We address the kinetic competition between charge striped order and superconductivity in La$_{1.675}$Eu$_{0.2}$Sr$_{0.125}$CuO$_{4}$. Ultrafast optical excitation is tuned to a mid-infrared vibrational resonance that destroys charge order and promptly establishes transient coherent interlayer coupling in this material. This effect is evidenced by the appearance of a longitudinal plasma mode reminiscent of a Josephson plasma resonance. We find that coherent interlayer coupling can be generated up to the charge order transition $T_{CO} \approx$ 80 K, far above the equilibrium superconducting transition temperature of any lanthanide cuprate. Two key observations are extracted from the relaxation kinetics of the interlayer coupling. Firstly, the plasma mode relaxes through a collapse of its coherence length and not its density. Secondly, two distinct kinetic regimes are observed for this relaxation, above and below spin order transition $T_{SO} =$ 25 K. Especially, the temperature independent relaxation rate observed below $T_{SO}$ is anomalous and suggests coexistence of superconductivity and stripes rather than competition. Both observations support arguments that a low temperature coherent stripe (or pair density wave) phase suppresses c-axis tunnelling by disruptive interference rather than by depleting the condensate.
The oxygen isotope effect on the superconductivity, stripe phase and structure transition is systematically investigated in La$_{1.6-x}$Nd$_{0.4}$Sr$_{x}$CuO$_4$ with static stripe phase. Substitution of $^{16}$O by $^{18}$O leads to a decrease in superconducting transition temperature T$_C$, while enhances the temperature of the structural transition from low-temperature-orthorhombic (LTO) phase to low-temperature-tetragonal (LTT) phase. Compared to the Nd free sample, a larger isotope effect on $T_C$ is observed in La$_{1.6-x}$Nd$_{0.4}$Sr$_{x}$CuO$_4$. These results indicate that the distor…
We present a detailed analysis on the hopping between monolayer CuO$_2$ and bulk CuO$_2$ plane in the Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ substrate. With a two-band model, we demonstrate that the nodeless gap can only exist when the hole concentration in monolayer CuO$_2$ plane is very large or very small. We argued that the possible phase separation may play important role in the recent experimental observation of nodeless gap.
Superconductivity has recently been discovered in Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-δ}$ with a maximum $T_c$ of about 15K. Since the CuO planes in this material are believed to be insulating, it has been proposed that the superconductivity occurs in the double (or zigzag) CuO chain layer. On phenomenological grounds, we propose a theoretical interpretation of the experimental results in terms of a new phase for the zigzag chain, labelled by C$_1$S$_{3/2}$. This phase has a gap for some of the relative spin and charge modes but no total spin gap, and can have a divergent superconducting susceptibi…
This paper has been withdrawn by the authors, because we had probably observed some spurious intensity with x=0.29 sample (Fig.3(b)). This came out after further studies of the detailed x-dependence of the highest energy LO phonon branch in LSCO.
Superlattices of the repeated structure La(1.56)Sr(0.44)CuO(4)/La(2)CuO(4) (LSCO-LCO), where none of the constituents is superconducting, show a superconducting transition of T_c \simeq 25 K. In order to elucidate the nature of the superconducting state we have performed a low-energy muSR study. By applying a magnetic field parallel (Meissner state) and perpendicular (vortex state) to the film planes, we could show that superconductivity is sheet like, resulting in a very anisotropic superconducting state. This result is consistent with a simple charge-transfer model, which takes into account …
Meissner type superconductivity extending up to 13 - 18 degrees Celsius was confirmed in the composite material consisting of metallic particles Ag5Pb2O6 dispersed in an insulating CuO matrix, and superconductivity mechanism is based upon inter particle interaction acting in the quantum tunnelling regime.
The recently discovered cuprate superconductor Ba$_2$CuO$_{3+δ}$ exhibits a high $T_c\simeq73$K at $δ\simeq0.2$. The polycrystal grown under high pressure has a structure similar to La$_2$CuO$_4$, but with dramatically different lattice parameters due to the CuO$_6$ octahedron compression. The crystal field in the compressed Ba$_2$CuO$_4$ leads to an inverted Cu $3d$ $e_g$ complex with the $d_{x^2-y^2}$ orbital sitting below the $d_{3z^2-r^2}$ and an electronic structure highly unusual compared to the conventional cuprates. We construct a two-orbital Hubbard model for the Cu $d^9$ state at hol…
We report a doping dependant Electronic Raman Scattering (ERS) study of HgBa$_2$CuO$_{4+δ}$ (Hg-1201) single crystals. We investigate the dynamics of the antinodal and nodal quasiparticles. We show that the dynamical response of the antinodal quasiparticles is strongly reduced towards the underdoped regime in both the normal and superconducting states. When probing the nodal quasiparticles, we are able to distinguish between the energy scale of the pseudogap and that of the superconducting gap. A simple model relating the suppression of the dynamical response of the antinodal quasiparticles to…
We report the local magnetic response of an electron-doped cuprate superconductor, Pr$_{0.89}$LaCe$_{0.11}$CuO$_{4}$ ($T_c\simeq26$ K), studied by muon spin rotation (\msr) over a field range from 200 Oe to 50 kOe. In the paramagnetic state, the muon Knight shift along the crystal c-axis ($K_μ^z$) is proportional to the in-plane susceptibility $χ_{ab}$. More surprisingly, $K_μ^z$ is strongly enhanced by the occurrence of superconductivity (below $\sim$40 kOe), changing its sign from positive to negative around $\sim1$ kOe with increasing field. This finding can be understood by considering the…
Recently, Matsukawa et al. have discovered a new superconductor Pr_2Ba_4Cu_7O_15-delta in which metallic CuO double chains are responsible for the superconductivity. To investigate the superconductivity, we employ the d-p double chain model where the tight-binding parameters are determined so as to fit the LDA band structure. On the basis of the Tomonaga-Luttinger liquid theory, we obtain the phase diagram including the superconducting phase in the weak coupling limit. We also calculate the Luttinger liquid parameter K_rho as a function of the electron density $n$ by using the Hartree-Fock app…
Composite material was prepared from Byström-Evers metallic particles Ag5Pb2O6 dispersed in a semiconducting matrix CuO-Cu2O. Partial substitution of CuO by Cu2O increases electric conductivity at 673 K for 2-3 orders of magnitude above Landauer conductivity e2/ha indicated by pure CuO matrix. Onset of superconductivity at 86-375 K presented in this and previous works is discussed in the framework of the exciton-polariton mechanism occurring on the grain surfaces.
We have performed a series of elastic neutron scattering measurements on 1/8-hole doped La$_{1.875}$Ba$_{0.125-x}$Sr$_{x}$CuO$_{4}$ single crystals with {\it x} = 0.05, 0.06, 0.075 and 0.085. % Both charge-density-wave (CDW) and spin-density-wave (SDW) orders are found to develop simultaneously below the structural transition temperature between the low-temperature orthorhombic (LTO) and low-temperature tetragonal (LTT) or low-temperature less-orthorhombic (LTLO) phases. % In the ground state the CDW order is observed only in the LTT/LTLO phase and drastically degrades towards the LTO boundary…
This paper describes the first 63-Cu NMR study of an electron-doped infinitely-layered high Tc superconductor Sr$_0.9$La$_0.1$CuO$_2$ (Tc=42K). The spin dynamics in the normal state above Tc exhibits qualitatively the same behavior as some hole-doped materials with significantly enhanced spin fluctuations. Below Tc, we observed no signature of a Hebel-Slichter coherence peak, suggesting an unconventional nature of the symmetry of the superconducting order parameter.
We study the electronic structure and superconductivity in CuO$_2$ monolayer grown recently on $d$-wave cuprate superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$. Density functional theory calculations indicate significant charge transfer across the interface such that the CuO$_2$ monolayer is heavily overdoped into the hole-rich regime yet inaccessible in bulk cuprates. We show that both the Cu $d_{x^2-y^2}$ and $d_{3z^2-r^2}$ orbitals become important and the Fermi surface contains one electron and one hole pocket associated with the two orbitals respectively. Constructing a minimal correlated tw…
We identify a distinct superconducting phase at the interface of a La$_{1.48}$Nd$_{0.4}$Sr$_{0.12}$CuO$_4$ (LNSCO)/La$_{1.84}$Sr$_{0.16}$CuO$_4$ (LSCO) epitaxial bilayer system using ac screening measurements. A model based on inter-diffusion of quasiparticles and condensate at the interface yields a thickness of $\sim$ 25 nm for the interfacial layer. Two-dimensional superconductivity of the interface layer appears to be governed by Kosterlitz-Thouless-Berezinskii transition. A parallel magnetic field suppresses the superconducting transition temperature of this layer with a pair breaking par…
Superconductivity in high temperature superconductors is achieved by introducing charge carriers into cuprate insulators containing CuO$_2$ planes. Perturbation in these CuO$_2$ planes suppresses superconductivity by strongly affecting the electronic environment. Here we have use photoinduced electronic modification of Cu ion in CuO$_2$ plane to investigate the effect of local perturbation in Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+δ}$. This method has been used to suppress superconducting transition temperature T$_c$. We show that our results on photoinduced suppression of superconductivity are consis…
The possible inhomogeneity of superconductivity has been investigated by means of bulk-sensitive probes, using La_2-x_Sr_x_CuO_4_ (LSCO) single crystals from the underdoped to optimally doped regime. Measurements of the magnetic susceptibility, chi, on field cooling and specific heat have revealed that both the absolute value of chi at 2 K, regarded as corresponding to the superconducting (SC) volume fraction in a sample, and the Sommerfeld constant, reflecting the density of states of quasiparticles at the Fermi level, exhibit significant dependence on x, namely, on the hole concentration. Th…
The interplay between superconductivity and the pseudogap is an important aspect of cuprate physics. However, the nature of the pseudogap remains controversial, in part because different experiments have suggested different gap functions. Here we present a photon-energy-dependence angle-resolved photoemission spectroscopy (ARPES) study on Bi$_{1.5}$Pb$_{0.55}$Sr$_{1.6}$La$_{0.4}$CuO$_{6+δ}$. We find that antinodal ARPES spectra at low photon energies are dominated by background signals which can lead to a misevaluation of the spectral gap size. Once background is properly accounted for, indepe…
Electron-doped and hole-doped superconducting cuprates exhibit a symmetric phase diagram as a function of doping. This symmetry is however only approximate. Indeed, electron-doped cuprates become superconductors only after a specific annealing process: This annealing affects the oxygen content by only a tiny amount, but has a dramatic impact on the electronic properties of the sample. Here we report the occurrence of superconductivity in oxygen-deficient Nd$_{2-x}$Ce$_x$CuO$_4$ thin films grown in an oxygen-free environment, after annealing in pure argon flow. As verified by x-ray diffraction,…
Strong correlation between field-induced antiferromagnetic (AF) order and superconductivity is demonstrated for an electron-doped cuprate superconductor, Pr$_{1-x}$LaCe$_{x}$CuO$_{4-δ}$ (PLCCO). In addition to the specimen with $x=0.11$ (which is close to the AF phase boundary, $x\simeq0.10$), we show that the one with $x=0.15$ ($T_c\simeq16$ K at zero field) also exhibits the field-induced AF order with a reduced magnitude of the induced moment. The uniform muon Knight shift at a low magnetic field ($\sim10^2$ Oe) indicates that the AF order is not localized within the cores of flux lines, wh…
Comment on "Light-induced melting of competing stripe orders without introducing superconductivity in La$_{1.875}$Ba$_{0.125}$CuO$_4$" (arXiv:2306.07869v1)
Optical excitation of stripe-ordered La$_{2-x}$Ba$_x$CuO$_4$ has been shown to transiently enhance superconducting tunneling between the CuO$_2$ planes. This effect was revealed by a blue-shift, or by the appearance of a Josephson Plasma Resonance in the terahertz-frequency optical properties. Here, we show that this photo-induced state can be strengthened by the application of high external magnetic fields oriented along the c-axis. For a 7-Tesla field, we observe up to a ten-fold enhancement in the transient interlayer phase correlation length, accompanied by a two-fold increase in the relax…
Recent experiments on Pr$_{0.89}$LaCe$_{0.11}$CuO$_4$ observe an anisotropic spin-correlation gap and a nonmonotonic superconducting (SC) gap, which we analyze within the framework of a $t-t^{\prime}-t^{\prime\prime}-t^{\prime\prime\prime}-t^{iv}-U$ model with a $d_{x^2-y^2}$ pairing interaction including a third harmonic contribution. By introducing a realistic broadening of the quasiparticle spectrum to reflect small-angle scattering, our computations explain the experimental observations, especially the presence of a maximum in the leading edge gap in the vicinity of the hot-spots. Our anal…
We report enhanced superconductivity in bilayer thin films consisting of superconducting La$_{1.6-x}$Nd$_{0.4}$Sr$_{x}$CuO$_{4}$ with 0.06 $\leq x<$ 0.20 and metallic but non-superconducting La$_{1.55}$Sr$_{0.45}$CuO$_{4}$. These bilayers show a maximum increase in superconducting transition temperature ($T_c$) of more than 200% for $x$ = 0.06 while no change in $T_c$ is observed for the bilayers with $x\geq$ 0.20. The analysis of the critical current and kinetic inductance data suggests 2-3 unit cells thick interfacial layer electronically perturbed to have a higher $T_c$. A simple charge tra…
Two critical points have been revealed in the normal-state phase diagram of the electron-doped cuprate superconductor Nd$_{2-x}$Ce$_x$CuO$_4$ by exploring the Fermi surface properties of high quality single crystals by high-field magnetotransport. First, the quantitative analysis of the Shubnikov-de Haas effect shows that the weak superlattice potential responsible for the Fermi surface reconstruction in the overdoped regime extrapolates to zero at the doping level $x_c = 0.175$ corresponding to the onset of superconductivity. Second, the high-field Hall coefficient exhibits a sharp drop right…
Anelastic relaxation and $^{139}$La NQR relaxation measurements in La$_{2-x}$Sr$_x$CuO$_4$ for Sr content x around 2 and 3 percent, are presented and discussed in terms of spin and lattice excitations and ordering processes. It is discussed how the phase diagram of La$_{2-x}$Sr$_x$CuO$_4$ at the boundary between the antiferromagnetic (AF) and the spin-glass phase (x = 0.02) could be more complicate than previous thought, with a transition to a quasi-long range ordered state at T = 150 K, as indicated by recent neutron scattering data. On the other hand, the $^{139}$La NQR spectra are compatibl…
The fluctuation exchange, or FLEX, approximation for interacting electrons is applied to study instabilities in the standard three-band model for CuO2 layers in the high-temperature superconductors. Both intra-orbital and near-neigbor Coulomb interactions are retained. The filling dependence of the d(x2-y2) transition temperature is studied in both the "hole-doped" and "electron-doped" regimes using parameters derived from constrained-occupancy density-functional theory for La2CuO4. The agreement with experiment on the overdoped hole side of the phase diagram is remarkably good, i.e., transiti…
Using the numerical diagonalization method, we examine the one-dimensional t_1-t_2-J_1-J_2 model (zigzag chain t-J model) which represents an effective model for metallic CuO double chain in the superconductor Pr_2Ba_4Cu_7O_15-δ. Based on the Tomonaga-Luttinger liquid theory, we calculate the Luttinger-liquid parameter K_ρas a function of electron density n. It is found that superconductivity is realized in parameter region corresponding to the experimental result. We show phase diagram of spin gap on the t_2/|t_1|-n plane by analyzing the expectation value of twist-operator Z_σin the spin sec…
The evolution of the electronic state through the reduction annealing has been investigated in electron-doped Pr_1.3-x_La_0.7_Ce_x_CuO_4+delta_ (x=0.10) single crystals with the so-called T' structure. From the ab plane and c axis electrical resistivity measurements in magnetic fields, it has been found that, through the reduction annealing, the strongly localized state of carriers accompanied by the antiferromagnetic (AF) pseudogap in the as-grown crystal changes to a metallic state bringing about the Kondo effect without AF pseudogap and to a superconducting state. These results are able to …
We report a site selective Cu-NMR study on under-doped Hg-based five-layered high-$T_{\rm c}$ cuprate HgBa2Ca4Cu5Oy with a Tc=72 K. Antiferromagnetism (AF) has been found to take place at TN=290 K, exhibiting a large antiferromagnetic moment of 0.67-0.69uB at three inner planes (IP's). This value is comparable to the values reported for non-doped cuprates, suggesting that the IP may be in a nearly non-doped regime. Most surprisingly, the AF order is also detected with M(OP)=0.1uB even at two outer planes (OP's) that are responsible for the onset of superconductivity (SC). The high-Tc SC at Tc …
To understand the recently observed high temperature superconductivity in the monolayer CuO$_2$ grown on the Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ substrates, we propose a two band model of the hybridized oxygen $p_x$ and $p_y$ orbitals with the proximity effect of the substrate. We demonstrate that both the nodal and nodeless d-wave superconducting states can be induced by the proximity effect, depending on the strengths of the pairing parameters.
Bulk crystals of electron-doped cuprates with the T'-type structure require both Ce substitutions and reduction annealing for the emergence of superconductivity while the reduction annealing alone can induce superconductivity in thin films of the T'-type cuprates. In order to reveal low-energy electronic states which are responsible for the superconductivity, we have conducted angle-resolved photoemission spectroscopy measurements on thin films of the superconducting Ce-free T'-type cuprate Pr$_2$CuO$_4$. The results indicate that the overall band structure and the Fermi surface area of the su…
The magnetic ground state of an electron-doped cuprate superconductor Pr$_{1-x}$LaCe$_x$CuO$_{4+α-δ}$ ($x=0.11, α\simeq0.04$) has been studied by means of muon spin rotation/relaxation (\msr) over a wide variety of oxygen depletion, $0.03\leδ\le0.12$. Appearance of weak random magnetism over entire crystal volume has been revealed by a slow exponential relaxation. The absence of $δ$-dependence for the random magnetism and the multiplet pattern of muon Knight shift at higher fields strongly suggest that the random moments are associated with excited Pr$^{3+}$ ions under crystal electric field.
The reflectivity $R (ω)$ of both the $ab$ plane and the c axis of two single crystals of La$_{1.875}$Ba$_{0.125-y}$Sr$_{y}$CuO$_4$ has been measured down to 5 cm$^{-1}$, using coherent synchrotron radiation below 30 cm$^{-1}$. For $y$ = 0.085, a Josephson Plasma Resonance is detected at $T \ll T_c$ = 31 K in $R_{c} (ω)$, and a far-infrared peak (FIP) appears in the optical conductivity below 50 K, where non-static charge ordering (CO) is reported by X-ray scattering. For $y$ = 0.05 ($T_c$ = 10 K), a FIP is observed in the low-temperature tetragonal phase below the ordering temperature $T_{CO}$…
We show that hole-doped cuprates can harbor {\it Fermi-surface-free superconductivity} similar to the case of the pnictides. This occurs near the doping at which a new Fermi surface pocket appears in the antinodal region. The change in Fermi surface topology is accompanied by a characteristic rise in spectral weight. Our results support the presence of a trisected superconducting dome, and suggest that superconductivity is responsible for stabilizing the $(π,π)$ magnetic order.
We study electronic states of multilayer cuprates in the normal phases as functions of the number of CuO_2 planes and the doping rate. The resonating valence bond wave function and the Gutzwiller approximation are used for a two-dimensional multilayer t-t'-t''-J model. We calculate the electron-removal spectral functions at (π,0) in the CuO_2 plane next to the surface to understand the angle-resolved photoemission spectroscopy (ARPES) spectra. We find that the trilayer spectrum is narrower than the bilayer spectrum but is wider than the monolayer spectrum. In the tri- and tetralayer systems, t…
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…
A mixture of powdered Cu and CuO has been subjected to a shock-wave pressure of 350 kbar with following quenching of the vacuum-encapsulated product to 77 K. The ac magnetic susceptibility measurements of the samples have revealed metastable superconductivity with Tc = 19.5 K, characterized by glassy dynamics of the shielding currents below Tc . Comparison of the ac susceptibility and the dc magnetization measurements infers that the superconductivity arises within the granular interfacial layer formed between metallic Cu and its oxides due to the shock-wave treatment.
Electron-doped infinite-layer Sr$_{1-x}$Eu$_{x}$CuO$_{2+y}$ films over a wide doping range have been prepared epitaxially on SrTiO$_3$(001) using reactive molecular beam epitaxy. In-plane transport measurements of the single crystalline samples reveal a dome-shaped nodeless superconducting phase centered at $x$ $\sim$ 0.15, a Fermi-liquid behavior and pronounced upturn in low temperature resistivity. We show that the resistivity upturn follows square-root temperature dependence, suggesting the emergence of superconductivity via a three-dimensional percolation process. The percolative supercond…
The relaxation function theory of doped two-dimensional $S=1/2$ Heisenberg antiferromagnetic (AF) system in the paramagnetic state is presented taking into account the hole subsystem as well as both the electron and AF correlations. The expression for fourth frequency moment of relaxation shape function is derived within the $t-J$ model. The presentation obeys rotational symmetry of the spin correlation functions and is valid for all wave vectors through the Brillouin zone. The spin diffusion contribution to relaxation rates is evaluated and is shown to play a significant role in carrier free …
In superconducting copper oxides some Cu-O bond-stretching phonons around 70meV show anomalous giant softening and broadening of electronic origin and electronic dispersions have large renormalization kinks near the same energy. These observations suggest that phonon broadening originates from quasiparticle excitations across the Fermi surface and the electronic dispersion kinks originate from coupling to anomalous phonons. We measured the phonon anomaly in underdoped (x=0.05) and overdoped (x=0.20,0.25) La$_{2-x}$Sr$_x$CuO$_4$ by inelastic neutron and x-ray scattering with high resolution. Co…
A nodeless superconducting (SC) gap was reported in a recent scanning tunneling spectroscopy experiment of a copper-oxide monolayer grown on the Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi2212) substrate [Y. Zhong {\it et al.}, Sci. Bull. {\bf 61}, 1239 (2016)], which is in stark contrast to the nodal d-wave pairing gap in the bulk cuprates. Motivated by this experiment, we first show with first-principles calculations that the tetragonal CuO (T-CuO) monolayer on the Bi2212 substrate is more stable than the commonly postulated CuO$_{2}$ structure. The T-CuO monolayer is composed of two CuO$_2$ layers sh…
The infinite-layer compound ACuO$_{2}$ (A $=$ alkaline-earth ions) is regarded as the most suitable material for exploring the fundamental nature of the CuO$_2$ plane because it does not contain a charge-reservoir block, such as a rock-salt or a fluorite like block. We report that superconductivity in the infinite-layer compound Sr$_{0.9}$La$_{0.1}$CuO$_2$ is of a three-dimensional nature, in contrast to the quasi two-dimensional superconducting behavior of all other cuprates. The key observation is that the $c$-axis coherence length is longer than the $c$-axis lattice constant even at zero te…
Recent spectroscopic observations of a d-wave-like gap in stripe-ordered La(2-x)Ba(x)CuO(4) with x=1/8 have led us to critically analyze the anisotropic transport and magnetization properties of this material. The data suggest that concomitant with the spin ordering is an electronic decoupling of the CuO(2) planes. We observe a transition (or crossover) to a state of two-dimensional (2D) fluctuating superconductivity, which eventually reaches a 2D superconducting state below a Berezinskii-Kosterlitz-Thouless transition. Thus, it appears that the stripe order in La(2-x)Ba(x)CuO(4) frustrates th…
In order to realize superconductivity in cuprates with the T'-type structure, not only chemical substitution (Ce doping) but also post-growth reduction annealing is necessary. In the case of thin films, however, well-designed reduction annealing alone without Ce doping can induce superconductivity in the T'-type cuprates. In order to unveil the origin of superconductivity in the Ce-undoped T'-type cuprates, we have performed bulk-sensitive hard x-ray photoemission and soft x-ray absorption spectroscopies on superconducting and non-superconducting Nd$_{2-x}$Ce$_x$CuO$_4$ ($x=$ 0, 0.15, and 0.19…
The microscopic understanding of high-temperature superconductivity in cuprates has been hindered by the apparent complexity of crystal structures in these materials. We used scanning tunneling microscopy and spectroscopy to study an electron-doped copper oxide compound Sr$_{1-x}$Nd$_x$CuO$_2$ that has only bare cations separating the CuO$_2$ planes and thus the simplest infinite-layer structure among all cuprate superconductors. Tunneling conductance spectra of the major CuO$_2$ planes in the superconducting state revealed direct evidence for a nodeless pairing gap, regardless of variation of…
We have systematically studied the transport properties of the La$_{2-x}$Y$_{x}$CuO$_{4}$(LYCO) films of T'-phase ($0.05\leq x \leq 0.30$). In this nominally "undoped" system, superconductivity was acquired in certain Y doping range ($0.10\leq x \leq 0.20$). Measurements of resistivity, Hall coefficients in normal states and resistive critical field ($H^ρ_{c2}$)in superconducting states of the T'-LYCO films show the similar behavior as the known Ce-doped n-type cuprate superconductors, indicating the intrinsic electron-doping nature. The charge carriers are induced by oxygen deficiency. Non-su…
This paper reports muon spin relaxation (MuSR) measurements of two single crystals of the title high-Tc cuprate systems where static incommensurate magnetism and superconductivity coexist. By zero-field MuSR measurements and subsequent analyses with simulations, we show that (1) the maximum ordered Cu moment size (0.36 Bohr magneton) and local spin structure are identical to those in prototypical stripe spin systems with the 1/8 hole concentration; (2) the static magnetism is confined to less than a half of the volume of the sample, and (3) regions with static magnetism form nano-scale islands…
In this article, we studied the role of oxygen in Pr$_{2}$CuO$_{4\pmδ}$ thin films fabricated by polymer assisted deposition method. The magnetoresistance and Hall resistivity of Pr$_{2}$CuO$_{4\pmδ}$ samples were systematically investigated. It is found that with decreasing the oxygen content, the low-temperature Hall coefficient ($R_H$) and magnetoresistance change from negative to positive, similar to those with the increase of Ce-doped concentration in R$_{2-x}$Ce$_{x}$CuO$_{4}$ (R= La, Nd, Pr, Sm, Eu). In addition, $T_c$ versus $R_H$ for both Pr$_{1-x}$LaCe$_{x}$CuO$_{4}$ and Pr$_{2}$CuO$…
Electronic Structure and Superconductivity in La$_{1.55}$Sr$_{0.45}$CuO$_4$/La$_2$CuO$_4$ Artificial High-$T_c$ Superlattices Probed by Hard and Soft X-ray Spectroscopy
Temple University（天普大学）；Diamond Light Source Ltd.（钻石光源有限公司）；Advanced Light Source, Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室先进光源中心）；Max Planck Institute for Solid State Research（马克斯·普朗克固态研究所）；Institute of Crystallography, Italian National Research Council, IC-CNR（意大利国家研究委员会晶体学研究所）；Rome International Center for Materials Science Superstripes, RICMASS（罗马国际材料科学超条带研究中心）
The effect of Pr substitution on the superconductivity and interlayer coupling of Bi2212 system is investigated. Magnetic and transport measurements were performed for purposes of characterization. The superconducting transition temperature Tc first increased and then decreased till it became zero at x=0.6. The effective superconducting volume also decreases due to Pr substitution. From the fluctuation conductivity analyses it is found that the interlayer coupling constant J decreases monotonically with increase of the Pr content. This result shows that the Pr doping weakens the CuO2 interlaye…
We present the first demonstration of vortices in an electron-type cuprate superconductor, the highest $T_c$ (= 43 K) electron-type cuprate $Sr_{0.9}La_{0.1}CuO_2$. Our spatially resolved quasiparticle tunneling spectra reveal a hidden low-energy pseudogap inside the vortex core and unconventional spectral evolution with temperature and magnetic field. These results cannot be easily explained by the scenario of pure superconductivity in the ground state of high-$T_c$ superconductivity.
We have measured out-of-plane resistivity $ρ_c$ for La$_{2-x}$Sr$_{x}$CuO$_{4}$ under anisotropic pressure. c-axis compression, which decreases $ρ_c$, reduces $T_{\rm c}$ drastically, whereas c-axis extention, which increases $ρ_c$, enhances $T_{\rm c}$ from 38K at ambient pressure to 51.6K at 8GPa. We find that the variation of $T_{\rm c}$ scales as a function of $ρ_c$, and that the c-axis pressure coefficient is much stronger than the ab-axis one. These imply that $T_{\rm c}$ depends primarily on the interlayer, rather than the in-plane, lattice parameter.
The influence of nonstoichiometric disorder on the in-plane resistivity and SC-transition has been investigated for Nd{2-x}Ce{x}CuO{4+δ} single crystal films (x=0.15 and 0.18). It is shown that with increasing of $δ$ the in-plane normal state resistivity increases (the mean free path diminishes) and SC-transition temperature decreases with essential broadening of the transition region. The observed evolution from homogeneous metallic (and superconducting) Nd{2-x}Ce{x}CuO{4+δ} system to inhomogeneous dielectric one is described as Anderson-type disorder-induced transition in a two-dimensional e…
