NaFe_{0.56}Cu_{0.44}As: A Pnictide Insulating Phase Induced by On-Site Coulomb Interaction.
In the studies of iron pnictides, a key question is whether their bad-metal state from which the superconductivity emerges lies in close proximity with a magnetically ordered insulating phase. Recently, it was found that at low temperatures, the heavily Cu-doped NaFe_{1-x}Cu_{x}As (x>0.3) iron pnictide is an insulator with long-range antiferromagnetic order, similar to the parent compound of cuprates but distinct from all other iron pnictides. Using angle-resolved photoemission spectroscopy, we determined the momentum-resolved electronic structure of NaFe_{1-x}Cu_{x}As (x=0.44) and identified that its ground state is a narrow-gap insulator. Combining the experimental results with density functional theory (DFT) and DFT+U calculations, our analysis reveals that the on-site Coulombic (Hubbard) and Hund's coupling energies play crucial roles in the formation of the band gap about the chemical potential. We propose that at finite temperatures, charge carriers are thermally excited from the Cu-As-like valence band into the conduction band, which is of Fe 3d-like character. With increasing temperature, the number of electrons in the conduction band becomes larger and the hopping energy between Fe sites increases, and finally the long-range antiferromagnetic order is destroyed at T>T_{N}. Our study provides a basis for investigating the evolution of the electronic structure of a Mott insulator transforming into a bad metallic phase and eventually forming a superconducting state in iron pnictides.
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.|Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland.
C E
CE
Matt
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.|Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne, CH-10 15 Lausanne, Switzerland.
N
N
Xu
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.|Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Baiqing
B
Lv
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.|Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Junzhang
J
Ma
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
F
F
Bisti
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
J
J
Park
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.|Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne, CH-10 15 Lausanne, Switzerland.|Laboratory for Developments and Methods, Paul Scherrer Institut, CH-5232 Villigen, Switzerland.
T
T
Shang
Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA.|Department of Applied Physics, Northwestern Polytechnical University, Xian 710072, China.
Chongde
C
Cao
Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA.
Yu
Y
Song
Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA.
Andriy H
AH
Nevidomskyy
Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA.
Pengcheng
P
Dai
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
L
L
Patthey
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
N C
NC
Plumb
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
M
M
Radovic
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.|Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland.|Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne, CH-10 15 Lausanne, Switzerland.
J
J
Mesot
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
M
M
Shi