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Defect-induced 4p-magnetism in layered platinum diselenide 层状铂二硒化物中缺陷诱导的4p磁性
Pub Date : 2020-10-27 DOI: 10.1103/PHYSREVB.103.144403
P. Manchanda, Pankaj Kumar, P. Dev
Platinum diselenide (PtSe$_{2}$) is a recently-discovered extrinsic magnet, with its magnetism attributed to the presence of Pt-vacancies. The host material to these defects itself displays interesting structural and electronic properties, some of which stem from an unusually strong interaction between its layers. To date, it is not clear how the unique intrinsic properties of PtSe$_2$ will affect its induced magnetism. In this theoretical work, we show that the defect-induced magnetism in PtSe$_{2}$ thin films is highly sensitive to: (i) the layer-thickness (ii) defect density, and (iii) substrate choice. These different factors dramatically modify all magnetic properties, including the magnitude of local moments, strength of the coupling, and even nature of the coupling between the moments. We further show that the strong inter-layer interactions are key to understanding these effects. A better understanding of the various influences on magnetism, can enable controllable tuning of the magnetic properties in Pt-based dichalcogenides, which can be used to design novel devices for magnetoelectric and magneto-optic applications.
二硒化铂(PtSe$_{2}$)是最近发现的一种外在磁体,其磁性归因于pt空位的存在。这些缺陷的主体材料本身显示出有趣的结构和电子特性,其中一些源于其层之间异常强烈的相互作用。迄今为止,尚不清楚PtSe$_2$的独特内在性质如何影响其感应磁性。在这项理论工作中,我们证明了PtSe$_{2}$薄膜中的缺陷感应磁性对:(i)层厚度(ii)缺陷密度和(iii)衬底选择高度敏感。这些不同的因素极大地改变了所有的磁性,包括局部矩的大小、耦合的强度,甚至是矩之间耦合的性质。我们进一步表明,强层间相互作用是理解这些效应的关键。更好地了解对磁性的各种影响,可以实现基于pt的二硫族化合物的磁性能的可控调谐,这可以用于设计磁电和磁光应用的新型器件。
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引用次数: 1
Magnetic excitations in an ionic spin-chain system with a nonmagnetic ferroelectric instability 具有非磁性铁电不稳定性的离子自旋链体系中的磁激发
Pub Date : 2020-10-26 DOI: 10.1103/physrevresearch.2.043333
K. Sunami, Y. Sakai, R. Takehara, H. Adachi, K. Miyagawa, S. Horiuchi, K. Kanoda
Cross-correlation between magnetism and dielectric is expected to offer novel emergent phenomena. Here, magnetic excitations in the organic donor-acceptor spin-chain system, TTF-BA, with a ferroelectric ground state is investigated by $^1$H-NMR spectroscopy. A nonmagnetic transition with a ferroelectric order is marked by sharp drops in NMR shift and nuclear spin relaxation rate $T_1^{-1}$ at 53 K. Remarkably, the analyses of the NMR shift and $T_1^{-1}$ dictate that the paramagnetic spin susceptibility in TTF-BA is substantially suppressed from that expected for the 1D Heisenberg spins. We propose that the spin-lattice coupling and the ferroelectric instability cooperate to promote precursory polar singlet formation in the ionic spin system with a nonmagnetic ferroelectric instability.
磁与介电相互关系有望提供新的涌现现象。本文用$^1$H-NMR谱研究了具有铁电基态的有机给体-受体自旋链体系TTF-BA中的磁激发。在53 K时,核磁共振位移和核自旋弛豫速率T_1^{-1}$急剧下降,标志着铁电序的非磁性跃迁。值得注意的是,对核磁共振位移和$T_1^{-1}$的分析表明,TTF-BA的顺磁自旋磁化率与1D海森堡自旋的预期值相比有很大的抑制。我们提出,在具有非磁性铁电不稳定性的离子自旋体系中,自旋-晶格耦合和铁电不稳定性共同促进了前驱极性单线态的形成。
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引用次数: 2
Remarkable low-energy properties of the pseudogapped semimetal Be5Pt 伪叠半金属Be5Pt的显著低能特性
Pub Date : 2020-10-26 DOI: 10.1103/physrevb.102.155206
L. Fanfarillo, J. Hamlin, R. Hennig, A. Hire, P. Hirschfeld, Jungsoo Kim, Jinhyuk Lim, Y. Quan, G. Stewart, S. Xie
We report measurements and calculations on the properties of the intermetallic compound Be$_5$Pt. High-quality polycrystalline samples show a nearly constant temperature dependence of the electrical resistivity over a wide temperature range. On the other hand, relativistic electronic structure calculations indicate the existence of a narrow pseudogap in the density of states arising from accidental approximate Dirac cones extremely close to the Fermi level. A small true gap of order 3 meV is present at the Fermi level, yet the measured resistivity is nearly constant from low to room temperature. We argue that this unexpected behavior can be understood by a cancellation of the energy dependence of density of states and relaxation time due to disorder, and discuss a model for electronic transport. With applied pressure, the resistivity becomes semiconducting, consistent with theoretical calculations that show that the band gap increases with applied pressure. We further discuss the role of Be inclusions in the samples.
本文报道了金属间化合物Be$_5$Pt的性质的测量和计算。高质量的多晶样品在很宽的温度范围内表现出电阻率几乎恒定的温度依赖性。另一方面,相对论电子结构计算表明,在非常接近费米能级的偶然近似狄拉克锥产生的态密度中存在狭窄的赝隙。在费米能级上存在一个3 meV量级的小间隙,但测量到的电阻率从低温到室温几乎是恒定的。我们认为这种意想不到的行为可以通过消除态密度和无序弛豫时间的能量依赖来理解,并讨论了电子输运的模型。随着施加压力,电阻率变为半导体,这与理论计算一致,表明带隙随着施加压力而增加。我们进一步讨论了铍包裹体在样品中的作用。
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引用次数: 1
Microscopic mechanisms behind hyperferroelectricity 超铁电性背后的微观机制
Pub Date : 2020-10-25 DOI: 10.1103/PHYSREVB.103.014116
M. Khedidji, D. Amoroso, H. Djani
Hyperferroelectrics are receiving a growing interest thanks to their unique property to retain a spontaneous polarization even in presence of a depolarizing field. Nevertheless, general microscopic mechanisms driving hyperferroelectricity, which is ascribed to the softening of a polar $LO$ mode, are still missing. Here, by means of phonons calculations and force constants analysis in two class of hyperferroelectrics, the ABO$_3$-LiNbO3-type systems and the prototypical hexagonal-ABC systems, we unveiled common features in the dynamical properties of a hyperferroelectric behind such $LO$ instability: negative or vanishing on-site force constant associated to the cation driving the $LO$ polar distortion, and destabilizing cation-anion interactions, both induced by short-range forces. We also predict possible enhancement of the hyperferroelectric properties by applying an external positive pressure; pressure strengthens the destabilizing short-range interactions. Particularly, the increase in the mode effective charges associated to the unstable $LO$ mode under pressure suggests an eventual enhancement of the $D$=0 polarization under compressive strain.
超铁电体由于其独特的性质,即使在去极化场的存在下也能保持自发极化,因此受到越来越多的关注。然而,驱动超铁电性的一般微观机制(归因于极性$LO$模式的软化)仍然缺失。本文通过对两类超铁电体(ABO$_3$- linbo3型体系和典型六边形- abc体系)的声子计算和力常数分析,揭示了这种超铁电体不稳定性背后的动力学特性的共同特征:与驱动$LO$极性畸变的阳离子相关的负或消失的现场力常数,以及不稳定的阳离子-阴离子相互作用,都是由短程力引起的。我们还预测了施加外部正压可能增强超铁电性能;压力加强了破坏稳定的短程相互作用。特别是,与压力下不稳定的$LO$模式相关的模式有效电荷的增加表明,在压缩应变下,$D$=0极化最终会增强。
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引用次数: 2
Directed long-range transport of a nearly pure component atom clusters by the electromigration of a binary surface alloy 二元表面合金电迁移致近纯组分原子团簇的定向远程输运
Pub Date : 2020-10-25 DOI: 10.1103/PhysRevMaterials.5.024001
M. Khenner
A continuum model for electromigration-driven transport of an embedded, compact atom cluster across a surface terrace of a phase-separating binary surface alloy is presented. Computations show that the electron wind reliably transports the cluster over hundreds of lattice spacings and in the set direction, while the cluster purity improves during the drift. Impacts on cluster's drift speed and purity of the A to B atom's jump frequencies ratio, the magnitude and the sign of the A and B atoms's effective surface charges, the applied voltage, and the diffusion anisotropy are studied.
提出了电迁移驱动的嵌入式致密原子团簇在相分离二元表面合金表面平台上输运的连续统模型。计算结果表明,电子风可靠地在数百个晶格间隔上沿设定的方向传输团簇,同时在漂移过程中团簇纯度得到提高。研究了A - B原子跃迁频率比、A和B原子有效表面电荷的大小和符号、外加电压以及扩散各向异性对团簇漂移速度和纯度的影响。
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引用次数: 4
Comparison of coherent phonon generation by electronic and ionic Raman scattering in LaAlO3 LaAlO3中电子和离子拉曼散射产生相干声子的比较
Pub Date : 2020-10-24 DOI: 10.1103/PHYSREVRESEARCH.3.013126
M. Neugebauer, D. M. Juraschek, M. Savoini, P. Engeler, L. Boie, E. Abreu, N. Spaldin, S. Johnson
In ionic Raman scattering, infrared-active phonons mediate a scattering process that results in the creation or destruction of a Raman-active phonon. This mechanism relies on nonlinear interactions between phonons and has in recent years been associated with a variety of emergent lattice-driven phenomena in complex transition-metal oxides, but the underlying mechanism is often obscured by the presence of multiple coupled order parameters in play. Here, we use time-resolved spectroscopy to compare coherent phonons generated by ionic Raman scattering with those created by more conventional electronic Raman scattering on the nonmagnetic and non-strongly-correlated wide band-gap insulator LaAlO$_3$. We find that the oscillatory amplitude of the low-frequency Raman-active $E_g$ mode exhibits a sharp peak when we tune our pump frequency into resonance with the high-frequency infrared-active $E_u$ mode, consistent with first-principles calculations. Our results suggest that ionic Raman scattering can strongly dominate electronic Raman scattering in wide band-gap insulating materials. We also see evidence of competing scattering channels at fluences above 28~mJ/cm$^2$ that alter the measured amplitude of the coherent phonon response.
在离子拉曼散射中,红外主动声子介导散射过程,导致拉曼主动声子的产生或破坏。这种机制依赖于声子之间的非线性相互作用,近年来与复杂过渡金属氧化物中出现的各种晶格驱动现象有关,但潜在的机制往往被多个耦合顺序参数的存在所掩盖。在这里,我们使用时间分辨光谱来比较离子拉曼散射产生的相干声子与更传统的电子拉曼散射在非磁性和非强相关的宽带隙绝缘体LaAlO$_3$上产生的相干声子。我们发现,当我们将泵浦频率调整为与高频红外主动$E_u$模式共振时,低频拉曼主动$E_g$模式的振荡幅度呈现出一个尖锐的峰值,这与第一性原理计算一致。我们的研究结果表明,离子拉曼散射在宽禁带绝缘材料中可以强烈地支配电子拉曼散射。我们还看到在28~mJ/cm$^2$以上的影响下存在竞争散射通道的证据,这改变了相干声子响应的测量振幅。
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引用次数: 5
Current-induced orbital magnetization in systems without inversion symmetry 非反转对称系统的电流诱导轨道磁化
Pub Date : 2020-10-23 DOI: 10.1103/PhysRevB.102.184404
Daisuke Hara, M. Bahramy, S. Murakami
In systems with time-reversal symmetry, the orbital magnetization is zero in equilibrium. Recently, it has been proposed that the orbital magnetization can be induced by an electric current in a helical crystal structure in the same manner as that in a classical solenoid. In this paper, we extend this theory and study the current-induced orbital magnetization in a broader class of systems without inversion symmetry. First, we consider polar metals which have no inversion symmetry. We find that the current-induced orbital magnetization appears in a direction perpendicular to the electric current even without spin-orbit coupling. Using the perturbation method, we physically clarify how the current-induced orbital magnetization appears in polar metals. As an example, we calculate the current-induced orbital magnetization in SnP, and find that it might be sufficiently large for measurement. Next, we consider a two-dimensional system without inversion symmetry. We establish a method to calculate the current-induced orbital magnetization in the in-plane direction by using real-space coordinates in the thickness direction. By applying this theory to surfaces and interfaces of insulators, we find that an electric current along surfaces and interfaces induces an orbital magnetization perpendicular to the electric current.
在具有时间反转对称性的系统中,轨道的平衡磁化强度为零。最近,有人提出,电流可以在螺旋晶体结构中以与经典螺线管相同的方式诱导轨道磁化。在本文中,我们扩展了这一理论,并在更广泛的无反转对称性系统中研究了电流诱导轨道磁化。首先,我们考虑没有反转对称性的极性金属。我们发现,即使没有自旋轨道耦合,电流诱导的轨道磁化也呈现在与电流垂直的方向上。利用微扰方法,从物理上阐明了电流诱导轨道磁化在极性金属中的表现。作为一个例子,我们计算了SnP中电流诱导的轨道磁化强度,发现它可能足够大,可以进行测量。接下来,我们考虑一个没有逆对称的二维系统。建立了一种在厚度方向上用实空间坐标计算平面内电流感应轨道磁化强度的方法。将这一理论应用于绝缘体的表面和界面,我们发现沿表面和界面的电流会引起垂直于电流的轨道磁化。
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引用次数: 6
Absorption mechanism of dopamine/DOPAC-modified TiO2 nanoparticles by time-dependent density functional theory calculations 用时间依赖密度泛函理论计算多巴胺/ dopac修饰TiO2纳米粒子的吸收机理
Pub Date : 2020-10-22 DOI: 10.1016/j.mtener.2020.100571
C. Ronchi, F. Soria, L. Ferraro, S. Botti, C. Di Valentin
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引用次数: 2
Multicaloric effects in metamagnetic Heusler Ni-Mn-In under uniaxial stress and magnetic field 在单轴应力和磁场作用下,变磁性Heusler Ni-Mn-In中的多热效应
Pub Date : 2020-10-22 DOI: 10.1063/5.0020755
A. Gràcia-Condal, T. Gottschall, L. Pfeuffer, O. Gutfleisch, A. Planes, L. Mañosa
The world's growing hunger for artificial cold on the one hand, and the ever more stringent climate targets on the other, pose an enormous challenge to mankind. Novel, efficient and environmentally friendly refrigeration technologies based on solid-state refrigerants can offer a way out of the problems arising from climate-damaging substances used in conventional vapor-compressors. Multicaloric materials stand out because of their large temperature changes which can be induced by the application of different external stimuli such as a magnetic, electric, or a mechanical field. Despite the high potential for applications and the interesting physics of this group of materials, only few studies focus on their investigation by direct methods. In this paper, we report on the advanced characterization of all relevant physical quantities that determine the multicaloric effect of a Ni-Mn-In Heusler compound. We have used a purpose-designed calorimeter to determine the isothermal entropy and adiabatic temperature changes resulting from the combined action of magnetic field and uniaxial stress on this metamagnetic shape-memory alloy. From these results, we can conclude that the multicaloric response of this alloy by appropriate changes of uniaxial stress and magnetic field largely outperforms the caloric response of the alloy when subjected to only a single stimulus. We anticipate that our findings can be applied to other multicaloric materials, thus inspiring the development of refrigeration devices based on the multicaloric effect.
一方面,世界对人工冷的需求日益增长,另一方面,气候目标越来越严格,这对人类构成了巨大的挑战。基于固态制冷剂的新型、高效和环保制冷技术可以解决传统蒸汽压缩机中使用的破坏气候的物质所带来的问题。多色材料之所以引人注目,是因为它们的温度变化很大,这种变化可以由不同的外部刺激(如磁场、电场或机械场)引起。尽管这类材料具有很高的应用潜力和有趣的物理性质,但很少有研究关注于直接方法的研究。在本文中,我们报告了决定Ni-Mn-In Heusler化合物多色效应的所有相关物理量的高级表征。我们用专门设计的量热计测定了在磁场和单轴应力共同作用下,这种超磁形状记忆合金的等温熵和绝热温度变化。通过这些结果,我们可以得出结论,适当改变单轴应力和磁场的合金的多色响应在很大程度上优于仅受单一刺激时合金的热响应。我们期望我们的发现可以应用于其他多色材料,从而启发基于多色效应的制冷装置的发展。
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引用次数: 28
First-principles LCAO study of the low- and room-temperature phases of CdPS3 CdPS3低温相和室温相的第一性原理LCAO研究
Pub Date : 2020-10-21 DOI: 10.1063/10.0002477
A. Kuzmin
The electronic and atomic structure of a bulk 2D layered van-der-Waals compound CdPS3 was studied in the low (R3) and room (C2/m) temperature phases using first-principles calculations within the periodic linear combination of atomic orbitals method with hybrid meta exchange-correlation M06 functional. The calculation results reproduce well the experimental crystallographic parameters. The value of the indirect band gap Eg=3.4 eV for the room-temperature monoclinic C2/m phase is close to the experimental one, while the indirect band gap Eg=3.3 eV was predicted for the low-temperature trigonal R3 phase. The effect of hydrostatic pressure on the band gap in both phases was studied in the pressure range from 0 to 40 GPa. In both cases, the pressure dependence of the band gap passes through a maximum, but at different pressures. In the R3 phase, the band gap reaches its maximum value of ~4 eV at ~30 GPa, whereas in the C2/m phase, the maximum value of ~3.6 eV is reached already at ~8 GPa.
采用原子轨道周期性线性组合方法和杂化元交换相关M06泛函,研究了块状二维层状范德瓦尔斯化合物CdPS3在低温(R3)和室温(C2/m)相的电子和原子结构。计算结果较好地再现了实验晶体学参数。室温单斜C2/m相的间接带隙Eg=3.4 eV与实验值接近,而低温三角R3相的间接带隙Eg=3.3 eV是预测值。在0 ~ 40 GPa的压力范围内,研究了静水压力对两相带隙的影响。在这两种情况下,带隙的压力依赖性都达到最大值,但在不同的压力下。在R3相中,带隙在~30 GPa时达到最大值~4 eV,而在C2/m相中,带隙在~8 GPa时已经达到最大值~3.6 eV。
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引用次数: 2
期刊
arXiv: Materials Science
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