Overdoped Cuprate Superconductors Research Articles

Low-temperature electrical transport in the normal-state of overdoped cuprate superconductors

The low-temperature electrical transport in the normal-state of overdoped cuprate superconductors is investigated based on the t-J model. The momentum relaxation due to the umklapp scattering between electrons by the exchange of the effective spin propagator is employed to evaluate the electrical resistivity within the framework of the Boltzmann transport theory. It is shown that the quadratic temperature dependence of the resistivity develops in the far-lower-temperature region, and is followed by a nonlinear temperature dependence of the resistivity in an extremely-narrow-crossover region and a linear temperature dependence of the resistivity in the low-temperature region. The obtained results also show that the same spin excitation governs both superconductivity and the electron umklapp scattering responsible for the low-temperature linear in temperature resistivity in the overdoped regime.

Puddle formation and persistent gaps across the non-mean-field breakdown of superconductivity in overdoped (Pb,Bi)2Sr2CuO6+δ

The cuprate high-temperature superconductors exhibit many unexplained electronic phases, but the superconductivity at high doping is often believed to be governed by conventional mean-field Bardeen–Cooper–Schrieffer theory1. However, it was shown that the superfluid density vanishes when the transition temperature goes to zero2,3, in contradiction to expectations from Bardeen–Cooper–Schrieffer theory. Our scanning tunnelling spectroscopy measurements in the overdoped regime of the (Pb,Bi)2Sr2CuO6+δ high-temperature superconductor show that this is due to the emergence of nanoscale superconducting puddles in a metallic matrix4,5. Our measurements further reveal that this puddling is driven by gap filling instead of gap closing. The important implication is that it is not a diminishing pairing interaction that causes the breakdown of superconductivity. Unexpectedly, the measured gap-to-filling correlation also reveals that pair breaking by disorder does not play a dominant role and that the mechanism of superconductivity in overdoped cuprate superconductors is qualitatively different from conventional mean-field theory.

Vanishing nematic order beyond the pseudogap phase in overdoped cuprate superconductors

During the last decade, translational and rotational symmetry-breaking phases-density wave order and electronic nematicity-have been established as generic and distinct features of many correlated electron systems, including pnictide and cuprate superconductors. However, in cuprates, the relationship between these electronic symmetry-breaking phases and the enigmatic pseudogap phase remains unclear. Here, we employ resonant X-ray scattering in a cuprate high-temperature superconductor [Formula: see text] (Nd-LSCO) to navigate the cuprate phase diagram, probing the relationship between electronic nematicity of the Cu 3d orbitals, charge order, and the pseudogap phase as a function of doping. We find evidence for a considerable decrease in electronic nematicity beyond the pseudogap phase, either by raising the temperature through the pseudogap onset temperature T* or increasing doping through the pseudogap critical point, p*. These results establish a clear link between electronic nematicity, the pseudogap, and its associated quantum criticality in overdoped cuprates. Our findings anticipate that electronic nematicity may play a larger role in understanding the cuprate phase diagram than previously recognized, possibly having a crucial role in the phenomenology of the pseudogap phase.

Exploration of Charge Order in Over-doped Cuprate Superconductors

Exploration of Charge Order in Over-doped Cuprate Superconductors

Band structure of overdoped cuprate superconductors: Density functional theory matching experiments

A comprehensive angle resolved photoemission spectroscopy study of the band structure in single layer cuprates is presented with the aim of uncovering universal trends across different materials. Five different hole- and electron-doped cuprate superconductors (La$_{1.59}$Eu$_{0.2}$Sr$_{0.21}$CuO$_4$, La$_{1.77}$Sr$_{0.23}$CuO$_4$, Bi$_{1.74}$Pb$_{0.38}$Sr$_{1.88}$CuO$_{6+\delta}$, Tl$_{2}$Ba$_{2}$CuO$_{6+\delta}$, and Pr$_{1.15}$La$_{0.7}$Ce$_{0.15}$CuO$_{4}$) have been studied with special focus on the bands with predominately $d$-orbital character. Using light polarization analysis, the $e_g$ and $t_{2g}$ bands are identified across these materials. A clear correlation between the $d_{3z^2-r^2}$ band energy and the apical oxygen distance $d_\mathrm{A}$ is demonstrated. Moreover, the compound dependence of the $d_{x^2-y^2}$ band bottom and the $t_{2g}$ band top is revealed. Direct comparison to density functional theory (DFT) calculations employing hybrid exchange-correlation functionals demonstrates excellent agreement. We thus conclude that the DFT methodology can be used to describe the global band structure of overdoped single layer cuprates on both the hole and electron doped side.

Erratum: Disorder and superfluid density in overdoped cuprate superconductors [Phys. Rev. B 96, 024501 (2017)

We calculate superfluid density for a dirty d-wave superconductor. The effects of impurity scattering are treated within the self-consistent t-matrix approximation, in weak-coupling BCS theory. Working from a realistic tight-binding parameterization of the Fermi surface, we find a superfluid density that is both correlated with T_c and linear in temperature, in good correspondence with recent experiments on overdoped La2-xSrxCuO4.

Doping and energy dependences of thermal conductivity in cuprate superconductors

By considering the pseudogap effect, the doping and energy dependences of thermal conductivity in cuprate superconductors are studied. Our results show that the thermal conductivity as a function of energy exhibits a characteristic peak from underdoping to overdoping due to the presence of the pseudogap in pseudogap phase of cuprate superconductors. The thermal conductivity is strongly doping dependent. On the one hand, with increasing doping concentration, the weight of thermal conductivity increases quickly, especially the residual thermal conductivity which is in qualitative agreement with the experimental data. On the other hand, the characteristic energy corresponding to the position of the characteristic peak decreases monotonically upon increasing doping concentration, and it scales with the doping dependence of pseudogap. In particular, we have studied the doping dependence of the ratio of quasiparticle velocities normal and tangential to the Fermi surface at the nodes [Formula: see text]. It is shown that [Formula: see text] increases with the increase of doping concentration. Moreover, we explain that both the residual thermal conductivity and [Formula: see text] increase rapidly upon the increase in doping concentration in heavily overdoped cuprate superconductors.

Disorder and superfluid density in overdoped cuprate superconductors

One of the hallmarks of clean, $d$-wave superconductivity is a linear temperature dependence of superfluid density in the low-temperature limit. Here, the authors show that weak scattering, combined with a realistic model of the cuprate Fermi surface, allows the linear behavior of superfluid density to persist in the presence of disorder even in the regime where the superfluid density and the transition temperature are strongly suppressed from their clean-limit values. This leads to a superfluid density that is both correlated with the transition temperature and linear in temperature, consistent with recent experiments on overdoped La${}_{2-x}$Sr${}_{x}$CuO${}_{4}$.

Upper critical field, pressure-dependent superconductivity and electronic anisotropy of Sm4Fe2As2Te1−xO4−yFy

We present a detailed study of the electrical transport properties of a recently discovered iron-based superconductor: Sm4Fe2As2Te0.72O2.8F1.2. We followed the temperature dependence of the upper critical field by resistivity measurement of single crystals in magnetic fields up to 16 T, oriented along the two main crystallographic directions. This material exhibits a zero-temperature upper critical field of 90 T and 65 T parallel and perpendicular to the Fe2As2 planes, respectively. An unprecedented superconducting magnetic anisotropy is observed near Tc, and it decreases at lower temperatures as expected in multiband superconductors. Direct measurement of the electronic anisotropy was performed on microfabricated samples, showing a value of that rises up to 19 near Tc. Finally, we have studied the pressure and temperature dependence of the in-plane resistivity. The critical temperature decreases linearly upon application of hydrostatic pressure (up to 2 GPa) similarly to overdoped cuprate superconductors. The resistivity shows saturation at high temperatures, suggesting that the material approaches the Mott–Ioffe–Regel limit for metallic conduction. Indeed, we have successfully modelled the resistivity in the normal state with a parallel resistor model that is widely accepted for this state. All the measured quantities suggest strong pressure dependence of the density of states.

Normal-state conductivity of underdoped to overdoped cuprate superconductors: Pseudogap effects on the in-plane and c-axis charge transports

We have developed a theory of the unusual in-plane and c-axis charge transports in hole-doped cuprate superconductors and explain the temperature- and doping-dependent in-plane resistivity ρab, c-axis resistivity ρc and resistivity anisotropy ρc/ρab seen experimentally above Tc. We argue that the relevant current carriers in these materials above Tc are hole-like. The in-plane conductivity of underdoped to overdoped cuprates is considered as the conductivity of hole polarons and preformed Cooper pairs at their scattering by lattice vibrations in hole-rich CuO2 layers (with nonzero thickness). The appropriate Boltzmann transport equations were used to calculate the conductivity of polaronic carriers and bosonic Cooper pairs above and below the pseudogap (PG) temperature T⁎ in the relaxation time approximation. We show that the linearity of ρab(T) above T⁎ is associated with the polaron–phonon scattering, while different deviations from the T-linear behavior in ρab(T) below T⁎ are caused by transition to the BCS-like PG regime. The specific model for layered cuprates is used to simulate the c-axis transport and to calculate the c-axis conductivity associated with the thermal dissociation of localized bipolarons in carrier-poor regions between the CuO2 layers into hole polarons which subsequently move by hopping along the c-axis. It is shown that the bipolaronic PG and carrier-confinement together cause the insulating ρc(T) behavior in the cuprates. The calculated results for ρab(T), ρc(T) and ρc(T)/ρab(T) were compared with the experimental data obtained for various hole-doped cuprates. For all the considered cases, a good quantitative agreement was found between theory and experimental data.

Doping evolution of the oxygenK-edge x-ray absorption spectra of cuprate superconductors using a three-orbital Hubbard model

We study oxygen K-edge x-ray absorption spectroscopy (XAS) and investigate the validity of the Zhang-Rice singlet (ZRS) picture in overdoped cuprate superconductors. Using large-scale exact diagonalization of the three-orbital Hubbard model, we observe the effect of strong correlations manifesting in a dynamical spectral weight transfer from the upper Hubbard band to the ZRS band. The quantitative agreement between theory and experiment highlights an additional spectral weight reshuffling due to core-hole interaction. Our results confirm the important correlated nature of the cuprates and elucidate the changing orbital character of the low-energy quasi-particles, but also demonstrate the continued relevance of the ZRS even in the overdoped region.

Transport properties of the metallic state of overdoped cuprate superconductors from an anisotropic marginal Fermi liquid model

We consider the implications of a phenomenological model self-energy for the charge transport properties of the metallic phase of the overdoped cuprate superconductors. The self-energy is the sum of two terms with characteristic dependencies on temperature, frequency, location on the Fermi surface, and doping. The first term is isotropic over the Fermi surface, independent of doping, and has the frequency and temperature dependence characteristic of a Fermi liquid. The second term is anisotropic over the Fermi surface (vanishing at the same points as the superconducting energy gap), strongly varies with doping (scaling roughly with $T_c$, the superconducting transition temperature), and has the frequency and temperature dependence characteristic of a marginal Fermi liquid. Previously it has been shown this self-energy can describe a range of experimental data including angle-dependent magnetoresistance (ADMR) and quasi-particle renormalisations determined from specific heat, quantum oscillations, and angle-resolved photo-emission spectroscopy (ARPES). Without introducing new parameters and neglecting vertex corrections we show that this model self-energy can give a quantitative description of the temperature and doping dependence of a range of reported transport properties of Tl2201 samples. These include the intra-layer resistivity, the frequency dependent optical conductivity, the intra-layer magnetoresistance, and the Hall coefficient. The temperature dependence of the latter two are particularly sensitive to the anisotropy of the scattering rate and to the shape of the Fermi surface. In contrast, the temperature dependence of the Hall angle is dominated by the Fermi liquid contribution to the self-energy that determines the scattering rate in the nodal regions of the Fermi surface.

Consistent Description of the Metallic Phase of Overdoped Cuprate Superconductors as an Anisotropic Marginal Fermi Liquid

We consider a model self-energy consisting of an isotropic Fermi liquid term and a marginal Fermi liquid term which is anisotropic over the Fermi surface, vanishing in the same directions as the superconducting gap and the pseudogap. This model self-energy gives a consistent description of experimental results from angle-dependent magnetoresistance, specific heat, de Haas-van Alphen, and measurements of the quasiparticle dispersion near the Fermi surface from photoemission. In particular, we reconcile the strongly doping-dependent anomalous scattering rate observed in angle-dependent magnetoresistance with the almost doping-independent specific heat.

Comment on “X-ray Absorption Spectra Reveal the Inapplicability of the Single-Band Hubbard Model to Overdoped Cuprate Superconductors”

A Comment on the Letter by D. C. Peets et al., Phys. Rev. Lett. 103, 087402 (2009). The authors of the Letter offer a Reply.

Erratum: X-Ray Absorption Spectra Reveal the Inapplicability of the Single-Band Hubbard Model to Overdoped Cuprate Superconductors [Phys. Rev. Lett.103, 087402 (2009)

Received 1 April 2010DOI:https://doi.org/10.1103/PhysRevLett.104.169903©2010 American Physical Society

X-Ray Absorption Spectra Reveal the Inapplicability of the Single-Band Hubbard Model to Overdoped Cuprate Superconductors

X-ray absorption spectra on the overdoped high-temperature superconductors Tl2Ba2CuO(6+delta) and La(2-x)SrxCuO(4+/-delta) reveal a striking departure in the electronic structure from that of the underdoped regime. The upper Hubbard band, identified with strong correlation effects, is not observed on the oxygen K edge, while the lowest-energy prepeak gains less intensity than expected above p approximately 0.21. This suggests a breakdown of the Zhang-Rice singlet approximation and a loss of correlation effects or a significant shift in the most fundamental parameters of the system, rendering single-band Hubbard models inapplicable. Such fundamental changes suggest that the overdoped regime may offer a distinct route to understanding in the cuprates.

Enhanced coherence of antinodal quasiparticles in a dirtyd-wave superconductor

Recent ARPES experiments show a narrow quasiparticle peak at the gap edge along the antinodal [1,0]-direction for the overdoped cuprate superconductors. We show that within weak coupling BCS theory for a d-wave superconductor the s-wave single-impurity scattering cross section vanishes for energies of the gap edge. This coherence effect occurs through multiple scattering off the impurity. For small impurity concentrations the spectral function has a pronounced increase of the (scattering) lifetime for antinodal quasiparticles but shows a very broad peak in the nodal direction, in qualitative agreement with experiment and in strong contrast to the behavior observed in underdoped cuprates.

Novel boundary effect in high temperature superconductors: superconductivity induced by pseudogap proximity effect

The boundary between highly under-doped and over-doped cuprate superconductors is studied within the framework of the slave-boson mean-field theory of the t – J model. We assume that the under-doped region is in the pseudogap state and the singlet resonating valence bond (s-RVB) order is formed there. The over-doped region, on the other hand, is in a hole-rich state and the pseudogap is destroyed by the holes. Because of the proximity effect, the s-RVB order and high-density holes can coexist, leading to the superconducting behavior. Remarkably, the transition temperature of this “boundary superconductivity” exceeds the maximum superconducting transition temperature of the bulk region, thus possessing a new possibility of application for superconducting devices.

Heterogeneous high temperature cuprate superconductors

The boundary between highly under-doped and over-doped cuprate superconductors is studied within the framework of the slave-boson mean-field theory of the t–J model. Because of the proximity effect of singlet resonating valence bond order, the superconductivity appears at the boundary even when there is no bulk superconductivity. Remarkably, the transition temperature of this “boundary superconductivity” exceeds the maximum superconducting transition temperature of the base material in the bulk.

An unconventional Fermi liquid model for the optimally doped and overdoped cuprate superconductors

We present an unconventional Fermi liquid model for the optimally doped and overdoped cuprate superconductors. For the normal state, we provide an analytic demonstration, backed by self-consistent Baym–Kadanoff (BK) numerical calculations, of the linear in T resistivity and linear in 1/ ϵ optical conductivity, provided the interacting Fermi liquid has strong peaks in its density of states (van-Hove singularities (vHs) in two dimensions) near the chemical potential μ. The origin of this linearity is the linear in energy term of the imaginary part of the carrier susceptibility. The interactions tend to pin these strong density of states peaks close to μ. Moreover, we show that the energy dependence of the Millis–Monien–Pines susceptibility χ MMP can have a fermionic origin. We obtain particularly high transition temperatures T c from our BK–Eliashberg scheme by introducing an ansatz for the susceptibility of the carriers. We postulate that the latter is enhanced in an additive manner due to the weak antiferromagnetic (AF) order of the CuO 2 planes. We have obtained a d x 2− y 2 gap with T c>120°K for n.n. hopping t=250 meV.