  Excitons are electron-hole (e-h) pair quasiparticles, which may form a
Bose-Einstein condensate (BEC) and collapse into the phase coherent state at
low temperature. However, because of ephemeral strength of pairing, a clear
evidence for BEC in electron-hole system has not yet been observed. Here, we
report electron-hole pair condensation in graphene (Gr)/MoS2 heterointerface at
10K without magnetic field. As a direct indication of e-h pair condensation, we
demonstrate a vanished Hall drag voltage and the resultant divergence of drag
resistance. While strong excitons are formed at Gr/MoS2 heterointerface without
insulating layer, carrier recombination via interlayer tunneling of carriers is
suppressed by the vertical p-Gr/n-MoS2 junction barrier, consequently yielding
high BEC temperature of 10K, ~1000 times higher than that of two-dimensional
electron gas in III-V quantum wells. The observed excitonic transport is mainly
governed by the interfacial properties of the Gr/MoS2 heterostructure, rather
than the intrinsic properties of each layer. Our approach with available
large-area monolayer graphene and MoS2 provides a high feasibility for quantum
dissipationless electronics towards integration.
