Anisotropic breakdown of Fermi liquid quasiparticle excitations in overdoped La2$-x$Sr$x$CuO4

High-temperature superconductivity emerges from an un-conventional metallic state. This has stimulated strong efforts to understand exactly how Fermi liquids breakdown and evolve into an un-conventional metal [1,2]. A fundamental question is how Fermi liquid quasiparticle excitations break down in momentum space. Here we show, using angle-resolved photoemission spectroscopy, that the Fermi liquid quasiparticle excitations of the overdoped superconducting cuprate La1.77Sr0.23CuO4 is highly anisotropic in momentum space [3]. Fermi liquid excitations are found in the anti-nodal region whereas conventional Fermi liequid excitations are probed around the nodal point [3].\\[4pt] [1] R. A. Copper \textit{et al}., \textit{Science} \textbf{323}, 603--607 (2009).\\[0pt] [2] K. Jin \textit{et al}., \textit{Nature} \textbf{476}, 73--75 (2011).\\[0pt] [3] J. Chang \textit{et al}., \textit{Nature Communications }\textbf{4}, 2559 (2013).