No abstract

Topological properties of matters have attracted tremendous interest in the past years due to the scientific and technological importance. It is of great interest to discover the analogs of topological phases in molecular architectures, if the key constituents of the phases are properly mimicked. Using scanning tunneling microscopy, we demonstrate that quasi-1D molecular chains assembled from conformation-switchable dibenzo[ g, p]chrysene molecules show hidden antiparallel order analogous to the hidden antiferromagnetic order in the Haldane phase, a known topological phase of quantum spin-1 chains. This is realized by mimicking the spin degree of freedom with the intramolecular helicene chiral switches and by emulating the interspin antiferromagnetic coupling with intermolecular homochiral coupling. The discovery of the molecular analog of topological matters may inspire the search of molecular architectures with nontrivial topological properties.

A new carbon-based two-dimensional crystalline nanostructure was discovered. The nanostructure was facilely constructed by chemical vapor deposition of benzene on Cu(111) in an ultrahigh vacuum chamber. A low temperature scanning tunneling microscopy and spectroscopy study of the nanostructure indicated that it has an orthorhombic superstructure and a semiconductor character with an energy gap of 0.8 eV. An X-ray photoelectron spectroscopy study showed that C-C(sp(2)) bonding is predominantly preserved, suggesting a framework consisting of π-conjugated building blocks. The periodic nanostructure was found to be a surprisingly excellent template for isolating and stabilizing magnetic atoms: Co atoms deposited on it can be well dispersed and form locally ordered atomic chains with their atomic magnetism preserved. Therefore the nanostructure may be suitable for organic spintronic applications. The most likely structural model for the nanostructure is proposed with the aid of density functional theory calculations and simulations, suggesting that the 2D nanostructure may consist of polyphenylene chains interconnected by Cu adatoms.