In conventional superconductors, phonons glue two electrons with opposite spins to form Cooper pairs and condensation of these pairs leads to the superconductivity. Identifying the underlying mechanism of the high temperature superconductivity in cuprates is among the most important problems in physics. Even quarter of a century after the first report of high temperature superconductor by Bednorz and Muller in 1986, there is still no general consensus on the pairing mechanism of superconductivity in these materials. So far, many theories have been developed to explain the exotic properties of cuprates, but they can explain only a limited number of experiments. In this article, we present a new pairing mechanism that incorporates both strong correlation and phonon mediated interaction on an equal footing to produce superconductivity. In this framework, strong correlation and anti-ferromagnetic interaction between electrons, create RVB pairs and phonons provide the phase coherence between these RVB pairs. Both of these are required in this approach to obtain the superconductivity. This approach resolves three limitations of the U(1) slave boson method. We achieve a better estimation of $T_c$, we only predict $\frac{h}{2ec}$ vortices and the linear $T$ coefficient of the superfluid is not sensitive to the doping. This formalism provides a framework that connects Anderson's idea of preformed Cooper pairs and phonon based theories.
Thermal Hall conductivity of electron-doped cuprates: Electrons and phonons
Université de Sherbrooke（舍布鲁克大学）；Univ. Grenoble Alpes（格勒诺布尔阿尔卑斯大学）；Univ. Toulouse（图卢兹大学）；INSA-T（图卢兹国立应用科学学院）；École Polytechnique（巴黎综合理工学院）；Institut Polytechnique de Paris（巴黎理工学院）；Stanford University（斯坦福大学）；SLAC National Accelerator Laboratory（斯坦福线性加速器中心）
Superconductivity originates from the coupling between charge carriers and bosonic excitations of either phononic or electronic origin. Identifying the most relevant pairing glue is a key step towards a clear understanding of the unconventional superconductivity. Here, by applying the ultrafast optical spectroscopy on the electron-doped cuprates La$_{1.9}$Ce$_{0.1}$CuO$_{4\pmδ}$, we discern a bosonic mode of electronic origin that has the strongest coupling with the charge carriers near $T_c$. We argue that this mode is associated with the two-dimensional antiferromagnetic spin fluctuations, a…
Temperature dependence of the angle resolved photoemission spectra in the undoped cuprates: self-consistent approach to the t-J-Holstein model
我们开发了一种新的自洽方法来研究角分辨光电子能谱（ARPES）的一个洞的t-J-Holstein模型给出完美的协议与数字精确的Diagrammatic Monte Carlo数据在零温度下的所有制度的电子-声子耦合。推广到有限温度的方法，我们发现，在未掺杂的铜酸盐的ARPES的异常温度依赖性的解释合作的相互作用的耦合的孔的磁波动和强的电子-声子相互作用。
Raman scattering near a d-wave Pomeranchuk instability
最近的运输和中子散射实验表明，在欠掺杂的铜氧化物的取向对称性破缺的动机，我们提出了一个理论研究的拉曼散射附近的d波波Pomeranchuk不稳定性（PI）。拉曼散射的d-波分量的电子和声子允许直接研究与PI相关的序参量波动。接近PI从正常状态，通过降低温度的中心峰出现在电子和，作为一个额外的低频功能，在声子散射。在低温超导态下，通过降低掺杂浓度来接近PI，中心峰被一个宽度和能量都大大减小、谱权增大的软模所取代。这些预测的低能量特征在拉曼散射可以确认在一个相当直接的方式存在的PI在高温铜酸盐超导体和Sr 3Ru 2 O 7。
The recently discovered infinite-layer nickelates show great promise in helping to disentangle the various cooperative mechanisms responsible for high-temperature superconductivity. However, lack of antiferromagnetic order in the pristine nickelates presents a challenge for connecting the physics of the cuprates and nickelates. Here, by using a quantum many-body Green's function-based approach to treat the electronic and magnetic structures, we unveil the presence of many two- and three-dimensional magnetic stripe instabilities that are shown to persist across the phase diagram of LaNiO$_2$. O…
Static spin-stripe order and superconductivity were systematically studied in La_2-xBa_xCuO_4 (0.11 - 0.17) at ambient pressure by means of magnetization and muSR experiments. We find that all the investigated La_2-xBa_xCuO_4 samples exhibit static spin-stripe order and that the quasi two-dimensional superconducting (SC) transition temperature T_c1 and the static spin-stripe order temperature T_so have very similar values throughout the phase diagram. Moreover, the magnetic and the SC properties of the x = 0.155 (LBCO-0.155) and x = 0.17 (LBCO-0.17) samples were studied under hydrostatic press…
Electron-phonon coupling revealed by charge density fluctuations in cuprate superconductors
Politecnico di Milano（米兰理工大学）；European XFEL（欧洲X射线自由电子激光装置）；ESRF, The European Synchrotron（欧洲同步辐射光源）；Chalmers University of Technology（查尔姆斯理工大学）；Università di Roma “La Sapienza”（罗马第一大学）
We employ Momentum-Resolved Electron Energy Loss Spectroscopy (M-EELS) on Bi2.1Sr1.9CaCu2O8+x to resolve the issue of the kink feature in the electron dispersion widely observed in the cuprates. To this end, we utilize the GW approximation to relate the density response function measured in in M-EELS to the self-energy, isolating contributions from phonons, electrons, and the momentum dependence of the effective interaction to the decay rates. The phononic contributions, present in the M-EELS spectra due to electron-phonon coupling, lead to kink features in the corresponding single-particle sp…
Understanding the electron pairing in hole-doped cuprate superconductors has been a challenge, in particular because the "normal" state from which it evolves is unprecedented. Now, after three and a half decades of research, involving a wide range of experimental characterizations, it is possible to delineate a clear and consistent cuprate story. It starts with doping holes into a charge-transfer insulator, resulting in in-gap states. These states exhibit a pseudogap resulting from the competition between antiferromagnetic superexchange $J$ between nearest-neighbor Cu atoms (a real-space inter…
Correlation between unconventional superconductivity and strange metallicity revealed by operando superfluid density measurements
Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；Fudan University（复旦大学）；Southern University of Science and Technology（南方科技大学）；Harvard University（哈佛大学）；University of Chinese Academy of Sciences（中国科学院大学）；Songshan Lake Materials Laboratory（松山湖材料实验室）；Beijing Academy of Quantum Information Sciences（北京量子信息科学研究院）
Unveiling the Interplay of Charge and Magnetic Excitations in HgBa$_2$Ca$_2$Cu$_3$O$_{8+δ}$
Chalmers University of Technology（查尔姆斯理工大学）；Politecnico di Milano（米兰理工大学）；ESRF, The European Synchrotron（欧洲同步辐射装置）；CEA Saclay（法国原子能和替代能源委员会萨克雷中心）；Université Paris Cité（巴黎西岱大学）；BTU Cottbus-Senftenberg（科特布斯-森夫滕贝格勃兰登堡工业大学）
In high-temperature cuprate superconductors, superconductivity is accompanied by a "plethora of orders", and phenomena that may compete, or cooperate with superconductivity, but which certainly complicate our understanding of origins of superconductivity in these materials. While prominent in the underdoped regime, these orders are known to significantly weaken or completely vanish with overdoping. Here, we approach the superconducting phase from the more conventional highly overdoped side. We present angle-resolved photoemission spectroscopy (ARPES) studies of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (B…
The classical Bardeen-Cooper-Schrieffer and Eliashberg theories of the electron-phonon-mediated superconductivity are based on the Migdal theorem, which is an assumption that the energy of charge carriers, $k{_B}T{_F}$, significantly exceeds the phononic energy, $\hbar{ω{_D}} $, of the crystalline lattice. This assumption, which is also known as adiabatic approximation, implies that the superconductor exhibits fast charge carriers and slow phonons. This picture is valid for pure metals and metallic alloys because these superconductors exhibit $\hbar{ω{_D}}$/$k{_B}T{_F}<0.01$. However, n-type d…
Unconventional superconductors are often characterized by numerous competing and even intertwined orders in their phase diagrams. In particular, the electronic nematic phases, which spontaneously break rotational symmetry and often simultaneously involve spin, charge and/or orbital orders, appear conspicuously in both the cuprate and iron-based superconductors. The fluctuations associated with these phases may provide the exotic pairing glue that underlies their high-temperature superconductivity. Helimagnet MnP, the first Mn-based superconductor under pressure, lacks high rotational symmetry.…
The proximity effect from a spin-triplet $p_x$-wave superconductor to a dirty normal-metal has been shown to result in various unusual electromagnetic properties, reflecting a cooperative relation between topologically protected zero-energy quasiparticles and odd-frequency Cooper pairs. However, because of a lack of candidate materials for spin-triplet $p_x$-wave superconductors, observing this effect has been difficult. In this paper, we demonstrate that the anomalous proximity effect, which is essentially equivalent to that of a spin-triplet $p_x$-wave superconductor, can occur in a semicond…
Enhanced $s^\pm$-wave superconductivity in electron-doped La$_3$Ni$_2$O$_7$
Institute for Quantum Science, School of Physical Science and Technology, Soochow University（苏州大学物理科学与技术学院量子科学研究所）；School of Physics, Northwest University（西北大学物理学院）；Institute of Solid State Physics, TU Wien（维也纳工业大学固体物理研究所）；Shaanxi Key Laboratory for Theoretical Physics Frontiers（陕西省理论物理前沿重点实验室）；Fundamental Discipline Research Center for Quantum Science and technology of Shaanxi Province（陕西省量子科学与技术基础学科研究中心）；State Key Laboratory of Surface Physics and Department of Physics, Fudan University（复旦大学表面物理国家重点实验室及物理系）
The microscopic mechanism for electron pairing in heavy-fermion superconductors remains a major challenge in quantum materials. Some form of magnetic mediation is widely accepted with spin fluctuations as a prime candidate. A novel mechanism, 'composite pairing' based on the cooperative two-channel Kondo effect directly involving the f-electron moments has also been proposed for some heavy fermion compounds including CeCoIn$_5$. The origin of the spin resonance peak observed in neutron scattering measurements on CeCoIn$_5$ is still controversial and the corresponding hump-dip structure in the …
