Fermi Surface and Quasiparticle Excitations of OverdopedTl2Ba2CuO6+δ

The high-$T_c$ superconductor ${\mathrm{Tl}}_2{\mathrm{Ba}}_2{\mathrm{CuO}}_{6+\delta }$ is studied by angle-resolved photoemission spectroscopy. For a very overdoped $T_c=30\mathrm{K}$ sample, the Fermi surface consists of a single large hole pocket centered at $(\pi ,\pi )$ and is approaching a topological transition. Although a superconducting gap with $d_{x^2-y^2}$ symmetry is tentatively identified, the quasiparticle evolution with momentum and binding energy exhibits a marked departure from the behavior observed in under and optimally doped cuprates. The relevance of these findings to scattering, many-body, and quantum-critical phenomena is discussed.