A. Taraphder

Double exchange and orbital correlations in electron-doped manganites

A double-exchange model for degenerate eg orbitals with intra- and inter-orbital interactions has been studied for the electron-doped manganites A 1 − x B x MnO3 (x > 0.5). We show that such a model reproduces the observed phase diagram and orbital ordering in the intermediate-bandwidth regime and the Jahn-Teller effect, considered to be crucial for the region x < 0.5, does not play a major role in this region. Brink and Khomskii have already pointed this out and stressed the relevance of the anistropic hopping across the degenerate eg orbitals in the infinite Hunds coupling limit. From a more realistic calculation with finite Hunds coupling, we show that inclusion of interactions stabilizes the C-phase, the antiferromagnetic metallic A-phase moves closer to x = 0.5 while the ferromagnetic phase shrinks. This is in agreement with the recent observations of Kajimoto et al.and Akimoto et al.

First-Principles Correlated Approach to the Normal State of Strontium Ruthenate

The interplay between multiple bands, sizable multi-band electronic correlations and strong spin-orbit coupling may conspire in selecting a rather unusual unconventional pairing symmetry in layered Sr2RuO4. This mandates a detailed revisit of the normal state and, in particular, the T-dependent incoherence-coherence crossover. Using a modern first-principles correlated view, we study this issue in the actual structure of Sr2RuO4 and present a unified and quantitative description of a range of unusual physical responses in the normal state. Armed with these, we propose that a new and important element, that of dominant multi-orbital charge fluctuations in a Hund’s metal, may be a primary pair glue for unconventional superconductivity. Thereby we establish a connection between the normal state responses and superconductivity in this system.

Orbital Ordering in Fe

Long range orbital order has been investigated in Fe

_{1-x}

_{1-x}

Mn

Mn

_x

_x

V

V

_2

_2

O

O

_4

_4