Ubiquitous coexisting electron-mode couplings in high-temperature cuprate superconductors

In conventional superconductors, electron-phonon coupling plays a dominant role in generating superconductivity. In high-temperature cuprate superconductors, the existence of electron coupling with phonons and other boson modes and its role in producing high-temperature superconductivity remain unclear. The evidence of electron-boson coupling mainly comes from angle-resolved photoemission (ARPES) observations of ∼ 70-meV nodal dispersion kink and ∼ 40-meV antinodal kink. However, the reported results are sporadic and the nature of the involved bosons is still under debate. Here we report findings of ubiquitous two coexisting electron-mode couplings in cuprate superconductors. By taking ultrahigh-resolution laser-based ARPES measurements, we found that the electrons are coupled simultaneously with two sharp modes at ∼ 70meV and ∼ 40meV in different superconductors with different dopings, over the entire momentum space and at different temperatures above and below the superconducting transition temperature. These observations favor phonons as the origin of the modes coupled with electrons and the observed electron-mode couplings are unusual because the associated energy scales do not exhibit an obvious energy shift across the superconducting transition. We further find that the well-known “peak-dip-hump” structure, which has long been considered a hallmark of superconductivity, is also omnipresent and consists of “peak-double dip-double hump” finer structures that originate from electron coupling with two sharp modes. These results provide a unified picture for the ∼ 70-meV and ∼ 40-meV energy scales and their evolutions with momentum, doping and temperature. They provide key information to understand the origin of these energy scales and their role in generating anomalous normal state and high-temperature superconductivity. High-temperature cuprate superconductors are derived from doping the parent Mott insulators ( 1, 2). They exhibit anomalous normal-state properties and unconventional superconductivity which are attributed to strong electron correlation and electron interactions with other collective excitations (boson modes) like phonons, magnetic fluctuations, and so on ( 3, 4). Revealing such many-body effects is crucial to understanding the unusual properties and superconductivity mechanism in cuprate superconductors ( 5). With the dramatic improvement of the instrumental resolutions, angle-resolved photoemission spectroscopy (ARPES) has emerged as a powerful technique to probe the many-body effects in cuprate superconductors ( 6– 9). It has been found that the band dispersion along the nodal direction exhibits a kink at ∼ 70 meV in various cuprate superconductors although its origin remains under debate ( 10– 20). Another dispersion kink at ∼ 40 meV is also revealed near the antinodal region which is attributed to electron coupling with either phonon or magnetic resonance mode ( 18, 20– 25). The well-known peak–dip–hump structure observed in the superconducting state near the antinodal region is considered a hallmark of the electron-mode coupling in cuprate superconductors ( 13, 26, 27). It has been shown that superconductivity is closely related to the strength of the electron-mode couplings ( 27, 28). However, the observations of the electron–boson couplings in cuprate superconductors have been mostly sporadic and sometimes controversial ( SI Appendix, Table S1). First, it remains unclear how the ∼ 70-meV nodal mode-coupling evolves with momentum from nodal to antinodal regions and how the ∼ 40-meV antinodal mode-coupling evolves with momentum from antinodal to nodal regions, in particular, whether these two mode-couplings represent electron coupling with a single mode with its energy varying from ∼ 70 meV near the nodal region to ∼ 40 meV near the antinodal region or they represent electron coupling with two different modes ( 18– 20). Second, the ∼ 40-meV mode-coupling has been onlyobserved near the antinodal region in the superconducting state in Bi 2 Sr 2 CaCu 2 O 8 + δ (Bi2212). It remains unclear whether this mode-coupling can be present in other cuprates like Bi 2 Sr 2 CuO 6 + δ (Bi2201), in other momentum space off the antinodal region or even in the normal state. Third, it remains controversial on the temperature dependence of the mode-couplings, particularly whether the energy scale exhibits an energy shift from the normal state to superconducting state because of the gap opening ( 14, 16– 21, 23, 24, 29). Fourth, the peak–dip–hump structure has been only observed in Bi2212 near the antinodal region in the superconducting state, and the energy position of the dip is considered to represent the mode energy combined with the superconducting gap ( 14, 16– 21, 23, 24, 29). It remains unclear whether this peak–dip–hump structure can be present in other cuprates like Bi2201, in other momentum space off the antinodal region or even in the normal state. Whether the peak–dip–hump structure contains finer structures and whether the dip position really corresponds to the mode energy need further investigations. Resolving the above issues can help to establish a consistent picture to pin down on the nature of the mode-couplings and their role in generating anomalous normal state and high-temperature superconductivity in cuprate superconductors.

成果名称:低表面能涂层

合作方式:技术开发

联 系 人:周老师

联系电话:13321314106

成果名称:低表面能涂层

合作方式:技术开发

联 系 人:周老师

联系电话:13321314106

成果名称:低表面能涂层

合作方式:技术开发

联 系 人:周老师

联系电话:13321314106

成果名称:低表面能涂层

合作方式:技术开发

联 系 人:周老师

联系电话:13321314106

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