Image of the Month

February 2017

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

Figure 2 | Charge density wave (CDW) transition in MTBs. (a) STM images of a single MTB at low temperatures (120 K) exhibit three times the periodicity than the atomic corrugation imaged at room temperature. In (b) a larger scale low-T STM image and the corresponding cross-section along the indicated MTB is shown that measured the periodicity of the CDW as B1.0 nm. The schematic in (c) illustrates the relationship between CDW period and nesting vector q = 2kF. Also the opening of a band gap at kF is illustrated. Temperature dependent resistance measurements, shown in (d), indicate two CDW transitions. The transitions at 235 and 205 K correspond to incommensurate and commensurate CDW transitions, respectively. Depending on the applied bias voltage we also observe a drop in resistance below the CDW transition temperatures, which is attributed to CDW-sliding. The inset shows the control measurement on a bare MoS2 substrate and shows no transitions.

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/π, 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.

Credits:
Yujing Ma1, Horacio Coy Diaz1, José Avila2,3, Chaoyu Chen2,3, Vijaysankar Kalappattil1, Raja Das1, Manh-Huong Phan1, Čadež4,5, Josè M.P. Carmelo4,5,6, Maria C. Asensio2,3 & Matthias Batzill1

1 Department of Physics, University of South Florida, Tampa, Florida 33620, USA. 2 Synchrotron SOLEIL, L’Orme des Merisiers, Saint Aubin-BP 48, Gif sur Yvette Cedex 91192, France. 3 Universite ́ Paris-Saclay, L’Orme des Merisiers, Saint Aubin-BP 48, Gif sur Yvette Cedex 91192, France. 4 Beijing Computational Science Research Center, Beijing 100193, China. 5 Center of Physics of University of Minho and University of Porto, Oporto P-4169-007, Portugal. 6 Department of Physics, University of Minho, Campus Gualtar, Braga P-4710-057, Portugal.

Microscope:
PanScan Freedom UHV

Control System:
RHK R9 Control System