Electron pairing instabilities and magnetic properties in nanoclusters and nanomaterials

A.N. Kocharian, G.W. Fernando, K. Fung, K. Palandage
California State University Los Angeles, US

Keywords: magnetism, superconductivity, phase transitions


Studies of assembled clusters, nanoparticles and optical lattices in various topologies provide intriguing insights into several many body problems in condensed matter physics1. A new, emerging guiding principle for the search of new materials can be identified as spatial inhomogeneities and density phase separation instabilities in the proximity to quantum critical points (QCPs). Electron coherent and incoherent pairings and formation of various types of magnetic correlations in different bipartite and frustrated geometries are studied under variation of interaction strength, electron doping, inter-site coupling and temperature. The exact calculations of charge and spin phase separation, collective excitations and pseudogaps yield level crossing phase separation instabilities, Mott-Hubbard localization, Bose-Einstein condensation and possible superconductivity. Criteria for spin-charge separation, reconciliation and recombination driven by interaction strength, next nearest coupling and temperature are found. Resulting phase diagrams resemble a number of inhomogeneous, coherent and incoherent nanoscale phases in the ground state and finite temperatures seen recently in high Tc cuprates, manganites and CMR nanomaterials. The relationship of these results to superconductivity and ferromagnetism in larger size systems is discussed. [1] A. N. Kocharian, et al., Phys. Lett. A 376, 538 (2012); Phys. Rev. B78, 075431 (2008).