Spin, Orbital, and Spin-Orbital Polarons in Transition Metal Oxides
Krzysztof Wohlfeld
备注：
6 pages, 3 figures; to appear in AIP Conference Proceedings; this is a very short (and introductory) review on the basic differences between spin, orbital and spin-orbital polarons
发表信息：
Lectures on the Physics of Strongly Correlated Systems XIII, eds. A. Avella and F. Mancini, AIP Conference Proceedings Vol. 1162, 220-225, New York 2009
我简要概述了三种不同的过渡金属氧化物中极化子的形成：（i）当空穴被添加到La $_2$ CuO $_4$中的反铁磁（AF）有序平面时的自旋极化子，（ii）当空穴被添加到LaMnO $_3$中的交替轨道（AO）有序平面时的轨道极化子，当在LaVO $_3$中的AF和AO有序平面上添加空穴时，产生自旋轨道极化子。比较上述极化子的不同特征，可以揭示轻掺杂过渡金属氧化物La $_{2-x}$ Sr $_x$ CuO $_4$、La $_{1-x}$ Sr $_x$ MnO $_3$和La $_{1-x}$ Sr $_{x}$ VO $_3$实验相图之间的基本差异。
英文摘要：
I give a brief overview of a polaron formation in three distinct transition metal oxides: (i) spin polaron when a hole is added to the antiferromagnetic (AF) ordered plane in La$_2$CuO$_4$, (ii) orbital polaron when a hole is added to the alternating orbital (AO) ordered plane in LaMnO$_3$, and (iii) spin-orbital polaron when a hole is added to the AF and AO ordered plane in LaVO$_3$. Comparison of the distinct features of the above polarons can shed some light on the basic differences between the experimental phase diagrams of the lightly doped transition metal oxides La$_{2-x}$Sr$_x$CuO$_4$, La$_{1-x}$Sr$_x$MnO$_3$, and La$_{1-x}$Sr$_{x}$VO$_3$.
Pairing interactions and pairing mechanism in high temperature copper oxide superconductors
在未掺杂的母体铜氧化物的极化子结合能E_{p}已被确定为约1.0 eV的反铁磁有序温度的非常规氧同位素效应。推导出的E_{p}值与由独立光学数据估计的值和由测量的介电常数理论估计的值在定量上是一致的。在最佳掺杂的铜酸盐中观察到的面内超载流子质量上的大量氧同位素效应表明极化子被束缚到库珀对中。我们还确定了声子模式，强烈耦合到传导电子的角度分辨的光电子能谱，隧穿光谱，和光学数据。我们一贯表明，有一个非常强的电子-声子耦合功能，在声子能量约20毫电子伏沿波腹方向，这种耦合变得越来越弱的对角方向。我们进一步指出，铜酸盐的高温超导电性是由强的电子-声子耦合、极化子效应以及与2 eV Cu-O电荷转移涨落的显著耦合引起的。
Many transition metal oxides (TMOs) are Mott insulators due to strong Coulomb repulsion between electrons, and exhibit metal-insulator transitions (MITs) whose mechanisms are not always fully understood. Unlike most TMOs, minute doping in CaMnO3 induces a metallic state without any structural transformations. This material is thus an ideal platform to explore band formation through the MIT. Here, we use angle-resolved photoemission spectroscopy to visualize how electrons delocalize and couple to phonons in CaMnO3. We show the development of a Fermi surface where mobile electrons coexist with h…
Magnetic properties of spin-orbital polarons in lightly doped cobaltates
本文对Na_xCoO_2在小空穴浓度（0.7 < x < 1）下的自旋轨道极化子模型进行了数值处理。我们演示了极化子如何解释这种层状化合物的特殊磁性：它们解释了大的磁化率;它们的内部自由度导致负居里-外斯温度和铁磁层内相互作用，从而解决了这些观察之间令人困惑的矛盾。我们对极化子内部自由度引起的激发的动量和能量位置进行了具体的预测，并讨论了它们对自旋波阻尼的影响。
The origin of the effect of colossal magneto-resistance (CMR) remains still unexplained. In this work we revisit the spin dynamics of the pseudo-cubic La1-xSrxMnO3 along the Mn-O-Mn bond direction at four x doping values (x < 0.5) and various temperatures and report a new lattice dynamics study at x0=0.2, representative of the optimal doping for CMR. We propose an interpretation of the spin dynamics in terms of orbital polarons. This picture is supported by the observation of a discrete magnetic energy spectrum Enmag (q) characteristic of the internal excitations of "orbital polarons" defined …
Bismuth perovskites ABiO$_3$ (A = Sr, Ba) host a variety of peculiar phenomena including bond-disproportionated insulating phases and high-temperature superconductivity upon hole doping. While the mechanisms underlying these phenomena are still debated, off-diagonal electron-phonon ($e$-ph) coupling originating from the modulation of the orbital overlaps has emerged as a promising candidate. Here, we employ classical Monte Carlo simulations to study a semiclassical three-orbital model with off-diagonal $e$-ph interactions. We demonstrate the existence of a (bi)polaron correlations that persist…
Transition metal oxides are a rich group of materials with very interesting physical properties that arise from the interplay of the charge, spin, orbital, and lattice degrees of freedom. One interesting consequence of this, encountered in systems with orbital degeneracy, is the coexistence of long range magnetic and orbital order, and the coupling between them. In this paper we develop and study an effective spin-orbital superexchange model for $e_g^3$ systems and use it to investigate the spectral properties of a charge (hole) injected into the system, which is relevant for photoemission spe…
Spin-Fluctuation-Driven Orbital Nematic Order in Ru-Oxides: Self-Consistent Vertex Correction Analysis for Two-Orbital Model
为了揭示Sr $_3$ Ru $_2$ O $_7$中“电子流体相”的起源，我们对（$d_{xz},d_{yz}$）轨道哈伯德模型进行了自洽顶点修正分析.结果表明，Aslamazov-Larkin型顶点修正导致自旋与轨道涨落之间的强耦合，对应于局域图中的Kugel-Khomskii自旋-轨道耦合.由于这一机制，在多轨道系统中，磁量子临界性诱导了具有$C_2$对称性的轨道有序，而在随机相位近似中，这一机制被忽略。本研究自然地解释了Sr $_3$、Ru $_2$ O $_7$和Fe基超导体中磁量子临界性与超导态之间的密切关系。
Orbital-lattice coupling and polaronic dressing of electronic states in Pr$_{0.5}$Ca$_{1.5}$MnO$_4$ revealed by ultrafast broadband spectroscopy
ICFO - Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology（巴塞罗那科学技术学院光子科学研究所（ICFO））；Aarhus University（奥胡斯大学）；ALBA Synchrotron Light Source（ALBA同步辐射光源）；Univ Rennes（雷恩大学）；CNRS（法国国家科学研究中心）；IMDEA Nanoscience（IMDEA纳米科学研究所）
We explore the competiton of doped holes and defects that leads to the loss of orbital order in vanadate perovskites. In compounds such as La$_{1-{\sf x}}$Ca$_{\,\sf x}$VO$_3$ spin and orbital order result from super-exchange interactions described by an extended three-orbital degenerate Hubbard-Hund model for the vanadium $t_{2g}$ electrons. Long-range Coulomb potentials of charged Ca$^{2+}$ defects and $e$-$e$ interactions control the emergence of defect states inside the Mott gap. The quadrupolar components of the Coulomb fields of doped holes induce anisotropic orbital rotations of degener…
Understanding the interplay between the structural, chemical and physical properties of nanomaterials is crucial for designing new devices with enhanced performance. In this regards, doping of metal oxides is a general strategy to tune size, morphology, charge, lattice, orbital and spin degrees of freedoms and has been shown to affect nanomaterials properties for photoelectrochemical water splitting, batteries, catalysis, magnetic applications and optics. Here we report the role of lattice small polaron in driving the morphological transition from nearly isotropic to nanowire crystals in Si do…
Fingerprints of spin-orbital polarons and of their disorder in the photoemission spectra of doped Mott insulators with orbital degeneracy
以$R_{1-x}$ Ca $_x$ VO $_3$钙钛矿为例，探讨了无序带电缺陷对掺杂过渡金属氧化物在Mott绝缘区光电发射谱中观察到的电子激发的影响，其中$R=$ La，$\dots$，Lu.这些具有部分填充的$t_{2g}$价轨道的钒$d^2$化合物的基本特征是自旋和轨道有序的持久性直到高掺杂，与高- $T_c$铜酸盐在低缺陷浓度下的磁有序的损失相反。我们证明了掺杂Mott-Hubbard绝缘体的无序电子结构可以得到高精度的非限制性Hartree-Fock近似。特别是：（i）在逆光电发射光谱和各种缺陷相关的状态和卫星的原子多重激发被很好地再现，（ii）一个强大的莫特间隙生存到大掺杂，和（iii）我们表明，莫特间隙内的缺陷状态发展一个软间隙在费米能量。软缺陷状态间隙可以通过从化学势附近的状态密度的威布尔统计采样中提取的形状和尺度参数来表征。我们证明，电荷缺陷触发小自旋轨道极化子，其内部动能负责软缺陷态间隙的开放。自旋轨道极化子的小尺寸推断的反参与比的分析，解释了起源的自旋和轨道秩序的鲁棒性。使用现实的参数为La $_{1-x}$ Ca $_x$ VO $_3$，我们表明，它的软带隙是很好地再现，以及边缘掺杂的化学势的位置相对于中心的较低的哈伯德带。
Dispersive-phonon-driven room-temperature Ni1+-Ni2+ polaron hopping in spin-charge coupled rutile niobate
Rajiv Gandhi Institute of Petroleum Technology（拉吉夫·甘地石油技术研究所）；ISIS Neutron and Muon Source, STFC, Rutherford Appleton Laboratory（ISIS中子与缪子源，STFC，卢瑟福阿普尔顿实验室）；University of Johannesburg（约翰内斯堡大学）
