Giant effective Zeeman splitting in a monolayer semiconductor realized by spin-selective strong light-matter coupling

TL;DR

This paper demonstrates giant effective Zeeman splitting in a monolayer semiconductor through spin-selective strong light-matter coupling, revealing new opportunities for quantum phases and optical non-linearities in 2D materials.

Contribution

It introduces a novel method to achieve large Zeeman splitting and optical non-linearity in monolayer MoSe₂ via spin-selective strong coupling in a microcavity.

Findings

Giant Zeeman splitting with g-factor >20 observed in trion-polaritons.

Optical non-linearity enables tuning of Zeeman splitting from 4 to >10 meV.

Spin polarization influences light-matter interactions and polariton formation.

Abstract

Strong coupling between light and the fundamental excitations of a two-dimensional electron gas (2DEG) are of foundational importance both to pure physics and to the understanding and development of future photonic nanotechnologies. Here we study the relationship between spin polarization of a 2DEG in a monolayer semiconductor, MoSe$_2$, and light-matter interactions modified by a zero-dimensional optical microcavity. We find robust spin-susceptibility of the 2DEG to simultaneously enhance and suppress trion-polariton formation in opposite photon helicities. This leads to observation of a giant effective valley Zeeman splitting for trion-polaritons (g-factor >20), exceeding the purely trionic splitting by over five times. Going further, we observe robust effective optical non-linearity arising from the highly non-linear behaviour of the valley-specific strong light-matter coupling regime, and allowing all-optical tuning of the polaritonic Zeeman splitting from 4 to >10 meV. Our experiments lay the groundwork for engineering quantum-Hall-like phases with true unidirectionality in monolayer semiconductors, accompanied by giant effective photonic non-linearities rooted in many-body exciton-electron correlations.