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Register a new userParticle-hole asymmetric superconducting coherence peaks in overdoped cuprates
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To elucidate the superconductor to metal transition at the end of superconducting dome, the overdoped regime has stepped onto the center stage of cuprate research recently. Here, we use scanning tunneling microscopy to investigate the atomic-scale electronic structure of overdoped trilayer Bi-2223 and bilayer Bi-2212 cuprates. At low energies the spectroscopic maps are well described by dispersive quasiparticle interference patterns. However, as the bias increases to the superconducting coherence peak energy, a virtually non-dispersive pattern with sqrt(2)*sqrt(2) periodicity emerges. Remarkably, the position of the coherence peaks exhibits evident particle-hole asymmetry which also modulates with the same period. We propose that this is an extreme quasiparticle interference phenomenon, caused by pairing-breaking scattering between flat anti-nodal Bogoliubov bands, which is ultimately responsible for the superconductor to metal transition.
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Overdoped high-temperature cuprate superconductors have been widely believed to be described by the physics of d-wave BCS-like superconductivity. However, recent measurements indicate that as the doping is increased, the superfluid density decreases smoothly to zero rather than increasing as expected by BCS theory in the absence of disorder. Here, we combine time-domain THz spectroscopy with kHz range mutual inductance measurements on the same overdoped La$_{2-x}$Sr$_{x}$CuO$_{4}$ films to determine both the superfluid and the uncondensed carrier density as a function of doping. A significant fraction of the carriers remains uncondensed in a wide Drude-like peak even as $Trightarrow0$, which, when taken with the linear-in-temperature superfluid density, is inconsistent with existing theories for the role of disorder in suppressing the superfluid density in a d-wave superconductor. Our almost eight orders of magnitude in measurement frequency range gives us a unique look at the low frequency spectral weight distribution, which may suggest the presence of quantum phase fluctuations as the critical doping is approached.
In this paper we analyze, using scanning tunneling spectroscopy, the density of electronic states in nearly optimally doped BSCCO in zero field. Focusing on the superconducting gap, we find patches of what appear to be two different phases in a background of some average gap, one with a relatively small gap and sharp large coherence peaks and one characterized by a large gap with broad weak coherence peaks. We compare these spectra with calculations of the local density of states for a simple phenomenological model in which a 2 xi_0 * 2 xi_0 patch with an enhanced or supressed d-wave gap amplitude is embedded in a region with a uniform average d-wave gap.
The thermoelectric power S(T) of single-layer Bi2Sr2CuO6+d is studied as a function of oxygen doping in the strongly overdoped region of the phase diagram (T, d). As other physical properties in this region, diffusion thermopower Sdiff(T) also shows an important deviation from conventional Fermi liquid behaviour. This departure from T-linear S(T) dependence together with the results of susceptibility on the same samples suggest that the origin of the observed non-metallic behaviour is the existence of a singularity in the density of states near the Fermi level. The doping and temperature dependence of themopower is compared with a tight-binding band model.
We present a theoretical framework for understanding the behavior of the normal and superconducting states of overdoped cuprate high temperature superconductors in the vicinity of the doping-tuned quantum superconductor-to-metal transition. The key ingredients on which we focus are d-wave pairing, a flat antinodal dispersion, and disorder. Even for homogeneous disorder, these lead to effectively granular superconducting correlations and a superconducting transition temperature determined in large part by the superfluid stiffness rather than the pairing scale.
Recently, we have argued that experimental data on superfluid density and terahertz conductivity of overdoped LSCO are compatible with a Landau Fermi liquid/Bardeen-Cooper-Schrieffer description of these samples, provided dopants are treated within dirty $d$-wave theory as weak scatterers. Here we test these ideas by comparing to specific heat and thermal conductivity data on LSCO, showing that the theory works extremely well across the overdoped region for similar disorder parameters. We then study the same properties in another overdoped cuprate, Tl-2201, thought to be quite clean since it exhibits quantum oscillations, low residual resistivities and small superconducting state Sommerfeld coefficients. Our results are consistent with the Tl-2201 system being $approx 3$ times cleaner due in part to the dopant atoms being located further from the CuO$_2$ plane. We conclude that cuprates can be described semiquantitatively in the overdoped regime by dirty $d$-wave theory, subject to significant Fermi liquid renormalizations, without introducing physics beyond the Landau-BCS paradigm.
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