Selected multiferroic perovskite oxides containing rare earth and transition metal elements

Multiferroic materials are currently the subject of intensive research worldwide, because of both their fundamental scientific problems and also possible technological applications. Among a number of candidates in the laboratories, compounds consisting of rare earth and transition metal perovskite oxides have very unusual structural and physical properties. In contrast to the so-called type I multiferroics, ferroelectricity may be induced by magnetic ordering or by applying external fields. In this review, the recent progress on the experimental and theoretical studies of some selected type II multiferroics is presented, with a focus on the perovskite oxides containing rare earth and transition metal elements. The rare earth orthoferrite crystals, rare earth titanate strained film, and rare earthbased superlattices are systematically reviewed to provide a broad overview on their promising electric, magnetic, and structural properties. The recent experimental advances in single-crystal growth by optical floating zone method are also presented. First-principles investigations, either supported by experimental results or awaiting for experimental verifications, are shown to offer useful guidance for the future applications of unconventional multiferroics.

Combined subsampling and analytical integration for efficient large-scale GW calculations for 2D systems

Accurate and efficient predictions of the quasiparticle properties of complex materials remain a major challenge due to the convergence issue and the unfavorable scaling of the computational cost with respect to the system size.Quasiparticle GW calculations for two-dimensional(2D)materials are especially difficult.The unusual analytical behaviors of the dielectric screening and the electron self-energy of 2D materials make the conventional Brillouin zone(BZ)integration approach rather inefficient and require an extremely dense k-grid to properly converge the calculated quasiparticle energies.In this work,we present a combined nonuniform subsampling and analytical integration method that can drastically improve the efficiency of the BZ integration in 2D GW calculations.

Prediction of protected band edge states and dielectric tunable quasiparticle and excitonic properties of monolayer MoSi_(2)N_(4)

The electronic structure of two-dimensional(2D)materials are inherently prone to environmental perturbations,which may pose significant challenges to their applications in electronic or optoelectronic devices.A 2D material couples with its environment through two mechanisms:local chemical coupling and nonlocal dielectric screening effects.The local chemical coupling is often difficult to predict or control experimentally.Nonlocal dielectric screening,on the other hand,can be tuned by choosing the substrates or layer thickness in a controllable manner.Therefore,a compelling 2D electronic material should offer band edge states that are robust against local chemical coupling effects.Here it is demonstrated that the recently synthesized MoSi_(2)N_(4)is an ideal 2D semiconductor with robust band edge states protected from capricious environmental chemical coupling effects.Detailed many-body perturbation theory calculations are carried out to illustrate how the band edge states of MoSi_(2)N_(4)are shielded from the direct chemical coupling effects,but its quasiparticle and excitonic properties can be modulated through the nonlocal dielectric screening effects.This unique property,together with the moderate band gap and the thermodynamic and mechanical stability of this material,paves the way for a range of applications of MoSi_(2)N_(4)in areas including energy,2D electronics,and optoelectronics.