Investigation of energy gap and observation of electron-phonon interaction in high-temperature superconductor $La_{1.8}Sr_{0.2}CuO_{4}$ - normal metal point contacts
I. K. Yanson, L. F. Rybal'chenko, V. V. Fisun, N. L. Bobrov, M. A. Obolenskii, Yu. D. Tret'yako, A. R. Kaul', I. E. Graboi
Electrical characteristics $(I(eV), dV/dI(eV), d^{2}V/dI^{2}(eV))$ are studied comprehensively for pressed submicron point contacts between fresh fractures of LaSrCuO ceramic pellets and a normal metal (Cu). Point contacts (PC) with the direct-type conductivity are investigated, which are characterized by a considerable excess current due to Andreev reflection of quasiparticles at an NS boundary of high transparency. Basic requirements for point contacts suitable for PC measurements are formulated. The models of investigated point contacts permitting the interpretation of the observed characteristics are considered. The results of measurement of the energy gap reveal that LaSrCuO is a superconductor with a strong coupling since the maximum value of the ratio $2Δ/kT\simeq 11$. It is found that superconducting properties may vary appreciably over distances of several tens of angstroms, resulting in some cases in the simultaneous emergence of two gaps corresponding to two critical temperatures. The $dV/dI(eV)$ and $d^{2}V/dI^{2}(eV)$ curves display some high-intensity singularities whose position on the eV-axis is practically independent of temperature and correlates with the phonon spectrum obtained in neutron scattering experiments. This points to a strong electron-phonon interaction in LaSrCuO.
The study of electronic nematicity in an overdoped (Bi, Pb)$_2$Sr$_2$CuO$_{6+δ}$ superconductor using scanning tunneling spectroscopy
赝能隙（PG）态及其相关的晶胞内对称性破缺一直是铜氧化物超导体研究的热点。虽然在$_2$ $_2$ O $_{8+δ}$，特别是欠掺杂样品中已经研究了向列性，但是它在其他铜酸盐和不同掺杂区域中的行为仍然不清楚。在这里，我们应用扫描隧道显微镜探索过掺杂（Bi，Pb）$_2$ Sr $_2$ CuO $_{6+δ}$与一个大的费米面（FS）。当能量尺度接近PG时，可以看到一个有序的建立及其实空间分布。
Doping dependence of the vortex glass and sublimation transitions in the high-$T_{c}$ superconductor La$_{2-x}$Sr$_{x}$CuO$_{4}$ as determined from macroscopic measurements
磁化强度和交流磁化率测量用于表征高温铜酸盐超导体La $_{2-x}$ Sr $_{x}$ CuO $_{4}$在大范围的掺杂（0.075 $\leq x\leq$ 0.20）的混合相。研究了高磁场（垂直于$CuO_2$面施加8特斯拉）下的一级涡旋晶格相变线$H_{FOT}(T)$、上临界场$H_{c2}(T)$和第二峰$H_{sp}(T)$。我们的研究结果揭示了一个强大的掺杂依赖的磁相图，这主要可以解释与欠掺杂的各向异性增加。在我们的解释，第一阶涡晶格相变是由于升华（而不是熔化）的涡晶格成气体的煎饼涡，而第二个峰值是有关的过渡到一个更无序的涡玻璃态。
Two-dimensional weak localization effects in high temperature superconductor Nd{2-x}Ce{x}CuO{4-d}
A systematic study of the resistivity and Hall effect in single crystal Nd{2-x}Ce{x}CuO{4-d} films (0.12 < x < 0.20) is presented, with special emphasis on the low-temperature dependence of the normal state conductance. Two-dimensional weak localization effects are found both in a normally conducting underdoped sample (x = 0.12) and in situ superconducting optimally doped (x = 0.15) or overdoped (x = 0.18) samples in a high magnetic field B > B{c2}. The phase coherence time and the effective thickness of a CuO{2} conducting layer {d} (~ 1.5 A) have been estimated by fitting 2D weak localizatio…
Shubnikov-de Haas quantum oscilations reveal a reconstructed Fermi surface near optimal doping in a thin film of the cuprate superconductor Pr$_{1.86}$Ce$_{0.14}$CuO$_{4\pmδ}$
Comment on "Low-temperature phonon thermal conductivity of single-crystalline Nd_{2}CuO_{4}: Effects of sample size and surface roughness" by Li et al.
在这篇评论中，我们表明Li { \it et al.}（Phys. Rev. B { \bf 77}，134501（2008））不支持高T_c铜酸盐在低温下的声子镜面反射，因为对于Nd_{2} CuO_{4}和YBa_{2} Cu_{3} O_{6.0}单晶两者，从其热导率数据计算的声子平均自由程\ell远小于高于\sim 100 mK的平均样品宽度。
Reply to "Comment on `Low-temperature phonon thermal conductivity of single-crystalline Nd$_2$CuO$_4$: Effects of sample size and surface roughness' " by Sun et al
Proof of bulk charge ordering in the CuO$_2$ plane of the cuprate superconductor YBa$_2$Cu$_3$O$_{6.9}$ by high pressure NMR
铜氧化物超导体仍然有许多悬而未决的问题，特别是关于它们的正常状态属性，包括电荷有序的作用。在CuO $_2$平面中的$^{63,65}$ Cu和$^{17}$ O上的核磁共振是电荷变化的非常灵敏的本体探针，但未被正确理解。从早期的核磁共振谱来看，YBa $_2$ Cu $_3$ O $_{6+y}$中氧卫星线的分裂是由于正交畸变引起的，同时也可能是由于电荷有序化引起的.我们采用高压NMR对YBa $_2$ Cu $_3$ O $_{6.9}$，希望电荷顺序将响应不同的压力比化学晶格。这就是我们所发现的，我们证明了存在的电荷排序，即使在环境条件下。随着压力的增加，我们可以遵循它的局部对称性和振幅作为温度的函数。我们的发现与迄今为止报道的其他技术不同，但也显示出相似之处，将进行讨论。我们还提供了证据，从文献NMR数据表明，这种电荷排序是普遍存在的CuO $_2$平面。
Hybrid Crystals of Cuprates and Iron-Based Superconductors
我们提出了两种可能的新化合物，Ba $_2$ CuO $_2$ Fe $_2$ As $_2$和K $_2$ CuO $_2$ Fe $_2$ Se $_2$，它们混合了两种高温超导体，铜酸盐和铁基超导体的构建块。这些化合物由正方形CuO $_2$层和反萤石型Fe $_2$ X $_2$（X=As，Se）层组成，中间由Ba/K隔开。结合能和声子谱的计算表明，它们是动态稳定的，这保证了它们可以在实验上合成。这两种化合物的费米面和电子结构继承了铜酸盐和铁基超导体的特征。这些化合物可以是具有有趣的物理性质的超导体，以帮助确定高$T_c$超导性的配对机制。
Two characteristic energies in the low-energy antiferromagnetic response of the electron-doped high-temperature superconductor Nd$_{2-x}$Ce$_x$CuO$_{4+δ}$
The hidden competing phase revealed by first-principles calculations of phonon instability in the nearly optimally doped cuprate La$_{1.875}$Sr$_{0.125}$CuO$_4$
通过第一性原理计算研究了具有代表性的铜氧化物La $_{2-x}$ M $_x$ CuO $_4$（M = Sr）和$x = 1/8$的高温四方晶系（HTT）、低温正交晶系（LTO）和低温少正交晶系（LTLO）结构。通过抑制磁性和超导电性，发现在$_{2-x}$ CuO $_4$中很少观察到的LTLO相为基态，其中结构相变HTT $\rightarrow$ LTO $\rightarrow$ LTLO可以通过声子不稳定性来理解.虽然La-O组合物被确定为负责声子软化，超导CuO $_2$层是动态稳定的。的LTLO阶段，它可以表现出$\sim$ 20毫电子伏分裂的状态密度，提出了与所观察到的赝能隙和电荷密度波给出的条纹有密切的关系。我们认为，在低温下，超导LTO La $_{1.875}$ Sr $_{0.125}$ CuO $_4$竞争的声子优先LTLO相自发地形成库珀对，从而抑制条纹。因此，揭示的LTLO相对于理解La $_{2-x}$ Sr $_x$ CuO $_4$是必不可少的。
Transport and spectroscopic properties of superconductor - ferromagnet - superconductor junctions of $La_{1.9}Sr_{0.1}CuO_4$ - $La_{0.67}Ca_{0.33}MnO_3$ - $La_{1.9}Sr_{0.1}CuO_4$
Charge-density-wave order takes over antiferromagnetism in Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6}$ superconductors
当自旋序被破坏时，铜氧化物中出现超导性，而电荷的作用则鲜为人知。最近，电荷密度波（CDW）被发现低于超导圆顶在YBa $_2$ Cu $_3$ O $_y$当施加一个高磁场垂直于CuO $_2$平面，这被认为是产生初始CDW的涡核，成为重叠。在这里，通过$^{63}$ Cu-核磁共振，我们报告了在单层Bi $_2$ Sr $_{2-x}$ La $_x$ CuO $_6$中，由不在平面中产生涡核的面内场诱导的CDW的发现。起始温度$T_{\rm CDW}$接管反铁磁有序温度$T_{\rm N}$，超过临界掺杂水平，超导性开始出现，并与伪能隙温度$T^{*}$成比例。这些结果提供了重要的见解自旋序，CDW和赝能隙之间的关系，以及它们与高温超导性的联系。
Charge Order Lock-in by Electron-Phonon Coupling in La$_{1.675}$Eu$_{0.2}$Sr$_{0.125}$CuO$_4$
本文报道了条形有序铜氧化物La $_{1.675}$ Eu $_{0.2}$ Sr $_{0.125}$ CuO $_4$的面内键伸缩声子模的高分辨共振非弹性X射线散射（RIXS）研究.声子软化和寿命缩短被发现周围的电荷有序波矢量。除了这些自能效应，电子-声子耦合探测其比例的RIXS截面。我们发现，在冷却到低温四元结构相时，电荷条纹有序波矢周围的电子-声子耦合增强。这些结果表明，除了电子关联，电子-声子耦合显着的铜酸盐的长程电荷条纹秩序的出现。
