Ultrafast transition between exciton phases in van der Waals heterostructures
Introductory text in journal, 2019

© 2019, The Author(s), under exclusive licence to Springer Nature Limited. Heterostructures of atomically thin van der Waals bonded monolayers have opened a unique platform to engineer Coulomb correlations, shaping excitonic1–3, Mott insulating4 or superconducting phases5,6. In transition metal dichalcogenide heterostructures7, electrons and holes residing in different monolayers can bind into spatially indirect excitons1,3,8–11 with a strong potential for optoelectronics11,12, valleytronics1,3,13, Bose condensation14, superfluidity14,15 and moiré-induced nanodot lattices16. Yet these ideas require a microscopic understanding of the formation, dissociation and thermalization dynamics of correlations including ultrafast phase transitions. Here we introduce a direct ultrafast access to Coulomb correlations between monolayers, where phase-locked mid-infrared pulses allow us to measure the binding energy of interlayer excitons in WSe2/WS2 hetero-bilayers by revealing a novel 1s–2p resonance, explained by a fully quantum mechanical model. Furthermore, we trace, with subcycle time resolution, the transformation of an exciton gas photogenerated in the WSe2 layer directly into interlayer excitons. Depending on the stacking angle, intra- and interlayer species coexist on picosecond scales and the 1s–2p resonance becomes renormalized. Our work provides a direct measurement of the binding energy of interlayer excitons and opens the possibility to trace and control correlations in novel artificial materials.

Author

Philipp Merkl

University of Regensburg

F. Mooshammer

University of Regensburg

Philipp Steinleitner

University of Regensburg

A. Girnghuber

University of Regensburg

K. Q. Lin

University of Regensburg

P. Nagler

University of Regensburg

J. Holler

University of Regensburg

C. Schuller

University of Regensburg

J. M. Lupton

University of Regensburg

T. Korn

University of Rostock

University of Regensburg

Simon Ovesen

Chalmers, Physics, Condensed Matter Theory

Samuel Brem

Chalmers, Physics, Condensed Matter Theory

Ermin Malic

Chalmers, Physics, Condensed Matter Theory

R. Huber

University of Regensburg

Nature Materials

1476-1122 (ISSN) 1476-4660 (eISSN)

Vol. 18 7 691-696

Subject Categories

Atom and Molecular Physics and Optics

Other Physics Topics

Condensed Matter Physics

DOI

10.1038/s41563-019-0337-0

PubMed

30962556

More information

Latest update

7/2/2019 2