Disappearance of nodal gap across the insulator-superconductor transition in a copper-oxide superconductor.
The parent compound of the copper-oxide high-temperature superconductors is a Mott insulator. Superconductivity is realized by doping an appropriate amount of charge carriers. How a Mott insulator transforms into a superconductor is crucial in understanding the unusual physical properties of high-temperature superconductors and the superconductivity mechanism. Here we report high-resolution angle-resolved photoemission measurement on heavily underdoped Bi₂Sr₂-xLaxCuO(₆+δ) system. The electronic structure of the lightly doped samples exhibit a number of characteristics: existence of an energy gap along the nodal direction, d-wave-like anisotropic energy gap along the underlying Fermi surface, and coexistence of a coherence peak and a broad hump in the photoemission spectra. Our results reveal a clear insulator-superconductor transition at a critical doping level of ~0.10 where the nodal energy gap approaches zero, the three-dimensional antiferromagnetic order disappears, and superconductivity starts to emerge. These observations clearly signal a close connection between the nodal gap, antiferromagnetism and superconductivity.
National Laboratory for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Yingying
Y
Peng
Jianqiao
J
Meng
Daixiang
D
Mou
Junfeng
J
He
Lin
L
Zhao
Yue
Y
Wu
Guodong
G
Liu
Xiaoli
X
Dong
Shaolong
S
He
Jun
J
Zhang
Xiaoyang
X
Wang
Qinjun
Q
Peng
Zhimin
Z
Wang
Shenjin
S
Zhang
Feng
F
Yang
Chuangtian
C
Chen
Zuyan
Z
Xu
T K
TK
Lee
X J
XJ
Zhou