Condensed Matter Seminars

Conventional BCS mechanism of HTSC in hydrides, a la' Ashcroft works remarkably well in H_3S, LaH_{10} etc. We pointed out (GB 2015) [1] that H-atom networks in hydrides is a Mott insulating subsystem, which supports RVB superconductivity via internal doping. We will present a case for occurrence of both BCS and RVB pairing to varying degrees, in different hydrides. It resolves several existing puzzles. In our theory, H-C-S and Lu-N-H systems have dominant RVB pairing, which favors competing orders create, encouraged by structural variations and disorder, wide variation in Tc (like in cuprates). On the other hand, H_3S and LaH_{10} is a dominant phonon mediated BCS system; consequently Tc is protected by Anderson theorem and varies less. We provide support for our electronic mechanism from the works of Ng et al. (1996) and Eder et al., (1997) on emergence of Kondo insulating states in LaH_3 and YH_3, via Kondo coupling of band electrons to localized H atom spins.