We have conducted temperature dependent Angle Resolved Photoemission
Spectroscopy (ARPES) study of the electronic structures of PbTe, PbSe and PbS.
Our ARPES data provide direct evidence for the \emph{light} hole upper valence
bands (UVBs) and hitherto undetected \emph{heavy} hole lower valence bands
(LVBs) in these materials. An unusual temperature dependent relative movement
between these bands leads to a monotonic decrease in the energy separation
between their maxima with increasing temperature, which is referred as band
convergence and has long been believed to be the driving factor behind
extraordinary thermoelectric performances of these compounds at elevated
temperatures.Comment: 6 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1404.180