Xiang-Guo Li

Conformational Electroresistance and Hysteresis in Nanoclusters

The existence of multiple thermodynamically stable isomer states is one of the most fundamental properties of small clusters. This work shows that the conformational dependence of the Coulomb charging energy of a nanocluster leads to a giant electroresistance, where charging induced conformational distortion changes the blockade voltage. The intricate interplay between charging and conformation change is demonstrated in a nanocluster Zn3O4 by combining a first-principles calculation with a temperature-dependent transport model. The predicted hysteretic Coulomb blockade staircase in the current-voltage curve adds another dimension to the rich phenomena of tunneling electroresistance. The new mechanism provides a better controlled and repeatable platform to study conformational electroresistance.

Molecular analogue of the perovskite repeating unit and evidence for direct Mn III -Ce IV -Mn III exchange coupling pathway

The perovskite manganites AMnO3 and their doped analogues A1–xBxMnO3 (A and B = main group and lanthanide metals) are a fascinating family of magnetic oxides exhibiting a rich variety of properties. They are thus under intense investigation along multiple fronts, one of which is how their structural and physical properties are modified at the nanoscale. Here we show that the molecular compound [Ce3Mn8O8(O2CPh)18(HO2CPh)2] (CeIII2CeIVMnIII8; hereafter Ce3Mn8) bears a striking structural resemblance to the repeating unit seen in the perovskite manganites. Further, magnetic studies have established that Ce3Mn8 exhibits both the combination of pairwise MnIII2 ferromagnetic and antiferromagnetic exchange interactions, and the resultant spin vector alignments that are found within the 3-D C-type antiferromagnetic perovskites. First-principles theoretical calculations reveal not only the expected nearest-neighbor MnIII2 exchange couplings via superexchange pathways through bridging ligands but also an unusual, direct MnIII–CeIV–MnIII metal-to-metal channel involving the CeIVf orbitals.Perovskite manganites exhibit intriguing but poorly understood properties, including multiferroicity. Here, the authors synthesize a Ce3Mn8 cluster that structurally resembles a perovskite repeat unit, and use this molecular analogue to elucidate mechanisms driving bulk perovskite properties.