Transcript The new iron-based superconductor

The new iron-based
superconductor
Hao Hu
The University of Tennessee Department of Physics and Astronomy,
Knoxville
Course: Advanced Solid State Physics II (Spring 2009)
Instructor: Elbio Dagotto
(Dated: March 22, 2009)
Outline
• Introduction
• Typical iron based superconductor ‘111’ and
‘122’
• Experiment results
• Summary
Introduction
• Hideo Hosono, at the Tokyo Institute of Technology, and colleagues found
the first compound, fluorine-doped lanthanum oxygen iron arsenide
(LaO1–xFxFeAs), as they reported online 23 February 2008 in the Journal of
the American Chemical Society. It weighed in with a Tc of 26 Kelvin.
Y. Kamihara, et al, J. Am. Chem. Soc. 130, 3296 (2008).
Introduction
• Four Chinese groups quickly pushed the critical temperatures higher by
replacing the lanthanum with other rare earth elements.
Xianhui Chen reported
on the arXiv preprint
server (www.arXiv.org)
a Tc=43K
Four days later, ZhongXian Zhao reported on
the server that
praseodymium oxygen
fluorine iron arsenide
has a Tc=52K
55 kelvin for the
samarium compound
grown under pressure
Crystal Structure of LaOFeAs
Schematic crystal structure of
LaOFeAs.
Electron carriers generated by Fdoping into oxygen sites are
injected into FeAs metallic layers
as a result of the large energy
offset between these two layers.
Note that the carrier doping layer
is spatially separated from the
conduction layer.
They got Tc=43k at 4GPa on this
F-doped LaOFeAs
Fe is sitting on a tetrahedral coordination. And Fe
is formally divalent.
Hiroki Takahashi, et al, Nature 06972 (2008)
Magnetic Structure
Plainly similar. The old and the new superconductors both contain planes of ions
magnetized in opposite directions. In the older ones, electrons hop from copper
to copper (arrow). For Fe-based SC, early results shows the As-Fe-As layer is
responsible for the superconductivity.
Adrian Cho, Science 320, 870(2008)
Crystal and magnetic Structure of BaFe2As2
The structural and electronic
properties of the parent compound
BaFe2As2 are closely related to
LaFeAsO.
By hole doping potassium in this
barium compound they get a
Tc=38K
Marianne Rotter, et al, PRL 101 107006 (2008)
Phase diagram
Cuprate
The red circles indicate the onset
temperature of the P4=nmm to Cmma
phase transition.
The black squares and green triangles
designate the Ne´ el temperatures of Fe,
TN (Fe), and Cerium, TN (Ce), respectively,
as determined from neutron measurements
J.Zhao, et.al, Nature Mater. 7, 953(2008)
Simplified doping dependent phase diagrams of iron-based superconductors for
both Ln-1111 and Ba-122 materials. The phases shown are the
antiferromagnetic/spin density wave (AF/SDW) phase close to zero doping and the
superconducting phase around optimal doping.
the superconducting phase is close to or overlapping with the magnetic phase.
Fermi surface topology of Ba1-xKxFe2As2
ARPES measurement:
Fermi surface maps of Ba1-xKxFe2As2 measured
using respective excitation energies of hν=80
and 50 eV at T=14K
A sharp disagreement with band structure
calculation
this paper reported that the electronic
structure of Ba1-xKxFe2As2 revealed a
reconstruction characterized by a (π, π) wave
vector. This electronic order coexist with
superconductivity and persists up to room
temperature.
T=300k
V.B.Zabolotnyy, et.al, Nature 457, 569(2009)
STM measurement
Topography reveals stripes. (a) 300 Å constant current topography reveals a stripe
ordered region of the strontium sample, bounded by unit cell height step edges in
the upper left and lower right leading to non-atomically resolved regions. (b) 30 Å
field of view more clearly showing resolution of atoms
Boyer et al, STM of (Sr1-xKx)Fe2As2 arXiv:0806.4400
Summary
• Compare to cuprate Fe- based SC have a lower Tc up to
now
• The magnetic moment in Fe-based SC are aligned with
in the FeAs plane. In cuprate, it is up and down.
• For the magnetic ordered state in the cuprate, the AFM
phase parent is Mott insulator whose electrons are
localized. For the Fe-based superconductors, the AFM
phase or SDW phase remains metallic.
• Its Superconductivity is competing with the spin wave
density state. SC and SDW may coexist in underdoped
samples.
Reference
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Adrian Cho, Science 320, 870(2008)
J.Zhao, et.al, Nature Mater. 7, 953(2008)
Marianne Rotter, et al, PRL 101 107006 (2008)
Y. Kamihara, et al, J. Am. Chem. Soc. 130, 3296 (2008)
Hiroki Takahashi, et al, Nature 06972 (2008)
Boyer et al, STM of (Sr1-xKx)Fe2As2 arXiv:0806.4400
V.B.Zabolotnyy, et.al, Nature 457, 569(2008)
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