Fuente: Nature Physics - Issue - nature.com science feeds
Expuesto el: domingo, 04 de abril de 2010 2:00
Autor: Makoto Hashimoto
Asunto: Particle–hole symmetry breaking in the pseudogap state of Bi2201
| Particle–hole symmetry breaking in the pseudogap state of Bi2201 Nature Physics 6, 414 (2010). doi:10.1038/nphys1632 Authors: Makoto Hashimoto, Rui-Hua He, Kiyohisa Tanaka, Jean-Pierre Testaud, Worawat Meevasana, Rob G. Moore, Donghui Lu, Hong Yao, Yoshiyuki Yoshida, Hiroshi Eisaki, Thomas P. Devereaux, Zahid Hussain & Zhi-Xun Shen In conventional superconductors, a gap exists in the energy absorption spectrum only below the transition temperature (Tc), corresponding to the price to pay in energy for breaking a Cooper pair of electrons and creating two excited states. In high-Tc cuprate superconductors above Tc but below a temperature T*, an energy gap called the pseudogap exists, and is controversially attributed either to pre-formed superconducting pairs, which would show particle–hole symmetry, or to competing phases that would typically break it. Scanning tunnelling microscopy (STM) studies suggest that the pseudogap stems from lattice translational symmetry breaking and is associated with a different characteristic spectrum for adding or removing electrons (particle–hole asymmetry; refs 2, 3). However, no signature of either energy or spatial symmetry breaking of the pseudogap has previously been observed by angle-resolved photoemission spectroscopy (ARPES). Here we report ARPES data from Bi2201, which reveal both particle–hole symmetry breaking and pronounced spectral broadening—indicative of spatial symmetry breaking without long-range order at the opening of the pseudogap. Our finding supports the STM proposal that the pseudogap state is a broken-symmetry state that is distinct from homogeneous superconductivity. |
