Disorder-induced static antiferromagnetism in cuprate superconductors

Using model calculations of a disordered d-wave superconductor with on-site Hubbard repulsion, we show how dopant disorder can stabilize novel states with antiferromagnetic order. We find that the critical strength of correlations or impurity potential necessary to create an ordered magnetic state in the presence of finite disorder is reduced compared to that required to create a single isolated magnetic droplet. This may explain why, in cuprates such as La2-xSrxCuO4, low-energy probes have identified a static magnetic component which persists well into the superconducting state, whereas, in cleaner systems such as YBa(2)Cu(3)O(6+delta), it is absent or minimal.     

Delocalized fermions in underdoped cuprate superconductors

Low-temperature heat transport was used to investigate the ground state of high-purity single crystals of the lightly doped cuprate YBa2Cu3O6.33. Samples were measured with doping concentrations on either side of the superconducting phase boundary. We report the observation of delocalized fermionic excitations at zero energy in the nonsuperconducting state, which shows that the ground state of underdoped cuprates is a thermal metal. Its low-energy spectrum appears to be similar to that of the d-wave superconductor, i.e., nodal. The insulating ground state observed in underdoped La2-xSrxCuO4 is attributed to the competing spin-density-wave order.     

Andreev and single-particle tunneling spectra of underdoped cuprate superconductors

We study tunneling spectroscopy between a normal metal and an underdoped cuprate superconductor modeled by a phenomenological theory in which the pseudogap is a precursor to the undoped Mott insulator. In the low barrier tunneling limit, the spectra are enhanced by Andreev reflection only within a voltage region of the small superconducting energy gap. In the high barrier tunneling limit, the spectra show a large energy pseudogap associated with single particle tunneling. Our theory semiquantitatively describes the two gap behavior observed in tunneling experiments.     

Operator projection theory for electron differentiation in underdoped cuprate superconductors

Metals approaching the Mott insulator generate a new hierarchy in the electronic structure accompanied by an electron differentiation with emergence of strongly momentum dependent structure, beyond the Mott-Hubbard, Brinkman-Rice and Slater pictures of the Mott transition. To consider such nonlinear phenomenon, we develop an analytic nonperturbative theory based on operator projections combined with a self-consistent treatment of the low-energy excitations. This reproduces the Hubbard bands, Mott gap, spin fluctuations, mass divergence, diverging charge compressibility, and strongly renormalized flat and damped dispersion similar to angle-resolved photoemission data in high-T_c cuprates. Electronic spectra show a remarkable similarity to numerical results.     

Fermi arcs in the superconducting clustered state for underdoped cuprate superconductors

The one-particle spectral function of a state formed by superconducting (SC) clusters is studied via Monte Carlo techniques. The clusters have similar SC amplitudes but randomly distributed phases. This state is stabilized by competition with the antiferromagnetism expected to be present in the cuprates and after quenched disorder is introduced. A Fermi surface composed of disconnected segments, i.e., Fermi arcs, is observed between the critical temperature T_(c) and the cluster formation temperature scale T*.     

Isotope effects in underdoped cuprate superconductors: a quantum critical phenomenon

We show that the unusual doping dependence of the isotope effects on transition temperature and zero temperature in-plane penetration depth naturally follows from the doping driven 3D-2D crossover and the 2D quantum superconductor to insulator transition in the underdoped limit. Since lattice distortions are the primary consequence of isotope substitution, our analysis clearly reveals the strong involvement of lattice degrees of freedom in mediating superconductivity.     

Phenomenological description of the two energy scales in underdoped cuprate superconductors

Raman and angle-resolved photoemission spectroscopy experiments have demonstrated that in superconducting underdoped cuprates nodal and antinodal regions are characterized by two energy scales instead of the one expected in BCS theory. The nodal scale decreases with underdoping while the antinodal one increases. Contrary to the behavior expected for an increasing energy scale, the antinodal Raman intensity decreases with decreasing doping. Using the Yang-Rice-Zhang model, we show that these features are a consequence of the nonconventional nature of the superconducting state in which superconductivity and pseudogap correlations are both present and compete for the phase space.     

Observability of quantum phase fluctuations in cuprate superconductors

We study the order parameter phase fluctuation effects in cuprate superconductors near T = 0, using a quasi-two-dimensional d-wave BCS model. An effective phason theory is obtained which is used to estimate the strength of the fluctuations, the fluctuation correction to the in-plane penetration depth, and the pair-field susceptibility. We find that, while the phase fluctuation effects are difficult to observe in the renormalization of the superfluid phase stiffness, they may be observed in a pair tunneling experiment which measures the pair-field susceptibility.     

Evolution of spin dynamics in electron-doped cuprate superconductors

Within the kinetic energy driven superconducting mechanism, the evolution of the magnetic excitations of the electron-doped cuprates in the superconducting state is studied. It is shown that there is a broad commensurate low energy magnetic scattering peak, while the magnetic resonance energy is located among this broad commensurate low energy scattering range. This broad commensurate low energy magnetic scattering disperses outward into a continuous ring-like incommensurate magnetic scattering at high energy.     

Superfluid density of strongly underdoped cuprate superconductors from a four-dimensional XY model

A new phenomenology is proposed for the superfluid density rhos of strongly underdoped cuprate superconductors based on recent data for ultraclean single crystals of YBa2Cu3O7-x. We show that the puzzling departure from Uemura scaling and the decline of the slope as the Tc=0 quantum critical point is approached can be understood in terms of the renormalization of quasiparticle effective charge by quantum fluctuations of the superconducting phase. We then employ a (3+1)-dimensional XY model to calculate, within particular approximations, the renormalization of rhos and its slope, explain the new phenomenology, and predict its eventual demise close to the quantum critical point.     

Theory of the quantum critical fluctuations in cuprate superconductors

The statistical mechanics of the time-reversal and inversion symmetry breaking order parameter, possibly observed in the pseudogap region of the phase diagram of the cuprates, can be represented by the Ashkin-Teller model. We add kinetic energy and dissipation to the model for a quantum generalization and show that the spectrum of the quantum-critical fluctuations is of the form postulated in 1989 to give the marginal Fermi-liquid properties. The model solved and the methods devised are likely to be of interest also to other quantum phase transitions.     

Magnetic fluctuations of stripes in the high temperature cuprate superconductors

Within the time-dependent Gutzwiller approximation for the Hubbard model we compute the magnetic fluctuations of vertical metallic stripes with parameters appropriate for La(1.875)Ba(0.125)CuO(4) (LBCO). For bond- and site-centered stripes the excitation spectra are similar, consisting of a low-energy incommensurate acoustic branch which merges into a "resonance peak" at the antiferromagnetic wave vector and several high-energy optical branches. The acoustic branch is similar to the result of theories assuming localized spins whereas the optical branches are significantly different. Results are in good agreement with a recent inelastic neutron study of LBCO.     

Low-energy spin fluctuations in the ground states of electron-doped Pr1-x LaCexCuO4+delta cuprate superconductors

Low-energy spin fluctuations have been investigated in the electron-doped Pr{1-x}LaCe{x}CuO{4+delta} over a wide concentration range of 0.07相似文献   

Quantum oscillations in the underdoped cuprate

Quantum oscillations occur via Landau quantisation of the quasiparticle in a Fermi liquid at low temperature. In the light of currently popular notions their detection in the ortho-II-YBa₂Cu₃O_6.45 and YBa₂Cu₄O₈ crystals is inconsistent with this. We explain this in terms of multichannel Kondo model of the underdoped cuprate.     

Pseudogap and precursor superconductivity in underdoped cuprate high temperature superconductors: A far-infrared ellipsometry study

With the technique of infrared ellipsometry we performed a detailed study of the temperature- and doping dependence of the c-axis response of a series of YBa₂Cu₃O_7−δ single crystals. In particular, we explored the anomalous electronic properties at temperatures above the macroscopic superconducting transition temperature, T _c, whose conflicting explanations range from a precursor superconducting state to electronic correlations that compete with superconductivity. We show that the c-axis spectra provide evidence that both kinds of correlations are present and that their contributions can be disentangled based on an analysis with a so-called multilayer-model. We find that the onset temperature, T ^*, and the energy scale, Δ_PG, of the competing pseudogap increase rapidly towards the underdoped side whereas they vanish on the overdoped side. In addition, we provide evidence that in a strongly underdoped sample the precursor superconducting correlations develop below an onset temperature, T ^ons, that is considerably lower than T ^* but still much higher than T _c.