Condensed Matter Physics Seminar
Friday, February 19, 1999, 2 p.m.
Plant Sciences Building, Room 1130
Dirac fermions, gauge fields, and the mixed-state electronic structure
of high-Tc cuprates
Marcel Franz
(Department of Physics & Astronomy, Johns Hopkins University)
Abstract: In conventional s-wave superconductors the
electronic excitations are gapped and the physics at low temperatures is
dominated entirely by the collective response of the U(1) order
parameter. High-Tc cuprates, on the other hand, exhibit
low-energy fermionic excitations originating from the vicinity of the nodes
in the
d-wave gap, best described as massless Dirac fermions.
When external magnetic field is applied, both the Dirac fermions and the
U(1)
collective mode respond in a highly non-trivial manner, forming a vortex
lattice with spontaneously broken translational symmetry. Understanding
the physics of a d-wave superconductor in the mixed state poses
an entirely new theoretical challenge which is at the same time of great
practical interest. I shall review the recent progress in this field with
the particular emphasis on the theoretical results with broader implications
and issues relevant to experiments. I will discuss the absence of quasiparticle
bound states associated with the individual vortex cores, the anomalous
transport properties of the mixed state, and the Landau level quantization
at low fields.
Host: Sankar Das Sarma
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