Observation of small Fermi pockets protected by clean CuO <sub>2</sub> sheets of a high- <i>T</i> <sub>c</sub> superconductor
So Kunisada, Shunsuke Isono, Yoshimitsu Kohama, Shiro Sakai, Cédric Bareille, Shunsuke Sakuragi, Ryo Noguchi, Kifu Kurokawa, Kenta Kuroda, Yukiaki Ishida, Shintaro Adachi, Ryotaro Sekine, Timur K. Kim, Cephise Cacho, Shik Shin, Takami Tohyama, Kazuyasu Tokiwa, Takeshi Kondo
Abstract
An elusive pocket Superconductivity in copper oxide materials emerges by doping a special kind of correlated state called the Mott insulator. However, studying what happens when a small concentration of charge carriers—holes or electrons—is added to a Mott insulator is experimentally challenging. It has been predicted that the so-called “Fermi pockets” should become visible during experimentation, but such pockets have not been unambiguously observed. Kunisada et al. studied the unusual cuprate Ba 2 Ca 4 Cu 5 O 10 (F,O) 2 , which has five copper oxide planes in a unit cell, whereas most cuprates have one or two (see the Perspective by Vishik). They observed two Fermi pockets in both photoemission and quantum oscillations data, with the innermost copper oxide planes playing a crucial role. Science , this issue p. 833 ; see also p. 775