Superconducting Coherence Peak in the Electronic Excitations of a Single-LayerBi2Sr1.6La0.4CuO6+δCuprate Superconductor

Abstract

Angle resolved photoemission spectroscopy study is reported on a high quality optimally doped Bi2Sr1.6La0.4CuO 6+δ high-Tc superconductor. In the antinodal region with maximal d-wave gap, the symbolic superconducting coherence peak, which has been widely observed in multi-CuO2-layer cuprate superconductors, is unambiguously observed in a single layer system. The associated peakdip separation is just about 19 meV, which is much smaller than its counterparts in multi-layered compounds, but correlates with the energy scales of spin excitations in single layer cuprates.In search of the mechanism of high temperature superconductivity, one central issue is whether there are certain bosons that play the critical mediating role of phonons in conventional BCS superconductor. Specifically, if there were such bosons, what would they be? So far, signatures of electron-boson interactions have been identified in single particle excitations measured by angle resolved photoemission spectroscopy (ARPES). For example, in the so-called nodal region, where the d-wave superconducting gap diminishes, a characteristic kink [1,2] was discovered in the dispersion of various cuprate superconductors. However, the nature of the corresponding boson, particularly whether it is due to lattice or spin excitations, was intensively debated.For multi-CuO 2 -layer cuprate superconductors, such as Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212), Bi 2 Sr 2 Ca 2 Cu 3 O 10+δ (Bi2223) and YBa 2 Cu 3 O 7−δ (YBCO) [3,4,5,6,7], a sharp peak emerges out of the normal state broad spectrum when temperature is lowered below the superconducting transition temperature (T c ), forming a so-called "peak-dip-hump"(PDH) structure (see Fig. 4c for illustration) in the antinodal region, where d-wave superconducting gap is at its maximum. This sharp peak, also termed as superconducting coherence peak (SCP), contains rich information about superconductivity. Its position reflects the maximal pairing strength, while its intensity grows with decreasing temperature, illustrating the gain of coherence through the development of superconducting condensate or superfluid [4,8,9]. The PDH structure has been regarded as an evidence for interactions with a bosonic mode [10,11,12,13,14,15,16,17,18]. However, since this mode energy (∼ 35 meV) coincides with the energy of certain oxygen phonon and spin excitations near (π, π), scenarios based on both kinds of bosons have been put forward.In spite of its importance, an unambiguous observation of SCP or two-component spectrum in the antinodal region of single layer compounds is so far lacking [6,19,20,21,22]. In this letter, we report the discovery of the antinodal SCP in an optimally doped single layer Bi 2 Sr 2 CuO 6+δ (Bi2201). We found the peak-dip distance to be about 19 meV, suggesting the possibility of a bosonic mode in Bi2201 with a much lower energy than that in Bi2212. This low energy mode seems to correlate with the superconducting gap and the energy scale of spin excitations observed in various single layer compounds.Bi 2 Sr 1.6 La 0.4 ...

Competition between the pseudogap and superconductivity in the high-Tc copper oxides

“…2(r) for the three samples as a function Fermi angle φ. We note that the coherent peak is present at antinode in optimally and overdoped samples consistent with previous results [18,21]. Our careful measurements reveal that suppression of the coherent peak near the antinode (φ=0) occurs even in the overdoped samples and becomes stronger with underdoping.…”

“…peak-hump-dip structure) and bilayer splitting that are present [6,7] in double layered Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212). This feature, however, means the spectral changes associated with the superconducting transition in Bi2201 are much more difficult to observe [18]. By acquiring very high resolution and stable ARPES data with high statistics, we are able to study the temperature and momentum dependence of the spectral weight near the chemical potential, with unprecedented accuracy.…”

Determination of the superconducting gap in near optimally doped Bi2Sr2−xLaWang1, Liu2, Lin3 et al. 2011Phys. Rev. B

“…[8][9][10][11][12] As shown in LSCO, 6,7 the present study further demonstrates the virtue of LTSH as a bulk method to probe the superconducting gap near the nodes in high-T c cuprates.…”

“…Note that although the dwave pairing has been probed for La-Bi2201 by other experimental techniques such as ARPES, [8][9][10][11][12] present LTSH findings confirm that it is a bulk property of the sample.…”

“…4 we have plotted the ∆ 0 for near optimal-doped La-Bi2201 inferred from LTSH [according to Eq. (4)] and aforementioned ARPES and STM studies, 8,[10][11][12] where the doping level of the sample (p ∼ 0.16) is determined by the empirical relation 27,28 between p and the reported La content. Unlike the above-compared ARPES experiments,…”