# Publications

### Oriol T. Valls

**Stability of the pi junction configuration in ferromagnet-superconductor heterostructures**K. halterman and O.T. Valls,

*Phys. Rev B70, 104516 (2004)*
Download from http://xxx.lanl.gov/abs/cond-mat/0404058

**Abstract**

We investigate the stability of possible order parameter configurations in clean layered heterostructures of the $SFS...FS$ type,
where $S$ is a superconductor and $F$ a ferromagnet. We find that for most reasonable values of the geometric parameters
(layer thicknesses and number) and of the material parameters (such as magnetic polarization, wavevector mismatch, and
oxide barrier strength) several solutions of the {\it self consistent} microscopic equations can coexist, which differ in the
arrangement of the sequence of ``0'' and ``$\pi$'' junction types (that is, with either same or opposite sign of the pair potential in
adjacent $S$ layers). The number of such coexisting self consistent solutions increases with the number of layers. Studying the
relative stability of these configurations requires an accurate computation of the small difference in the condensation free
energies of these inhomogeneous systems. We perform these calculations, starting with numerical self consistent solutions of the
Bogoliubov-de Gennes equations. We present extensive results for the condensation free energies of the different possible
configurations, obtained by using efficient and accurate numerical methods, and discuss their relative stabilities. Results for the
experimentally measurable density of states are also given for different configurations and clear differences in the spectra are
revealed. Comprehensive and systematic results as a function of the relevant parameters for systems consisting of three and
seven layers (one or three junctions) are given, and the generalization to larger number of layers is discussed.