Spin and orbital magnetic state ofUGe2under pressure

The correlated band theory picture $(\mathrm{LSDA}+\mathrm{U})$ has been applied to $\mathrm{U}{\mathrm{Ge}}_2$, in which superconductivity has been found to coexist with robust ferromagnetism. Over a range of volumes (i.e., pressures), two nearly degenerate states, which differ most strikingly in their orbital character (on uranium), are obtained. The calculated moment (and its separation into spin and orbital parts) is consistent with one set of recent polarized neutron scattering data. These two states are strong candidates for the two ferromagnetic phases, one low-temperature–low-pressure, the other higher-temperature–higher pressure. Orbital (and spin) waves built from fluctuations between these uranium configurations provide a possible different mechanism of pairing in $\mathrm{U}{\mathrm{Ge}}_2$.