The Positronium state in quartz

The positronium state in quartz is described by a linear superposition of two states: the first describing the free positron in the crystal and the second corresponding to a positronium Bloch wavefunction in the lattice. The condition for positronium formation in the electron gas is deduced by using variational calculations of the positron binding energy to the electron system. The self annihilation parameter $\kappa$ introduced in positron lifetime experiments can be properly justified by using the mixed state. A variational method to calculate $\kappa$ is proposed.Comment: 3 pages, 1 figure, to appear in Physica Status Solidi (c), presented at the 15th International Conference of Positron Annihilation ICPA-1

Two-Nucleon L·S Potential in Pseudoscalar Meson Theory

Nonstatic corrections to the two-nucleon potential of Brueckner and Watson and of Gartenhaus are computed within the framework of the γ5 theory. These terms appear as spin-orbit corrections of order μ/M to the static potentials. The S matrix is calculated in second and fourth order for a reduced form of the relativistic theory. The potential is then chosen so as to duplicate this S matrix to the required order in the coupling constant and μ/M. We consider to what extent our reduction of the γ5 theory changes its character. The resulting potentials are given in analytic form for no cutoff in momentum space and in numerical form for the Gaussian cutoff employed by Gartenhaus. We give also some additional static corrections to previous potentials. A qualitative comparison is made with the experimental observations in nucleon-nucleon scattering, the fine structure in the splitting of the He5 nucleus, and the contribution of the nonstatic potential to the magnetic moment of the deuteron

Opposing shear senses in a subdetachment mylonite zone: Implications for core complex mechanics

[1] Global studies of metamorphic core complexes and low‐angle detachment faults have highlighted a fundamental problem: Since detachments excise crustal section, the relationship between the mylonitic rocks in their footwalls and the brittle deformation in their hanging walls is commonly unclear. Mylonites could either reflect ductile deformation related to exhumation along the detachment fault, or they could be a more general feature of the extending middle crust that has been “captured ” by the detachment. In the first case we would expect the kinematics of the mylonite zone to mirror the sense of movement on the detachment; in the second case both the direction and sense of shear in the mylonites could be different. The northern Snake Range décollement (NSRD) is a classic Basin and Range detachment fault with a well‐documented top‐east of displacement. We present structural, paleo-magnetic, geochronological, and geothermometric evidence to suggest that the mylonite zone below the NSRD locally experienced phases of both east ‐ and west‐directed shear, inconsistent with movement along a single detachment fault. We therefore propose that the footwall mylonites represent a predetachment dis-continuity in the middle crust that separated localized deformation above from distributed crustal flow below (localized‐distributed transition (LDT)). The mylonites were subsequently captured by a moderately dipping brittle detachment that soled down to the middle crust and exhumed them around a rolling hinge into a subhorizontal orientation at the surface, produc-ing the present‐day NSRD. In this interpretation the brittle hanging wall represents a series of rotated upper crustal normal faults, whereas the mylonitic footwall represents one or more exhumed middl

Physisorption of positronium on quartz surfaces

The possibility of having positronium (Ps) physisorbed at a material surface is of great fundamental interest, since it can lead to new insight regarding quantum sticking and is a necessary first step to try to obtain a Ps$_2$ molecule on a material host. Some experiments in the past have produced evidence for physisorbed Ps on a quartz surface, but firm theoretical support for such a conclusion was lacking. We present a first-principles density-functional calculation of the key parameters determining the interaction potential between Ps and an $\alpha$-quartz surface. We show that there is indeed a bound state with an energy of 0.14 eV, a value which agrees very well with the experimental estimate of $\sim0.15$ eV. Further, a brief energy analysis invoking the Langmuir-Hinshelwood mechanism for the reaction of physisorbed atoms shows that the formation and desorption of a Ps$_2$ molecule in that picture is consistent with the above results.Comment: 5 pages, 3 figures, submitte

Surface Josephson plasma waves in layered superconductors

We predict the existence of surface waves in layered superconductors in the THz frequency range, below the Josephson plasma frequency $\omega_J$. This wave propagates along the vacuum-superconductor interface and dampens in both transverse directions out of the surface (i.e., towards the superconductor and towards the vacuum). This is the first prediction of propagating surface waves in any superconductor. These predicted surface Josephson plasma waves are important for different phenomena, including the complete suppression of the specular reflection from a sample (Wood's anomalies) and a huge enhancement of the wave absorption (which can be used as a THz detector).Comment: 4 pages, 2 figure

Deuteron Momentum Distribution in KD2HPO4

The momentum distribution in KD2PO4(DKDP) has been measured using neutron Compton scattering above and below the weakly first order paraelectric-ferroelectric phase transition(T=229K). There is very litte difference between the two distributions, and no sign of the coherence over two locations for the proton observed in the paraelectric phase, as in KH2PO4(KDP). We conclude that the tunnel splitting must be much less than 20mev. The width of the distribution indicates that the effective potential for DKDP is significantly softer than that for KDP. As electronic structure calculations indicate that the stiffness of the potential increases with the size of the coherent region locally undergoing soft mode fluctuations, we conclude that there is a mass dependent quantum coherence length in both systems.Comment: 6 pages 5 figure