We report the analysis of pseudogap Delta* derived from resistivity experiments in FeAs-based superconductor SmFeAsO(0.85), having a critical temperature T_c = 55 K. Rather specific dependence Delta*(T) with two representative temperatures followed by a minimum at about 120 K was observed. Below T_s = 147 K, corresponding to the structural transition in SmFeAsO, Delta*(T) decreases linearly down to the temperature T_AFM = 133 K. This last peculiarity can likely be attributed to the antiferromagnetic (AFM) ordering of Fe spins. It is believed that the found behavior can be explained in terms of Machida, Nokura, and Matsubara (MNM) theory developed for the AFM superconductors.
The pseudogap state is one of the most enigmatic characteristics in the anomalous normal state properties of the high temperature cuprate superconductors. A central issue is to reveal whether there is a symmetry breaking and which symmetries are broken across the pseudogap transition. By performing high resolution laser-based angle-resolved photoemission measurements on the optimally-doped Bi2Sr1.6La0.4CuO6+δ superconductor, we report the observations of the particle-hole symmetry conservation in both the superconducting state and the pseudogap state along the entire Fermi surface. These resul…
The influence of the hydrostatic pressure P up to 0.95 GPa on the excess conductivity and the pseudogap Δ*(T) in optimally doped YBCO single crystals (T_c = 91.1K at ambient pressure) is investigated by electrical resistivity measurements. A pronounced enhancement of the pseudogap under pressure of dlnΔ*/dP= 0.32, which is only a factor of 1.12 smaller than in slightly doped single crystals, is revealed for the first time. This implies a somewhat more moderate increase of the coupling strength in optimally doped cuprates with increasing pressure. Simultaneously, the ratio 2Δ*(T_c)/k_BT_c=5 at …
Monotonic d-wave Superconducting Gap in Optimally-Doped Bi$_2$Sr$_{1.6}$La$_{0.4}$CuO$_6$ Superconductor by Laser-Based Angle-Resolved Photoemission Spectroscopy
利用超高分辨激光角分辨光电子能谱研究了最佳掺杂Bi $_2$ Sr $_{1.6}$ La $_{0.4}$ CuO $_6$超导体的超导能隙和赝能隙随动量和温度的变化关系。在超导状态下测得的能隙表现出标准的{ \it d}-波形。赝能隙在T $_c$以上的费米面的很大一部分打开，在结区附近形成“费米弧”。在“费米弧”以外的区域，赝能隙具有与超导态类似的能隙大小和动量依赖性，能隙随温度变化很小，在T_PDMATHABMR上没有突变。这些观测结果表明赝能隙和超导能隙是密切相关的，并支持赝能隙是超导能隙的先驱的观点。
Pseudogap-less high T$_{c}$ superconductivity in BaCo$_{x}$Fe$_{2-x}$As$_{2}$
赝能隙态是铜氧化物高温超导体的特性之一。在这里，我们调查它的存在下，在BaCo $_{x}$ Fe $_{2-x}$ As $_{2}$，一个成员的磷族元素，与温度相关的扫描隧道光谱。我们观察到，根据，最佳和过掺杂系统的隧道光谱中的间隙总是关闭在散装T $_{c}$，排除了赝隙状态的存在。对于欠掺杂的情况下，我们观察超导间隙在大视场，设置一个下限为几十纳米的长度尺度上可能的相分离区域。
Pseudogap-like phase in Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$ revealed by $^{75}$As NQR
我们报告了单晶Ca（Fe $_{1-x}$ Co $_x$）$_2$ As $_2$（$0\leq x \leq 0.09$）的$^{75}$ As NQR测量。核自旋晶格弛豫速率$T_1^{-1}$作为温度$T$和Co掺杂剂浓度$x$的函数揭示了低于交叉温度$T^*$的下和最佳掺杂区域中的正常状态赝隙状相。所得的$x$-$T$相图显示，在抑制自旋密度波阶之后，$T^*$与$T_c$相交，在最佳掺杂制度附近迅速下降到零。赝能隙行为的可能起源进行了讨论。
Novel Isotope Effects on the Pairing Pseudogap in High-$T_{c}$ Cuprates: Evidences for Polaronic Metal and Precursor BCS-Like Pairing of Large Polarons
This study focuses on the temperature and hole content dependent fluctuation diamagnetism of hole doped YBa2Cu3O7-delta (Y123) high-Tc superconductors. Two different compositions of Y123 have been considered with in-plane hole content (p): 0.161 (optimally doped) and 0.143 (underdoped). The fluctuation induced excess diamagnetic susceptibility, Delta_chi(T), has been investigated via the mean-field Gaussian-Ginzburg-Landau (MFGGL) formalism with and without a total energy cut-off in the fluctuating modes. It has been found that inclusion of total energy cut-off describes the Delta_chi(T) data …
We conducted $^{77}$Se-nuclear magnetic resonance studies of the iron-based superconductor FeSe in magnetic fields of 0.6 to 19 T to investigate the superconducting and normal-state properties. The nuclear spin-lattice relaxation rate divided by the temperature $(T_1T)^{-1}$ increases below the structural transition temperature $T_\mathrm{s}$ but starts to be suppressed below $T^*$, well above the superconducting transition temperature $T_\mathrm{c}(H)$, resulting in a broad maximum of $(T_1T)^{-1}$ at $T_\mathrm{p}(H)$. This is similar to the pseudogap behavior in optimally doped cuprate supe…
The effect of electron irradiation with the energy of 2.5 MeV on the temperature dependences of the resistivity of an optimally doped $YBa_2Cu_3O_{7-δ}$ single crystal has been studied. The temperature dependences of both fluctuation conductivity $σ^\prime(T)$ and the pseudogap $Δ^*(T)$ on irradiation dose $ϕ$ have been calculated within the local pair model. Here we show that with an increase in $ϕ$, the value of $ρ(300 K)$ increases linearly, while $T_c$ decreases linearly. Concurrently, the value of $ρ{100 K}$ increases nonlinearly, demonstrating a feature for $ϕ_3$ = 4.3 10$^{18}$ e/$cm^2$…
No anomalous spin fluctuation in optimally doped and overdoped iron-based oxypnictide superconductors LaFeAsO$_{1-x}$F$_x$ probed by muon spin relaxation
在最佳掺杂和过掺杂超导体LaFeAsO $_{1-x}$ F $_x$中进行了零场和纵向场μ子自旋弛豫测量，以研究在较宽的温度和纵向场范围内的磁涨落.在μ子的时间窗（10 $^{-5}\sim$ 10 $^{-9}$ s）内，我们没有观察到磁涨落随温度变化的迹象.考虑到目前的结果和其他结果，即，通过中子散射观察到的自旋涨落、核磁共振和光电子能谱观察到的类赝能隙行为，表明不仅自旋涨落，而且费米表面具有几种不同轨道贡献的多带特征可能在LaFeAsO $_{1-x}$ F $_x$的超导配对机制中发挥重要作用。
Intra-Unit-Cell magnetic correlations near optimal doping in $\rm YBa_2Cu_3O_{6.85}$
理解高温超导性需要先了解神秘的赝能隙金属态的性质，超导态从金属态中凝聚出来。除了最近报道的赝能隙态内的电荷自由度的电子顺序外，在各种铜酸盐中还发现了磁单元内（IUC）顺序，仅在赝能隙温度T* 下设置。在近最佳掺杂的YBa $_2$ Cu $_3$ O $_{6.85}$，极化中子散射测量，进行了两个不同的光谱仪，揭示了新的功能。该顺序是由有限大小的平面域，几乎不相关的沿c轴。在高温下，只有平面外的磁分量相关，揭示了一个强大的伊辛各向异性，最初预测的环路电流模型。在T* 以下，相关的面内响应发展，在低温下引起磁矩的明显倾斜。这两种机制的发现对IUC有序的内在性质提出了严格的限制，与赝能隙物理紧密相连。
We present an extended zero-field muon spin relaxation (ZF-$μ$SR) study of overdoped Bi$_{2+x}$Sr$_{2-x}$CaCu$_2$O$_{8+δ}$ (Bi2212) single crystals, intended to elucidate the origin of weak quasistatic magnetism previously detected by $μ$SR in the superconducting and normal states of optimally-doped and overdoped samples. New results on heavily-overdoped single crystals show a similar monotonically decreasing ZF-$μ$SR relaxation rate with increasing temperature that persists above the pseudogap (PG) temperature $T^*$ and does not evolve with hole doping ($p$). Additional measurements using an …
We first present detailed measurements of the rounding behavior around the superconducting transition temperature, $T_c$, of the in-plane electrical conductivity, magnetoconductivity and magnetization, including the low and moderate magnetic field regimes, in a high-quality single crystal and a thin film of the prototypical optimally-doped YBa$_2$Cu$_3$O$_{7-δ}$ (OPT Y-123), in which the inhomogeneity effects are minimized. Then, it is presented a comparison of these experimental data with the phenomenological Ginzburg-Landau (GL) approach that takes into account the unavoidable contribution o…
Tunneling spectra of submicron Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ intrinsic Josephson junctions: evolution from superconducting gap to pseudogap
本文给出了近最佳掺杂亚微米Bi $_2$ Sr $_2$ CaCu $_2$ O $_{8+δ}$本征约瑟夫森结的隧穿谱，并在超导能隙演变为赝能隙的区域进行了研究。使用Norman { \it et al.}提出的自能模型分析光谱，其中考虑了准粒子散射率$Γ$和对衰变率$Γ_Δ$。从该模型导出的态密度具有熟悉的Dynes形式，其中用$γ_+$ =（$Γ$ + $Γ_Δ$）/2简单地替换$Γ$。通过拟合实验光谱得到的$γ_+$参数显示出大致线性的温度依赖性，这对$Γ$和$Γ_Δ$之间的关系提出了很强的约束。我们从隧穿和角分辨光电子能谱实验中讨论和比较了赝能隙相中的费米弧行为。我们的结果表明，两个实验之间的一个很好的协议，这是有利于前体配对的赝能隙的观点。
By measuring the polarization changes in THz, infrared, and visible radiation over an extended energy range (3-2330 meV), we observe symmetry-breaking in cuprate high temperature superconductors over wide energy, doping, and temperature ranges. We measure the polarization rotation and ellipticity of transmitted radiation though thin films as the sample is rotated. We observe a two-fold rotational symmetry in the Faraday angle, which is associated with linear dichroism (LD) and occurs when electromagnetic radiation polarized along one direction is absorbed more strongly than radiation polarized…
