我们发现，由于Dzyaloshinskiii-Moriya和XY各向异性，在绝缘的La $_{2-x}$ Sr $_x$ CuO $_4$中的无序对角自旋螺旋产生的对角电荷密度波（CDW）的波矢量的自旋螺旋的两倍。CDW的振幅取决于各向异性的值、掺杂水平和化学势下的态密度。基于现有的实验数据，我们估计，对于4%的掺杂，CDW的振幅约为掺杂水平的1/10。我们认为这一机制解释了最近在Zn共掺杂的La $_{2-x}$ Sr $_x$ CuO $_4$中观察到的CDW。
英文摘要：
We show that, due to the Dzyaloshinskii-Moriya and the XY anisotropies, the disordered diagonal spin spiral in the insulating La$_{2-x}$Sr$_x$CuO$_4$ generates a diagonal charge density wave (CDW) with the wave vector twice of that of the spin spiral. The amplitude of the CDW depends on values of the anisotropies, the doping level, and on the density of states at the chemical potential. Based on available experimental data we estimate that for 4% doping the amplitude of CDW is about 1/10 of the doping level. We believe that this mechanism explains the CDW observed recently in Zn-codoped detwinned La$_{2-x}$Sr$_x$CuO$_4$.
In contrast to the "Pr-issue" that neither PrBa2Cu3O7 (Pr123) nor PrBa2Cu4O8 (Pr124) shows superconductivity (SC), we have observed 100%-fraction of SC in an oxygen-reduced Pr2Ba4Cu7O(15-delta) (Pr247) which has a hybrid structure that Pr247 = Pr123 + Pr124. It is found that Cu nuclear-spin signals from the CuO2 planes observed at 300K are completely wiped out down at 2K. Instead, plane signals at 2K are observed at higher frequencies. This indicates that, despite the bulk SC, the CuO2 planes in Pr247 are found to be in an insulating and antiferromagnetically ordered state.
Understanding the complex phase diagram of cuprate superconductors is an outstanding challenge. The most actively studied questions surround the nature of the pseudogap and strange metal states and their relationship to superconductivity. In contrast, there is general agreement that the low energy physics of the Mott insulating parent state is well captured by a two-dimensional spin $S$ = 1/2 antiferromagnetic (AFM) Heisenberg model. However, recent observations of a large thermal Hall conductivity in several parent cuprates appear to defy this simple model and suggest proximity to a magneto-c…
The transition temperature $T_\textrm{c}$ of unconventional superconductivity is often tunable. For a monolayer of FeSe, for example, the sweet spot is uniquely bound to titanium-oxide substrates. By contrast for La$_{2-\mathrm{x}}$Sr$_\mathrm{x}$CuO$_4$ thin films, such substrates are sub-optimal and the highest $T_\textrm{c}$ is instead obtained using LaSrAlO$_4$. An outstanding challenge is thus to understand the optimal conditions for superconductivity in thin films: which microscopic parameters drive the change in $T_\mathrm{c}$ and how can we tune them? Here we demonstrate, by a combinat…
The pseudogap phenomenon in cuprates is the most mysterious puzzle in the research of high-temperature superconductivity. In particular, whether the pseudogap is associated with a crossover or phase transition has been a long-standing controversial issue. The tetragonal cuprate HgBa$_2$CuO$_{4+δ}$, with only one CuO$_2$ layer per primitive cell, is an ideal system to tackle this puzzle. Here, we measure the anisotropy of magnetic susceptibility within the CuO$_2$ plane with exceptionally high-precision magnetic torque experiments. Our key finding is that a distinct two-fold in-plane anisotropy…
We present results from light scattering experiments on three insulating antiferromagnetic cuprates, YBa$_2$Cu$_3$O$_{6.05}$, Bi$_2$Sr$_2$YCu$_2$O$_{8+δ}$, and La$_2$CuO$_4$ as a function of polarization and excitation energy {using samples of the latest generation. From the raw data we derive symmetry-resolved spectra.} The spectral shape in $B_{1g}$ symmetry is found to be nearly universal and independent of the excitation energy. The spectra agree quantitatively with predictions by field theory [\onlinecite{Weidinger:2015}] facilitating the precise extraction of the Heisenberg coupling $J$.…
We present an $\textit{ab initio}$ study of the excitonic states of a prototypical high-temperature superconductor La$_2$CuO$_4$ and compare them to the isostructural single-layer nickelate La$_2$NiO$_4$. Key difference in the low-energy electronic structure leads to very different excitonic behavior. Excitons in La$_2$CuO$_4$ are delocalized and can freely move in the CuO$_2$ plane without disturbing the antiferromagnetic order. In contrast, in La$_2$NiO$_4$ we find the low-lying excitonic states to be extremely localized, producing a nearly flat dispersion. The theoretically obtained exciton…
Anisotropic dressing of charge-carriers in the electron-doped cuprate superconductor Sm(1.85)Ce(0.15)CuO(4) from angle-resolved photoemission measurements
最近在Pr $_{2}$ Ba $_{4}$ Cu $_{7}$ O $_{15-δ}$中发现了超导电性，其最大值$T_c$约为15K。由于这种材料中的CuO平面被认为是绝缘的，因此已经提出超导性发生在双（或锯齿形）CuO链层中。唯象的理由，我们提出了一个理论解释的实验结果在一个新的阶段的锯齿形链，标记为C $_1$ S $_{3/2}$。这个阶段有一个相对的自旋和电荷模式的间隙，但没有总的自旋间隙，并可以有一个发散的超导排斥相互作用的磁化率。提出了一个锯齿形CuO链的微观模型，并在此模型的密度矩阵重整化群（DMRG）和玻色化研究的基础上，给出了支持这一观点的证据.
Strongly correlated insulators are broadly divided into two classes: Mott-Hubbard insulators, where the insulating gap is driven by the Coulomb repulsion $U$ on the transition-metal cation, and charge-transfer insulators, where the gap is driven by the charge transfer energy $Δ$ between the cation and the ligand anions. The relative magnitudes of $U$ and $Δ$ determine which class a material belongs to, and subsequently the nature of its low-energy excitations. These energy scales are typically understood through the local chemistry of the active ions. Here we show that the situation is more co…
We performed systematic angle-resolved photoemission spectroscopy measurements $in$-$situ$ on $T'$-${\rm La}_{2-x}{\rm Ce}_x\rm {CuO}_{4\pmδ}$ (LCCO) thin films over the extended doping range prepared by the refined ozone/vacuum annealing method. Electron doping level ($n$), estimated from the measured Fermi surface volume, varies from 0.05 to 0.23, which covers the whole superconducting dome. We observed an absence of the insulating behavior around $n \sim$ 0.05 and the Fermi surface reconstruction shifted to $n \sim$ 0.11 in LCCO compared to that of other electron-doped cuprates at around 0.…
Evolution of Fermi surface and normal-state gap in chemically substituted cuprates Bi$_{2}$Sr$_{2-x}$Bi$_{x}$CuO$_{6+δ}$
我们对化学取代的铜酸盐Bi $_{2}$ Sr $_{2-x}$ Bi $_{x}$ CuO $_{6+δ}$进行了系统的角分辨光电子能谱研究。我们观察到费米表面积与Bi取代含量$x$线性收缩，反映了这种化学取代的电子掺杂性质。此外，谱线宽度随着$x$的增加而迅速加宽，并且在超导-绝缘边界处变得完全不相干。在轻欠掺杂区观察到的d波状正常态带隙逐渐演变成大的软带隙，这在激发能量和温度方面线性地抑制了波腹光谱权重。结合在相同样品上获得的体电阻率数据，我们建立了在非常欠掺杂制度的库仑隙行为的出现。我们的研究结果揭示了高$T_c$铜酸盐中离面化学取代的双重作用，即掺杂和无序，并阐明了强关联和无序导致的量子电子态的本质.
Frustration-induced insulating chiral spin state in itinerant triangular-lattice magnets
结合精确对角化和Monte-Carlo方法，研究了三角格子上具有竞争超交换作用的半满双交换模型。我们发现，在预期的巡回铁磁和$120^{\circ}$ Yafet-Kittel阶段之间的一个强大的标量手性，绝缘自旋状态出现。在有限温度下，铁磁体标量手征量子临界点的特征是在阻挫巡游磁体R $_2$ Mo $_{2}$ O $_7$中观察到的电荷输运中的异常坏金属行为.
Strongly correlated electrons in layered perovskite structures have been the birthplace of high-temperature superconductivity, spin liquid, and quantum criticality. Specifically, the cuprate materials with layered structures made of corner sharing square planar CuO$_4$ units have been intensely studied due to their Mott insulating grounds state which leads to high-temperature superconductivity upon doping. Identifying new compounds with similar lattice and electronic structures has become a challenge in solid state chemistry. Here, we report the hydrothermal crystal growth of a new copper tell…
The large thermal Hall conductivity recently detected in Mott insulating cuprates has been attributed to chiral neutral spin excitations. A quantum spin liquid with Majorana excitations, Chern number +/-4 and large thermal Hall conductivity is found to be an excited state of a frustrated Heisenberg model on the square lattice. Using a Majorana mean-field theory and exact diagonalizations, we explore two possible routes to achieve this chiral quantum spin liquid, an orbital effect of an applied magnetic field and spin orbit couplings as present in cuprates. In particular, we show how only the o…
Extensive infrared spectroscopic study of CuO: signatures of strong spin-phonon interaction and structural distortion
Optical properties of single-crystal monoclinic CuO in the range 70 - 6000 \cm were studied at temperatures from 7 to 300 K. Normal reflection spectra were obtained from the (001) and (010) crystal faces thus giving for the first time separate data for the $A_{u}$ and $B_{u}$ phonon modes excited in the purely transverse way (TO modes). Mode parameters, including polarizations of the $B_{u}$ modes not determined by the crystal symmetry, were extracted by the dispersion analysis of reflectivity curves as a function of temperature. Spectra of all the components of the optical conductivity tensor…
