S. Sakai, S. Blanc, M. Civelli, Y. Gallais, M. Cazayous, M. -A. Measson, J. S. Wen, Z. J. Xu, G. D. Gu, G. Sangiovanni, Y. Motome, K. Held, A. Sacuto, A. Georges, M. Imada
Superconductivity - charge flow with no resistance under a critical temperature Tc - is due to the pairing of electrons, signaled by a superconducting gap in the electronic spectrum. Key aspects of high-Tc superconductivity in copper oxides remain unexplained however. There, (i) the superconducting gap has a d-wave symmetry with gapless nodes, in contrast to the s-wave gap of conventional superconductors, (ii) another gap (the pseudogap) exists even above Tc. The relation between pseudo and superconducting gaps is still controversial. Based on observations of the occupied part of the electronic spectra, most studies have assumed a d-wave structure also for the pseudogap. Here we show that the pseudogap actually has an s-wave-like nodeless structure and hence has a distinct origin from that of the d-wave superconducting gap. This is established by combining theory with Raman experiments, which allows us to access electronic excitations associated with unoccupied states - a "dark side" forbidden to most momentum-resolved spectroscopic probes. These findings put strong constraints on theories of high-Tc superconductivity.
View original:
http://arxiv.org/abs/1207.5070
No comments:
Post a Comment