High temperature superconductivity was achieved by introducing holes in a parent compound consisting of copper oxide layers separated by spacer layers. It is possible to dope some of the parent compounds with electrons, and their physical properties are bearing some similarities but also significant differences from the hole doped counterparts. Here, we use a recently developed first principles method, to study the electron doped cuprates and elucidate the deep physical reasons why their behavior is so different than the hole doped materials. We find that electron doped compounds are Slater insulators, e.g. a material where the insulating behavior is the result of the presence of magnetic long range order. This is in sharp contrast with the hole doped materials, where the parent compound is a Mott charge transfer insulator, namely a material which is insulating due to the strong electronic correlations but not due to the magnetic order.
Motivated by recent observations of charge order in the pseudogap regime of hole-doped cuprates, we show that {\it crisscrossed} stripe order can be stabilized by coherent, momentum-dependent interlayer tunneling, which is known to be present in several cuprate materials. We further describe how subtle variations in the couplings between layers can lead to a variety of stripe ordering arrangements, and discuss the implications of our results for recent experiments in underdoped cuprates.
The superconductivity of cuprates, which has been a mystery ever since its discovery decades ago, is created through doping electrons or holes into a Mott insulator. There, however, exists an inherent electron-hole asymmetry in cuprates. The layered crystal structures of cuprates enable collective charge excitations fundamentally different from those of three-dimensional metals, i.e., acoustic plasmons. Acoustic plasmons have been recently observed in electron-doped cuprates by resonant inelastic X-ray scattering (RIXS); in contrast, there is no evidence for acoustic plasmons in hole-doped cup…
Spectral functions are evaluated numerically within the t-t'-J model as relevant for electron-doped cuprates. The Fermi surface develops from a pocket-like into a large one with doping. The corresponding pseudogap in the nodal direction is well resolved at low doping and vanishes at intermediate doping. Its presence is strongly temperature dependent and thus connected to longer-range antiferromagnetic correlations. Features including double effective band and optical conductivity are consistent with experiments on electron-doped cuprates without invoking the closing of the Mott-Hubbard gap.
We study a periodic polaronic system, which exhibits a nanoscale superlattice structure, as a model for hole-doped cuprates with checkerboard-like heterogeneity, as has been observed recently by scanning tunneling microscopy (STM). Within this model, the electronic and phononic excitations are investigated by applying an unrestricted Hartree-Fock and a random phase approximation (RPA) to a multiband Peierls-Hubbard Hamiltonian in two dimensions.
The optical effects due to the loop-current order parameter in under-doped cuprates are studied in order to understand the recent observation of unusual birefringence in electromagnetic propagation in under-doped cuprates. It is shown why birefringence occurs even in multiple domains of order with size of domains much smaller than the wave-length and in twinned samples. Not only is there a rotation of polarization of incident light but also a rotation of the principal optical axis from the crystalline axes. Both are calculated in relative agreement with experiments in terms of the same paramet…
Pr$_4$Ni$_3$O$_8$ is an overdoped analog of hole-doped layered cuprates. Here we show via ab initio calculations that Ce-doped Pr$_4$Ni$_3$O$_8$ (Pr$_3$CeNi$_3$O$_8$) has the same electronic structure as the antiferromagnetic insulating phase of parent cuprates. We find that substantial Ce-doping should be thermodynamically stable and that other 4+ cations would yield a similar antiferromagnetic insulating state, arguing this configuration is robust for layered nickelates of low enough valence. The analogies with cuprates at different $d$ fillings suggest that intermediate Ce-doping concentrat…
After three decades of enormous scientific inquiry, the emergence of superconductivity in the cuprates remains an unsolved puzzle. One major challenge has been to arrive at a satisfactory understanding of the unusual metallic normal state from which the superconducting state emerges upon cooling. A second challenge has been to achieve a unified understanding of hole- and electron-doped compounds. Here we report detailed magnetoresistivity measurements for the archetypal electron-doped cuprate Nd$_{2-x}$Ce$_x$CuO$_{4+δ}$ that, in combination with prior data, provide crucial links between the no…
The high-temperature superconductivity in copper oxides emerges under strong influence of spin correlations in doped Mott insulators. Recent discoveries of charge-order (CO) correlations in Y-based hole-doped cuprates as well as in electron-doped cuprates suggest that charge correlations should also play an important role on the electronic states of cuprates, although those correlations have been so far detected mainly by x-ray scattering measurements. Here we show signatures of CO correlations in transport properties of electron-doped cuprates as anomalous enhancement of the metal-to-insulato…
Light hole doping of lanthanum cuprate strongly suppresses the onset of antiferromagnetic (AF) order. Surprisingly, it simultaneously suppresses the extrapolated zero temperature sub-lattice magnetization. 139La NQR results in lightly Li-doped lanthanum cuprate have demonstrated that these effects are independent of the details of the mobility of the added holes. We propose a model in which doped holes phase separate into charged domain walls that surround ``anti-phase'' domains. These domains are mobile down to ~30 K where they either become pinned to the lattice or evaporate as their constit…
We develop a formalism to study indirect resonant inelastic x-ray scattering (RIXS) in systems with itinerant electrons, accounting for the attraction between valence electrons and the positively-charged core hole exactly, and apply this formalism to the hole-doped cuprate superconductors. We focus on the relationship between RIXS lineshapes and band structure, including broken symmetries. We show that RIXS is capable of distinguishing between competing order parameters, establishing it as a useful probe of the pseudogap phase.
We report the observation of resistivity saturation in lightly doped ($x\sim 0.10)$ as-grown samples of the electron-doped cuprate La$_{2-x}$Ce$_x$CuO$_4$ (LCCO). The saturation occurs at resistivity values roughly consistent with the phenomenological Mott-Ioffe-Regel criterion once the low effective carrier density of these materials is included in the analysis. These results imply that, at least for light doping, the high-temperature metallic phase of these materials is not necessarily strange and may be understood as simply a low-density metal.
We present an approximation for efficient calculation of the Lindhard susceptibility $χ^{L}(q,ω)$ in a periodic system through the use of simple products of real space functions and the fast Fourier transform (FFT). The method is illustrated by providing $χ^{L}(q,ω)$ results for the electron doped cuprate Nd$_{2-x}$Ce$_{x}$CuO$_{4}$ extended over several Brillouin zones. These results are relevant for interpreting inelastic X-ray scattering spectra from cuprates.
The single hole doped CuO_2 plane is studied by the O(3) non-linear σmodel and its CP^1 representation. It is argued that the spin configuration around a Zhang-Rice singlet is described by a half-skyrmion. The form of the excitation spectrum of the half-skyrmion is the same as that in the π-flux phase.
Within the t-t'-J model, the doping dependence of charge dynamics in electron-doped cuprates is studied. The conductivity spectrum shows a pseudogap structure with a low-energy peak appearing at $ω\sim 0$ and an rather sharp midinfrared peak appearing around $ω\sim 0.3\mid t\mid$, and the resistivity exhibits a crossover from the high temperature metallic-like to low temperature insulating-like behavior in the relatively low doped regime, and a metallic-like behavior in the relatively high doped regime, in qualitative agreement with experiments. Our results also show that these unusual behavio…
Antiferromagnetic fluctuations in two dimensions cause a decrease in spectral weight at so-called hot spots associated with the pseudogap in electron-doped cuprates. In the 2D Hubbard model, these hot spots occur when the Vilk criterion is satisfied, namely when the spin correlation length exceeds the thermal de Broglie wavelength. Using the two-particle self-consistent approach, here we show that this criterion may be violated near the antiferromagnetic quantum critical point when sufficient disorder is added to the model. Static disorder decreases inelastic scattering, in contradiction with …
The phase diagram for hole-doped cuprates is discussed. By examining some recent inelastic neutron scattering data obtained on hole-doped cuprates we conclude that the coherent gap in hole-doped cuprates has most likely the magnetic origin and scales with Tc, on average, as 2Delta/kTc = 5.4.
We investigate electronic excitations in La2-x(Br,Sr)xCuO4 using resonant inelastic x-ray scattering (RIXS) at the oxygen K edge. RIXS spectra of the hole-doped cuprates show clear momentum dependence below 1 eV. The spectral weight exhibits positive dispersion and shifts to higher energy with increasing hole concentration. Theoretical calculation of the dynamical charge structure factor on oxygen orbitals in a three-band Hubbard model is consistent with the experimental observation of the momentum and doping dependence, and therefore the dispersive mode is ascribed to intraband charge excitat…
We present a combined study of the angle-resolved-photoemission spectroscopy (ARPES) and quantum Monte Carlo simulations to propose a novel polaronic metallic state in underdoped cuprates. An approximation scheme is proposed to represent underdoped cuprates away from 1/2 filling, replacing the many-body Hamiltonian by that of a single polaron with effective electron-phonon interaction (EPI), that successfully explains many puzzles such as a large momentum-dependent dichotomy between nodal and anti-nodal directions, and an unconventional doping dependence of ARPES in the underdoped region.
Quantum Monte Carlo is used to calculate various pairing correlations of the 2D Hubbard model possessing band features experimentally observed in the cuprates. In the hole-doped case, where the Fermi level lies close to the van Hove singularities around $(0,π)$, the d$_{x^2-y^2}$ pairing correlation is selectively enhanced, while in the electron-doped case, where the singularities are far below the Fermi level and the Fermi surface runs through $(\pm π/2,\pm π/2)$, both d$_{x^2-y^2}$ and d$_{xy}$ correlations are enhanced with the latter having a $\sqrt{2}\times \sqrt{2}$ structure. The two pa…
We examine the effect of core-hole lifetime on the spectral weight of resonant inelastic x-ray scattering (RIXS) in hole-doped cuprates. We calculate the spectral weight by using exact diagonalization technique for a 4x4 doped Hubbard lattice and find that spin-flip channel detecting single-magnon excitation is less sensitive to the core-hole lifetime while in non-spin-flip channel the spectral weight is strongly dependent on the lifetime. In the latter, charge and two-magnon excitations predominately contribute to RIXS for short and long core-hole lifetimes, respectively. For a realistic valu…
We study the evolution of the single-particle spectrum with electron doping in a scheme which adds multiple exchange of transverse spin excitations to the mean-field antiferromagnetic insulator. Away from half-filling small Fermi surface pockets appear first around the X-points, and simultaneously new spectral weight grows in the insulating gap. With further doping the in-gap states develop the character of a renormalized quasiparticle band near the chemical potential. The essential features in momentum-energy space agree well with recent studies using angle-resolved photoemission spectroscopy…
A mean field calculation of the $T\to 0$ limit of the Hall conductance of electron-doped cuprates such as $Pr_{2-x}Ce_xCuO_{4+δ}$ is presented. The data are found to be qualitatively consistent with the reconstruction of the Fermi surface expected upon density wave ordering. The magnitude of the density wave gap is found to be large. The Hall resistance exhibits a nonanalyticity at the quantum critical point for density wave ordering, but the amplitude of the anomaly is found to be unobservably small. The quantum critical contribution to $R_H(B)$ is determined. Quantitative discrepancies betwe…
We have studied the evolution of magnetic and orbital excitations as a function of hole-doping in single crystal samples of Sr2Ir(1-x)Rh(x)O4 (0.07 < x < 0.42) using high resolution Ir L3-edge resonant inelastic x-ray scattering (RIXS). Within the antiferromagnetically ordered region of the phase diagram (x < 0.17) we observe highly dispersive magnon and spin-orbit exciton modes. Interestingly, both the magnon gap energy and the magnon bandwidth appear to increase as a function of doping, resulting in a hardening of the magnon mode with increasing hole doping. As a result, the observed spin dy…
We report magnetoresistance and Hall angle measurements of the electron-doped cuprate La$_{2-x}$Ce$_x$CuO$_4$ over a wide range of dopings from $x = 0.08 - 0.17$. Above 100 K, we find an unconventional $\sim H^{3/2}$ magnetic field dependence of the magnetoresistance observed in all samples doped within the superconducting dome. Further, the measured magnetoresistance violates Kohler's rule. Given the ubiquity of this anomalous magnetoresistance at high temperatures above the superconducting dome, we speculate that the origin of this behavior is linked to the unusual $ρ\sim T^2$ resistivity ob…
The extended and standard t-J models are computationally studied on ladders and planes, with emphasis on the small J/t region. At couplings compatible with photoemission results for undoped cuprates, half-doped stripes separating $π$-shifted antiferromagnetic (AF) domains are found, as in Tranquada's interpretation of neutron experiments. Our main result is that the elementary stripe `"building-block" resembles the properties of $one$ hole at small J/t, with robust AF correlations across-the-hole induced by the local tendency of the charge to separate from the spin (G. Martins {\it et al.}, Ph…
Within the t-t'-J model, the charge asymmetry in superconductivity of hole- and electron-doped cuprates is studied based on the kinetic energy driven superconducting mechanism. It is shown that superconductivity appears over a narrow range of doping in electron-doped cuprates, and the superconducting transition temperature displays the same kind of the doping controlled behavior that is observed in the hole-doped case. However, the maximum achievable superconducting transition temperature in the optimal doping in electron-doped cuprates is much lower than that of the hole-doped case due to the…
The tunneling spectra of the electron-doped cuprate Pr_2-xCe_xCuO4 as a function of doping and temperature is reported. We find that the superconducting gap, delta, shows a BCS-like temperature dependence even for extremely low carrier concentrations (studied here for the first time). Moreover, delta follows the doping dependence of Tc, in strong contrast with tunneling studies of hole-doped cuprates. From our results we conclude that there is a single superconducting energy scale in the electron-doped cuprates.
The symmetries of the order parameter (OP) responsible for pairing and the OP responsible for phase coherence in hole-doped cuprates are discussed. We analyze angle-resolved tunneling, ARPES, Raman scattering and torque measurements performed on hole-doped cuprates. We conclude that, most likely, the OP responsible for phase coherence has the d-wave symmetry whereas the OP responsible for pairing has an anisotropic s-wave symmetry.
Stripe fluctuations in La2NiO4.17 have been studied by 139La NMR using the field and temperature dependence of the linewidth and relaxation rates. In the formation process of the stripes the NMR line intensity is maximal below 230K, starts to diminish around 140K, disappears around 50K and recovers at 4K. These results are shown to be consistent with, but completely complementary to neutron measurements, and to be generic for oxygen doped nickelates and underdoped cuprates.
Within the t-t'-J model, the electron spectrum and quasiparticle dispersion in doped bilayer cuprates in the normal state are discussed by considering the bilayer interaction. It is shown that the bilayer interaction splits the electron spectrum of doped bilayer cuprates into the bonding and antibonding components around the $(π,0)$ point. The differentiation between the bonding and antibonding components is essential, which leads to two main flat bands around the $(π,0)$ point below the Fermi energy. In analogy to the doped single layer cuprates, the lowest energy states in doped bilayer cupr…
Within the t-t'-J model, the asymmetry of the electron spectrum and quasiparticle dispersion in hole-doped and electron-doped cuprates is discussed. It is shown that the quasiparticle dispersions of both hole-doped and electron-doped cuprates exhibit the flat band around the (π,0) point below the Fermi energy. The lowest energy states are located at the (π/2,π/2) point for the hole doping, while they appear at the (π,0) point in the electron-doped case due to the electron-hole asymmetry. Our results also show that the unusual behavior of the electron spectrum and quasiparticle dispersion is in…
We investigate the formation of charge domain walls in an electron-doped extended Hubbard model for the superconducting cuprates. Within an unrestricted Hartree-Fock approach, extended by the introduction of slave-bosons to obtain a more proper treatment of strong correlations, we demonstrate the occurrence of stripes in the (1,1) and (1,-1) directions having one doped electron per stripe site. The different filling, direction and width of these electron-doped stripes with respect to those obtained in the hole-doped systems have interesting observable consequences, which are discussed.
There is a clear discrepancy among the energy-gap values for different 90 K cuprates, inferred from tunneling measurements. By using the phase diagram for hole-doped cuprates we show that tunneling measurements performed on 90 K cuprates, simply, detect two different energy gaps: the pairing gap and the coherent gap, which are identical in conventional superconductors. We find that there are two reasons why tunneling measurements show in one cuprate exclusively the coherent gap while, in another cuprate, they show the pairing gap: (i) the number of CuO2 planes per unit cell in the cuprate, and…
We report neutron scattering studies on single crystals of the electron-doped (n-type) superconducting cuprate Nd2-xCexCuO4 (x=0.15) with Tc = 18 K and 25 K. Unlike the hole-doped (p-type) superconducting cuprates where incommensurate magnetic fluctuations commonly exist, the n-type cuprate shows commensurate magnetic fluctuations at the tetragonal (1/2 1/2 0) reciprocal points both in the superconducting and in the normal state. A spin gap opens up when the n-type cuprate becomes superconducting, as in the optimally doped p-type La2-xSrxCuO4. The gap energy, however, increases gradually up to…
We calculate the normal state Nernst signal in the cuprates resulting from a reconstruction of the Fermi surface due to spin density wave order. An order parameter consistent with the reconstruction of the Fermi surface detected in electron-doped materials is shown to sharply enhance the Nernst signal close to optimal doping. Within a semiclassical treatment, the obtained magnitude and position of the enhanced Nernst signal agrees with Nernst measurements in electron-doped cuprates.
A new electron-doped superconductor Li_x_Sr_2_CuO_2_Br_2_ with x = 0.15 has successfully been synthesized by an electrochemical Li-intercalation technique. The magnetic susceptibility shows superconductivity of bulk with the superconducting transition temperature Tc = 8 K. This compound is the first electron-doped superconducting cuprate with the K_2_NiF_4_ structure.
We present experimental data obtained by different techniques. Some of them are not easy to explain by any theoretical model presented in the literature. However, a MCS model of the superconductivity in hole-doped cuprates, proposed in our previous work, is capable to explain them. Thus, we present an evidence in favor of the MCS model.
Within the kinetic energy driven superconducting mechanism, the effect of the pressure on superconductivity in doped two-leg ladder cuprates is studied. It is shown that the superconducting transition temperature in doped two-leg ladder cuprate superconductors increases with increasing pressure in the underpressure regime, and reaches a maximum in the optimal pressure, then decreases in the overpressure regime. This domed shape of the pressure dependence of the superconducting transition temperature is similar to that of the pressure dependence of the longitudinal part of the superconducting g…
Within the framework of the kinetic energy driven d-wave superconductivity, the electronic structure of the electron doped cuprate superconductors is studied. It is shown that although there is an electron-hole asymmetry in the phase diagram, the electronic structure of the electron-doped cuprates in the superconducting-state is similar to that in the hole-doped case. With increasing the electron doping, the spectral weight in the $(π,0)$ point increases, while the position of the superconducting quasiparticle peak is shifted towards the Fermi energy. In analogy to the hole-doped case, the sup…
Using as a model the Hubbard Hamiltonian we determine various basic properties of electron-doped cuprate superconductors like ${Nd}_{2-x}{Ce}_{x}{CuO}_{4}$ and ${Pr}_{2-x}{Ce}_{x}{CuO}_{4}$ for a spin-fluctuation-induced pairing mechanism. Most importantly we find a narrow range of superconductivity and like for hole-doped cuprates $d_{x^{2}-y^{2}}$ - symmetry for the superconducting order parameter. The superconducting transition temperatures $T_{c}(x)$ for various electron doping concentrations $x$ are calculated to be much smaller than for hole-doped cuprates due to the different Fermi surf…
Within the t-J ladder model, superconductivity with a modified d-wave symmetry in doped two-leg ladder cuprates is investigated based on the kinetic energy driven superconducting mechanism. It is shown that the spin-liquid ground-state at the half-filling evolves into the superconducting ground-state upon doping. In analogy to the doping dependence of the superconducting transition temperature in the planar cuprate superconductors, the superconducting transition temperature in doped two-leg ladder cuprates increases with increasing doping in the underdoped regime, and reaches a maximum in the …
We present the first ab-initio band-theory-based description of spin-compensated polarons (known as Zhang-Rice singlets) in a hole-doped cuprate, specifically one-dimensional Ca_{2+x} Y_{2-x} Cu_5 O_10. Zhang-Rice singlets are many-particle configurations relevant to the exotic behavior of hole-doped cuprates, stemming from spontaneous charge localization. They appear in our case-study material above a threshold doping, successively turning the insulating undoped antiferromagnet into a gap insulator, a singlet-rich metallic paramagnet, and finally, a singlet-saturated insulating diamagnet.
The doping and temperature dependent conductivity of electron-doped cuprates is analysed. The variation of kinetic energy with doping is shown to imply that the materials are approximately as strongly correlated as the hole-doped materials. The optical spectrum is fit to a quasiparticle scattering model; while the model fits the optical data well, gross inconsistencies with photoemission data are found, implying the presence of a large, strongly doping dependent Landau parameter.
Inelastic Neutron Scattering (INS) data in LSCO, YBCO and Bi2212 are discussed. In the literature, the INS spectra remain far from being comprehensively understood. We show that local (Q-integrated) susceptibility data and the energy dependence of the spin susceptibility at antiferromagnetic vector, Q = (p,p), can be interpreted by using the phase diagram for hole-doped cuprates. We analyze also the origin of the resonant peak which relates to the order parameter for long-range phase coherence in hole-doped cuprates. Thus, we present an interpretation of neutron data in LSCO, YBCO and Bi2212 p…
We amend ab initio strongly-correlated band structures by taking into account the band-tailing phenomenon in doped charge-transfer Mott-Hubbard insulators. We show that the photoemission from band tails accounts for sharp "quasi-particle" peaks, rapid loss of their intensities in some directions of the Brillouin zone ("Fermi-arcs") and high-energy "waterfall" anomalies as a consequence of matrix-element effects of disorder-localised states in the charge-transfer gap of doped cuprates.
Systematic analysis of the planar resistivity, Hall effect and cotangent of the Hall angle for the electron-doped cuprates reveals underlying Fermi-liquid behavior even deep in the antiferromagnetic part of the phase diagram. The transport scattering rate exhibits a quadratic temperature dependence, and is nearly independent of doping, compound and carrier type (electrons vs. holes), and hence universal. Our analysis moreover indicates that the material-specific resistivity upturn at low temperatures and low doping has the same origin in both electron- and hole-doped cuprates.
Recent quantum oscillation measurements on underdoped cuprates are shown to be consistent with the predictions of a mean field theory of the 1/8 magnetic antiphase stripe order proposed to occur in high-$T_c$ cuprates. In particular, for intermediate values of the stripe order parameter, the magneto-transport is found to be dominated by an electron pocket.
We study charge ordered d-wave resonating valence bond states (dRVB) in the doped cuprates, and estimate the energies of these states in a generalized $t-J $ model by using a renormalized mean field theory. The long range Coulomb potential tends to modulate the charge density in favor of the charge ordered RVB state. The possible relevance to the recently observed $4 \times 4$ checkerboard patterns in tunnelling conductance in high $T_c$ cuprates is discussed.
We present conductance-voltage (G-V) data for point contact junctions between a normal metal and the electron doped cuprate superconductor Pr{2-x}Ce{x}CuO4 (PCCO). We observe a zero bias conductance peak (ZBCP) for the under-doped composition of this cuprate (x=0.13) which is consistent with d-wave pairing symmetry. For optimally-doped (x=0.15) and over-doped (x=0.17) PCCO, we find that the G-V characteristics indicate the presence of an order parameter without nodes. We investigate this further by obtaining point contact spectroscopy data for different barrier strengths and as a function of m…
Recent experiments in underdoped hole-doped cuprates have shown the presence of two energy scales in the Raman spectrum in the superconducting state. This feature has a natural explanation in some models in which pseudogap and superconductivity compete. In electron-doped cuprates antiferromagnetic correlations are believed to survive in the superconducting state, and to produce a pseudogap above the critical temperature. Contrary to hole-doped systems, in electron-doped compounds only one energy scale appear since the pair breaking Raman intensity peaks in both B$_{1g}$ (antinodal) and B$_{2g}…
We report a tunneling study between Pr_2-xCe_xCuO_{4-delta} (PCCO) and Lead as a function of doping, temperature and magnetic field. The temperature dependence of the gap follows the BCS prediction. Our data fits a nonmonotonic d-wave order parameter for the whole doping range studied. From our data we are able to conclude that the electron-doped cuprate PCCO is a weak coupling, BCS, dirty superconductor.
Many important questions for high-$T_c$ cuprates are closely related to the insulating nature of parent compounds. While there has been intensive discussion on this issue, all arguments rely strongly on, or are closely related to, the correlation strength of the materials. Clear understanding has been seriously hampered by the absence of a direct measure of this interaction, traditionally denoted by $U$. Here, we report a first-principles estimation of $U$ for several different types of cuprates. The $U$ values clearly increase as a function of the inverse bond distance between apical oxygen a…
Superconductivity research is like running a marathon. Three decades after the discovery of high-Tc cuprates, there have been mass data generated from transport measurements, which bring fruitful information. In this review, we give a brief summary of the intriguing phenomena reported in electron-doped cuprates from the aspect of electrical transport as well as the complementary thermal transport. We attempt to sort out common features of the electron-doped family, e.g. the strange metal, negative magnetoresistance, multiple sign reversals of Hall in mixed state, abnormal Nernst signal, comple…
We study the quantum transition from an antiferromagnet to a superconductor in a model for electron- and hole-doped cuprates by means of a variational cluster perturbation theory approach. In both cases, our results suggest a tendency towards phase separation between a mixed antiferromagnetic-superconducting phase at low doping and a pure superconducting phase at larger doping. However, in the electron-doped case the energy scale for phase separation is an order of magnitude smaller than for hole doping. We argue that this can explain the different pseudogap and superconducting transition scal…
We investigate the electronic states in the antiferromagnetic (AF) phase of electron-doped cuprates by using numerically exact diagonalization technique for a t-t'-t''-J model. When AF correlation develops with decreasing temperature, a gaplike behavior emerges in the optical conductivity. Simultaneously, the coherent motion of carriers due to the same sublattice hoppings is enhanced. We propose that the phase is characterized as an AF state with small Fermi surface around the momentum k=(π,0) and (0,π). This is a remarkable contrast to the behavior of hole-doped cuprates.
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…
The purpose of this paper is to discuss a phase diagram of hole-doped cuprates. Hole-doped cuprates have a very rich phase diagram as a function of doping. This is due to a charge inhomogeneity in CuO_2 planes: the charge distribution in CuO_2 planes is inhomogeneous both on a nanoscale and macroscale. Depending on doping level, the CuO_2 planes comprise at least four different types of clusters having a size of a few nanometers. Each type of clusters has its own features. As a consequence, the common phase diagram consists of, at least, seven different energy/temperature scales. As an example…
AgF$_2$ is a correlated charge-transfer insulator with properties remarkably similar to insulating cuprates which have raised hope that it may lead to a new family of unconventional superconductors upon doping. We use ab initio computations to study doping strategies leading to metallization. Because the upper Hubbard band is very narrow electron doping leads to undesired strongly self-trapped states (polarons). For the hole-doped case, polaron tendency is stronger than for cuprates but still moderate enough to expect that heavily doped compounds may become metallic. Since the strong electron …
An antiferromagnetic (AF) spin fluctuation induced pairing model is proposed for the electron-doped cuprate superconductors. It suggests that, similar to the hole-doped side, the superconducting gap function is monotonic d_{x^2-y^2}-wave and explains why the observed gap function has a nonmonotonic d_{x^2-y^2}-wave behavior when an AF order is taken into account. Dynamical spin susceptibility is calculated and shown to be in good agreement with the experiment. This gives a strong support to the proposed model.
Pairing Correlations are studied numerically in the hole-doped spin-fermion model for cuprates. Simulations performed on up to 12x12 clusters provide robust indications of D-wave superconductivity away from half-filling. The pairing correlations are the strongest in the direction perpendicular to the dynamic stripe-like inhomogeneities that appear in the ground state at some densities. An optimal doping, where the correlations reach a maximum value, was observed at about 25% doping, in qualitative agreement with hight T_{c} cuprates' experiments. On the other hand, pairing correlations are sup…
