Anisotropic positronium in crystalline quartz

Citation
T. Gessmann et al., Anisotropic positronium in crystalline quartz, PHIL MAG B, 81(8), 2001, pp. 771-791
Citations number
48
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science
Journal title
PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICSELECTRONIC OPTICAL AND MAGNETIC PROPERTIES
ISSN journal
13642812 → ACNP
Volume
81
Issue
8
Year of publication
2001
Pages
771 - 791
Database
ISI
SICI code
1364-2812(200108)81:8<771:APICQ>2.0.ZU;2-D
Abstract
Positronium (Ps = (e(+) e(-))) in synthetic crystalline quartz is investiga ted by means of the positron spin relaxation (e(+)SR) technique. The set-up employed measures the change in the Doppler broadening of the 511 keV anni hilation photon line caused by the reversal of large magnetic fields applie d along the spin polarization axis of positrons (e(+)) emitted from a Ge-68 /Ga-68 source. In contrast with other methods. the technique allows the det ection of Ps in condensed matter even if the Ps-forming e(+) fraction r is quite small. Moreover, because in single crystals the magnetic field define s a preferred crystallographic direction, thee-SR technique permits the stu dy of the anisotropy of the hyperfine interaction of Ps in matter. The theo ry necessary to deduce the Ps hyperfine tensor from the e(+) SR measurement s is developed. Room-temperature measurements show that in synthetic quartz crystals (i) the Ps-forming e(+) fraction is r = 0.15, (ii) the electron d ensity at the e(+) in Ps is about 0.3 of the vacuum value and, (iii) the Ps hyperfine interaction is strongly anisotropic. The relationship of the las t-mentioned result to the much smaller anisotropy of the muonium hyperfine interaction is discussed.