We report detailed 17O, 139La, and 63Cu Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) measurements in a stripe ordered La1.875Ba0.125CuO4 single crystal and in oriented powder samples of La1.8-xEu0.2SrxCuO4. We observe a partial wipeout of the 17O NMR intensity and a simultaneous drop of the 17O electric field gradient (EFG) at low temperatures where the spin stripe order sets in. In contrast, the 63Cu intensity is completely wiped out at the same temperature. The drop of the 17O quadrupole frequency is compatible with a charge stripe order. The 17O spin lattice relaxation rate shows a peak similar to that of the 139La, which is of magnetic origin. This peak is doping dependent and is maximal at x ~ 1/8.
We report $^{139}$La nuclear magnetic resonance (NMR) measurements on La$_{2-x}$Sr$_x$CuO$_4$ ($0.07\leq x \leq 0.15$) and La$_{2-x}$Ba$_x$CuO$_4$ ($x=1/8$) single crystals, focusing on the spin freezing observed in 1/8-doped lanthanum cuprates. Charge stripe order seems to induce the inhomogeneous slowing down of spin fluctuations toward spin order and compete with superconductivity.
We report the analysis of the magnetic fluctuations in the superconducing La_{2-x}Sr_xCuO_4 and the related lanthanum cuprates having the different symmetry of the low temperature structure. The NMR and ESR investigations revealed the dynamical coexistence of the superconductivity and the antiferromagnetic correlations in the large part of superconductivity region of the phase diagram. We show that for all compounds, independent on their low temperature symmetry and on their superconducting properties, the enhancement of the spin stiffness near 1/8 doping takes place.
Using Cu NQR in Eu-doped La_(2-x)Sr_xCuO_4 we find the evidence of the pinned stripe phase at 1.3K for 0.08<x<0.18. The pinned fraction increases by one order of magnitude near hole doping x=1/8. The NQR lineshape reveals three inequivalent Cu positions. A dramatic change of the NQR signal for x > 0.18 correlating with the onset of bulk superconductivity corresponds to the depinning of the stripe phase.
Superlattice of spin vortices has been proposed in an earlier article as an alternative to the stripe interpretation of spin modulations in 1/8-doped lanthanum cuprates. The present article addresses several additional characteristics of the spin vortex lattice, namely: (i) the nature of extended charge states; (ii) the position of neutron spin peaks as a function of doping; and (iii) the absence of higher order spin harmonics. All these characteristics afford straightforward connection to the experimental results produced by angle-resolved photoemission spectroscopy, resistivity measurements,…
We investigate the dimensionality of inhomogeneous spin modulation patterns in the cuprate family of high-temperature superconductors with particular focus on 1/8-doped lanthanum cuprates. We compare one-dimensional stripe modulation pattern with two-dimensional checkerboard of spin vortices in the context of nuclear quadrupole resonance(NQR) and muon spin rotation(muSR) experiments. In addition, we also consider the third pattern, a two-dimensional superposition of spin spirals. Overall, we have found that none of the above patterns leads to a consistent interpretation of the two types of exp…
It is proposed, that a two-dimensional magnetic superstructure closely related to the one mentioned recently by Christensen et al. [cond-mat/0608204] constitutes a viable interpretation of the four-fold splitting of the magnetic (π, π) peak in lanthanum cuprates. (This splitting is usually interpreted as the evidence for stripes.) The superstructure in question has the topology of the square crystal of magnetic vortices with approximate periodicity (4a x 4a). This vortex crystal exhibits no magnetic antiphase lines. It is shown that such a superstructure is magnetically stable in the approxima…
The doping, temperature and energy dependence of the dynamical spin structure factors of the underdoped lanthanum cuprates in the normal state is studied within the t-J model using the fermion-spin transformation technique. Incommensurate peaks are found at $[(1\pmδ)π,π]$, $[π,(1\pmδ)π]$ at relatively low temperatures with $δ$ linearly increasing with doping at the beginning and then saturating at higher dopings. These peaks broaden and weaken in amplitude with temperature and energy, in good agreement with experiments. The theory also predicts a rotation of these peaks by $π/4$ at even higher…
Suppression of superconductivity in favour of a striped phase, and its coincidence with a structural transition from a low-temperature orthorhombic (LTO) to a low-temperature tetragonal (LTT) phase, is a ubiquitous feature of hole-doped lanthanum cuprates. We study the effect of anisotropic strain on this transition using density-functional theory on both La$_2$CuO$_4$ and the recently-synthesised surrogate La$_2$MgO$_4$ to decouple electronic and structural effects. Strikingly, we find that compressive strain applied diagonally to the in-plane metal-oxygen bonds dramatically stabilises the LT…
Using Cu NQR in Eu-doped La_{2- x}Sr_xCuO_4 we show the evidence of the pinned stripe phase for moderate doping at 1.3K. The pinned fraction increases by one order of magnitude near hole doping x=1/8. The NQR lineshape reveals three inequivalent Cu positions: i) sites in the charged stripe; ii) nonmagnetic sites outside the stripes; iii) sites with a magnetic moment of 0.29 Bohr magnethon in the AF correlated regions. A dramatic change of the NQR signal for x > 0.18 correlating with the onset of bulk superconductivity corresponds to the depinning of the stripe phase. .
High Tc superconductors show a rich variety of phases associated with their charge degrees of freedom. Valence charges can give rise to charge ordering or acoustic plasmons in these layered cuprate superconductors. While charge ordering has been observed for both hole- and electron-doped cuprates, acoustic plasmons have only been found in electron-doped materials. Here, we use resonant inelastic X-ray scattering (RIXS) to observe the presence of acoustic plasmons in two families of hole-doped cuprate superconductors [La2-xSrxCuO4 (LSCO) and Bi2Sr1.6La0.4CuO6+d (Bi2201)], crucially completing t…
By comparing experimental results obtained in the study of the electron transport and magnetic properties of samples of lightly strontium-substituted lanthanum cuprates and the results of a previously published numerical analysis in the reduced elastic scattering space (RPS) of the elastic scattering cross-section, we construct a phenomenological classical self-consistent strong-binding energy density profile in the superconducting $La_{2-x}Sr_xCuO_4$ cuprate. It is found that the imaginary part of the reduced phase scattering space can be zero, almost constant, or strongly self-consistent, de…
Based on the time-dependent Gutzwiller approximation we study the possibility that the diagonal incommensurate spin scattering in strongly underdoped lanthanum cuprates originates from antiferromagnetic domain walls (stripes). Calculation of the dynamic spin response for stripes in the diagonal phase yields the characteristic hour glass dispersion with the crossing of low energy Goldstone and high-energy branches at a characteristic energy Ecross at the antiferromagnetic wave-vector Q_{AF}. The high energy part is close to the parent antiferromagnet. Our results suggest that inelastic neutron …
We use the idea of the Wigner probability distribution (WPD) in a reduced scattering phase space (RPS) for the elastic scattering cross-section, with the help of a Tight-Binding (TB) numerical procedure allowing us to consider the anisotropic quantum effects, to phenomenologically predict several phases in these two novel unconventional superconductors. Unlike our previous works with pieces of evidence that these two compounds are in the unitary strong scattering regime and that superconductivity is suppressed by the atoms of strontium in both materials, several phases are built. In the case o…
Within a model that supports stripe spin and charge order coexisting with a d$_{x^2-y^2}$-wave superconducting phase, we study the self-consistently obtained electronic structure and the associated transverse dynamical spin susceptibility. In the coexisting phase of superconducting and static stripe order, the resulting particle-hole continuum can strongly damp parts of the low-energy spin wave branches. This provides insight into recent inelastic neutron scattering data revealing the dispersion of the low-energy collective magnetic modes of lanthanum based cuprate superconductors.
We study a model for low doped cuprates where holes aggregate into oriented stripe segments which have a vortex and an antivortex fixed to the extremes. We argue that due to the interaction between segments a state with macroscopic polarization is stabilized, which we call a ferronematic. This state can be characterized as a charge nematic which, due to the net polarization, breaks inversion symmetry and also exhibits an incommensurate spin modulation. Our calculation can reproduce the doping dependent spin structure factor of lanthanum cuprates in excellent agreement with experiment and allow…
The Hall coefficient data for cuprates show that number of carriers exceeds external doping $x$ at higher $x$ and varies with temperature. Hence, spins on the Cu-sites are not conserved. Activation energy for thermally excited carriers equals the energy between the Fermi surface "arc" and the band bottom near the van Hove singularities. Crossover from marginal Fermi liquid- to pseudogap- regime happens at temperatures at which number of activated carriers gets comparable with the number of externally doped holes. Implications for the $(T,x)$-phase diagram of cuprates are discussed.
Based on the unrestricted Gutzwiller approximation we study the possibility that the diagonal incommensurate spin scattering in the spin glass phase of lanthanum cuprates originates from stripe formation. Similar to the metallic phase two types of diagonal stripe structures appear to be stable: (a) site-centered textures which have one hole per site along the stripe and (b) ferromagnetic stair-case structures which are the diagonal equivalent to bond-centered stripes in the metallic phase and which on average have a filling of 3/4 holes per stripe site. We give a detailed analysis of the stabi…
The last few years have seen significant experimental progress in characterizing the copper-based hole-doped high temperature superconductors in the regime of low hole density, p. Quantum oscillations, NMR, X-ray, and STM experiments have shed much light on the nature of the ordering at low temperatures. We review evidence that the order parameter in the non-Lanthanum-based cuprates is a d-form factor density-wave. This novel order acts as an unexpected window into the electronic structure of the pseudogap phase at higher temperatures in zero field: we argue in favor of a `fractionalized Fermi…
Although phase diagrams can be leveraged to investigate high transition temperature (high-$T_c$) superconductivity, the issue has not been discussed thoroughly. In this study, we elucidate the phase diagram of the overdoped side of high-$T_c$ cuprates via systematic anisotropic transport measurements for Pb-doped Bi-2212 single crystals. We demonstrate that the characteristic temperatures of the "weak" pseudogap opening and electronic coherence cross each other at a critical doping level, while those of the "strong" pseudogap merges into that of superconducting fluctuations above the critical …
The electron-doped cuprates are usually characterized by a more robust antiferromagnetic phase and a much narrower superconducting (SC) dome than those of the hole-doped counterparts. Recently, bulk single crystals of Pr1.3-xLa0.7CexCuO4-δ (PLCCO) prepared by the protect annealing method have been studied extensively and revealed many intriguing properties that were different from those obtained from samples annealed by the conventional methods. Here, we report on a systematic angle-resolved photoemission spectroscopy study of PLCCO single crystals after protect annealing. The results indicate…
The magnetic susceptibility of underdoped yttrium and lanthanum cuprates is interpreted based on the self-consistent solution of the t-J model of a Cu-O plane. The calculations reproduce correctly the frequency dependencies of the susceptibility in YBa2Cu3O_{7-y} and La_{2-x}Sr_xCuO4 attributing their dissimilarity to the difference in the damping of spin excitations. In YBa2Cu3O_{7-y} these excitations are well defined at the antiferromagnetic wave vector Q=(π,π) even in the normal state which manifests itself in a pronounced maximum -- the resonance peak -- in the susceptibility. In La_{2-x}…
The nature of the pseudogap and its relationship with superconductivity are one of the central issues of cuprate superconductors. Recently, a possible scenario has been proposed that the pseudogap state is a distinct phase characterized by spontaneous rotational symmetry breaking called "nematicity" based on transport and magnetic susceptibility measurements, where the symmetry breaking was observed below the pseudogap temperature $T^*$. Here, we report a temperature-dependent ARPES study of nematicity in slightly overdoped Bi${}_{1.7}$Pb${}_{0.5}$Sr${}_{1.9}$CaCu${}_2$O${}_{8+δ}$ triggered by…
We investigated the nature of the quasi-particle state in the vortex core by means of the flux-flow Hall effect measurements at 15.8 GHz. We measured the flux-flow Hall effect in cuprate superconductors, Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{y}$ and YBa$_{2}$Cu$_{3}$O$_{y}$ single crystals, whose equilibrium $B$-$T$ phase diagrams were different. As a result, we found that the Hall angle is independent of the magnetic field, and reaches an order of unity at low temperatures in BSCCO. However, in YBCO, the angle increases with increasing magnetic field even at low temperatures. We understood that this …
Anisotropy, thermal and quantum fluctuations and their dependence on dopant concentration appear to be present in all cuprate superconductors, interwoven with the microscopic mechanisms responsible for superconductivity. Here we review anisotropy, in-plane and c-axis penetration depths, isotope effect and conductivity measurements to reassess the universal behavior of cuprates as revealed by the doping dependence of these phenomena and of the transition temperature.
A new method to measure the superconducting stiffness tensor $\overlineρ_s$, without subjecting the sample to magnetic field, is applied to La$_{1.875}$Sr$_{0.125}$CuO$_4$ (LSCO). The method is based on the London equation $\bf{J}=-\overlineρ_s \bf{A}$, where $\bf{J}$ is the current density and $\bf{A}$ is the vector potential. Using rotor free $\bf{A}$ and measuring $\bf{J}$ via the magnetic moment of superconducting rings, we extract $\overlineρ_s$ at $T\rightarrow T_c$. The technique, named Stiffnessometer, is sensitive to very small stiffness, which translates to penetration depth on the o…
High magnetic field studies of the cuprate superconductors revealed a non-BCS temperature dependence of the upper critical field $H_{c2}(T)$ determined resistively by several groups. These determinations caused some doubts on the grounds of the contrasting effect of the magnetic field on the in-plane, $ρ_{ab}$, and out-of-plane, $ρ_{c}$ resistances reported for large sample of Bi2212. Here we present careful measurements of both $ρ_{ab}(B)$ and $ρ_{c}(B)$ of tiny Bi2212 crystals in magnetic fields up to 50 Tesla. None of our measurements revealed a situation when on field increase $ρ_c$ reache…
High magnetic field studies of cuprate superconductors revealed a non-BCS temperature dependence of the upper critical field $H_{c2}(T)$ determined resistively by several groups. These determinations caused some doubts on the grounds of both the contrasting effect of the magnetic field on the in-plane and out-of-plane resistances reported for large Bi2212 sample and the large Nernst signal \emph{well above} $T_{c}$. Here we present both $ρ_{ab}(B)$ and $ρ_{c}(B)$ of tiny Bi2212 crystals in magnetic fields up to 50 Tesla. None of our measurements revealed a situation when on the field increase …
It is proposed that the 50-70 meV dispersion anomaly (kink) in electron-doped cuprates revealed by recent angle-resolved photoemission spectroscopy experiments is caused by coupling with the spin fluctuation. We elaborate that the kink exists both along nodal and antinodal directions, and both in the superconducting and normal state. The renormalized effect for the density of states is also studied and the hump feature outside the superconducting coherent peak is established, consistent with recent scanning tunnelling microscopy experiments.
We follow the line of reasoning that hidden broken symmetries are the root of quantum oscillations observed in underdoped superconductors and examine the role of bilayer splitting and incommensuration. This is a view that eschews the notion of a featureless Mott liquid as the source of complexity. Instead, our view is grounded in a conventional Fermi surface and quasiparticles. We show that bilayer splitting and/or incommensurate $d$-density wave order can lead to many interesting results, in particular a splitting of the main frequency of the quantum oscillations.
We present in-plane infrared reflectance measurement on two superconducting cuprates with relatively low T$_c$: a nearly optimally-doped Bi$_2$Sr$_{1.6}$La$_{0.4}$CuO$_{6+δ}$ with T$_c$=33 K and an underdoped La$_{1.89}$Sr$_{0.11}$CuO$_4$ with T$_c$=30 K. The measurement clearly reveals that the superconducting energy gap is distinct from the pseudogap. They have different energy scales and appear at different temperatures. The results suggest that the pseudogap is not a precursor to the superconducting state. The data also challenge the longstanding viewpoint that the superconductivity within…
We report an angular quantum oscillation study of Tl_2Ba_2CuO_{6+delta} for two different doping levels (Tc = 10K and 26 K) and determine the Fermi surface size and topology in considerable detail. Our results show that Fermi liquid behavior is not confined to the edge of the superconducting dome and is robust up to at least T_c^{max}/3.5. Superconductivity is found to survive up to a larger doping p_c = 0.31 than in La_{2-x}Sr_xCuO_4. Our data imply that electronic inhomogeneity does not play a significant role in the loss of superconductivity and superfluid density in overdoped cuprates, and…
The recent observation of superconductivity with critical temperatures up to 55 K in the FeAs based pnictide compounds marks the first discovery of a non copper-oxide based layered high-Tc superconductor (HTSC) [1-3]. It has raised the suspicion that these new materials share a similar pairing mechanism to the cuprates, since both exhibit superconductivity following charge doping of a magnetic parent material. Here we present a muon spin rotation study on SmFeAsO1-xFx (x=0-0.30), which shows that static magnetism persists well into the superconducting regime. The analogy with the cuprates is q…
We study the systematic doping evolution of nodal dispersions by in-situ angle-resolved photoemission spectroscopy on the continuously doped surface of a high-temperature superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$. We reveal that the nodal dispersion has three segments separated by two kinks, located at ~10 meV and roughly 70 meV, respectively. The three segments have different band velocities and different doping dependence. In particular, the velocity of the high-energy segment increases monotonically as the doping level decreases and can even surpass the bare band velocity. We propose tha…
Grain boundary bicrystal Josephson junctions of the electron-doped infinite-layer superconductor Sr$_{1-x}$La$_x$CuO$_2$ ($x = 0.15$) were grown by pulsed laser deposition. BaTiO$_3$-buffered $24\,^\circ$ [001]-tilt symmetric SrTiO$_3$ bicrystals were used as substrates. We examined both Cooper pair (CP) and quasiparticle (QP) tunneling by electric transport measurements at temperatures down to 4.2\,K. CP tunneling revealed an extraordinary high critical current density for electron-doped cuprates of $j_c > 10^3\,$A/cm$^2$ at 4.2\,K. Thermally activated phase slippage was observed as dissipati…
A general quantitative measure of the tendency towards phase separation is introduced for systems exhibiting phase transitions or crossovers controlled by charge carrier concentration. This measure is devised for the situations when the quantitative knowledge of various contributions to free energy is incomplete, and is applied to evaluate the chances of electronic phase separation associated with the onset of antiferromagnetic correlations in high-temperature cuprate superconductors. The experimental phenomenology of lanthanum- and yittrium-based cuprates was used as input to this analysis. I…
Using resonant inelastic x-ray scattering (RIXS) at the Cu $L$-absorption edge, we have observed intense, dispersive spin excitations in highly overdoped Tl$_2$Ba$_2$CuO$_{6+δ}$ (superconducting $T_c =6$ K), a compound whose normal-state charge transport and thermodynamic properties have been studied extensively and shown to exhibit canonical Fermi-liquid behavior. Complementary RIXS experiments on slightly overdoped Tl$_2$Ba$_2$CuO$_{6+δ}$ ($T_c =89$ K) and on Y$_{1-x}$Ca$_{x}$Ba$_2$Cu$_3$O$_{6+δ}$ compounds spanning a wide range of doping levels indicate that these excitations exhibit energi…
Understanding of the precise mechanisms of high-temperature superconductivity is elusive. In particular, in order to solve the puzzle of the pairing mechanism, it is important to understand the detailed nature of the excitations at energies around the superconducting gap. While measurements of the dynamics of excited electronic populations have been able to give some insight, they have largely neglected the intricate dynamics of quantum coherence. Here, we apply multidimensional coherent spectroscopy for the first time to a prototypical cuprate and report unprecedented coherent dynamics persis…
All underdoped high-temperature cuprate superconductors appear to exhibit charge density wave (CDW) order, but both the underlying symmetry breaking and the origin of the CDW remain unclear. We use X-ray diffraction to determine the microscopic structure of the CDW in an archetypical cuprate YBa$_2$Cu$_3$O$_{6.54}$ at its superconducting transition temperature Tc ~ 60 K. We find that the CDWs present in this material break the mirror symmetry of the CuO2 bilayers. The ionic displacements in a CDW have two components: one perpendicular to the CuO$_2$ planes, and another parallel to these planes…
Understanding the thermodynamic properties of high-$T_c$ cuprate superconductors is a key step to establish a satisfactory theory of these materials. The electronic specific heat is highly unconventional, distinctly non-BCS, with remarkable doping-dependent features extending well beyond $T_c$. The pairon concept, bound holes in their local antiferromagnetic environment, has successfully described the tunneling and photoemission spectra. In this article, we show that the model explains the distinctive features of the entropy and specific heat throughout the temperature-doping phase diagram. Th…
Recently, machine learning was applied to extract both the normal and the anomalous components of the self-energy from photoemission data at the antinodal points in Bi-based cuprate high-temperature superconductors [Y. Yamaji {\it et al.}, arXiv:1903.08060]. It was argued that both components do show prominent peaks near 50 meV, which hold information about the pairing glue, but the peaks are hidden in the actual data, which measure only the total self-energy. We analyze the self-energy within an effective fermion-boson theory. We show that soft thermal fluctuations give rise to peaks in both …
We undertake a detailed high-resolution diffraction study of a novel plain band insulator, La$_2$MgO$_4$, which may be viewed as a structural surrogate system of the undoped end-member of the high-T$_c$ superconductors, La$_{2-x-y}$A$^{2+}_x$RE$^{3+}_y$CuO$_{4}$ (A = Ba, Sr, RE= Rare Earth). We find that La$_2$MgO$_4$ exhibits the infamous low-temperature orthorhombic (LTO) to low-temperature tetragonal (LTT) phase transition that has been linked to the suppression of superconductivity in a variety of underdoped cuprates, including the well known La$_{2-x}$Ba$_{x}$CuO$_4$ ($x=0.125$). Furtherm…
Recent low-temperature scanning tunnelling spectroscopy experiments on the surface of BSCCO-2212 have revealed a strong positive correlation between the position of localized resonances at -960 meV identified with interstitial oxygen dopants and the size of the local spectral gap. We review efforts to understand these correlations within a model where the dopants modulate the pair interaction on an atomic scale. We provide further evidence for this model by comparing the correlations between the dopants and the local density of states with experimental results.
We report $^{63,65}$Cu NQR measurements on slightly underdoped NdBa$_{2}$Cu$_{3}$O$_{6+y}$ single crystals heavily doped by Ni and Zn impurities. Owing to the impurity doping superconductivity is fully suppressed in both cases. The Ni strongly enhances magnetic correlations and induces a wipeout of the NQR signal comparable to that found in stripe ordered lanthanum cuprates. In contrast, the magnetism is suppressed in the Zn doped sample where no wipeout effect is observed and the nuclear spin relaxation rate is reduced. Our findings are in a striking correspondence with the different impact o…
The representative cuprate, La$_{2-x}$M$_x$CuO$_4$, with M = Sr and $x = 1/8$ is studied via first-principles calculations in the high-temperature tetragonal (HTT), low-temperature orthorhombic (LTO), and low-temperature less-orthorhombic (LTLO) structures. By suppressing the magnetism and superconductivity, the LTLO phase, which has rarely been observed in La$_{2-x}$Sr$_x$CuO$_4$, is found to be the ground state, where the structural phase transitions, HTT$\rightarrow$LTO$\rightarrow$LTLO, can be understood via phonon instability. While the La-O composition is identified to be responsible for…
Inhomogeneous reduction-annealing effects on the electron-doped cuprate superconductor revealed by micro-focused angle-resolved photoemission spectroscopy
Electron-phonon coupling (EPC) is one of the most common and fundamental interactions in solids. It not only dominates many basic dynamic processes like resistivity, thermal conductivity etc, but also provides the pairing glue in conventional superconductors. But in high-temperature superconductors (HTSC), it is still controversial whether or not EPC is in favor of paring. Despite the controversies, many experiments have provided clear evidence for EPC in HTSC. In this paper, we briefly review EPC in cuprate and iron-based superconducting systems revealed by Raman scattering. We introduce how …
We present an overview of angle-resolved photoemission spectroscopy (ARPES) studies of high-temperature cuprate superconductors aiming at elucidating the relationship between the superconductivity, the pseudogap, and the Fermi arc. ARPES studies of underdoped samples show a momentum dependence of the energy gap below Tc which deviates from a simple d-wave form, suggesting the coexistence of multiple energy scales in the superconducting state. Hence, two distinct energy scales have been introduced, namely, the gap near the node (characterized by Delta_0) and in the anti-nodal region (characteri…
A fundamental connection between superconductivity and quantum spin fluctuations in underdoped cuprates, is revealed. A variational calculation shows that {\em Cooper pair hopping} strongly reduces the local magnetization $m_0$. This effect pertains to recent neutron scattering and muon spin rotation measurements in which $m_0$ varies weakly with hole doping in the poorly conducting regime, but drops precipitously above the onset of superconductivity.
Using 61-T pulsed magnetic fields, the normal-state ρ_{ab} and ρ_{c} are measured in Bi-2201 system down to 0.66 K, and the coexistence of the "metallic" ρ_{ab} and the "semiconducting" ρ_{c}, usually called the charge confinement behavior, was confirmed to extend far below T_c. Recent measurement of the c-axis magnetoresistance under 16 T dc magnetic field in heavily underdoped Y-123 crystals revealed that the peculiar c-axis charge transport, and thus the charge confinement, is fundamentally related to the antiferromagnetic spin fluctuations.
Electron-phonon coupling revealed by charge density fluctuations in cuprate superconductors
Politecnico di Milano（米兰理工大学）；European XFEL（欧洲X射线自由电子激光装置）；ESRF, The European Synchrotron（欧洲同步辐射光源）；Chalmers University of Technology（查尔姆斯理工大学）；Università di Roma “La Sapienza”（罗马第一大学）
Several recent experiments have revealed that the charge density $ρ$ in a given compound (mostly underdoped) is intrinsic inhomogeneous with large nanoscale spatial variations. Therefore it is appropriate to define a local charge density $ρ(r)$. These differences in the local charge concentration yield insulator and metallic regions, either in an intrinsic granular or in a stripe morphology. In the metallic region, the inhomogeneous charge density produces spatial or local distributions of superconducting critical temperatures $T_c(r)$ and zero temperature gap $Δ_0(r)$. We propose that the sup…
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…
Transport measurements provide important characterizations of the nature of stripe order in the cuprates. Initial studies of systems such as La(1.6-x)Nd(0.4)Sr(x)CuO(4) demonstrated the strong anisotropy between in-plane and c-axis resistivities, but also suggested that stripe order results in a tendency towards insulating behavior within the planes at low temperature. More recent work on La(2-x)Ba(x)CuO(4) with x=1/8 has revealed the occurrence of quasi-two-dimensional superconductivity that onsets with spin-stripe order. The suppression of three-dimensional superconductivity indicates a frus…
