μ+knight shifts and trapping in diluteSbSn alloys

Abstract

Giant μ⁺ Knight shifts K_μ have been studied previously in Sb andSbBi alloys. Here we report μ⁺SR measurements on Sb with dilute heterovalent Sn impurities. A dramatic concentration dependence is observed: K_μ is increased slightly (relative to the value in pure Sb) by Sn concentrations of <0.1%, whereas larger concentrations cause a drastic reduction of K_μ. One concern could be that K_μ values in the alloy might reflect local band structure in trap sites near Sn impurities rather than the bulk “host” band structure of the alloy. This is indeed the case in bothSbSn (0.03%) andSbSn (0.06%), where a second, lower frequency TF-μSR signal begins to appear for T>60K. The amplitude of the low K_μ signal grows with increasing T at the expense of the amplitude of the high-K_μ, low-T signal, suggesting that the μ⁺ migrates through the host lattice to trap sites. A simple trapping model correctly describes the observed T-dependence of the amplitudes, phases and relaxation rates of the two signals. We conclude that the low-T Knight shift is truly characteristic of the host band structure while the much lower K_μ value of the high-T site is characteristic of a specific trap site, presumably adjacent to a Sn impurity.