Evidence for a small hole pocket in the Fermi surface of underdoped YBa2Cu3Oy

Understand

The Fermi surface of a metal is the fundamental basis from which its properties can be understood.

• In underdoped cuprate superconductors, the Fermi surface undergoes a reconstruction that produces a small electron pocket, but whether there is another, as yet undetected portion to the Fermi surface is unknown.
• Establishing the complete topology of the Fermi surface is key to identifying the mechanism responsible for its reconstruction.
• Here we report the discovery of a second Fermi pocket in underdoped YBa2Cu3Oy, detected as a small quantum oscillation frequency in the thermoelectric response and in the c-axis resistance.