Supercluster of electrons in ultrathin TaSe2 nanocrystals

摘要

We discover a supercluster of electrons in the ultrathin TaSe2 crystals synthesized by our developed de-chalcogenide method. The supercluster has all unexpected structure containing 61 electrons denoted by root 61 x root 61, in addition to a root 49 x root 49 supercluster based on root 7 x root 7 clusters expected in triangle lattices. This new hierarchal structure and successive clustering cannot be explained by a conventional electron clustering mechanism assisted by background lattice distortions, i.e., charge-density-wave formation mechanism based on Fermi surface nesting. We propose an alternative possible formation mechanism based on saddle-point nesting, taking into account a trigonal symmetry as well as lattice distortion energy.