Conductivity in Pseudogapped Superconductors: The Role of the Fermi Arcs

Paraconductivity of pseudogapped superconductors

We calculate Aslamazov-Larkin paraconductity $σ_{AL}(T)$ for a model of strongly disordered superconductors (dimensions $d=2,3$) with a large pseudogap whose magnitude strongly exceeds transition temperature $T_c$. We show that, within Gaussian approximation over Cooper-pair fluctuations, paraconductivity is just twice larger that the classical AL result at the same $ε= (T-T_c)/T_c$. Upon decreasing $ε$, Gaussian approximation is violated due to local fluctuations of pairing fields that become relevant at $ε\leq ε_1 \ll 1 $. Characteristic scale $ε_1 $ is much larger than the width $ε_2$ of th…

赝能隙巨磁电阻锰氧化物中的节状准粒子

Nodal quasiparticle in pseudogapped colossal magnetoresistive manganites

铜氧化物高温超导体的一个特征是在动量空间中沿着节（对角线）和反节（平行于Cu-O键）方向的电子激发之间的二分法，通常被认为与超导态的“d波”对称性有关。角分辨光电子能谱测量在超导状态下揭示了一个准粒子的光谱与d-波隙结构，表现出沿波腹方向的最大值和沿节点方向消失。随后的测量表明，在低掺杂水平下，即使在高温金属状态下，这种带隙结构仍然存在，尽管超导状态的节点以有限的“费米弧”展开。这就是所谓的赝能隙相，人们认为它与超导态密切相关，要么将其归因于波动的超导性，要么引用d波超导体的天然竞争者的顺序。在这里，我们报告的实验证据表明，一个非常相似的赝能隙状态与一个pseudogap-antinodal二分字符存在于一个系统，是显着不同的超导体：铁磁金属基态的巨磁阻双层锰氧化物La1.2Sr1.8Mn2O7。因此，我们的研究结果对铜氧化物中的赝能隙态和超导-反结二分法是超导态标志的假设提出了质疑。

欠掺杂$_{2}$ Cu $_{3}$ O $_{6.50}$的费米面弧和红外电导

Fermi surface arcs and the infrared conductivity of underdoped YBa$_{2}$Cu$_{3}$O$_{6.50}$

我们重新分析了欠掺杂$_{2}$（YBCO $_{6.50}$）的面内远红外电导率的数据，在这个模型中，赝能隙在费米面的一部分上打开，而剩余的未被覆盖的部分与温度成正比.我们的模型的动机来自于最近的角度分辨光电子能谱数据欠掺杂的Bi $_2$ Sr $_2$ CaCu $_2$ O $_{8+δ}$（Bi-2212），这揭示了费米表面上的弧的存在。我们发现的光学数据是一致的电弧形成。此外，我们发现一些证据表明，电子状态下失去的赝能隙$Δ_{pg}$恢复的能量区域，至少在$T_c$附近的温度。

Two regimes in conductivity and the Hall coefficient of underdoped cuprates in strong magnetic fields

We address recent experiments shedding light on the energy spectrum of under- and optimally doped cuprates at temperatures above superconducting transition. Angle resolved photoemission reveals coherent excitation only near nodal points on parts of the "bare" Fermi surface known as the Fermi arcs. The question debated in the literature is whether the small normal pocket, seen via quantum oscillations exists at higher temperatures or forms below a charge order transition in strong magnetic fields. Assuming the former case as possibility, expressions derived for the resistivity and the Hall coef…

Fermi arcs and pseudogap emerging from dimensional crossover at the Fermi surface in La$_{2-x}$Sr$_x$CuO$_4$

The doping mechanism and realistic Fermi surface (FS) evolution of La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) are modelled within an extensive ab-initio framework including advanced band-unfolding techniques. We show that ordinary Kohn-Sham DFT+U can reproduce the observed metal-insulator transition, when not restricted to the paramagnetic solution space. Arcs are self-doped by orbital charge transfer within the Cu-O planes, while the introduced Sr charge is strongly localized. Arc protection and the inadequacy of the rigid-band picture are consequences of a rapid change in orbital symmetry at the Fermi e…

Unconventional electronic order in a codoped high-Tc superconductor

Charge stripe order has recently been established as an important ingredient of the physics of cuprate high-T$_c$ superconductors. However, due to the complex interplay between competing phases and the influence of disorder, it is unclear how it emerges from the parent metallic state. Here we report on the discovery of an unconventional electronic ordered phase between charge-stripe order and (pseudogapped) metal in the cuprate La$_{2-x-y}$Eu$_{y}$Sr$_x$CuO$_4$ with $y = 0.2$ (LESCO). The peculiar properties of the intermediate phase are revealed through three complementary experiments: nuclea…