5 research outputs found
Spectroscopic evidence for temperature-dependent convergence of light and heavy hole valence bands of PbQ (Q=Te, Se, S)
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
Orbital selectivity causing anisotropy and particle-hole asymmetry in the charge density wave gap of -TaS
We report an in-depth Angle Resolved Photoemission Spectroscopy (ARPES) study
on -TaS, a canonical incommensurate Charge Density Wave (CDW) system.
This study demonstrates that just as in related incommensurate CDW systems,
-TaSe and -NbSe, the energy gap () of
-TaS is localized along the K-centered Fermi surface barrels and is
particle-hole asymmetric. The persistence of even at
temperatures higher than the CDW transition temperature
in -TaS, reflects the similar pseudogap (PG) behavior observed
previously in -TaSe and -NbSe. However, in sharp contrast to
-NbSe, where is non-zero only in the vicinity
of a few "hot spots" on the inner K-centered Fermi surface barrels,
in -TaS is non-zero along the entirety of both
K-centered Fermi surface barrels. Based on a tight-binding model, we attribute
this dichotomy in the momentum dependence and the Fermi surface specificity of
between otherwise similar CDW compounds to the
different orbital orientations of their electronic states that are involved in
CDW pairing. Our results suggest that the orbital selectivity plays a critical
role in the description of incommensurate CDW materials.Comment: 6 pages, 4 figure