A hidden pseudogap under the ‘dome’ of superconductivity in electron-doped high-temperature superconductors

Abstract

The ground state of superconductors is characterized by the long-range order of condensed Cooper pairs: this is the only order present in conventional superconductors. The high-transition-temperature (high-T(c)) superconductors, in contrast, exhibit more complex phase behaviour, which might indicate the presence of other competing ground states. For example, the pseudogap--a suppression of the accessible electronic states at the Fermi level in the normal state of high-T(c) superconductors-has been interpreted as either a precursor to superconductivity or as tracer of a nearby ground state that can be separated from the superconducting state by a quantum critical point. Here we report the existence of a second order parameter hidden within the superconducting phase of the underdoped (electron-doped) high-T(c) superconductor Pr2-xCe(x)CuO4-y and the newly synthesized electron-doped material La2-xCe(x)CuO4-y (ref. 8). The existence of a pseudogap when superconductivity is suppressed excludes precursor superconductivity as its origin. Our observation is consistent with the presence of a (quantum) phase transition at T = 0, which may be a key to understanding high-T(c) superconductivity. This supports the picture that the physics of high-T(c) superconductors is determined by the interplay between competing and coexisting ground states.

c-axis longitudinal magnetoresistance of the electron-doped superconductorPr1.85Ce0.15CuOYu1, Liang2, Greene3 2006Phys. Rev. B4140View full textAdd to dashboardCite

“…The only difference is that superconducting fluctuations in PCCO seem to occur in a smaller range of temperature and field. Our n-MR does not seem to be related to the low-energy normal-state tunneling gap 24,25,26,27 , because the tunneling gap is also found for x = 0.11 where we see only positive magnetoresistance. Now we discuss the low-temperature c-axis resistivity and magnetoresistance.…”

Weak-coupling Bardeen-Cooper-Schrieffer superconductivity in the electron-doped cuprate superconductors

“…It is well known that when temperature rises across the superconducting transition, the junction becomes normal and the background conductance drops notably due to a finite normal-state resistance of the sample (R s ) in series with the junction [24]. In this work, R s varies from 0 to 2 ohm depending on the samples' property and the configuration of the electrodes and the point contacts.…”

Angle-Resolved Photoemission Spectroscopy of the Antiferromagnetic SuperconductorNd1.87Ce0.13CMatsui1, Terashima2, Sato3 et al. 2005Phys. Rev. Lett.12711412View full textAdd to dashboardCite

“…3 and may suggest that the strength of the AF scattering has momentum dependence, with the stronger amplitude close to the hot spot. A recent tunneling spectroscopy reported a pseudogap comparable in the size to the superconducting gap, suggesting the second order parameter hidden within the supercondcting state in electron-doped HTSCs [11]. However, the one-order smaller energy scale compared to the AF gap suggests the different nature between these two gaps.…”