Possibility of a Lifshitz phase transition in Cd observed by a singularity in the muon Knight shift

Abstract

During the past much effort has been devoted to a systematic study of the muon Knight shiftK _μ in metallic environments and its implications on the local electronic structure of hydrogen in metals [1]. These measurements in simple metals were essentially all carried out in polycrystalline samples at room temperature. The present measurements in Cd in polycrystalline and single crystal samples cover a temperature range between 20 K and the melting point of this strongly anisotropic metal (hcp crystal structure,c/a ratio 1.89 — idealc/a ratio 1.63). These measurements add qualitatively new and interesting aspects and insights on the screening of a light hydrogen isotope in a metal as well as on certain properties of the host material itself. The outstanding features of the muon Knight shift in Cd are: (i) a strong intrinsic temperature dependence with an increase ofK _μ of more than 100% between 20 K and the melting point (T=593 K), (ii) an anomaly at 110 K in the form of a singularity in the isotropic part ofK _μ which is interpreted as a band structure effect, (iii) an anisotropic Knight shift contribution fitting the expressionK(T,θ)=K _iso(T)+K _ax(T) * (3 · cos² θ−1)/2, where both, the isotropic and the axial contribution ofK _μ, are strongly temperature dependent.