The new iron-based superconductor

1
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)

2
Outline

• Introduction
• Typical iron based superconductor 111 and 122
• Experiment results
• Summary

3
Introduction

• Hideo Hosono, at the Tokyo Institute of
  Technology, and colleagues found the first
  compound, fluorine-doped lanthanum oxygen iron
  arsenide (LaO1xFxFeAs), 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).
4
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 Tc43K Four days
later, Zhong-Xian Zhao reported on the server
that praseodymium oxygen fluorine iron arsenide
has a Tc52K 55 kelvin for the samarium compound
grown under pressure
5
Crystal Structure of LaOFeAs
Schematic crystal structure of LaOFeAs.
Electron carriers generated by F-doping 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 Tc43k 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)
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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)
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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 Tc38K
Marianne Rotter, et al, PRL 101 107006 (2008)
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Phase diagram
The red circles indicate the onset temperature of
the P4nmm 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
Cuprate
J.Zhao, et.al, Nature Mater. 7, 953(2008)
9
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.
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Fermi surface topology of Ba1-xKxFe2As2
ARPES measurement Fermi surface maps of
Ba1-xKxFe2As2 measured using respective
excitation energies of h?80 and 50 eV at
T14K A sharp disagreement with band structure
calculation this paper reported that the
electronic structure of Ba1-xKxFe2As2 revealed a
reconstruction characterized by a (p, p) wave
vector. This electronic order coexist with
superconductivity and persists up to room
temperature.
T300k
V.B.Zabolotnyy, et.al, Nature 457, 569(2009)
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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
arXiv0806.4400
12
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.

13
Reference

• 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
  arXiv0806.4400
• V.B.Zabolotnyy, et.al, Nature 457, 569(2008)
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