THEORY OF PRESSURE EFFECTS AND THE CORRELATED-ELECTRON BEHAVIOR OF URANIUM MONOCHALCOGENIDES

Experimentally, hydrostatic pressure experiments provide a very sensitive way to probe the development of magnetic ordering in correlated-electron systems. The recent high pressure experiments of Link et al. on UTe provide extremely interesting results. With applied pressure, the Curie temperature T-C for UTe increases from 104 K to a maximum of 181 K at 7.5 GPa and then decreases to 156 K at 17.5 GPa. This experimental behavior is qualitatively what we expect on the basis of our theory of the correlated-electron behavior. Basically, increasing pressure causes increased hybridization which causes an increase in coupling between the moments associated with the relatively localized part of the f spectra density at each lattice site. However, as the pressure increases further, the loss of localized f spectra density caused by the increased merger with the non-f-band density causes a decrease in ordered moment and hence a decrease in T-C. We have performed calculations quantifying the above picture for UTe. First we calculate the pressure dependence of the lattice constant and obtain good agreement with the experiment. Next, at calculated lattice constants we calculated T-C using our correlated-electron theory for magnetic ordering. These results capture the initial increase in T-C resulting from increased hybridization as well as the reversal of this initial increase caused by the loss of localized f density.