Evolution of low-lying states in a doped CDW superconductor CuxTiSe2

A superconducting state has recently been observed by only a slight copper doping (similar to 4%) of the metallic 2D commensurate charge-density-wave (CDW) phase of titanium diselenide. We have employed high-resolution photoemission spectroscopy (ARPES) to probe the evolution of low-lying states, providing evidence that the CDW in the doped system is not due to Fermi surface nesting. With increasing copper concentration, we observe a significant rise of the chemical potential and a manifold of low-lying states at the top of the Fermi sea with increasing particle hole asymmetry. These effects taken together contribute to destabilize the observed commensurate electronic, possibly, excitonic order in the vicinity of the superconducting (loping in this system. (c) 2007 Elsevier B.V. All rights reserved.