Low temperature state in strontium titanate microcrystals using in situ multi-reflection Bragg coherent X-ray diffraction imaging
David Yang, Ana F. Suzana, Longlong Wu, Sung Soo Ha, Sungwook Choi, Hieu Minh Ngo, Muhammad Mahmood Nawaz, Hyunjung Kim, Jialun Liu, Daniel Treuherz, Nan Zhang,… 展开作者
David Yang, Ana F. Suzana, Longlong Wu, Sung Soo Ha, Sungwook Choi, Hieu Minh Ngo, Muhammad Mahmood Nawaz, Hyunjung Kim, Jialun Liu, Daniel Treuherz, Nan Zhang, Zheyi An, Gareth Nisbet, Daniel G. Porter, Ian K. Robinson
Strontium titanate is a classic quantum paraelectric oxide material that has been widely studied in bulk and thin films. It exhibits a well-known cubic-to-tetragonal antiferrodistortive phase transition at 105 K, characterized by the rotation of oxygen octahedra. A possible second phase transition at lower temperature is suppressed by quantum fluctuations, preventing the onset of ferroelectric order. However, recent studies have shown that ferroelectric order can be established at low temperatures by inducing strain and other means. Here, we used in situ multi-reflection Bragg coherent x-ray diffraction imaging to measure the strain and rotation tensors for two strontium titanate microcrystals at low temperature. We observe strains induced by dislocations and inclusion-like impurities in the microcrystals. Based on radial magnitude plots, these strains increase in magnitude and spread as the temperature decreases. Pearson's correlation heat maps show a structural transition at 50 K, which could possibly be the formation of a low-temperature ferroelectric phase in the presence of strain. We do not observe any change in local strains associated with the tetragonal phase transition at 105 K.
We demonstrate an approach for calculating temperature-dependent quantum and anharmonic effects with beyond density-functional theory accuracy. By combining machine-learned potentials and the stochastic self-consistent harmonic approximation, we investigate the cubic to tetragonal transition in strontium titanate and show that the paraelectric phase is stabilized by anharmonic quantum fluctuations. We find that a quantitative understanding of the quantum paraelectric behavior requires a higher-level treatment of electronic correlation effects via the random phase approximation. This approach e…
The magnetic and electronic properties of strontium titanate with different carbon dopant configurations are explored using first-principles calculations with a generalized gradient approximation (GGA) and the GGA+U approach. Our results show that the structural stability, electronic properties and magnetic properties of C-doped SrTiO3 strongly depend on the distance between carbon dopants. In both GGA and GGA+U calculations, the doping structure is mostly stable with a nonmagnetic feature when the carbon dopants are nearest neighbors, which can be ascribed to the formation of a C-C dimer pair…
Structural phase transitions in Ruddlesden-Popper phases of strontium titanate: {\em ab initio} and inhomogeneous Ginzburg-Landau approaches
本文首次系统地{ \em ab initio}研究了钛酸锶（Sr $_{1+n}$ Ti $_n$ O $_{3n+1}$）的Ruddlesden-Popper（RP）相的反铁电畸变（AFD）序随压缩外延应变和相数$n$的变化。我们发现所有RP相在一个显着的应变范围内表现出AFD顺序，恢复散装AFD顺序为$\sim 1/n^2$。一个广义的Ginzburg-Landau哈密顿量，包括八面体间的相互作用再现我们的{ \em从头算}结果以及，打开一条途径，了解其他纳米结构的钙钛矿系统。
The local structure and oxidation state of the cobalt impurity in SrTiO$_3$ is studied by X-ray absorption fine structure (XAFS) spectroscopy. The synthesis conditions, under which cobalt predominantly (up to 76%) substitutes the atoms at the $A$ site of the perovskite structure, is found for SrTiO$_3$(Co) samples. By varying the synthesis conditions, it is possible to appreciably change the ratio between the concentrations of cobalt atoms incorporated into the $A$ and $B$ sites. It is established that the oxidation state of cobalt is +2 at the $A$ site and +3 at the $B$ site. It is revealed t…
In the present study, structural changes due to gradual doping of Sr in BaTiO3 were investigated by both x-ray and neutron powder diffraction techniques. Ba1-xSrxTiO3 (x=0.0, 0.5 and 1.0) samples were synthesized by PVA evaporation method and purity was confirmed by x-ray diffraction experiment. After that, neutron diffraction experiments were carried out and diffraction data were analyzed by Rietveld least-square data refinement method using the computer program RIETAN-2000 and FullProf to determine various crystallographic structural parameters. The cation and anion position coordinates were…
Stoichiometric Epitaxial Strontium Titanate Thin Films on Silicon by High-Temperature Sr Segregation
Imec；Department of Materials Engineering (MTM), KU Leuven（荷语鲁汶大学材料工程系）；Physics Department, Jean Monnet University（圣艾蒂安让·穆内大学物理系）；Department of Information Technology (INTEC), Photonics Research Group, Ghent University（根特大学信息与科技学院光子学研究组）
We report measurements of the thermal Hall effect in single crystals of both pristine and isotopically substituted strontium titanate. We discovered a two orders of magnitude difference in the thermal Hall conductivity between $SrTi^{16}O_3$ and $^{18}O$-enriched $SrTi^{18}O_3$ samples. In most temperature ranges, the magnitude of thermal Hall conductivity ($κ_{xy}$) in $SrTi^{18}O_3$ is proportional to the magnitude of the longitudinal thermal conductivity ($κ_{xx}$), which suggests a phonon-mediated thermal Hall effect. However, they deviate in the temperature of their maxima, and the therma…
We show that the Bloch states in the conduction band of SrTiO$_3$ arise from the interplay between highly anisotropic hopping in sub-bands derived from the Ti $t_{2g}$ orbitals and spin-orbit coupling that mixes these orbitals. Because of the nearly flat-band characteristics for one of the principal axes, at sufficiently high doping these Bloch states become unstable with respect to electron interactions, resulting in Mott-like singlet correlations. These findings may be relevant to the anomalous electronic properties of SrTiO$_3$, including its unusual superconductivity.
Oxygen Vacancies at Dislocation Core Modulate Plasticity in Strontium Titanate
Ames National Laboratory（艾姆斯国家实验室）；North Carolina State University（北卡罗来纳州立大学）；Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院）；Iowa State University（爱荷华州立大学）；University of Virginia（弗吉尼亚大学）
Extended Mean-Field Theory for the 2D Hubbard Model in Degenerate Dilute Electron Gases: Fluctuations, Superconducting Dome, and Interaction Mechanisms in Strontium Titanate
School of Materials Science and Engineering, Guilin University of Electronic Technology（桂林电子科技大学材料科学与工程学院）
Thermal transport and phonon hydrodynamics in strontium titanate
我们提出了一个研究的热导率，$κ$，在未掺杂和掺杂的钛酸锶在很宽的温度范围内（2-400 K）和检测不同的制度的热流。在未掺杂的SrTiO $_{3}$中，$κ$在低于其峰值的温度和在窄的温度窗口中比立方更快地演化。先前在少数固体中观察到的这种行为被归因于声子的Poiffille流，预计当动量守恒散射事件超过动量退化事件时会出现。这种效应在掺杂剂存在下消失。在SrTi $_{1-x}$ Nb $_{x}$ O $_{3}$中，晶格热导率在低于平均掺杂剂间距离和声学声子的热波长变得相当的温度下开始显著降低。在高温状态下，热扩散率与温度的倒数成正比，前因子由声速和普朗克时间（$τ_{p}=\frac{\hbar}{k_{B}T}$）设置。
Spatial correlation between atoms can generate a depletion in the energy dispersion of acoustic phonons. Two well known examples are rotons in superfluid helium and the Kohn anomaly in metals. Here we report on the observation of a large softening of the transverse acoustic mode in quantum paraelectric SrTiO$_3$ by means of inelastic neutron scattering. In contrast to other known cases, this softening occurs at a tiny wave vector implying spatial correlation extending over a distance as long as 40 lattice parameters. We attribute this to the formation of mesoscopic fluctuating domains due to t…
SrTiO$_3$, although a wide gap insulator, has long been known to become metallic and superconducting at extremely low doping levels. This has given rise to questions concerning the coexistence or interdependence of metallicity, superconductivity, and the material's polar properties. This issue becomes especially intriguing in conjunction with the observation that filamentary metallicity can be induced by means of resistive switching at conditions well below relevant doping levels for homogeneous metallicity. In this study, we demonstrate that resistive switching can also be employed to generat…
The properties of quantum materials are commonly tuned using experimental variables such as pressure, magnetic field and doping. Here we explore a different approach: irreversible, plastic deformation of single crystals. We show for the superconductor SrTiO$_3$ that compressive plastic deformation induces low-dimensional superconductivity significantly above the superconducting transition temperature ($T_c$) of undeformed samples, with evidence of superconducting correlations at temperatures two orders of magnitude above the bulk $T_c$. The superconductivity enhancement is correlated with the …
SrTiO$_3$, a quantum paralectric, displays a detectable phonon thermal Hall effect (THE). Here we show that the amplitude of THE is extremely sensitive to stoichiometry. It drastically decreases upon substitution of a tiny fraction of Sr atoms with Ca, which stabilizes the ferroelectric order. It drastically increases by an even lower density of oxygen vacancies, which turn the system to a dilute metal. The enhancement in the metallic state exceeds by far the sum of the electronic and the phononic contributions. We explain this observation as an outcome of three features: i) heat is mostly tra…
Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory（斯坦福材料能源科学研究所，SLAC国家加速器实验室）；Stanford PULSE Institute, SLAC National Accelerator Laboratory（斯坦福PULSE研究所，SLAC国家加速器实验室）；Department of Chemistry, Massachusetts Institute of Technology（麻省理工学院化学系）；Elettra-Sincrotrone（埃莱特拉同步辐射中心）；Paul Scherrer Institut（保罗谢尔研究所）
The lattice constants of Strontium titanate perovskite has been studied using the Density functional theory formalism at the PBE and the HSE levels of theory. The study has been done in all the 3 existing phases; namely cubic, orthorhombic and tetragonal, however, experimental details are available only for the cubic phase so far.
我们报道了几个国家的团体独立发明的铁电纳米管。器件已经用三种不同的材料制成：锆钛酸铅PbZr 1-xTixO 3（PZT）;钛酸钡BaTiO 3;和钽酸锶铋SrBi 2 Ta 2 O 9（SBT）。几种不同的沉积技术已经成功地使用，包括雾化CSD（化学溶液沉积）和孔隙润湿。铁电滞后和高的光学非线性已被证明。通过SEM、TEM、XRD、AFM（压电模式）和SHG分析了结构。沟槽在硅动态随机存取存储器，喷墨打印机和光子器件的应用进行了讨论。已经研究了直径小至20 nm的铁电填充孔。
Strontium titanate is an incipient ferroelectric in which superconductivity emerges at exceptionally low doping levels. Remarkably, stabilizing the polar phase through strain or chemical substitution has been shown to significantly enhance the superconducting critical temperature, and the polar instability plays a pivotal role in the majority of proposed superconducting pairing mechanisms. A rigorous understanding of ferroelectricity is therefore essential to elucidate the electron pairing mechanism in this material. To investigate the nature of the polar order in strontium titanate, we develo…
