ARPES study of the YBCO phase diagram by in-situ K evaporation

The study of the YBCO phase diagram by ARPES has become of central interest since the observation of quantum oscillations in high-magnetic field $[1]$. However, until recently accessing the various electronic phases by photoemission has been hampered by the so-called polar catastrophe $[2]$. In this work, the overdoped metal (OD, p=0.37, T$_c$=0), the superconducting phase (OP, T$<$T$_c$), and the normal state of the pseudogap regime (UD, T$_c<$T $<$T$^*$) have been successfully explored by surface doping (i.e., in-situ K evaporation). This reveals that the dispersion, as well as the arc topology of the low energy excitations of the normal state, are universal $[3]$. While no traces of an electronic reconstruction have been observed in YBCO, we are able to identify the doping value at which the Luttinger description breaks down upon underdoping.\\ \\ $[1]$ N. Doiron-Leyraud \textit{et al.}, Nature 447, 565 (2007).\\ $[2]$ M. A. Hossain \textit{et al.}, Nat. Phys. 4, 527 (2008).\\ $[3]$ K. M. Shen \textit{et al.}, Science 307, 901 (2005).