Unveiling the nature of the pseudogap and its relation to both superconductivity and antiferromagnetic Mott insulators, the pairing mechanism, and a non-Fermi liquid phase is a key issue for understanding high temperature superconductivity in cuprates. A number of experimental results gathered especially in recently years have revealed an unexpected inhomogeneous nature of cuprates at the nanoscale, indicating the fundamental inapplicability of the conventional theories based on homogeneous systems. Here we show a microscopic model of pseudogap and pairing mechanisms on the basis of the consideration of the spin state around a bound hole in a CuO2 plane and the resulting magnetic orders, leading eventually to the spin-Peierls distortion responsible for the Cooper pair formation. The present model fits and accounts for the accumulated experimental findings reported previously for cuprates, including stripe-like electronic order, breaking of the rotational symmetry, and the so-called 1/8 anomaly. We believe that the present model can help to develop a complete theoretical framework applicable to a large family of high-temperature superconductors, including ferropnictides and ferrochalcogenides.
Planar oxygen nuclear magnetic resonance (NMR) relaxation and shift data from all cuprate superconductors available in the literature are analyzed. They reveal a temperature independent pseudogap at the Fermi surface, which increases with decreasing doping in family specific ways, i.e., for some materials the pseudogap is substantial at optimal doping while for others it is nearly closed at optimal doping. The states above the pseudogap, or in its absence are similar for all cuprates and doping levels, and Fermi liquid-like. If the pseudogap is assumed exponential it can be as large as about 1…
It has become clear that the anomalous properties of cuprate superconductors are intimately related to the formation of a pseudogap. Within the framework of the kinetic-energy-driven superconducting mechanism, the effect of the pseudogap on the electronic Raman response of cuprate superconductors in the superconducting-state is studied by taking into account the interplay between the superconducting gap and pseudogap. It is shown that the low-energy spectra almost rise as the cube of energy in the B_{1g} channel and linearly with energy in the B_{2g} channel. However, the pseudogap is strongly…
One of the most puzzling features of high-temperature cuprate superconductors is the pseudogap state, which appears above the temperature at which superconductivity is destroyed. There remain fundamental questions regarding its nature and its relation to superconductivity. But to address these questions, we must first determine whether the pseudogap and superconducting states share a common property: particle-hole symmetry. We introduce a new technique to test particle-hole symmetry by using laser pulses to manipulate and measure the chemical potential on picosecond time scales. The results st…
We propose a hybridization phenomenology to describe the pseudogap state of the underdoped cuprates. We show how a momentum independent pseudogap opens asymmetrically from the Fermi-surface but symmetric to the zeroes of the hybridized bonding dispersion, which results in false d-wave characteristics of the pseudogap at the Fermi level. By comparing against a d-wave form factor we illustrate the difficulty in identifying a momentum independent order in momentum averaged quantities such as the electronic Raman response. We identify a suppression in the single-particle density of states which pr…
Isotope Effect in the Superfluid Density of HTS Cuprates: Stripes, Pseudogap and Impurities
欠掺杂的铜氧化物表现出正常状态的赝能隙，它们的自旋和掺杂载流子往往在空间上分离成1-D或2-D条纹。有些人认为这些是超导性的核心，其他人则认为是外围的，只是竞争。使用La $_{2-x}$ Sr $_x$ Cu $_{1-y}$ Zn $_y$ O $_4$，我们表明，氧同位素效应在$T_c$和超流密度可以用来区分条纹和赝隙的作用，并检测杂质散射的存在。我们得出结论，条纹和赝隙是不同的，既竞争和共存的超导性。
We propose a new approach to the pseudogap problem in cuprates. Hole-doped cuprates display a broad plateau in the susceptibility centered near $(π,π)$. Competition between the softening of different $q$-modes on this plateau leads to anomalously slow growth of magnetic correlations with reducing temperature -- i.e., extended ranges of short-range correlations. The plateau arises from competition between Fermi- surface nesting and a `hidden' Van Hove singularity (VHS) nesting, associated with a bulk contribution to the susceptibility. As such, the VHS contribution is not tied to the Fermi leve…
High-temperature superconducting cuprates are distinguished by an enigmatic pseudogap which opens near optimal doping where the superconducting transition temperature is highest. Key questions concern its origin and whether it is essential in any way to superconductivity. Recent field-induced normal-state transport experiments on hole-doped cuprates have measured abrupt changes in the doping dependent Hall number and resistivity, consistent with a drop in carrier density from $1+p$ to $p$ holes per copper atom, on entering the pseudogap phase. In this work the change in resistivity is analyzed…
The nature of the pseudogap and its relationship with superconductivity are one of the central issues of cuprate superconductors. Recently, a possible scenario has been proposed that the pseudogap state is a distinct phase characterized by spontaneous rotational symmetry breaking called "nematicity" based on transport and magnetic susceptibility measurements, where the symmetry breaking was observed below the pseudogap temperature $T^*$. Here, we report a temperature-dependent ARPES study of nematicity in slightly overdoped Bi${}_{1.7}$Pb${}_{0.5}$Sr${}_{1.9}$CaCu${}_2$O${}_{8+δ}$ triggered by…
After providing a brief genealogy of our recently proposed model for High-Tc cuprates, we investigate the details of the microscopic mechanism that produces an attractive interaction between neighboring holes. We show that a peculiar arrangement of the $p_x$ and $p_y$ oxygen orbitals makes the mutual magnetic interaction of the holes with the localized copper ions to produce a net attractive interaction between themselves, which is responsible for the emergence of a superconducting phase. We also study the connection existing between the proposed pseudogap order parameter and the spectral dens…
In scanning tunneling microscopy (STM) conductance curves, the superconducting gap of cuprates is sometimes accompanied by small sub-gap structures at very low energy. This was documented early on near vortex cores and later at zero magnetic field. Using mean-field toy models of coexisting d-wave superconductivity ($d$SC), \emph{d}-form factor density wave ($d$FF-DW), and extended s-wave pair density wave ($s'$PDW), we find agreement with this phenomenon, with $s'$PDW playing a critical role. We explore the high variability of the gap structure with changes in band structure and density wave (…
Superconductivity in cuprates is achieved by doping holes into a correlated charge-transfer insulator. While the correlated character of the parent insulator is now understood, there is no accepted theory for the "normal" state of the doped insulator. I present a mostly empirical analysis of a large range of experimental characterizations, making the case for two pseudogaps: (1) a large pseudogap resulting from the competition between the energy of superexchange-coupled local Cu moments and the kinetic energy of doped holes; (2) a small pseudogap that results from dopant disorder and consequen…
One of the most intriguing puzzle is why there is a coexistence of Fermi arcs and Fermi pockets in the pseudogap phase of cuprate superconductors? This puzzle is calling for an explanation. Based on the t-J model in the fermion-spin representation, the coexistence of the Fermi arcs and Fermi pockets in cuprate superconductors is studied by taking into account the pseudogap effect. It is shown that the pseudogap induces an energy band splitting, and then the poles of the electron Green's function at zero energy form two contours in momentum space, however, the electron spectral weight on these …
Coexistence of the superconducting energy gap and pseudogap above and below the transition temperature of superconducting cuprates
我们表示的超导间隙，$Δ(T)$，在$s$和d波对称的热力学函数。应用到Bi $_2$ Sr $_2$ CaCu $_2$ O $_{8+δ}$和Y $_{0.8}$ Ca $_{0.2}$ Ba $_2$ Cu $_3$ O $_{7-δ}$，我们发现，对于所有的掺杂$Δ(T)$持续存在，作为一个部分的差距，高以上$T_c$由于强的超导涨落。因此，一般来说，在$T_c$上方存在两个能隙，超导能隙和赝能隙，有效地调和了关于赝能隙物理的两种高度极化的观点。
A consistent microscopic theory of pseudogap phenomena and novel Bose-liquid superconductivity (superfluidity) is presented, based on the fact that in high-$T_c$ cuprates and related systems the energy $\varepsilon_A$ of the effective attraction between fermions is comparable with their Fermi energy $\varepsilon_F$ and the bosonic Cooper pairs are formed above $T_c$ and then a part of such Cooper pairs condense into a Bose superfluid at $T_c$. High-$T_c$ cuprates and other systems with low Fermi energies ($\varepsilon_F\sim\varepsilon_A$) are bosonic superconductors/superfluids and exhibit pse…
One of the puzzling characteristics of the pseudogap phase of high-$T_c$ cuprates is the nodal-antinodal dichotomy. While the nodal quasiparticles have a Fermi liquid behaviour, the antinodal ones show non-Fermi liquid features and an associated pseudogap. Angle-resolved photoemission spectroscopy and electronic Raman scattering are two valuable tools which have shown universal features which are rather material-independent, and presumably intrinsic to the pseudogap phase. The doping and temperature dependence of the Fermi arcs and the pseudogap observed by photoemission near the antinode corr…
