arXiv subjects

C. -L. Jia

Publications and source records attributed to C. -L. Jia.

14 recordsLinked to original sources

arXiv2021

Ewald summation for ferroelectric perovskites with charges and dipoles

Ewald summation is an important technique used to deal with long-range Coulomb interaction. While it is widely used in simulations of molecules and solid state materials, many important results are dispersed in literature and their implementations are often buried deep in large software packages. Since reliable and systematic calculation of Coulomb interaction is critical for the investigation of perovskites, here we start from the fundamentals of Ewald summation and derive clear expressions for long-range charge-charge, dipole-dipole, and charge-dipole interactions, which can be readily used for numerical computations. We also provide the interaction matrix for efficient Monte Carlo simulations involving charges and dipoles, implementing them in a Python software package. A new type of interaction matrix, which accounts for the electrostatic energy change when ions are displaced, is also derived and implemented. These results are the foundations for the investigation of ferroelectric perovskites.

cond-mat.mtrl-sci↗

arXiv2020

ATiO$_{3}$/TiO (A=Pb, Sn) superlattice: bridging ferroelectricity and conductivity

We propose to insert TiO layers to perovskite ATiO$_{3}$ to form a superlattice and use first-principles calculations to investigate its basic properties. Our computational analysis shows that the structure, which consists of repeated ATiO_{3} and TiO layers, has strong anisotropic conductivity. The structure immediately suggests a possible control of its conductivity by ion displacements related to its intrinsic ferroelectricity. In addition, we have obtained the structural information of its low-energy phases with the aid of phonon calculation and examined their evolution with epitaxial strain. Since the number of possible combinations is huge, we have therefore suggested an approach to mix perovskites and simpler metal-oxides to build materials with novel properties.

cond-mat.mtrl-sci↗

arXiv2019

Origin of sawtooth domain walls in ferroelectrics

Domains and domain walls are among the key factors that determine the performance of ferroelectric materials. In recent years, a unique type of domain walls, i.e., the sawtooth-shaped domain walls, has been observed in BiFeO$_{3}$ and PbTiO$_{3}$. Here, we build a minimal model to reveal the origin of these sawtooth-shaped domain walls. Incorporating this model into Monte-Carlo simulations shows that (i) the competition between the long-range Coulomb interaction (due to bound charges) and short-range interaction (due to opposite dipoles) is responsible for the formation of these peculiar domain walls and (ii) their relative strength is critical in determining the periodicity of these sawtooth-shaped domain walls. Necessary conditions to form such domain walls are also discussed.

cond-mat.mtrl-sci↗

arXiv2019

Charge effects in donor doped perovskite ferroelectrics

Doping is a widely used method to tune physical properties of ferroelectric perovskites. Since doping can induce charges due to the substitution of certain elements, charge effects shall be considered in doped samples. To understand how charges can affect the system, we incorporate the dipole-charge interaction into our simulations, where the pinched hysteresis loops can well be reproduced. Two charge compensation models are proposed and numerically investigated to understand how lanthanum doping affect BaTiO$_{3}$'s ferroelectric phase transition temperature and hysteresis loop. The consequences of the two charge compensation models are compared and discussed.

cond-mat.mtrl-sci↗

arXiv2019

Thermally assisted Skyrmion drag in a nonuniform electric field

Magnetic skyrmions are topologically protected excitations of the magnetization vector field with promising applications in spintronics and spin-caloritronics, particularly due to their high mobility. Skyrmions can be steered by a spin-polarized charge current or by exposure to a magnonic spin current. Here, we propose a further method for driving skyrmions by applying an inhomogeneous electric field and a homogeneous thermal bias. We show that the inhomogeneous electric torque leads to an efficient skyrmionic drag which can be thermally assisted as to enhance the skyrmion velocity. The calculations and analysis are limited to insulating samples; for conducting materials the influence of the inhomogeneous electric field on the charge carriers need to be taken also into account.

cond-mat.mes-hall↗

arXiv2018

Understanding doped perovskite ferroelectrics with defective dipole model

While doping is widely used for tuning physical properties of perovskites in experiments, it remains a challenge to exactly know how doping achieves the desired effects. Here, we propose an empirical and computationally tractable model to understand the effects of doping with Fe-doped BaTiO$_{3}$ as an example. This model assumes that the lattice sites occupied by Fe ion and its nearest six neighbors lose their ability to polarize, giving rise to a small cluster of defective dipoles. Employing this model in Monte-Carlo simulations, many important features like reduced polarization and the convergence of phase transition temperatures, which have been observed experimentally in acceptor doped systems, are successfully obtained. Based on microscopic information of dipole configurations, we provide insights into the driving forces behind doping effects and propose that active dipoles, which exist in proximity to the defective dipoles, can account for experimentally observed phenomena. Close attention to these dipoles are necessary to understand and predict doping effects.

cond-mat.mtrl-sci↗

arXiv2017

Solution Monolayer Epitaxy for Tunable Atomically Sharp Oxide Interfaces

Epitaxial growth of atomically-sharp interfaces serves as one of the main building blocks of nanofabrication. Such interfaces are crucial for the operation of various devices including transistors, photo-voltaic cells, and memory components. In order to avoid charge traps that may hamper the operation of such devices, it is critical for the layers to be atomically-sharp. Fabrication of atomically sharp interfaces normally requires ultra-high vacuum techniques and high substrate temperatures. We present here a new self-limiting wet chemical process for deposition of epitaxial layers from alkoxide precursors. This method is fast, cheap, and yields perfect interfaces as we validate by various analysis techniques. It allows the design of heterostructures with half-unit cell resolution. We demonstrate our method by designing hole-type oxide interfaces SrTiO3/BaO/LaAlO3. We show that transport through this interface exhibits properties of mixed electron-hole contributions with hole mobility exceeding that of electrons. Our method and results are an important step forward towards a controllable design of a p-type oxide interface.

cond-mat.str-el↗

arXiv2016

Electrically driven magnetic antenna based on multiferroic composites

We suggest and demonstrate via large scale numerical simulations an electrically operated spin- wave inducer based on composite multiferroic junctions. Specifcally, we consider an interfacially coupled ferromagnetic/ferroelectric structure that emits controllably spin waves in the ferromagnets if the ferroelectric polarization is poled by an external electric field. The roles of geometry and material properties are discussed.

cond-mat.mes-hall↗

arXiv2016

Insight into dielectric response of ferroelectric relaxors by statistical modeling

Ferroelectric relaxors are complex materials with distinct properties. The understanding of their dielectric susceptibility, which strongly depends on both temperature and probing frequency, have interested researchers for many years. Here we report a macroscopic and phenomenological approach based on statistical modeling to investigate and better understand how the dielectric response of a relaxor depends on temperature. Employing the Maxwell-Boltzmann distribution and considering temperature dependent dipolar orientational polarizability, we propose a minimum statistical model and specific equations to understand and fit numerical and experimental dielectric responses versus temperature. We show that the proposed formula can successfully fit the dielectric response of typical relaxors, including Ba(Zr,Ti)O$_{3}$, Pb(Zn$_{1/3}$Nb$_{2/3}$)$_{0.87}$Ti$_{0.13}$O$_{3}$, and Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$-0.05Pb(Zr$_{0.53}$Ti$_{0.47}$)O$_{3}$, which demonstrates the general applicability of this approach.

cond-mat.mtrl-sci↗

arXiv2016

Topological insulator in a helicoidal magnetization field

A key feature of topological insulators is the robustness of the electron energy spectrum. At a surface of a topological insulator, Dirac point is protected by the characteristic symmetry of the system. The breaking of the symmetry opens a gap in the energy spectrum. Therefore, topological insulators are very sensitive to magnetic fields, which can open a gap in the electronic spectrum. Concerning "internal" magnetic effects, for example the situation with doped magnetic impurities, is not trivial. A single magnetic impurity is not enough to open the band gap, while in the case of a ferromagnetic chain of deposited magnetic impurities the Dirac point is lifted. However, a much more interesting case is when localized magnetic impurities form a chiral spin order. Our first principle density functional theory calculations have shown that this is the case for Fe deposited on the surface of Bi2Se3 topological insulator. But not only magnetic impurities can form a chiral helicoidal spin texture. An alternative way is to use chiral multiferroics (prototype material is LiCu2O2) that induce a proximity effect. The theoretical approach we present here is valid for both cases. We observed that opposite to a ferromagnetically ordered case, a chiral spin order does not destroy the Dirac point. We also observed that the energy gap appears at the edges of the new Brillouin zone. Another interesting result concerns the spin dynamics. We derived an equation for the spin density dynamics with a spin current and relaxation terms. We have shown that the motion of the conductance electron generates a magnetic torque and exerts a certain force on the helicoidal texture.

cond-mat.mes-hall↗

arXiv2016

Electrostriction coefficient of ferroelectric materials from ab initio computation

Electrostriction is an important material property that characterizes how strain changes with the development of polarization inside a material. We show that \textit{ab initio }techniques developed in recent years can be exploited to compute and understand electrostriction of ferroelectric materials. Here, electrostriction coefficients of ferroelectric BaTiO$_{3}$, PbTiO$_{3}$, as well as dielectric BaZrO$_{3}$, are obtained and analyzed. Possible causes of the difference between experimental and numerical results are discussed. We also identified that relative displacements between certain ions at a given polarization could be a good indicator of a material's electrostriction property.

cond-mat.mtrl-sci↗

arXiv2014

Electric dipole sheets in BaTiO$_{3}$/BaZrO$_{3}$ superlattices

We investigate two-dimensional electric dipole sheets in the superlattice made of BaTiO$_{3}$ and BaZrO$_{3}$ using first-principles-based Monte-Carlo simulations and density functional calculations. Electric dipole domains and complex patterns are observed and the complex dipole structures with various symmetries (e.g. Pma2, Cmcm and Pmc2_{1}) are further confirmed by density functional calculations, which are found to be almost degenerate in energy with the ferroelectric ground state of the Amm2 symmetry, therefore strongly resembling magnetic sheets. More complex dipole patterns, including vortices and anti-vortices, are also observed, which may constitute the intermediate states that overcome the high energy barrier of different polarization orientations previously predicted by Lebedev\onlinecite{Lebedev2013}. We also show that such system possesses large electrostrictive effects that may be technologically important.

cond-mat.mtrl-sci↗

arXiv2013

Beating the superparamagnetic size limit of nanoparticles on a ferroelectric substrate

When decreasing the size of nanoscale magnetic particles their magnetization becomes vulnerable to thermal fluctuations as approaching the superparamgnetic limit, hindering thus applications relying on a stable magnetization. Here, we show theoretically that a magnetoelectric coupling to a ferroelectric substrate renders possible the realization of substantially smaller nano clusters with thermally stable magnetization. For an estimate of cluster size we perform calculations with realistic material parameters for iron nano particles on ferroelectric BaTiO3 substrate. We find, steering the polarization of BaTiO3 with electric fields affects the magnetism of the deposited magnetic clusters. These findings point to a qualitatively new class of superparamagnetic composites.

cond-mat.mtrl-sci↗

arXiv2012

Magnetoelectric coupling in a ferroelectric/ferromagnetic chain revealed by ferromagnetic resonance

Understanding the multiferroic coupling is one of the key issues in the feld of multiferroics. As shown here theoretically, the ferromagnetic resonance (FMR) renders possible an access to the magnetoelectric coupling coefficient in composite multiferroics. This we evidence by a detailed analysis and numerical calculations of FMR in an unstrained chain of BaTiO3 in the tetragonal phase in contact with Fe, including the effect of depolarizing field. The spectra of the absorbed power in FMR are found to be sensitive to the orientation of the interface electric polarization and to an applied static electric field. Here we propose a method for measuring the magnetoelectric coupling coefficient by means of FMR.

cond-mat.mtrl-sci↗