Spectroscopic signatures and origin of hidden order in BaMgReO.

Clarifying the underlying mechanisms that govern ordering transitions in condensed matter systems is crucial for comprehending emergent properties and phenomena. While transitions are often classified as electronically driven or lattice-driven, we present a departure from this conventional picture in the case of the double perovskite BaMgReO. Leveraging resonant and non-resonant elastic x-ray scattering techniques, we unveil the simultaneous ordering of structural distortions and charge quadrupoles at a critical temperature of T ~ 33 K.

Charge self-consistent electronic structure calculations with dynamical mean-field theory usingQuantum ESPRESSO, Wannier 90andTRIQS.

We present a fully charge self-consistent implementation of dynamical mean field theory (DMFT) combined with density functional theory (DFT) for electronic structure calculations of materials with strong electronic correlations. The implementation uses theQuantum ESPRESSOpackage for the DFT calculations, theWannier90code for the up-/down-folding and theTRIQSsoftware package for setting up and solving the DMFT equations. All components are available under open source licenses, are MPI-parallelized, fully integrated in the respective packages, and use an hdf5 archive interface to eliminate file parsing.

Prediction of a Giant Magnetoelectric Cross-Caloric Effect around a Tetracritical Point in Multiferroic SrMnO_{3}.

We study the magnetoelectric and electrocaloric response of strain-engineered, multiferroic SrMnO_{3}, using a phenomenological Landau theory with all parameters obtained from first-principles-based calculations. This allows us to make realistic semiquantitative and materials-specific predictions about the magnitude of the corresponding effects. We find that in the vicinity of a tetracritical point, where magnetic and ferroelectric phase boundaries intersect, an electric field has a huge effect on the antiferromagnetic order, corresponding to a magnetoelectric response several orders of magnitude larger than in conventional linear magnetoelectrics.

Origins of the Inverse Electrocaloric Effect.

The occurrence of the inverse (or negative) electrocaloric effect, where the isothermal application of an electric field leads to an increase in entropy and the removal of the field decreases the entropy of the system under consideration, is discussed and analyzed. Inverse electrocaloric effects have been reported to occur in several cases, for example, at transitions between ferroelectric phases with different polarization directions, in materials with certain polar defect configurations, and in antiferroelectrics. This counterintuitive relationship between entropy and applied field is intriguing and thus of general scientific interest.

First principles studies of multiferroic materials.

Multiferroics, materials where spontaneous long-range magnetic and dipolar orders coexist, represent an attractive class of compounds, which combine rich and fascinating fundamental physics with a technologically appealing potential for applications in the general area of spintronics. Ab initio calculations have significantly contributed to recent progress in this area, by elucidating different mechanisms for multiferroicity and providing essential information on various compounds where these effects are manifestly at play. In particular, here we present examples of density-functional theory investigations for two main classes of materials: (a) multiferroics where ferroelectricity is driven by hybridization or purely structural effects, with BiFeO(3) as the prototype material, and (b) multiferroics where ferroelectricity is driven by correlation effects and is strongly linked to electronic degrees of freedom such as spin-, charge-, or orbital-ordering, with rare-earth manganites as prototypes.

Effect of epitaxial strain on the spontaneous polarization of thin film ferroelectrics.

Epitaxial strain can substantially enhance the spontaneous polarizations and Curie temperatures of ferroelectric thin films compared to the corresponding bulk materials. In this Letter we use first principles calculations to calculate the effect of epitaxial strain on the spontaneous polarization of the ferroelectrics , , and , and the multiferroic material . We show that the epitaxial strain dependence of the polarization varies considerably for the different systems, and in some cases is, in fact, very small.