Our detailed Angle Resolved Photoemission Spectroscopy (ARPES) study of 2H-TaS2 , a canonical incommensurate charge density wave (CDW) material, illustrates pronounced many-body renormalization in the system, which is manifested by the presence of multiple kink structures in the electronic dispersions. Temperature-dependent measurements reveal that these kink structures persist even at temperatures higher than the charge density wave transition temperature T cdw and the energy locations of the kinks are practically temperature-independent. Correlating kink energies with the published Raman scattering data and the theoretically calculated phonon spectrum of 2H-TaS2 , we conclude phononic mechanism for these kinks. We have also detected momentum-anisotropy in the band renormalization, which in turn indicates momentum-dependence of the electron-phonon coupling of the system. arXiv:1805.03580v1 [cond-mat.str-el]

We report an in-depth Angle Resolved Photoemission Spectroscopy (ARPES) study on 2H-TaS2 , a canonical incommensurate Charge Density Wave (CDW) system. This study demonstrates that just as in related incommensurate CDW systems, 2H-TaSe2 and 2H-NbSe2 , the energy gap (∆ cdw ) of 2H-TaS2 is localized along the K-centered Fermi surface barrels and is particle-hole asymmetric. The persistence of ∆ cdw even at temperatures higher than the CDW transition temperature T cdw in 2H-TaS2 , reflects the similar pseudogap (PG) behavior observed previously in 2H-TaSe2 and 2H-NbSe2 . However, in sharp contrast to 2H-NbSe2 , where ∆ cdw is non-zero only in the vicinity of a few "hot spots" on the inner K-centered Fermi surface barrels, ∆ cdw in 2H-TaS2 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 ∆ cdw 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.

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 light hole upper valence bands (UVBs) and hitherto undetected 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.