V. B. Zabolotnyy, A. A. Kordyuk, D. Evtushinsky, V. N. Strocov, L. Patthey, T. Schmitt, D. Haug, C. T. Lin, V. Hinkov, B. Keimer, B. Büchner, S. V. Borisenko
As established by scanning tunneling microscopy (STM) cleaved surfaces of the high temperature superconductor YBa$_2$Cu$_2$O$_{7-δ}$ develop charge density wave (CDW) modulations in the one-dimensional (1D) CuO chains. At the same time, no signatures of the CDW have been reported in the spectral function of the chain band previously studied by photoemission. We use soft X-ray angle resolved photoemission (SX-ARPES) to detect a chain-derived surface band that had not been detected in previous work. The $2k_\textup{F}$ for the new surface band is found to be 0.55\,Å$^{-1}$, which matches the wave vector of the CDW observed in direct space by STM. This reveals the relevance of the Fermi surface nesting for the formation of CDWs in the CuO chains in YBa$_2$Cu$_2$O$_{7-δ}$. In agreement with the short range nature of the CDW order the newly detected surface band exhibits a pseudogap, whose energy scale also corresponds to that observed by STM.
Close to optimal doping, the copper oxide superconductors show 'strange metal' behavior, suggestive of strong fluctuations associated with a quantum critical point. Such a critical point requires a line of classical phase transitions terminating at zero temperature near optimal doping inside the superconducting 'dome'. The underdoped region of the temperature-doping phase diagram from which superconductivity emerges is referred to as the 'pseudogap' because evidence exists for partial gapping of the conduction electrons, but so far there is no compelling thermodynamic evidence as to whether th…
Measurements of the angular dependence of conductance spectra in the a-b plane of underdoped YBCO junctions are reported. At zero magnetic field the superconducting gap shows a |d+is|-like symmetry. Application of a magnetic field strongly suppresses this gap leaving only the pseudogap feature which also shows a |d+is|-like angular dependence. We thus observe the same symmetry for the superconducting gap and the pseudogap characterizing the YBCO electrodes near the interface with the barrier. An H_{c2} value of about 5T of the secondary (is) order parameter can also be deduced from our results…
We report measurements of the magnetic penetration depth in YBCO films at various oxygen concentrations. At optimal doping, critical fluctuation effects are absent, and the penetration depth from 4 K to 0.99 Tc is well described by d-wave, BCS, strong-coupling theory with a gap, Delta0/ kT ~ 3.3. This implies that the T-dependence of the penetration depth comes largely from single-particle excitations. As in crystals, underdoping reduces the zero temperature superfluid density without affecting the low-T slope or curvature of the penetration depth. We show that these results, as well as heat c…
Critical fluctuations have been studied in the microwave conductivity of Bi_2Sr_2CaCu_2O_(8+δ), Bi_2Sr_2Ca_2Cu_3O_(10+delta), and YBa_2Cu_3O_(7-delta) thin films above T_c. It is found that a consistent analysis of the real and imaginary parts of the fluctuation conductivity can be achieved only if an appropriate wavevector or energy cutoff in the fluctuation spectrum is taken into account. In all of the three underdoped superconducting films one observes strong fluctuations extending far above T_c. The coherence length inferred from the imaginary part of the conductivity exhibits the static c…
The temperature dependences of g factors of underdoped YBa2Cu3O7-x (Tc approximates 86.5K) indicate that the pseudogap onset temperature T*( approximates 190 K) coincides with the phase boundary established by resistivity, Nernst effect, neutron diffraction and ultrasound measurements in YBCO phase diagram. The obtained empirical relationship between g factors and pseudogap is appropriate for the entire charactering temperature range of Ortho-III YBCO. The EPR signals are ascribed to the localized Cu2+(1) sites based on the quantitative calculations of the g factors by involving the local stru…
In the framework of the model assuming the formation of NUC on the pairs of Cu ions in CuO$_{2}$ plane the mechanism of hole carrier generation is considered and the interpretation of pseudogap and 60 K-phases in $YBa_{2}Cu_{3}O_{6+δ}$. is offered. The calculated dependences of hole concentration in $YBa_{2}Cu_{3}O_{6+δ}$ on doping $δ$ and temperature are found to be in a perfect quantitative agreement with experimental data. As follows from the model the pseudogap has superconducting nature and arises at temperature $T^{*}>T_{c\infty}>T_{c}$ in small clusters uniting a number of NUC's due to …
Meingast, et al. suggest that in YBCO the pseudogap is associated with preformed pairs. It is shown that in underdoped cuprates there is evidence for two pseudogaps, and superconducting fluctions terminate at the smaller pseudogap.
For orthorhombic superconductors we define thermodynamic anisotropy $N \equiv d T_c/d ε_{22} - dT_c/d ε_{11}$ as the difference in how superconducting $T_c$ varies with strains $ε_{ii}$, $i=(1, 2)$, along the in-plane directions. We study the hole doping ($p$) dependence of $N$ on detwinned single crystals of underdoped YBa$_2$Cu$_3$O$_y$ (YBCO) using ultrasound technique. While the structural orthorhombicity of YBCO reduces monotonically with decreasing doping over $0.065 <p<0.16$, we find that the thermodynamic anisotropy shows an intriguing enhancement at intermediate doping level, which is…
An unusual noise component is found near and below about 250 K in the normal state of underdoped YBCO and Ca-YBCO films. This noise regime, unlike the more typical noise above 250 K, has features expected for a symmetry-breaking collective electronic state. These include large individual fluctuators, a magnetic sensitivity, and aging effects. A possible interpretation in terms of fluctuating charge nematic order is presented.
The temperature dependence of the Hall coefficient is measured with a high accuracy in a series of Zn-doped YBCO_{6.78} crystals with the Zn concentration from 0% to 1.3%. We found that the cotangent of the Hall angle, cot(θ_H), starts to deviate upward from the T^2 dependence below T_0 (which is roughly 130 K), regardless of the Zn concentration. We discuss that this deviation is caused by the pseudogap; the direction of the deviation and its insensitivity to the Zn doping suggest that the pseudogap affects cot(θ_H) through a change in the effective mass, rather than through a change in the H…
The comprehensive study of the temperature dependent x-ray absorption spectroscopy (XAS) reveals a dynamical spectral weight $α$ in YBa$_2$Cu$_3$O$_y$ (YBCO). Large spectral weight changes for both the Upper Hubbard band and the Zhang-Rice band due to dynamics of holes are experimentally found in the underdoped regime. A large value of $α\geq 0.3$ is indispensable to describing XAS of YBCO with the conservation of states. The value of $α$ is linearly proportional to the pseudogap temperature in the underdoped regime, but becomes smaller as the doping level goes to the undoped limit. Our result…
The preformed-pairs theory of pseudogap physics in high-$T_C$ superconductors predicts a nonanalytic $T$-dependence for the $ab$-plane superfluid fraction, $ρ_S$, at low temperatures in underdoped cuprates. We report high-precision measurements of $ρ_S(T)$ on severely underdoped YBa$_2$Cu$_3$O$_{6+x}$ and Y$_{0.8}$Ca$_{0.2}$Ba$_2$Cu$_3$O$_{6+x}$ films. At low $T$, $ρ_S$ looks more like $1 - T^2$ than $1 - T^{3/2}$, in disagreement with theory.
In underdoped YBa_2Cu_3O_x (YBCO) with x = 6.63, the opening of the pseudogap at T^* ~ 160 K has a strong effect on the Hall angle tan(theta). While the Hall response is significantly reduced, the diagonal current is relatively unaffected. The Hall conductivity suppression continues deep into the flux-flow state (from T_c to 40 K), as an anomalous suppression of the vortex Hall current.
Cuprate superconductors have a universal tendency to form charge density-wave (CDW) order which competes with superconductivity and is strongest at a doping $p \simeq 0.12$. Here we show that in the archetypal cuprate YBa$_{2}$Cu$_{3}$O$_{y}$ (YBCO) pressure suppresses charge order, but does not affect the pseudogap phase. This is based on transport measurements under pressure, which reveal that the onset of the pseudogap at $T^*$ is independent of pressure, while the negative Hall effect, a clear signature of CDW order in YBCO, is suppressed by pressure. We also find that pressure and magneti…
We present magneto-transport calculations for YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) materials to show that the electron-like metallic chain state gives both the negative Hall effect and in-plane anisotropic large Nernst signal. We show that the inevitable presence of the metallic 1D CuO chain layer lying between the CuO2 bilayers in YBCO renders an electron-like Fermi surface in the doping range as wide as p=0.05 to overdoping. With underdoping, a pseudogap opening in the CuO2 state reduces its hole-carrier contribution, and therefore the net electron-like quasiparticles dominate the transport propert…
Although considerable studies have been carried out, the true nature of high-Tc superconductors (HTCS) is still not clear. Pseudogap phase at high temperature as well as possible time reversal symmetry breaking at low temperature need further investigations. The need of carefully made samples showing the intrinsic properties of superconductivity is essential to test new theoretical developments. We present in this paper how to control crystallographic orientation in the junction and a technique developed to determined the quality of the interface barrier between a gold electrode and a HTCS : Y…
We have measured the spin fluctuations in the YBa2Cu3O6.5 (YBCO6.5, Tc=59 K) superconductor at high-energy transfers above ~ 100 meV. Within experimental error, the momentum dependence is isotropic at high-energies, similar to that measured in the insulator for two dimensional spin waves, and the dispersion extrapolates back to the incommensurate wave vector at the elastic position. This result contrasts with previous expectations based on measurements around 50 meV which were suggestive of a softening of the spin-wave velocity with increased hole doping. Unlike the insulator, we observe a sig…
The underlying physics of the magnetic-field-induced resistive state in high temperature cuprate superconductors remains a mystery. One interpretation is that the application of magnetic field destroys the d-wave superconducting gap to uncover a Fermi surface that behaves like a conventional (i.e.Fermi Liquid) metal (1). Another view is that an applied magnetic field destroys long range superconducting phase coherence, but the superconducting gap amplitude survives (2, 3). By measuring the specific heat of ultra-clean YBa2Cu3O6.56 (YBCO 6.56), we obtain a measure of the quasi-particle density …
Parametrically amplified Josephson plasma waves in YBa_2Cu_3O_(6+x): evidence for local superconducting fluctuations up to the pseudogap temperature $T^*$
Max Planck Institute for the Physics of Complex Systems（马克斯·普朗克复杂系统物理研究所）；Max Planck Institute for the Structure and Dynamics of Matter（马克斯·普朗克物质结构与动力学研究所）；ETH Zurich（苏黎世联邦理工学院）；MIT（麻省理工学院）
研究通过强太赫兹脉冲作用于欠掺杂YBa₂Cu₃O₆₊x并在Tc和伪间隙尺度T*之间温度下，发现类似超导态的反射率边缘和探针脉冲的二次谐波产生，提出通过参数放大低约瑟夫森等离子体模式解释，但本文提出另一种解释，假设在Tc < T < T*时存在局部配对幅度和相位，从而解释反射率数据。
We study the static and dynamic behavior of charge ordering within a d-wave pair pseudogap (pg) scenario. This is addressed using a density-density correlation function derived from the standard pg self energy, $Σ$ and compatible with the longitudinal and transverse sum rules. The broadening factor $γ$ in $Σ$ reflects the breaking of pairs into constituent fermions. We apply this form for $Σ$ (derived elsewhere for high fields) to demonstrate the existence of quantum oscillations in a non-Fermi liquid pg state. Our conclusion is that the pseudogap-induced pairbreaking, via $γ$, allows the unde…
Clear experimental evidence of charge density wave correlations competing with superconducting order in YBCO have thrust their relationship with the pseudogap regime into the spotlight. To aid in characterizing the pseudogap regime, we propose a dimensionless ratio of the diamagnetic susceptibility to the correlation length of the charge density wave correlations. Using Monte Carlo simulations, we compute this ratio on the classical model of Hayward et. al. (Science 343, 1336 (2014)), which describes angular fluctuations of a multicomponent order, capturing both superconducting and density wav…
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 = …
Among high T_c materials, the YBCO (YBa_2Cu_3O_{7-x}) compounds are special since they have superconducting chains as well as planes. We show that a discontinuity in the density of states as a function of magnetic field may appear at a new energy scale, characteristic of the chain and distinct from that set by the d wave gap. This is observable in experimental studies of the thermodynamical properties of these systems, such as the specific heat.
Using series expansions and spin-wave theory we calculate the spin-stiffness anisotropy $ρ_{sx}/ρ_{sy}$ in Heisenberg models on the square lattice with anisotropic couplings $J_x,J_y$. We find that for the weakly anisotropic spin-half model ($J_x\approx J_y$), $ρ_{sx}/ρ_{sy}$ deviates substantially from the naive estimate $ρ_{sx}/ρ_{sy} \approx J_x/J_y$. We argue that this deviation can be responsible for pinning the electronic liquid crystal direction, a novel effect recently discovered in YBCO. For completeness, we also study the spin-stiffness for arbitrary anisotropy $J_x/J_y$ for spin-hal…
The interplay between the quasi 1-dimensional CuO-chains and the 2-dimensional CuO2 planes of YBa2Cu3O6+x (YBCO) has been in focus for a long time. Although the CuO-chains are known to be important as charge reservoirs that enable superconductivity for a range of oxygen doping levels in YBCO, the understanding of the dynamics of its temperature-driven metal-superconductor transition (MST) remains a challenge. We present a combined study using x-ray absorption spectroscopy and resonant inelastic x-ray scattering (RIXS) revealing how a reconstruction of the apical O(4)-derived interplanar orbita…
In this work, we study the relationship between the superconducting phase and pseudogap phase in a real-space picture. We suggest that the superconducting ground states are guaranteed by the energy minimum charge structure of the quasi-one-dimensional Peierls chains (static vortex lines). It is shown that there is a charge ordering phase transition from the Peierls chains (the superconducting ground state) to the periodic chains (the superconducting excited state) in any superconductors. In our scenarios, all the superconducting electrons can be considered as the "inertial electrons"at some st…
A pronounced xy-anisotropy was observed in recent neutron scattering experiments for magnetic excitations in untwinned YBa_{2}Cu_{3}O_{6+y} (YBCO). The small anisotropy of the bare band structure due to the orthorhombic crystal symmetry seems to be enhanced by correlation effects. A natural possibility is that the system is close to a Pomeranchuk instability associated with a d-wave Fermi surface deformation (dFSD). We investigate this possibility in the bilayer t-J model within a self-consistent slave-boson mean-field theory. We show that the dFSD correlations drive a pronounced xy-anisotropy…
We present a general scenario for high-temperature superconducting cuprates, based on the presence of dynamical charge density waves (CDWs) and to the occurrence of a CDW quantum critical point, which occurs, e.g., at doping p~0.16 in YBCO. In this framework, even the pseudogap temperature T* is interpreted in terms of a reduction of the density of states due to incipient CDW and, at lower temperature to the possible formation of incoherent superconducting pairs. The dynamically fluctuating character of CDW accounts for the different temperatures at which the pseudogap (T*), the CDW onset reve…
We have observed a Fermi-surface (FS) induced lattice modulation in a YBCO superconductor with a wavevector along CuO chains, {\it i.e.} ${\bf q}_1$=(0,$δ$,0). The value of $δ\sim0.21$ is twice the Fermi wavevector ($2{\bf k}_F$) along {\bf b*} connecting nearly nested FS `ridges'. The ${\bf q}_1$ modulation exists only within O-vacancy-ordered islands (characterized by ${\bf q}_0$=$(\frac14,0,0))$ and persists well above and below $T_c$. Our results are consistent with the presence of a FS-induced charge-density wave.
Intense experimental and theoretical efforts have recently been brought to bear on the determination of the symmetry of superconducting order parameter in high T$_c$ Cuprates as this would shed light on the nature of microscopic interactions that are responsible for superconductivity in these unusual systems. We use a two band model that reproduces the Fermi surface seen in ARPES experiments of Shen et al., and study the symmetry of order parameter in the YBCO system. The model incorporates the effects of tunnelling in the c-direction between the planes and chains of these Cuprates. It is obse…
We perform a numerical simulation of a three-band Hubbard model with two CuO$_2$ planes and a single CuO chain layer for YBCO cuprates. The spin-fluctuation mediated pairing interaction is computed within the multiband random-phase approximation, and its pairing eigenvalues and eigenfunctions are solved as a function of chain state filling factor $n_c$. We find that for the intrinsic value of $n_c$ in YBCO samples, one obtains the usual $d$-wave pairing symmetry. However, if we dope the chain layers with holes, while keeping the plane states doping fixed, the leading pairing symmetry solution …
We reanalyze the data on the in-plane far infrared conductivity of underdoped orthoII YBa$_{2}$Cu$_{3}$O$_{6.50}$ (YBCO$_{6.50}$) in terms of a model in which a pseudogap opens on part of the Fermi surface with the remaining ungaped piece proportional to the temperature. The motivation for our model comes from recent angle-resolved photoemission spectroscopy data in underdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi-2212), which have revealed the existence of arcs on the Fermi surface. We find the optical data to be consistent with arc formation. In addition we find some evidence that the electronic…
YBaCuO_7 is a trilayer material with a unit cell consisting of a CuO_2 bilayer with a CuO plane of chains in between. Starting with a model of isolated planes coupled through a transverse matrix element, we consider the possibility of intra as well as interplane pairing within a nearly antiferromagnetic Fermi liquid model. Solutions of a set of three coupled BCS equations for the gap exhibit orthorhombic symmetry with s- as well as d-wave contributions. The temperature dependence and a-b in plane anisotropy of the resulting penetration depth is discussed and compared with experiment.
The pseudogap (PG) derived from the analysis of the excess conductivity $σ'(T)$ in superlattices and double-layer films of $YBa_2Cu_3O_{7-δ}$-$PrBa_2Cu_3O_{7-δ}$(YBCO-PrBCO), prepared by pulsed laser deposition, is studied for the first time. The $σ'(T)$ analysis has been performed within the local-pair (LP) model based on the assumption of the paired fermion (LPs) formation in the cuprate high-$T_c$ superconductors (cuprates) below the representative temperature $T^*\gg T_c$ resulting in the PG opening. Within the model, the temperature dependencies of the PG, $Δ^*(T)$, for the samples with d…
Nuclear magnetic resonance (NMR) measurements of CuO chains of detwinned Ortho-II YBa$_2$Cu$_3$O$_{6.5}$ (YBCO6.5) single crystals reveal unusual and remarkable properties. The chain Cu resonance broadens significantly, but gradually, on cooling from room temperature. The lineshape and its temperature dependence are substantially different from that of a conventional spin/charge density wave (S/CDW) phase transition. Instead, the line broadening is attributed to small amplitude static spin and charge density oscillations with spatially varying amplitudes connected with the ends of the finite l…
We have grown untwinned YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) films on (110) MgO substrates that were pre-annealed at high temperature in oxygen atmosphere. The annealing results in surface reconstruction with shallow facets, which induce the suppression of the YBCO twinning domains, and the preferential alignment of the CuO chains along one of the in-plane directions of the substrate. Because of the large mismatch between the in-plane lattice parameters of film and substrate, the strain induced by the MgO into the YBCO layer is strong and very peculiar. The YBCO film is compressed, with respect to th…
We examine the effect of CuO intergrowths on the superconductivity in epitaxial La_{2/3}Ca_{1/3}MnO_3/YBa_2Cu_3O_{7-δ} (LCMO/YBCO) thin-film heterostructures. Scanning transmission electron microscopy on bilayer LCMO/YBCO thin films revealed double CuO-chain intergrowths which form regions with the 247 lattice structure in the YBCO layer. These nanoscale 247 regions do not appear in x-ray diffraction, but can physically account for the reduced critical temperature Tc of bilayer thin films relative to unilayer films with the same YBCO thickness, at least down to ~25 nm. We attribute the CuO int…
Superconductivity suppression and bilayer decoupling in Pr substituted YBa$_2$Cu$_3$O$_{7-δ}$
Yale University（耶鲁大学）；University of California, San Diego（加州大学圣迭戈分校）；Michigan State University（密歇根州立大学）；Stanford Synchrotron Radiation Lightsource, Stanford Linear Accelerator Center (SLAC) National Accelerator Laboratory（斯坦福同步辐射光源，斯坦福直线加速器中心（SLAC）国家加速器实验室）；Advanced Photon Source, Argonne National Laboratory（先进光子源，阿贡国家实验室）；Deutsches Elektronen-Synchrotron DESY（德国电子同步加速器 DESY）
The competition between superconductivity and charge density wave (CDW) order in underdoped cuprates has now been widely reported, but the role of disorder in this competition has yet to be fully resolved. A central question is whether disorder sets the length scale of the CDW order, for instance by pinning charge density fluctuations or disrupting an otherwise long range order. Using resonant soft x-ray scattering, we investigate the sensitivity of CDW order in YBa$_2$Cu$_3$O$_{6+x}$ (YBCO) to varying levels of oxygen disorder. We find that quench cooling YBCO$_{6.67}$ (YBCO$_{6.75}$) crystal…
We report hole and electron doping in La-doped YBa$_2$Cu$_3$O$_y$(YBCO) thin films synthesized by pulsed laser deposition technique and subsequent \emph{in-situ} postannealing in oxygen ambient and vaccum. The $n$-type samples show a metallic behavior below the Mott limit and a high carrier density of $\sim2.8$ $\times$ 10$^{21}$ cm$^{-3}$ at room temperature (\emph{T}) at the optimally reduced condition. The in-plane resistivity ($ρ$$_{ab}$) of the $n$-type samples exhibits a quadratic \emph{T} dependence in the moderate-\emph{T} range and shows an anomaly at a relatively higher \emph{T} prob…
Static charge-density wave (CDW) and spin-density wave (SDW) order has been convincingly observed in La-based cuprates for some time. However, more recently it has been suggested by quantum oscillation, transport and thermodynamic measurements that density wave order is generic to underdoped cuprates and plays a significant role in YBa_2Cu_3O_{6+delta} (YBCO). We use resonant soft x-ray scattering at the Cu L and O K edges to search for evidence of density wave order in Ortho-II and Ortho-VIII oxygen-ordered YBCO. We report a null result -- no evidence for static CDW order -- in both Ortho-II …
Charge-density-wave (CDW) correlations within the quintessential CuO$_2$ planes have been argued to either cause [1] or compete with [2] the superconductivity in the cuprates, and they might furthermore drive the Fermi-surface reconstruction in high magnetic fields implied by quantum oscillation (QO) experiments for YBa$_2$Cu$_3$O$_{6+δ}$ (YBCO) [3] and HgBa$_2$CuO$_{4+δ}$ (Hg1201) [4]. Consequently, the observation of bulk CDW order in YBCO was a significant development [5,6,7]. Hg1201 features particularly high structural symmetry and recently has been demonstrated to exhibit Fermi-liquid ch…
We have grown and characterized 30 nm thick YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) films, deposited by pulsed laser deposition on both MgO (110) and SrTiO$_3$ (001) substrates, which induce opposite strain to the superconducting layer. By carefully tuning the in-situ post-annealing oxygen pressure, we achieved, in a reproducible way, films at different oxygen doping, spanning from the slightly overdoped down to the strongly underdoped region of the phase diagram. The transport properties of the films, investigated through resistance versus temperature measurements, are in perfect qualitative agreement …
The electron dynamics in the CuO chains has been elusive in Y-Ba-Cu-O cuprate systems by means of standard angle-resolved photoemission spectroscopy (ARPES); cleaved sample exhibits areas terminated by both CuO-chain or BaO layers, and the size of a typical beam results in ARPES signals that are superposed from both terminations. Here, we employ spatially-resolved ARPES with submicrometric beam (nano-ARPES) to reveal the surface-termination-dependent electronic structures of the double CuO chains in YBa$_2$Cu$_4$O$_8$. We present the first observation of sharp metallic dispersions and Fermi su…
We propose that the NMR line shape on the chain Cu in the stoichiometric high-$T_c$ superconductor Ortho-II YBa$_2$Cu$_3$O$_{6.5}$ is determined by the magnetization induced on Cu near O vacancies, due to strong magnetic correlations in the chains. An unrestricted Hartree-Fock calculation of a coupled chain-plane Hubbard model with nearest-neighbor d-wave pairing interaction shows that the broadening of NMR lines is consistent with disorder-induced magnetization at low temperatures. In addition, we give a possible explanation of the anomalous bimodal line shape observed at high temperatures in…
This paper reveals the origin of variation in the magnitude and temperature dependence of the normal state resistivity frequently observed in different YBCO single crystal or thin film samples with the same $T_{c}$. We investigated temperature dependence of resistivity in $YBa_{2}Cu_{3}O_{7-δ}$ thin films with 7- $δ= 6.95$ and 6.90, which were subjected to annealing in argon at 400-420 K ($120-140^{o}C$). Before annealing these films exhibited a non-linear $ρ_{ab}(T)$, with a flattening below 230 K, similar to $ρ_{b}(T)$ and $ρ_{ab}(T)$ observed in untwinned and twinned YBCO crystals, respecti…
The application of large magnetic fields ($B \sim B_{c2}$) to layered cuprates suppresses their high temperature superconducting behaviour and reveals competing ground states. In the widely-studied material YBa$_2$Cu$_3$O$_{6+x}$ (YBCO), underdoped ($p \sim 1/8$) samples show signatures of field-induced electronic and structural changes at low temperatures. However, the microscopic nature of the field-induced reconstruction and the high-field state are unclear. Here we report an x-ray study of the high-field charge density wave (CDW) in YBCO, for doping, $0.1 \lesssim p \lesssim 0.13$. For $p …
The microwave conductivity of an ultra-pure single crystal of YBa$_2$Cu$_3$O$_{6.50}$ has been measured deep in the superconducting state as a continuous function of frequency from $0.5\to20$ GHz. Conductivity spectra were first measured at four temperatures below 10 K after having prepared the crystal in the so called ortho-II phase in which the CuO chain oxygen are ordered into alternating full and empty chains. These spectra exhibit features expected for quasiparticle scattering from dilute weak impurities (small scattering phaseshift) in an otherwise clean d-wave superconductor. The measur…
Extensive measurements of the microwave conductivity of highly pure and oxygen-ordered \YBCO single crystals have been performed as a means of exploring the intrinsic charge dynamics of a d-wave superconductor. Broadband and fixed-frequency microwave apparatus together provide a very clear picture of the electrodynamics of the superconducting condensate and its thermally excited nodal quasiparticles. The measurements reveal the existence of very long-lived excitations deep in the superconducting state, as evidenced by sharp cusp-like conductivity spectra with widths that fall well within our e…
YBCO, LSCO and Ru-1212 have been extensively studied by measuring the complex dynamic Young's modulus at 0.5-20 kHz between 1 and 900 K. The elastic energy loss is peaked at the temperatures where the relaxation rate of any microscopic process coupled to strain equals the measuring frequency. The reliability of the anelastic experiments and of the assignments to various microscopic mechanisms is also discussed. In LSCO, the layers of octahedra present solitonic tilt waves and fast local motion. The latter is driven by atomic tunneling and is enormously enhanced and accelerated by doping, demon…
Probing Electromigration of Oxygen Vacancies in YBa$_2$Cu$_3$O$_{7-δ}$ Devices by Multimodal X-ray Techniques
Universidade Federal de São Carlos（圣卡洛斯联邦大学）；National High Magnetic Field Laboratory, Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室国家高磁场实验室）；Université de Liège（列日大学）；Centro Brasileiro de Pesquisas Físicas（巴西物理研究中心）；Institut de Ciència de Materials de Barcelona, ICMAB-CSIC（巴塞罗那材料科学研究所）；Brazilian Nanotechnology National Laboratory, Brazilian Center for Research in Energy and Materials（巴西纳米技术国家实验室、巴西能源与材料研究中心）
We report the results a comprehensive study of charge density wave (CDW) correlations in untwinned YBCO6+x single crystals with 0.4<x<0.99 using Cu-L3 edge resonant x-ray scattering (RXS). Evidence of CDW formation is found for 0.45<x<0.93, but not for samples with x<0.44 that exhibit incommensurate spin-density-wave order, and in slightly overdoped samples with x=0.99. This suggests the presence of two proximate zero-temperature CDW critical points at doping pc1~0.08 and pc2~0.18. The CDW reflections are observed at incommensurate in-plane wave vectors (d_a, 0) and (0, d_b). Both decrease lin…
Much of what is known about high-temperature cuprate superconductors stems from studies based on two surface analytical tools, angle-resolved photoemission spectroscopy (ARPES) and spectroscopic imaging scanning tunneling microscopy (SI-STM). A question of general interest is whether and when the surface properties probed by ARPES and SI-STM are representative of the intrinsic properties of bulk materials. We find this question is prominent in thin films of a rarely studied cuprate DBCO. We synthesize DBCO films by oxide molecular beam epitaxy and study them by in situ ARPES and SI-STM. Both A…
We use microprobe Angle-Resolved Photoemission Spectroscopy to study the Fermi surface and band dispersion of the CuO2 planes in the high temperature superconductor, YBa2Cu4O8. We find a strong in-plane asymmetry of the electronic structure between directions along a and b axes. The saddle point of the antibonding band lies at a significantly higher energy in the a direction (pi,0) than the b direction (0,pi), whereas the bonding band displays the opposite behavior. We demonstrate that the abnormal band shape is due to a strong asymmetry of the bilayer band splitting, likely caused by a non-tr…
The metallic state of the underdoped high-Tc cuprates has remained an enigma: How may seemingly disconnected Fermi surface segments, observed in zero magnetic field as a result of the opening of a partial gap (the pseudogap), possess conventional quasiparticle properties? How do the small Fermi-surface pockets evidenced by the observation of quantum oscillations (QO) emerge as superconductivity is suppressed in high magnetic fields? Such QO, discovered in underdoped YBa2Cu3O6.5 (Y123) and YBa2Cu4O8 (Y124), signify the existence of a conventional Fermi surface (FS). However, due to the complexi…
