ARPES-derived Fermi surface asymmetry in the high-Tc cuprate Bi2201 and its consequences

Angle-resolved photoemission spectroscopy (ARPES) is known to measure a full (n = 1 + p) Fermi surface (FS) across the strange metal (SM) phase of the high-Tc cuprates. In contrast, transport measurements from the Hall effect across the same regime reveal an anomalous transition in carrier density (n = p to 1 + p). In the single-layer cuprate (Pb_1-yBi_y)Sr_2-xLa_xCuO_6+δ (Bi2201), an anomalously large spread in hole-doping (p) was previously measured by ARPES. Our high resolution ARPES measurements of the Fermi surface find an unexpected 6-10% nodal difference in the Fermi wavevectors along the GX and GY directions, significantly larger than the 2% orthorhombic crystal asymmetry determined by X-ray crystallography. The electronic structure of the cuprates is often assumed fourfold symmetric (tetragonal) in the k_x-k_y plane, which can lead to incorrect values of p_(ARPES) in Bi2201. We show that using an orthorhombic tight-binding model effectively eliminates the disparity in values of p_(ARPES) across the SM regime, revealing a new (linear) relation which indicates that ARPES effectively measures a shifted superconducting dome.