In semiconductors, photo-excited charge carriers exist as a gas of electrons and holes, bound electron–hole pairs (excitons), biexcitons and trions1,2,3,4. At sufficiently high densities, the non-equilibrium system of electrons (e−) and holes (h+) may merge into an electronic liquid droplet5,6,7,8,9,10. Here, we report on the electron–hole liquid in ultrathin MoTe2 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–MoTe2–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.
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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.
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The authors would like to acknowledge valuable discussions with C. Varma. This work was supported by the Air Force Office of Scientific Research Young Investigator Program (YIP) award number FA9550-16-1-0216, as part of the SHINES Center, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under award number SC0012670, and through support from the National Science Foundation Division of Materials Research CAREER award number 1651247. D.P. and N.M.G received support from SHINES. N.M.G. acknowledges support through a Cottrell Scholar Award, and through the Canadian Institute for Advanced Research (CIFAR) Azrieli Global Scholar Award. T.B.A. acknowledges support from the Fellowships and Internships in Extremely Large Data Sets (FIELDS) Program, a NASA MUREP Institutional Research Opportunity (MIRO) Program, grant number NNX15AP99A. V.A. acknowledges support from the National Science Foundation Division of Materials Research award number 1506707.