Polarization Selection Rules and Superconducting Gap Anisotropy in $Bi_2Sr_2CaCu_2O_8$

TL;DR

This paper investigates polarization effects in ARPES measurements of Bi2212, revealing that observed gap features are due to umklapp bands from superlattice effects, not the main CuO2 band, and suggests the intrinsic gap is small near the diagonals.

Contribution

It clarifies polarization selection rules in ARPES and identifies the origin of the superconducting gap features as umklapp bands caused by superlattice effects.

Findings

The hump in the superconducting gap is from an umklapp band, not the main band.

The intrinsic superconducting gap is likely small near the diagonal directions.

Polarization selection rules help distinguish band origins in ARPES data.

Abstract

We discuss polarization selection rules for angle-resolved photoemission spectroscopy in Bi2212. Using these we show that the ``hump'' in the superconducting gap observed in the $X$ quadrant in our earlier work is not on the main $CuO_2$ band, but rather on an umklapp band arising from the structural superlattice. The intrinsic gap is most likely quite small over a range of $\pm 10^\circ$ about the diagonal directions.