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- ItemPressure-driven magnetic moment collapse in the ground state of MnO(Milton Park : Taylor & Francis, 2007) Kasinathan, Deepa; Koepernik, K.; Pickett, W.E.The zero temperature Mott transition region in antiferromagnetic, spin S = 5/2 MnO is probed using the correlated band theory LSDA + U method. The first transition encountered is an insulator-insulator volume collapse within the rocksalt structure that is characterized by an unexpected Hund's rule violating 'spin-flip' moment collapse. This spin-flip to S = 1/2 takes fullest advantage of the anisotropy of the Coulomb repulsion, allowing gain in the kinetic energy (which increases with decreasing volume) while retaining a sizable amount of the magnetic exchange energy. While transition pressures vary with the interaction strength, the spin-flip state is robust over a range of interaction strengths and for both B1 and B8 structures.
- ItemPrediction of first-order martensitic transitions in strained epitaxial films(Milton Park : Taylor & Francis, 2015) Schönecke, S.; Richter, M.; Koepernik, K.; Eschrig, H.Coherent epitaxial growth allows us to produce strained crystalline films with structures that are unstable in the bulk. Thereby, the overlayer lattice parameters in the interface plane, (a, b), determine theminimum-energy out-of-plane lattice parameter, cmin (a, b).We showbymeans of density-functional total energy calculations that this dependence can be discontinuous and predict related firstorder phase transitions in strained tetragonal films of the elements V, Nb, Ru, La, Os, and Ir. The abrupt change of cmin can be exploited to switch properties specific to the overlayer material. This is demonstrated for the example of the superconducting critical temperature of a vanadium film which we predict to jump by 20% at a discontinuity of cmin.