prime valley transitions can be achieved, which corresponds to an effective pseudomagnetic field over 170 Tesla. Our study demonstrates efficient and ultrafast control of the valley excitons with optical light, and opens up the possibility to coherent manipulate the valley polarization for quantum information applications.