The last 15 years have witnessed important progresses in our understanding of the mechanism of superconductivity in the high-$T_{c}$ cuprates. There is now strong evidence that the strange metal behavior is induced by the quantum critical fluctuation at the pseudogap end point, where the Fermi surface changes its topology from hole-like to electron-like. However, experiments show that the quantum critical behavior in the high-$T_{c}$ cuprates is qualitatively different from that observed in the heavy Fermion systems and the iron-based superconductors, in both of which the quantum critical behavior can be attributed to the quantum phase transition toward a symmetry breaking phase. The fact that the pseudogap exists as a spectral gap without a corresponding symmetry breaking order, together with the fact that the strange metal behavior occurs as a quantum critical behavior without a corresponding symmetry breaking phase transition, exposes the central difficulty of the field: the lack of a universal low energy effective theory description of the high-$T_{c}$ phenomenology beyond the Landau paradigm. Recent experiments imply that the dualism between the local moment and the itinerant quasiparticle character of the electron in the high-$T_{c}$ cuprates may serve as an organizing principle to go beyond the Landau paradigm and may hold the key to the mystery of the pseudogap phenomena and the strange metal behavior.
We utilize a 1d Hubbard model to show that the superconductivity in cuprate superconductors likely arises due to the orbital entanglement between holes in the copper oxide plane mediated by orbitally-selective charge hopping. The main role of doping required to achieve superconductivity in cuprates is to suppress the Mott correlations and orbital ordering. The proposed mechanism explains superconductivity in other unconventional superconductors, and provides guidance in the search for new high-temperature superconductors.
We make use of the S=1 pseudospin formalism to describe the charge degree of freedom in a model high-$T_c$ cuprate with the on-site Hilbert space reduced to the three effective valence centers, nominally Cu$^{1+,\,2+,\,3+}$. Starting with a parent cuprate as an analogue of the quantum paramagnet ground state and using the Schwinger boson technique we found the pseudospin spectrum and conditions for the pseudomagnon condensation with phase transition to a superconducting state.
A pivotal step toward understanding unconventional superconductors would be to decipher how superconductivity emerges from the unusual normal state upon cooling. In the cuprates, traces of superconducting pairing appear above the macroscopic transition temperature $T_c$, yet extensive investigation has led to disparate conclusions. The main difficulty has been the separation of superconducting contributions from complex normal state behaviour. Here we avoid this problem by measuring the nonlinear conductivity, an observable that is zero in the normal state. We uncover for several representativ…
High temperature superconductivity due to the long-range electron-phonon interaction, application to isotope effects, thermomagnetic transport and nanoscale heterogeneity in cuprates
Experimental evidence of chemical-pressure-controlled superconductivity in cuprates
利用X射线吸收光谱（XAS）和高分辨X射线衍射（XRD）相结合的方法，研究了电荷补偿CaxLa_（1-x）Ba_（1.75-x）La_（0.25）+xCu_（30）O_y（0<x<0.5，y=7.13）体系中电子结构和晶格结构在控制铜氧化物超导电性中的相互作用.尽管在Tc的大的变化，掺杂的空穴，确定的Cu L和O K XAS，几乎没有表现出任何变化与x。另一方面，由于取代阳离子的大小不同，CuO 2的片晶尺寸表现出系统的变化。结果为化学压强是控制铜氧化物超导基态的关键参数提供了直接证据。
Resonating valence bond (RVB) theory of high Tc superconductivity, an electron correlation based mechanism, began as an insightful response by Anderson, to Bednorz and Muller's discovery of high Tc superconductivity in cuprates in late 1986. Shortly a theoretical framework for quantum spin liquids and superconductivity was developed. This theory adresses a formidable strong coupling quantum manybody problem, in modern times. It is built on certain key experimental facts: i) survival of a dynamical Mott localization in a metallic state, ii) proliferation of bond singlets and iii) absence of fer…
We present a comparative study of magnetic excitations in the first two Ruddlesden-Popper members of the Hg-family of high-temperature superconducting cuprates, which are chemically nearly identical and have the highest critical temperature ($T_\mathrm{c}$) among all cuprate families. Our inelastic photon scattering experiments reveal that the two compounds' paramagnon spectra are nearly identical apart from an energy scale factor of $\sim130\%$ that matches the ratio of $T_\mathrm{c}$'s, as expected in magnetic Cooper pairing theories. By relating our observations to other cuprates, we infer …
Suppression of superconductivity in favour of a striped phase, and its coincidence with a structural transition from a low-temperature orthorhombic (LTO) to a low-temperature tetragonal (LTT) phase, is a ubiquitous feature of hole-doped lanthanum cuprates. We study the effect of anisotropic strain on this transition using density-functional theory on both La$_2$CuO$_4$ and the recently-synthesised surrogate La$_2$MgO$_4$ to decouple electronic and structural effects. Strikingly, we find that compressive strain applied diagonally to the in-plane metal-oxygen bonds dramatically stabilises the LT…
We use scanning tunneling microscopy to investigate Bi2Sr2Ca2Cu3O10+δ trilayer cuprates from the optimally doped to overdoped regime. We find that the two distinct superconducting gaps from the inner and outer CuO2 planes both decrease rapidly with doping, in sharp contrast to the nearly constant Tc. Spectroscopic imaging reveals the absence of quasiparticle interference in the antinodal region of overdoped samples, showing an opposite trend to that in single- and double-layer compounds. We propose that the existence of two types of inequivalent CuO2 planes and the intricate interaction betwee…
Disorder Effects on Competition between Antiferromagnetism and Superconductivity in Cuprate Superconductors through the Enhancement in Charge Susceptibility
We develop a theory for light-induced superconductivity in underdoped cuprates in which the competing bond-density wave order is suppressed by driving phonons with light. Close to a bond-density wave instability in a system with a small Fermi surface, such as a fractionalized Fermi liquid, we show that the coupling of electrons to phonons is strongly enhanced at the bond-density wave ordering wavevectors, leading to a strong softening of phonons at these wavevectors. For a model of classical phonons with anharmonic couplings, we show that the combination of strong softening and driving can lea…
We investigate the spatial and doping evolutions of the superconducting properties of tri-layer cuprate Bi2Sr2Ca2Cu3O10+x by using scanning tunneling microscopy and spectroscopy. Both the superconducting coherence peak and gap size exhibit periodic variations with the structural supermodulation, but the effect is much more pronounced in the underdoped regime than at optimal doping. Moreover, a new type of tunneling spectrum characterized by two superconducting gaps emerges with increasing doping, and the two-gap features also correlate with the supermodulation. We propose that the interaction …
A spatial interpretation of emerging superconductivity in lightly doped cuprates
最近由Kohleman等人通过扫描隧道显微镜观察到的包括交替的“空穴丰富”和“空穴贫乏”阶梯的域的形成，轻孔掺杂的铜酸盐，被解释在一个有吸引力的机制，有利于存在掺杂的孔位于每个氧原子的一侧上的Cu网站。这种机制导致交替的空穴丰富和空穴贫乏的阶梯的几何图案的周期性等于4倍的晶格间距在CuO平面中，如实验观察到的。引用这篇文章：G. Deutscher，P. G. de Gennes，C. R. Physique 8（2007）.
