Thermopower across the pseudogap critical point of La(1.6-x)Nd(0.4)Sr(x)CuO(4): Evidence for a quantum critical point in a hole-doped high-Tc superconductor
R. Daou, Olivier Cyr-Choinière, Francis Laliberté, David LeBoeuf, Nicolas Doiron-Leyraud, J. -Q. Yan, J. -S. Zhou, J. B. Goodenough, Louis Taillefer
备注：
4 pages, 4 figures; Fig.1 updated to include pseudogap temperature from recent ARPES data
The thermopower S of the high-Tc superconductor La(1.6-x)Nd(0.4)Sr(x)CuO(4) was measured as a function of temperature T near its pseudogap critical point, the critical hole doping p* where the pseudogap temperature T* goes to zero. Just above p*, S/T varies as ln(1/T) over a decade of temperature. Below p*, S/T undergoes a large increase below T*. As with the temperature dependence of the resistivity, which is linear just above p* and undergoes a large upturn below T*, these are typical signatures of a quantum phase transition. This suggests that p* is a quantum critical point below which some order sets in, causing a reconstruction of the Fermi surface, whose fluctuations are presumably responsible for the linear-T resistivity and logarithmic thermopower. We discuss the possibility that this order is the "stripe" order known to exist in this material.
We report thermopower measurements under hydrostatic pressure on the cuprate superconductor La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ (Nd-LSCO), at low-temperature in the normal state accessed by suppressing superconductivity with a magnetic field up to $H = 31$ T. Using a newly developed AC thermopower measurement technique suitable for high pressure and high field, we track the pressure evolution of the Seebeck coefficient $S$. At ambient pressure and low temperature, $S/T$ was recently found to suddenly increase in Nd-LSCO at the pseudogap critical doping $p^{\star} = 0.23$, consistent with a dro…
Two pseudogaps with different energy scales at the antinode of the high-temperature Bi$_2$Sr$_2$CuO$_6$ superconductor using angle-resolved photoemission spectroscopy
我们已经进行了高分辨率角分辨光电子能谱的单层铜酸盐Bi $_2$ Sr $_2$ CuO $_6$澄清的赝能隙的起源。通过使用不同的光子能量，我们已经成功地直接观察到两个不同的赝能隙与两个不同的能量尺度共存的波腹区域：一个反映了$d_{x^2-y^2}$波配对强度，而另一个具有较大的能量尺度，表明起源不同于超导。观察到的双赝能隙行为提供了一个关键，以充分理解赝能隙现象的铜酸盐。
Antiferromagnetic correlations have been argued to be the cause of the d-wave superconductivity and the pseudogap phenomena exhibited by the cuprates. Although the antiferromagnetic response in the pseudogap state has been reported for a number of compounds, there exists no information for structurally simple HgBa$_2$CuO$_{4+δ}$. Here we report neutron scattering results for HgBa$_2$CuO$_{4+δ}$ (superconducting transition temperature T$_c$ $\sim$ 71 K, pseudogap temperature T* $\sim$ 305 K) that demonstrate the absence of the two most prominent features of the magnetic excitation spectrum of t…
Observation of vortices and hidden pseudogap from scanning tunneling spectroscopic studies of electron-doped cuprate superconductor $Sr_{0.9}La_{0.1}CuO_2$
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…
Superconductivity distorted by the coexisting pseudogap in the antinodal region of Bi$_{1.5}$Pb$_{0.55}$Sr$_{1.6}$La$_{0.4}$CuO$_{6+δ}$: A photon-energy-dependent angle-resolved photoemission study
超导电性和赝能隙之间的相互作用是铜氧化物物理的一个重要方面。然而，赝能隙的性质仍然存在争议，部分原因是不同的实验提出了不同的能隙函数。本文采用光子能量依赖角分辨光电子能谱（ARPES）研究了Bi $_{1.5}$ Pb $_{0.55}$ Sr $_{1.6}$ La $_{0.4}$ CuO $_{6+δ}$ .我们发现，在低光子能量的反节ARPES谱是由背景信号，这可能会导致一个错误的评估的光谱间隙的大小占主导地位。一旦背景是适当的占，独立的光子能量，在不同的能量下，主要归因于赝能隙和超导性，以及偏离一个简单的d-波形式的整体光谱间隙的波腹光谱鲁棒地显示两个共存的功能。这些结果支持了赝能隙和超导性之间的竞争导致能隙畸变的观点。
The specific heat $C$ of the single-layer cuprate superconductor HgBa$_2$CuO$_{4 + δ}$ was measured in an underdoped crystal with $T_{\rm c} = 72$ K at temperatures down to $2$ K in magnetic fields up to $35$ T, a field large enough to suppress superconductivity at that doping ($p \simeq 0.09$). In the normal state at $H = 35$ T, a residual linear term of magnitude $γ= 12 \pm 2$ mJ/K$^2$mol is observed in $C/T$ as $T \to 0$, a direct measure of the electronic density of states. This high value of $γ$ has two major implications. First, it is significantly larger than the value measured in overd…
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。
The specific heat $C$ of the cuprate superconductors La$_{2-x}$Sr$_x$CuO$_4$ and Bi$_{2+y}$Sr$_{2-x-y}$La$_x$CuO$_{6+δ}$ was measured at low temperature (down to $0.5~{\rm K}$), for dopings $p$ close to $p^\star$, the critical doping for the onset of the pseudogap phase. A magnetic field up to $35~{\rm T}$ was applied to suppress superconductivity, giving direct access to the normal state at low temperature, and enabling a determination of $C_e$, the electronic contribution to the normal-state specific heat, at $T \to 0$. In La$_{2-x}$Sr$_x$CuO$_4$ at $x=p = 0.22$, $0.24$ and $0.25$, $C_e / T …
The Seebeck coefficient (thermopower) $S$ of the cuprate superconductor La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ was measured across its doping phase diagram (from $p = 0.12$ to $p = 0.25$), at various temperatures down to $T \simeq 2$ K, in the normal state accessed by suppressing superconductivity with a magnetic field up to $H = 37.5$ T. The magnitude of $S/T$ in the $T=0$ limit is found to suddenly increase, by a factor $\simeq 5$, when the doping is reduced below $p^{\star} = 0.23$, the critical doping for the onset of the pseudogap phase. This confirms that the pseudogap phase causes a large …
A study of the ferromagnetic transition of $SrRuO_3$ in nanometer thick bilayers with $YBa_2Cu_3O_y$, $La_{1.88}Sr_{0.12}CuO_{4-y}$, Au and Cr: Signature of injected carriers in the pseudogap regime
The electrical resistivity $ρ$ and Hall coefficient R$_H$ of the tetragonal single-layer cuprate Nd-LSCO were measured in magnetic fields up to $H = 37.5$ T, large enough to access the normal state at $T \to 0$, for closely spaced dopings $p$ across the pseudogap critical point at $p^\star = 0.235$. Below $p^\star$, both coefficients exhibit an upturn at low temperature, which gets more pronounced with decreasing $p$. Taken together, these upturns show that the normal-state carrier density $n$ at $T = 0$ drops upon entering the pseudogap phase. Quantitatively, it goes from $n = 1 + p$ at $p = …
The nature of the pseudogap phase of cuprates remains a major puzzle. One of its new signatures is a large negative thermal Hall conductivity $κ_{\rm xy}$, which appears for dopings $p$ below the pseudogap critical doping $p^*$, but whose origin is as yet unknown. Because this large $κ_{\rm xy}$ is observed even in the undoped Mott insulator La$_2$CuO$_4$, it cannot come from charge carriers, these being localized at $p = 0$. Here we show that the thermal Hall conductivity of La$_2$CuO$_4$ is roughly isotropic, being nearly the same for heat transport parallel and normal to the CuO$_2$ planes,…
Andreev reflection in Au/La_{2-x}Sr_{x}CuO_{4} point-contact junctions: separation between pseudogap and phase-coherence gap
我们用Au探针在0.08 < x < 0.20的La_{2-x} Sr_{x} CuO_{4}样品上进行了点接触测量，研究了超导能隙与赝能隙的关系。在4.2 K ~ T_c^A的温度范围内，结的电导曲线呈现典型的Andreev反射特征，与体相T_c相近。如果使用（s+d）波隙对称性，则它们与BTK-Tanaka-Kashiwaya模型的拟合给出了良好的结果。低温主导的各向同性带隙分量Delta_{s}的掺杂依赖性非常好地遵循T_{c}对x曲线。这些结果支持了角分辨光电子能谱（ARPES）和隧穿测量的超导（Andreev）带隙和赝带隙之间的分离。
Electron Dynamics in Nd$_{1.85}$Ce$_{.15}$CuO$_{4+δ}$: Evidence for the Pseudogap State and Unconventional c-axis Response
红外反射率的测量与光偏振沿a-和c-轴的超导和反铁磁相的电子掺杂的Nd $_{1.85}$ Ce $_{.15}$ CuO $_{4+δ}$。结果进行了比较，在空穴掺杂铜酸盐的电磁响应的特性。在CuO $_2$平面内，依赖于频率的散射速率1/ $τ(ω)$被压低到$\sim$ 650 cm $^{-1}$以下;这种行为是赝能隙态的标志。虽然在几个空穴掺杂的化合物的赝能隙和超导态的能量标度是相当接近的，我们能够表明，在Nd $_{1.85}$ Ce $_{.15}$ CuO $_{4+δ}$的两个规模相差超过一个数量级。面内电荷响应的另一个特征是在50-110 cm $^{-1}$处的电导率实部中的峰值$σ_1(ω)$，这与其中$σ_1(ω)$以$ω=0$为中心的Drude样响应形成鲜明对比。后者的效果是类似于在无序的空穴掺杂的铜氧化物中发现的，并在载流子本地化的上下文中进行了讨论。对c轴电导率的研究证明了层间超流体在一个非常宽的频率范围内聚集。Nd $_{1.85}$ Ce $_{.15}$ CuO $_{4+δ}$中的赝能隙态以及电荷动力学的其他特征的令人信服的证据表明，铜氧化物相图在电子和空穴掺杂方面具有全局相似性。
Evolution of the resistivity anisotropy in Bi_{2}Sr_{2-x}La_{x}CuO_{6+δ} single crystals for a wide range of hole doping
To elucidate how the temperature dependence of the resistivity anisotropy of the cuprate superconductors changes with hole doping, both the in-plane and the out-of-plane resistivities (ρ_{ab} and ρ_{c}) are measured in a series of high-quality Bi_{2} Sr_{2-x} La_{x} CuO_{6+δ} (BSLCO) single crystals for a wide range of x (x = 0.23 - 1.02), which corresponds to the hole doping per Cu, p, of 0.03 - 0.18. The anisotropy ratio, ρ_{c}/ρ_{ab}, shows a systematic increase with decreasing p at moderate temperatures, except for the most underdoped composition where the localization effect enhances ρ_{a…
Charge modulations are considered as a leading competitor of high-temperature superconductivity in the underdoped cuprates, and their relationship to Fermi surface reconstructions and to the pseudogap state is an important subject of current research. Overdoped cuprates, on the other hand, are widely regarded as conventional Fermi liquids without collective electronic order. For the overdoped (Bi,Pb)2.12Sr1.88CuO6+δ (Bi2201) high-temperature superconductor, here we report resonant x-ray scattering measurements revealing incommensurate charge order reflections, with correlation lengths of 40-60…
Five transport coefficients of the cuprate superconductor Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+δ}$ were measured in the normal state down to low temperature, reached by applying a magnetic field (up to 66T) large enough to suppress superconductivity. The electrical resistivity, Hall coefficient, thermal conductivity, Seebeck coefficient and thermal Hall conductivity were measured in two overdoped single crystals, with La concentration $x = 0.2$ ($T_{\rm c}=18$K) and $x = 0.0$ ($T_{\rm c}=10$K). The samples have dopings $p$ very close to the critical doping $p^{\star}$ where the pseudogap phase ends. …
利用扫描隧道显微镜（STM）研究了高温超导体$_2$ O $_2$的解理面，发现一维CuO链中存在电荷密度波（CDW）调制.在同一时间，没有签名的CDW已被报道的光谱功能的链带先前研究的光电发射。我们使用软X射线角分辨光电子能谱（SX-ARPES）来检测在以前的工作中没有检测到的链衍生的表面带。发现新表面带的$2k_\textup{F}$为0.55 π，ε $^{-1}$，这与STM在直接空间中观察到的CDW波矢量相匹配。这揭示了费米面嵌套的相关性的CuO链中的CDW的形成在YBa $_2$ Cu $_2$ O $_{7-δ}$。与CDW顺序的短程性质的协议，新检测到的表面带表现出赝能隙，其能量尺度也对应于STM观察到的。
We use resonant inelastic x-ray scattering to investigate charge-stripe correlations in La$_{1.675}$Eu$_{0.2}$Sr$_{0.125}$CuO$_4$. By differentiating elastic from inelastic scattering, it is demonstrated that charge-stripe correlations precede both the structural low-temperature tetragonal phase and the transport-defined pseudogap onset. The scattering peak amplitude from charge stripes decays approximately as $T^{-2}$ towards our detection limit. The in-plane integrated intensity, however, remains roughly temperature independent. Therefore, although the incommensurability shows a remarkably l…
We use the Nernst effect to delineate the boundary of the pseudogap phase in the temperature-doping phase diagram of cuprate superconductors. New data for the Nernst coefficient $ν(T)$ of YBa$_{2}$Cu$_{3}$O$_{y}$ (YBCO), La$_{1.8-x}$Eu$_{0.2}$Sr$_x$CuO$_4$ (Eu-LSCO) and La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ (Nd-LSCO) are presented and compared with previous data including La$_{2-x}$Sr$_x$CuO$_4$ (LSCO). The temperature $T_ν$ at which $ν/T$ deviates from its high-temperature behaviour is found to coincide with the temperature at which the resistivity deviates from its linear-$T$ dependence, which…
Evolution of the electronic state through the reduction annealing in electron-doped Pr_1.3-x_La_0.7_Ce_x_CuO_4+delta_ (x=0.10) single crystals: Antiferromagnetism, Kondo effect and superconductivity
The oxygen isotope ($^{16}$O/$^{18}$O) effect (OIE) on the pseudogap (charge-stripe ordering) temperature $T^{\ast}$ is investigated for the cuprate superconductor La$_{2-x}$Sr$_{x}$CuO$_{4}$ as a function of doping $x$ by means of x-ray absorption near edge structure (XANES) studies. A strong $x$ dependent and sign reversed OIE on $T^{\ast}$ is observed. The OIE exponent $α_{T^{\ast}}$ systematically decreases from $α_{T^{\ast}} = - 0.6(1.3)$ for $x = 0.15$ to $α_{T^{\ast}} = - 4.4(1.1)$ for $x = 0.06$, corresponding to increasing $T^{\ast}$ and decreasing superconducting transition temperatu…
In the quest to understand high-temperature superconductivity in copper oxides, a vigorous debate has been focused on the pseudogap - a partial gap that opens over portions of the Fermi surface in the 'normal' state above the bulk critical temperature ($T_{c}$). The pseudogap has been attributed to precursor superconductivity, to the existence of preformed pairs, or to competing orders such as charge-density waves. A direct determination of the charge of carriers as a function of temperature and bias could help resolve among these alternatives. Here, we report measurements of the shot noise of…
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…
