Nonlinear spectroscopy of semiconductor moir\'e materials
- URL: http://arxiv.org/abs/2402.16630v1
- Date: Mon, 26 Feb 2024 15:02:51 GMT
- Title: Nonlinear spectroscopy of semiconductor moir\'e materials
- Authors: B. Evrard, A. Ghita, T. Uto, L. Ciorciaro, K. Watanabe, T. Taniguchi,
M. Kroner and A. \.Imamo\u{g}lu
- Abstract summary: We use time-resolved nonlinear pump--probe measurements to reveal features of semiconductor moir'e materials.
We generate a high density of virtual excitons or exciton--polarons in various moir'e minibands.
- Score: 0.0
- License: http://creativecommons.org/licenses/by-nc-sa/4.0/
- Abstract: We use time-resolved nonlinear pump--probe measurements to reveal features of
semiconductor moir\'e materials not accessible to linear spectroscopy. With an
intense, red-detuned pump pulse, we generate a high density of virtual excitons
or exciton--polarons in various moir\'e minibands. A broadband probe pulse in
turn measures the response of all optical resonances induced by the
pump-generated excitations. We generically observe a coherent blue shift
originating from contact-like exciton--exciton interactions. At charge
neutrality, these measurements allow us to assess the spatial overlap between
different optical excitations: in particular, we observe signatures of a bound
biexciton state between two different moire exciton modes. For integer fillings
$\nu=2$ and $\nu=3$ of the moir\'e lattice with electrons, the correlated Mott
state results in a suppression of the exciton--polaron interactions, providing
a nonlinear optical signature of electronic incompressibility. In stark
contrast, for lower electron fillings $\nu < 2$, the light shift of the
attractive polaron resonance is electron density independent. Deeply localized
moir\'e polarons are thus akin to an ensemble of non-interacting two-level
atoms, subject to the single-emitter ac Stark effect. Finally, tuning the pump
laser on resonance with the attractive polaron for $\nu < 2$, we demonstrate
the filling of the moir\'e lattice with localized polarons and thereby realize
a nonequilibrium Bose--Fermi mixture in moir\'e flat bands.
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