Phase control in a spin-triplet SQUID.

It is now well established that a Josephson junction made from conventional spin-singlet superconductors containing ferromagnetic layers can carry spin-triplet supercurrent under certain conditions. The first experimental signature of that fact is the propagation of such supercurrent over long distances through strong ferromagnetic materials. Surprisingly, one of the most salient predictions of the theory has yet to be verified experimentally-namely, that a Josephson junction containing three magnetic layers with coplanar magnetizations should exhibit a ground-state phase shift of either zero or π depending on the relative orientations of those magnetizations. We demonstrate this property using Josephson junctions containing three different types of magnetic layers, chosen so that the magnetization of one layer can be switched by 180° without disturbing the other two. Phase-sensitive detection is accomplished using a superconducting quantum interference device, or SQUID. Such a phase-controllable junction could be used as the memory element in a fully superconducting computer.

Structure and Properties of a New Electride, Rb+(cryptand[2.2.2])e.

This is the sixth electride whose crystal structure has been determined and the fourth to show polymorphism. Crystals of the title electride prepared from mixed solvents have a structure similar to that of Li+(cryptand[2.1.1])e-. Electrons occupy cavities that are connected by "ladder-like" channels. The static and spin magnetic susceptibilities of polycrystalline samples that contain this polymorph (called phase α) show Heisenberg 1D antiferromagnetic behavior with -J/kB = 30 K. Similar to other electrides with "localized" electrons, this electride is a poor conductor (σ < 10- 4 ohm-1cm-1). Thin films prepared by high vacuum co-deposition of Rb metal and cryptand[2.2.2] have optical spectra and near-metallic electrical conductivity nearly identical with those of K+(cryptand[2.2.2])e-. These properties would not be expected if the film structure were the same as that obtained for crystals. Rather, they suggest that the films consist of microcrystals whose structure is similar to that of K+(cryptand[2.2.2])e-. Polycrystalline samples prepared by slow evaporation of methylamine from stoichiometric solutions at -78 °C (called phase ß) have properties similar to those of K+(cryptand[2.2.2])e-. The conductivity of samples that contain phase ß is more than an order of magnitude larger than those with phase α. Magnetic and spin susceptibilities show that phase ß samples have much larger electron-electron interactions. As with K+(cryptand[2.2.2])e-, the magnetic susceptibility of phase ß is compatible with alternating linear chain Heisenberg antiferromagnetism, with -J/kB ≈ 300 K and -J'/kB ≈ 240 K. Thin vapor co-deposited films show abrupt changes in the conductivity and optical spectrum at -12 °C that suggest a transition that may be conversion of phase ß to phase α.