# Giant paramagnetism induced valley polarization of electrons in charge-tunable monolayer MoSe2

## TL;DR

This study demonstrates that a magnetic field induces near-complete valley polarization in monolayer MoSe2, revealing a giant paramagnetic response that could advance valleytronics technologies.

## Contribution

It uncovers a magnetic-field-induced giant paramagnetic response in MoSe2, enabling efficient valley polarization without requiring extremely high pseudospin g-factors.

## Key findings

- Near-complete valley polarization at 7 Tesla
- Observation of gate-dependent transfer of oscillator strength
- Evidence of interaction-induced giant paramagnetism

## Abstract

For applications exploiting the valley pseudospin degree of freedom in transition metal dichalcogenide monolayers, efficient preparation of electrons or holes in a single valley is essential. Here, we show that a magnetic field of 7 Tesla leads to a near-complete valley polarization of electrons in MoSe2 monolayer with a density 1.6x10^{12} cm^{-2}; in the absence of exchange interactions favoring single-valley occupancy, a similar degree of valley polarization would have required a pseudospin g-factor exceeding 40. To investigate the magnetic response, we use polarization resolved photoluminescence as well as resonant reflection measurements. In the latter, we observe gate voltage dependent transfer of oscillator strength from the exciton to the attractive-Fermi-polaron: stark differences in the spectrum of the two light helicities provide a confirmation of valley polarization. Our findings suggest an interaction induced giant paramagnetic response of MoSe2, which paves the way for valleytronics applications.