NaxCoO2in thex→0regime: Coupling of structure and correlat

Abstract

The study of the strength of correlations in NaxCoO2 is extended to the x = 0 end of the phase diagram where Mott insulating behavior has been widely anticipated. Inclusion of correlation as modeled by the LDA+U approach leads to a Mott transition in the ag subband if U≥Uc=2.5 eV. Thus U smaller than Uc is required to model the metallic, nonmagnetic CoO2 compound reported by Tarascon and coworkers. The orbital-selective Mott transition of the ag state, which is essentially degenerate with the e ′ g states, occurs because of the slightly wider bandwidth of the ag bands. The metal-insulator transition is found to be strongly coupled to the Co-O bond length, due to associated changes in the t2g bandwidth, but the largest effects occur only at a reduced oxygen height that lies below the equilibrium position.

Discovery of Li2(Pd,Pt)3B superconductors

“…Although electronic structure calculations [9][10][11] based on a new interpretation of the crystal structure led to similar conclusions as those resulted from the experimental works [7,8], there are several unclear aspects in the complex electronic structure of these materials which point toward significant differences between Pd-and Pt-end compounds. It also suggests possibility of special or unconventional effects which, for example, might determine T c of the Pt-end compound considered unusually low.…”

“…From this and other points of view, Pt-and Pd-end compounds are very different from MgNi 3 C [11]. It was anticipated that Li 2 (Pd 1-x ,Pt x ) 3 B might be an ideal candidate to study the influence of this type of broken symmetry on superconductivity.…”

“…The structure lacks mirror-like symmetry [10,11] as for CePt 3 Si [12] or UIr [13]. From this and other points of view, Pt-and Pd-end compounds are very different from MgNi 3 C [11].…”

Non-Centrosymmetric Superconductors with Topological Transition of Fermi Surfaces

“…Although our single-band model does not reproduce the multiband structure of Li 2 Pt 3 B, our finding indicates the important roles of TTFS. Indeed, the band structure calculation shows a lot of topological transitions in Li 2 Pt 3 B owing to the large ASOC, but not in Li 2 Pd 3 B because of the small ASOC [12,13]. In order to elucidate the effect of the intriguing topology of the Fermi surface on the superconducting phase in Li 2 Pt 3 B, it is desired to study the multiorbital model, which precisely describes the electronic structure of Li 2 (Pd 1−x Pt x ) 3 B.…”

“…For the difference between Li 2 Pt 3 B and Li 2 Pd 3 B, a substantial enhancement of ASOC has been pointed out for Li 2 Pt 3 B [12]. The increase in atomic LS-coupling on Pt ions as well as the deformation of crystal structure [5] significantly increases the ASOC of Li 2 Pt 3 B.…”