Reconciling the bulk metallic and surface insulating state in 1T-TaSe2

The origin of different electronic states of 1T-TaS2 and 1T-TaSe2 remains controversial due to the complicated correlated electronic properties. We apply scanning tunneling microscopy to study the electronic state of bulk 1T-TaSe2. Both insulating and metallic states are identified in different areas of the same sample. The insulating state is similar to that in 1T-TaS2, concerning both the dI/dV spectrum and the orbital texture. With detailed investigations in single-step areas, the electronic state measured on the upper-layer surface is found to be associated with different stacking orders and the lower layer's electronic state. The insulating state is most possibly a single-layer property, perturbed to a metallic state by particular stacking orders. Both the metallic and large-gap insulating spectra, together with their corresponding stacking orders, are stable states in 1T-TaSe2. The connected metallic areas lead to the metallic transport behavior. We then reconcile the bulk metallic and surface insulating state in 1T-TaSe2. The rich phenomena in 1T-TaSe2 deepen our understanding of the correlated electronic state in bulk 1T-TaSe2 and 1T-TaS2.