Electron–hole liquid in a van der Waals heterostructure photocell at room temperature

• Published in: Nature photonics 2019-04, Vol.13 (4), p.245-250
• Main Authors: Arp, Trevor B., Pleskot, Dennis, Aji, Vivek, Gabor, Nathaniel M.
• Format: Article
• Language: English
• Subjects: 639/624/1107/328; 639/766/119; 639/925/927; Applied and Technical Physics; Current carriers; Data acquisition; Dependence; Electronic devices; Electrons; Graphene; Heterostructures; Letter; Molybdenum compounds; Optoelectronic devices; phonons, thermal conductivity, thermoelectric, spin dynamics, spintronics; Photoelectric cells; Photoelectric effect; Photoelectric emission; Physics; Physics and Astronomy; Quantum Physics; Room temperature; Tellurides; Ultrafast lasers
• ISSN: 1749-4885; 1749-4893
• DOI: 10.1038/s41566-019-0349-y

In semiconductors, photo-excited charge carriers exist as a gas of electrons and holes, bound electron–hole pairs (excitons), biexcitons and trions 1 – 4 . At sufficiently high densities, the non-equilibrium system of electrons ( e − ) and holes ( h + ) may merge into an electronic liquid droplet 5 – 10 . Here, we report on the electron–hole liquid in ultrathin MoTe 2 photocells revealed through multi-parameter dynamic photoresponse microscopy (MPDPM). By combining rich visualization with comprehensive analysis of very large data sets acquired through MPDPM, we find that ultrafast laser excitation at a graphene–MoTe 2 –graphene interface leads to the abrupt formation of ring-like spatial patterns in the photocurrent response as a function of increasing optical power at T  = 297 K. The sudden onset to these patterns, together with extreme sublinear power dependence and picosecond-scale photocurrent dynamics, provide strong evidence for the formation of a two-dimensional electron–hole liquid droplet. The electron–hole liquid, which features a macroscopic population of correlated electrons and holes, may offer a path to room-temperature optoelectronic devices that harness collective electronic phenomena. Photoexcited charge carriers are typically approximated as a gas, but now it is shown that electrons and holes can behave as a liquid in MoTe 2 photocells.