Two-dimensional (2D) crystals have emerged as a class of materials with tuneable carrier density1. Carrier doping to 2D semiconductors can be used to modulate manybody interactions2and to explore novel composite particles. Holstein polaron is a small composite particle of an electron carrying a cloud of self-induced lattice deformation (or phonons)3-5, which has been proposed to play a key role in hightemperature superconductivity6and carrier mobility in devices7. Here, we report the discovery of Holstein polarons in a surface-doped layered semiconductor, MoS2, where a puzzling 2D superconducting dome with the critical temperature of 12 K was found recently8-11. Using a high-resolution band mapping of charge carriers, we found strong band renormalizations collectively identified as a hitherto unobserved spectral function of Holstein polarons12-18. The unexpected short-range nature of electron-phonon (e-ph) coupling in MoS2can be explained by its valley degeneracy that enables strong intervalley coupling mediated by acoustic phonons. The coupling strength is found to gradually increase along the superconducting dome up to the intermediate regime, suggesting bipolaronic pairing in 2D superconductivity.
|Publication status||Published - 2018 May 28|
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