Origin of multiple quantum oscillation frequencies from single carrier nodal pocket in the underdoped cuprate superconductor YBCO

Quantum oscillations are measured in the underdoped high $T_{\rm c}$ cuprate superconductor YBa$_2$Cu$_3$O$_{6+x}$, revealing multiple frequencies. An extended study over a broad angular range and magnetic field range up to 95 T accompanied by detailed harmonic analysis is presented, establishing the multiple frequencies to arise from Fermi surface reconstruction yielding a single carrier nodal pocket. Scenarios are presented for the origin of multiple frequencies from this nodal pocket.