The effect of intermixing at the interface of short period PbTiO$_3$/SrTiO$_3$ superlattices is studied using first-principles density functional theory. The results indicate that interfacial intermixing significantly enhances the polarization within the superlattice. This enhancement is directly related to the off-centering of Pb and Sr cations and can be explained through a discussion of interacting dipoles. This picture should be general for a wide range of multicomponent superlattices and may have important consequences for the design of ferroelectric devices.
Using the first-principles non-equilibrium Green's function technique with supercell disorder averaging, we study the influence of interfacial intermixing on the spin-orbit torque in Co$\mid$Pt bilayers. Intermixing is modeled by inserting one or more monolayers of a disordered CoPt alloy between Co and Pt. Dampinglike torque is moderately enhanced by interfacial intermixing, while the fieldlike torque, which is small for abrupt interfaces, is strongly enhanced and becomes comparable to the dampinglike torque. The enhancement of the fieldlike torque is attributed to the interface between Co an…
Sensitivity of Ag/Al Interface Specific Resistances to Interfacial Intermixing
我们已经测量到Ag/Al界面的电阻率，2AR（Ag/Al）（111）= 1.4 fOhm-m^2，这是完美界面时预测值的两倍，比2 ML 50%-50%合金的电阻率大50%，甚至比我们新预测的4 ML 50%-50%合金的电阻率1.3 fOhm^2还要大。如此大的2ARAg/Al（111）值证实了对界面无序的预测敏感性，并表明界面大于或等于4 ML厚。从我们的计算，预测的各向异性比，2AR（Ag/Al）（001）/2AR（Ag/Al）（111），大于4的一个完美的界面，应减少到小于2的4 ML界面，使其更难检测到任何这样的各向异性。
We report that atomic-layer alloying (intermixing) at a Pt/Co interface can increase, by approximately 30%, rather than degrade the interfacial spin transparency, and thereby strengthen the efficiency of the dampinglike spin-orbit torque arising from the spin Hall effect in the Pt. At the same time, this interfacial alloying substantially reduces fieldlike spin-orbit torque. Insertion of an ultrathin magnetic alloy layer at heavy-metal/ferromagnet interfaces represents an effective approach for improving interfacial spin transparency that may enhance not only spin-orbit torques but also the sp…
The interfacial abruptness and uniformity in heterostructures are critical to control their electronic and optical properties. With this perspective, this work demonstrates the 3-D atomistic-level mapping of the roughness and uniformity of buried epitaxial interfaces in Si/SiGe superlattices with a layer thickness in the 1.5-7.5 nm range. Herein, 3-D atom-by-atom maps were acquired and processed to generate iso-concentration surfaces highlighting local fluctuations in content at each interface. These generated surfaces were subsequently utilized to map the interfacial roughness and its spatial…
Excitonic insulators are long-sought-after quantum materials predicted to spontaneously open a gap by the Bose condensation of bound electron-hole pairs, namely, excitons, in their ground state. Since the theoretical conjecture, extensive efforts have been devoted to pursuing excitonic insulator platforms for exploring macroscopic quantum phenomena in real materials. Reliable evidences of excitonic character have been obtained in layered chalcogenides as promising candidates. However, owing to the interference of intrinsic lattice instabilities, it is still debatable whether those features, su…
We investigate the evolution of the cross-plane thermal conductivity $κ$ of superlattices (SLs) as interfaces change from perfectly abrupt to totally intermixed, by using non-equilibrium molecular dynamics simulations in combination with the spectral heat current calculations. We highlight the role of surface-interdiffusion-driven intermixing by calculating the $κ$ of SLs with changing interface roughness, whose tuning allows for the $κ$ values much lower than the "alloy limit" and the abrupt interface limit in same cases. The interplay between alloy and interface scattering in different frequ…
Anti-ferromagnetic materials have the possibility to offer ultra fast, high data density spintronic devices. A significant challenge is the reliable detection of the state of the antiferromagnet, which can be achieved using exchange bias. Here we develop an atomistic spin model of the athermal training effect, a well known phenomenon in exchange biased systems where the bias is significantly reduced after the first hysteresis cycle. We find that the setting process in granular thin films relies on the presence of interfacial mixing between the ferromagnetic and antiferromagnetic layers. We sys…
V-telluride superlattice thin films have shown promising performance for on-chip cooling devices. Recent experimental studies have indicated that device performance is limited by the metal/semiconductor electrical contacts. One challenge in realizing a low resistivity contacts is the absence of fundamental knowledge of the physical and chemical properties of interfaces between metal and V-telluride materials. Here we present a combination of experimental and theoretical efforts to understand, design and harness low resistivity contacts to V-tellurides. Ab initio calculations are used to explor…
We report on quantification and elastic strain mapping in two artificial BaZrO3/BaTiO3 (BZ/BT) superlattices having periods of 6.6 nm and 11 nm respectively, grown on (001) SrTiO3 single crystal substrate by pulsed laser deposition technique. The methodology consists of a combination of high-resolution scanning transmission electron microscopy and nanobeam electron diffraction associated with dedicated algorithm for diffraction patterns processing originally developed for semiconductors to record the strains at atomic scale. Both in-plane and out-of-plane elastic strains were then determined a…
Magnetic anisotropic pinning and symmetric breaking induced by interfacial coupling in topological-like ruthenate superlattices
University of Science and Technology of China（中国科学技术大学）；Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area（粤港澳大湾区量子科学中心）；Chinese Academy of Sciences（中国科学院）
Artificially fabricated 3$d$/5$d$ superlattices (SLs) involve both strong electron correlation and spin-orbit coupling in one material by means of interfacial 3$d$-5$d$ coupling, whose mechanism remains mostly unexplored. In this work we investigated the mechanism of interfacial coupling in LaMnO$_3$/SrIrO$_3$ SLs by several spectroscopic approaches. Hard x-ray absorption, magnetic circular dichroism and photoemission spectra evidence the systematic change of the Ir ferromagnetism and the electronic structure with the change of the SL repetition period. First-principles calculations further re…
Interfacial Phase Change Memory (iPCM) retrench unnecessary power consumption due to wasted heat generated during phase change by reducing unnecessary entropic loss. In this study, an advanced iPCM (GeTe/Ti-Sb2Te3 Superlattice) is synthesized by doping Ti into Sb2Te3. Structural analysis and density functional theory (DFT) calculations confirm that bonding distortion and structurally well-confined layers contribute to improve phase change properties in iPCM. Ti-Sb2Te3 acts as an effective thermal barrier to localize the generated heat inside active region, which leads to reduction of switching…
Transitions between bulk and interfacial fracture in diamond/$c$BN heterostructures
Tel Aviv University（特拉维夫大学）；Xi’an Jiaotong University（西安交通大学）；Inner Mongolia University of Science and Technology（内蒙古科技大学）；China Academy of Engineering Physics（中国工程物理研究院）
Order-disorder transitions are widely explored in various vortex structures in condensed matter physics, i.e., in the type-II superconductors and Bose-Einstein condensates. In this study, we have investigated the ordering of the polar vortex phase in the (PZT)n/(STO)n superlattice systems through phase-field simulations. An antiorder state is discovered for short periodicity superlattice on an SSO substrate, owing to the huge interfacial coupling between PZT and STO as well as the giant in-plane polarization in STO layers due to the large tensile strain. Increasing the periodicity leads to the…
Emergent behavior at complex oxide interfaces has driven much of the research in the oxide thin film community for the past twenty years. Interfaces have been engineered for potential applications in spintronics, topological quantum computing, and high-speed electronics in cases where the bulk materials would not exhibit the desired properties. Advances in thin film growth have made the synthesis of these interfaces possible, while surface characterization tools such as X-ray photoelectron spectroscopy have been critical to understanding surface and interfacial phenomena in these materials. In…
As the length-scales of materials decrease, heterogeneities associated with interfaces approach the importance of the surrounding materials. Emergent electronic and magnetic interface properties in superlattices have been studied extensively by both experiments and theory. $^{1-6}$ However, the presence of interfacial vibrations that impact phonon-mediated responses, like thermal conductivity $^{7,8}$, has only been inferred in experiments indirectly. While it is accepted that intrinsic phonons change near boundaries $^{9,10}$, the physical mechanisms and length-scales through which interfacia…
By means of ab initio calculations the possibilities of switchable spin-polarized two-dimensional electron gas (2DEG) at the interface of antiferromagnetic and ferroelectric perovskites, i.e., LaMnO3/BaTiO3 superlattice, were investigated. We demonstrate that at the heterostructure with TiO2/LaO interfacial layers the two-dimensional conducting state arises mainly localized within the interfacial MnO layer. The density of states at the Fermi-level can be tuned by ferroelectric polarization reversal. The conducting state coexists with magnetic one mainly arose from Mn atoms.
Atomic-Scale Characterization of Oxide Interfaces and Superlattices Using Scanning Transmission Electron Microscopy
National Laboratory of the Rockies（落基山国家实验室）；Metallurgical and Materials Engineering Department, Colorado School of Mines（科罗拉多矿业学院冶金与材料工程系）；Renewable and Sustainable Energy Institute, University of Colorado Boulder（科罗拉多大学博尔德分校可再生与可持续能源研究所）
Complex polar superstructure controlled thermal conductivity in ferroelectric PbTiO3/SrTiO3 superlattices
Universidade de Santiago de Compostela（圣地亚哥-德孔波斯特拉大学）；Universidad Rey Juan Carlos（胡安卡洛斯国王大学）；Universitat de Barcelona（巴塞罗那大学）；Catalan Institute of Nanoscience and Nanotechnology (ICN2)（加泰罗尼亚纳米科学与技术研究所）；ALBA Synchrotron Light Facility（阿尔巴同步辐射光源设施）
Charge transfer and competing symmetry breaking drive orbital reconstruction and emergent ferromagnetism in insulating oxide superlattices
Indian Institute of Science（印度科学学院）；Deutsches Elektronen-Synchrotron DESY（德国电子同步加速器中心）；ALBA Synchrotron Light Source（阿尔巴同步辐射光源）；Advanced Photon Source, Argonne National Laboratory（阿贡国家实验室先进光子源）
Interface-Controlled Defect Engineering in TiN/TaN Superlattices for Enhanced Hardness and Fracture Toughness
Technische Universität Wien（维也纳工业大学）；Plansee (Shanghai) High Performance Material Ltd.（普莱思（上海）高性能材料有限公司）；Guangdong University of Technology（广东工业大学）；RWTH Aachen University（亚琛工业大学）；Austrian Academy of Sciences（奥地利科学院）；Uppsala University（乌普萨拉大学）
The combination of charge and spin degrees of freedom with electronic correlations in condensed matter systems leads to a rich array of phenomena, such as magnetism, superconductivity, and novel conduction mechanisms. While such phenomena are observed in bulk materials, a richer array of behaviors becomes possible when these degrees of freedom are controlled in atomically layered heterostructures, where one can constrain dimensionality and impose interfacial boundary conditions. Here, we unlock a host of unique, hidden electronic and magnetic phase transitions in NdNiO$_3$ while approaching th…
Large magnetoelectric response in thin films is highly desired for high-throughput and high-density microelectronic applications. However, the d0 rule in single-phase compounds usually results in a weak interaction between ferroelectric and magnetic orders; the magnetoelectric coupling via elastic resonance in composites restricts their thin-film integration in broadband. Here, we effectuate a concurrence of ferroelectric-like and antiferromagnetic phase transitions in Sr2IrO4/SrTiO3 superlattices by artificial design periodically non-equivalent interfaces, where a maximum magnetoelectric coef…
Hybrid multiferroics such as BiFeO$_3$ (BFO) and La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) heterostructures are highly interesting functional systems due to their complex electronic and magnetic properties. One of the key parameters influencing the emergent properties is the quality of interfaces, where varying interdiffusion lengths can give rise to different chemistry and distinctive electronic states. Here we report high-resolution depth resolved chemical and electronic investigation of BFO/LSMO superlattice using standing-wave hard X-ray photoemission spectroscopy in the first-order Bragg as well…
Dimensionality-Driven Electronic and Orbital Transitions Mediating Interfacial Magnetism in LaNiO3/CaMnO3 Observed In Situ
Temple University（天普大学）；Flatiron Institute（平顿研究所）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Cornell University（康奈尔大学）；University of California, Berkeley（加州大学伯克利分校）；Rutgers University（罗格斯大学）；Advanced Light Source, Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室先进光源中心）；Deutsches Elektronen-Synchrotron, DESY（德国电子同步辐射中心）；CNR-IOM Istituto Officina dei Materiali（意大利国家研究委员会材料研究所）；Università degli Studi di Padova（帕多瓦大学）；AREA Science Park（AREA科学园）；Columbia University（哥伦比亚大学）
