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Muonium spectroscopy in ZnSe: metastability and conversion
Authors: R.C. Vilão, H.V. Alberto, J. Piroto Duarte, J.M. Gil, A. Weidinger, N. Ayres de Campos, R.L. Lichti, K.H. Chow, S.F.J. Cox
Ref.: Phys. Rev. B 72, 235203 (2005)
Abstract: High-precision spectroscopic information is obtained on the muonium states in ZnSe by high-field transverse mu SR measurements. At low temperatures, two muonium states Mu(I) and Mu(II) are observed with isotropic hyperfine parameters of A(I)=3283.63 +/- 0.51 MHz and A(II)=3454.26 +/- 0.02 MHz (74% and 77% of the vacuum value, respectively). State I is thermally unstable and converts to state II at approximately 40 K. State II is stable up to 300 K, at least. We assign Mu(II) to the cation interstitial tetrahedral site and discuss the possibility that Mu(I) may correspond either to muonium at the same site but in the unrelaxed lattice or to the anion interstitial tetrahedral site. The temperature dependence of the hyperfine interaction was fitted with a local vibrational model giving an oscillator energy of approximately 8 meV. The amplitudes and the depolarization rates are measured over the entire temperature range and are discussed in the text.
