Small Fermi Surface Pockets in Underdoped High Temperature Superconductors: Observation of Shubnikov–de Haas Oscillations inYBa2Cu4O8

Abstract

We report the observation of Shubnikov--de Haas oscillations in the underdoped cuprate superconductor ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{4}{\mathrm{O}}_{8}$ (Y124). For fields aligned along the $c$ axis, the frequency of the oscillations is $660\ifmmode\pm\else\textpm\fi{}30\text{ }\text{ }\mathrm{T}$, which corresponds to $\ensuremath{\sim}2.4%$ of the total area of the first Brillouin zone. The effective mass of the quasiparticles on this orbit is measured to be $2.7\ifmmode\pm\else\textpm\fi{}0.3$ times the free electron mass. Both the frequency and mass are comparable to those recently observed for ortho-II ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.5}$ (Y123-II). We show that although small Fermi surface pockets may be expected from band-structure calculations in Y123-II, no such pockets are predicted for Y124. Our results therefore imply that these small pockets are a generic feature of the copper oxide plane in underdoped cuprates.