Fermi Surface and Quasiparticle Excitations of Overdoped ${\mathrm{Tl}}_2{\mathrm{Ba}}_2{\mathrm{CuO}}_{6+\delta }$

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.

Figure 1

(a) LDA FS for two different doping levels corresponding to a volume, counting holes, of 50% (cyan, dashed line) and 63% (blue, solid line) of the BZ. (b),(c) ARPES spectra taken at $T=10\mathrm{K}$ on Tl2201-OD30 along the directions marked by arrows in (a). (d) ARPES FS of Tl2201-OD30 along with a tight-binding fit of the data (black lines).

Figure 2

(a),(b) Symmetrization of the ARPES spectra from along cuts I and II in Fig. 1. (c) Enlarged view of the FS of Tl2201-OD30 near $(\pi ,0)$. (d) Selected spectra from along cut II in (c); their $k$-space positions are indicated by circles of corresponding color. (e),(f) QP linewidth $\Gamma$ and peak position from a Lorentzian fit of the energy distribution curves along cut II in (c). (g) Similarly, QP peak position along cut III in (c). Black lines in (c),(f),(g) are the tight-binding fit results.

Figure 3

(a) Tl2201-OD30 ARPES spectra at $k$ slightly smaller than $k_F$ (QPs with $E_B\sim 35\mathrm{meV}$) at various FS angles $\alpha$. (b) Selected spectra from (a) along with corresponding $k\gg k_F$ background. (c),(d) Spectral weight integrated over different energy ranges and QP linewidth $\Gamma$, plotted vs $\alpha$.

Figure 4

(a) Tl2201-OD63 and (b) Tl2201-OD30 spectra at $k\lesssim k_F$ in the nodal and antinodal regions.