Determining the Electron-Phonon Coupling Strength in Correlated Electron Systems from Resonant Inelastic X-ray Scattering

We show that high resolution Resonant Inelastic X-ray Scattering (RIXS) provides direct, element-specific and momentum-resolved information on the electron-phonon (e-p) coupling strength. Our theoretical analysis demonstrates that the e-p coupling can be extracted from RIXS spectra by determining the differential phonon scattering cross section. An alternative, very direct manner to extract the coupling is to use the one and two-phonon loss ratio, which is governed by the e-p coupling strength and the core-hole life-time. This allows measurement of the e-p coupling on an absolute energy scale.Comment: 4 pages, 3 figure

Coloumb interaction and instability of CE-structure in half doped manganites

In their Letter (Phys. Rev. Lett. 83, 5118 (1999)), den Brink, Khaliullin, and Khomskii proposed theoretically that the one-dimensional ferromagnetic zigzag chains in CE phase in half-doped manganites play an essential role in forming the orbital ordering, and, more surprisingly, the on-site Coulomb interaction U between electrons with different orbitals leads to experimentally observed charge ordering. In this Comment, I point out that the strong U will destroy the stability of CE-type phase, which is stable in a very narrow regime in the parameter space for electronic model.To solve this issue finally, we have to take into account other interactions, such as the long-range Coulomb interaction, Jahn-Teller distortion, and physics of topological berry phase. For example, the effect of finite large J$_{H}$ leads to an attractive particle-hole interaction, which favors to stabilize the charge ordering.Comment: 1 page, 1 figure, To appear in Phys. Rev. Let

Orbital effects in manganites

In this paper I give a short review of some properties of the colossal magnetoresistance manganites, connected with the orbital degrees of freedom. Ions Mn{3+}, present in most of these compounds, have double orbital degeneracy and are strong Jahn-Teller ions, causing structural distortions and orbital ordering. Mechanisms leading to such ordering are shortly discussed, and the role of orbital degrees of freedom in different parts of the phase diagram of manganites is described. Special attention is paid to the properties of low-doped systems (doping 0.1 - 0.25), to overdoped systems (x > 0.5), and to the possibility of a novel type of orbital ordering in optimally doped ferromagnetic metallic manganites.Comment: 28 pages, 7 figures, to be published in J. Mod. Phys.

TaIrTe4 a ternary Type-II Weyl semi-metal

In metallic condensed matter systems two different types of Weyl fermions can in principle emerge, with either a vanishing (type-I) or with a finite (type-II) density of states at the Weyl node energy. So far only WTe2 and MoTe2 were predicted to be type-II Weyl semi-metals. Here we identify TaIrTe4 as a third member of this family of topological semi-metals. TaIrTe4 has the attractive feature that it hosts only four well-separated Weyl points, the minimum imposed by symmetry. Moreover, the resulting topological surface states - Fermi arcs connecting Weyl nodes of opposite chirality - extend to about 1/3 of the surface Brillouin zone. This large momentum-space separation is very favorable for detecting the Fermi arcs spectroscopically and in transport experiments

Coupled multiple-mode theory for s±s_{\pm} pairing mechanism in iron based superconductors

We investigate the interplay between the magnetic and the superconducting degrees of freedom in unconventional multi-band superconductors such as iron pnictides. For this purpose a dynamical mode-mode coupling theory is developed based on the coupled Bethe-Salpeter equations. In order to investigate the region of the phase diagram not too far from the tetracritical point where the magnetic spin density wave, (SDW) and superconducting (SC) transition temperatures coincide, we also construct a Ginzburg - Landau functional including both SC and SDW fluctuations in a critical region above the transition temperatures. The fluctuation corrections tend to suppress the magnetic transition, but in the superconducting channel the intraband and interband contribution of the fluctuations nearly compensate each other.Comment: 17 pages, 5 figure

Curvature induced magnonic crystal in nanowires

A new type of magnonic crystals, curvature induced ones, is realized in ferromagnetic nanowires with periodically deformed shape. A magnon band structure of such crystal is fully determined by its curvature: the developed theory is well confirmed by simulations. An application to nanoscale spintronic devises with the geometrically tunable parameters is proposed, namely, to filter elements.Comment: 21 pages, 6 figures, for submission to SciPos

Reentrant metallic transition at a temperature above Tc at the breakdown of cooperative Jahn-Teller orbital order in perovskite manganites

We report an interesting reentrant metallic resistivity pattern beyond a characteristic temperature T* which is higher than other such characteristic transition temperatures like T(c)(Curie point), T(N) (Neel point), T(CO) (charge order onset point) or T(OO) (orbital order onset point) in a range of rare-erath perovskite manganites (RE(1-x)A(x)MnO(3); RE = La, Nd, Y; A = Sr, Ca; x = 0.0-0.5). Such a behavior is normally observed in doped manganites with doping level (x) higher than the critical doping level x(c) (= 0.17-0.22) required for the metallic ground state to emerge and hence in a system where cooperative Jahn-Teller orbital order has already undergone a breakdown. However, the observation made in the La(1-x)Ca(x)MnO(3) (x = 0.0-0.5) series turns out to be an exception to this general trend.Comment: 15 pages including 3 figures; pdf onl