Abnormal behavior of crystalline methane in temperature interval   $60-70~K$. From experiment to theory
  The paper presents an analysis of mechanical, structural, thermophysical and spectral properties of solid methane in temperature interval $0.5T_{tr} -T_{tr}$ ($T_{tr}$ is the triple point temperature) under equilibrium vapor pressure. It is shown that the anomalies of the studied properties at temperatures 60--70~K have been observed in the body of the reviewed papers. A concept of "topons" (collective excitations of rotational degrees of freedom in solid methane) is proposed. A whole of the observed anomalies can be explained in the frames of this concept.   Key words: solid methane, quantum crystals, rotational degrees of freedom, thermophysical and mechanical properties of the crystals 
A.V.Leont'eva, A.Yu.Prokhorov, A.Yu.Zakharov, A.I.Erenburg
cond-mat.mtrl-sci cond-mat.quant-gas cond-mat.stat-mech