Orbital selectivity causing anisotropy and particle-hole asymmetry in the charge density wave gap of 2H−TaS2

Abstract

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.

Atomic-scale strain manipulation of a charge density wave

“…Our QPI measurements however have been unable to detect any scattering vectors larger than | Q Bragg |/2 in either CDW-2a 0 or CDW-4a 0 regions at any energy ( SI Appendix , section V ), and we therefore cannot directly observe the shift of Q 2 to higher momenta. A possible explanation for the lack of signal at higher momenta may be canting of the orbital texture toward more in-plane orientations ( 34 ), making them less likely to be detected by the STM tip. Nevertheless, our measurements reveal that a larger distortion to the Fermi surface accompanies the formation of a CDW-2a 0 .…”

Coexistence of Superconductivity and Charge Density Waves in Tantalum Disulfide: Experiment and Theory

“…[12] can be seen. This discrepancy might result from the presence of a pseudogap as reported by ARPES measurements at ambient pressure above T CDW and which may survive up to higher temperatures [41]. As displayed in Figs.…”

Pressure-Induced Collapse of the Charge Density Wave and Higgs Mode Visibility in 2H−TaS2

“…Notable differences are obtained with previous results from transport measurement [40] where signature of the ICDW were reported up to at least 17 GPa. This discrepancy might result from the presence of a pseudogap as reported by ARPES measurements [47] at ambient pressure above T CDW and which may survive above P c while being detected by transport measurements. Alternatively, application of high pressure could induce a loss of a long-range CDW order and a softening of the amplitudon energy [49,50], while a short-range CDW order may leave a broad signature detected by transport measurements.…”

“…The present data suggest this mechanism is also at play in 2H-TaS 2 . This would then imply that in this compound, even if the Fermi surface is significantly gapped by the CDW [47], the superconducting and CDW gaps must overlap on some parts of the Fermi surface.…”