University of Minnesota
School of Physics & Astronomy

Academic Calendar

Tuesday, July 13th 2010
10:30 am:
Speaker: Ruihua He, Stanford University
Subject: Experimental Studies of High-Tc Cuprate Superconductors with Density Wave Correlations

High-Tc cuprate superconductors remain the source of central intellectual challenges for condensed matter physicists two decades after their discovery. Accumulating evidence suggests possible ubiquity of coexisting superconducting and density wave correlations in the ground state of these materials. As both correlations in their spatially incoherent forms can in principle produce a pseudogap in the excitation spectrum, the nature of the pseudogap widely seen in cuprates above Tc comes to forefront of debate. I have been trying to address the relationship triangle between the pseudogap, superconductivity and density waves, by mainly using angle-resolved photoemission spectroscopy (ARPES) to study the momentum spaces of single-layer La-based (La214) and Bi-based (Bi2201) cuprates.

In this talk, I will first briefly mention our ARPES-neutron scattering joint effort (in collaboration with Tohoku University) in the stripe-ordered state of La214. We found around the 1/8 doping level a dual nature of the pseudogap (in LBCO) and a doping-dependent crossover between localized- and
itinerant-spin ground-state physics (in 1% Fe-doped LSCO). I will then focus on our ARPES findings in both the pseudogap and superconducting states of nearly optimally-doped Pb-Bi2201 obtained over unprecedented momentum, energy and temperature ranges. They suggest that the pseudogap is a broken-symmetry state that is density-wave like and distinct from homogeneous superconductivity; it explicitly coexists with coherent superconductivity below Tc, causing a striking, momentum-dependent distortion of the high-Tc ground state.

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