Reconciling the bulk metallic and surface insulating state in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>1</mml:mn><mml:mi>T</mml:mi><mml:mtext>−</mml:mtext><mml:msub><mml:mi mathvariant="normal">TaSe</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>

Abstract

The origin of different electronic states of $1T\ensuremath{-}{\mathrm{TaS}}_{2}$ and $1T\ensuremath{-}{\mathrm{TaSe}}_{2}$ remains controversial due to the complicated correlated electronic properties. We apply scanning tunneling microscopy to study the electronic state of bulk $1T\ensuremath{-}{\mathrm{TaSe}}_{2}$. Both insulating and metallic states are identified in different areas of the same sample. The insulating state is similar to that in $1T\ensuremath{-}{\mathrm{TaS}}_{2}$, 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 $1T\text{\ensuremath{-}}{\mathrm{TaSe}}_{2}$. The connected metallic areas lead to the metallic transport behavior. We then reconcile the bulk metallic and surface insulating state in $1T\ensuremath{-}{\mathrm{TaSe}}_{2}$. The rich phenomena in $1T\ensuremath{-}{\mathrm{TaSe}}_{2}$ deepen our understanding of the correlated electronic state in bulk $1T\ensuremath{-}{\mathrm{TaSe}}_{2}$ and $1T\ensuremath{-}{\mathrm{TaS}}_{2}$.

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