Spectroscopy of atomic and molecular defects in solid 4He using optical, microwave, radio frequency, magnetic and electric fields (Review Article)
P. Moroshkin, A. Hofer, S. Ulzega, and A. Weis
Physics Department, Université de Fribourg, Chemin du Musée 3, 1700 Fribourg, Switzerland
Received July 7, 2006, revised July 28, 2006
A little more than a decade ago our team extended the field of defect spectroscopy in cryocrystals to solid 4He matrices, in both their body-centered cubic (bcc) and hexagonally close-packed (hcp) configurations. In this review paper we survey our pioneering activities in the field and compare our results to those obtained in the related fields of doped superfluid helium and doped helium nanodroplets, domains developed in parallel to our own efforts. We present experimental
details of the sample preparation and the different spectroscopic techniques. Experimental results of purely optical spectroscopic studies in atoms, exciplexes, and dimers and their interpretation in terms of the so-called bubble model will be discussed. A large part of the paper is devoted to optically detected magnetic resonance, ODMR, processes in alkali atoms. The quantum nature of the helium matrix and the highly isotropic shape of the local trapping sites in the bcc phase
make solid helium crystals ideal matrices for high resolution spin physics experiments. We have investigated the matrix effects on both Zeeman and hyperfine magnetic resonance transitions and used ODMR to measure the forbidden electric tensor polarizability in the ground state of cesium. Several unexpected changes of the optical and spin properties during the bcc—hcp phase transition can be explained in terms of small bubble deformations.PACS: 32.30.-r - Atomic spectra 32.60.+i - Zeeman and Stark effects 33.35.+r - Electron resonance and relaxation (see also 76.30.-v Electron paramagnetic resonance and relaxation in condensed matter) 33.50.-j - Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion) (for energy transfer, see also section 34) 67.80.-s - Solid helium and related quantum crystals 76.70.Hb - Optically detected magnetic resonance (ODMR)
Key words: cryocrystals, quantum solids, matrix isolation spectroscopy, solid He, exiplexes, atomic bubbles, dimers, optical detected magnetic resonance, Stark effect.