Biexcitons in monolayer transition metal dichalcogenides tuned by magnetic fields

Christopher E Stevens,Myron D Kapetanakis,Timothy Cox,Humberto R Gutiérrez,Denis Karaiskaj,David J Hilton,Steven A Mcgill,Volodymyr Turkowski,Jagannath Paul,Dimitry Semenov,Prasana K Sahoo,Ilias E Perakis

doi:10.1038/s41467-018-05643-1

Abstract

We present time-integrated four-wave mixing measurements on monolayer MoSe2 in magnetic fields up to 25 T. The experimental data together with time-dependent density function theory calculations provide interesting insights into the biexciton formation and dynamics. In the presence of magnetic fields the coherence at negative and positive time delays is dominated by intervalley biexcitons. We demonstrate that magnetic fields can serve as a control to enhance the biexciton formation and help search for more exotic states of matter, including the creation of multiple exciton complexes and excitonic condensates.

Highlights

We present time-integrated four-wave mixing measurements on monolayer MoSe2 in magnetic fields up to 25 T
The time-integrated four-wave mixing (FWM) signal is plotted as function of the time delay between pulse A* and the pulses B and C is shown Fig. 2
We see an increase in the coherence time T2 to ~600 from ~400 fs when measured at 10 T compared to zero magnetic fields

Summary

Introduction

We present time-integrated four-wave mixing measurements on monolayer MoSe2 in magnetic fields up to 25 T. The time-integrated FWM signal in the negative time delay regime is the most striking signature of the difference between nonlinear optical response of a collection of atoms and a solid state This seemingly counterintuitive behavior that appears to violate causality is a result of the Coulomb interactions, which are dominant in semiconductors. In the absence of magnetic fields, the existence of the four-particle exciton–exciton interactions introduces the negative time delay decay on the time-integrated FWM signal. The underlying cause for this effect is that the excitons created in the semiconductor by one laser pulse are strongly distorted by the magnetic field They acquire a quadrupole moment and through it they generate a coherent four-particle correlation in the medium. This quantization leads to strong exciton–exciton interactions along the magnetic field axis and to a strong negative delay signal[41]

Methods

Results

Conclusion