ARPES investigation of two leg ladder compounds Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$

The so-called ``two leg ladder compounds'' Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ are interesting since it is well accepted that they form a resonating valence bond state. The crystal structure of two leg ladder compounds consists of one-dimensional motifs (ladders and chains), and it is within the ladders that the resonating valence bond state arises. As $x$ is varied, these compounds go through a metal-insulator transition, and become a superconductor, albeit under pressure. So far, a high resolution ARPES study shedding light on the near-Fermi-level electronic structure of these interesting compounds has been missing. Here, we report our ARPES results, providing the first view of the near-Fermi-level quasi-one-dimensional electronic structure arising from the ladders. We discuss line shape features that are indicative of strong electron correlations.