Angle resolved photoemission spectroscopy reveals spin charge separation in metallic MoSe2 grain boundary

Material line defects are one-dimensional structures but the search and proof of electron behaviour consistent with the reduced dimension of such defects has been so far unsuccessful. Here we show using angle resolved photoemission spectroscopy that twin-grain boundaries in the layered semiconductor MoSe2 exhibit parabolic metallic bands. The one-dimensional nature is evident from a charge density wave transition, whose periodicity is given by kF/p, consistent with scanning tunnelling microscopy and angle resolved photoemission measurements. Most importantly, we provide evidence for spin- and charge-separation, the hallmark of one-dimensional quantum liquids. Our studies show that the spectral line splits into distinctive spinon and holon excitations whose dispersions exactly follow the energy-momentum dependence calculated by a Hubbard model with suitable finite-range interactions. Our results also imply that quantum wires and junctions can be isolated in line defects of other transition metal dichalcogenides, which may enable quantum transport measurements and devices. The USF group acknowledges support from the National Science Foundation (DMR-1204924). V.K., R.D. and M.-H. P. acknowledges support from the Army Research Office (W911NF-15-1-0626) and thank Prof. Hari Srikanth for resistance measurements in his laboratory. M.C.A., J.A. and C.C. thank enlightening exchanges with Gabriel Kotliar and Zhi-Xun Shen. The Synchrotron SOLEIL is supported by the Centre National de la Recherche Scientifique (CNRS) and the Commissariat a` l’Energie Atomique et aux Energies Alternatives (CEA), France. T.Cˇ. and J.M.P.C. thank Eduardo Castro, Hai-Qing Lin and Pedro D. Sacramento for illuminating discussions. The theory group acknowledges the support from NSAF U1530401 and computational resources from CSRC (Beijing), the Portuguese FCT through the Grant UID/FIS/04650/2013 and the NSFC Grant 11650110443.