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Iron-based superconductor

 
Wikipedia: Iron-based superconductor
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Iron-based superconductors (sometimes misleadingly called iron superconductors) are chemical compounds (containing iron) with superconducting properties. In 2008, led by recently discovered iron pnictide compounds (originally known as oxypnictides), they were in the first stages of experimentation and implementation. (Previously most high-temperature superconductors were cuprates and being based on layers of copper and oxygen sandwiched between other (typically non-metal?) substances.[1] )

This new type of superconductors is based instead on conducting layers of iron and a pnictide (typically arsenic) and seems to show promise as the next generation of high temperature superconductors.[2]

Much of the interest is because the new compounds are very different than the cuprates and may help lead to a theory of non-BCS-theory superconductivity.

More recently these have been called the ferropnictides. The first ones found belong to the group of oxypnictides. Some of the compounds are known since 1995 [3] and their semiconductive properties are known and patented since 2006.[4] [5]

It has also been found that some iron chalcogens superconduct [6]; for example, doped FeSe can have a critical temperature (Tc) of 8 K at normal pressure, and 27 K under high pressure.

A subset of iron-based superconductors with properties similar to the oxypnictides, known as the 122 Iron Arsenides, attracted attention in 2008 due to their relative ease of synthesis.

The Oxypnictides such as LaOFeAs are often referred to as the '1111' pnictides.

The crystalline material, known chemically as LaOFeAs, stacks iron and arsenic layers, where the electrons flow, between planes of lanthanum and oxygen. Replacing up to 11 percent of the oxygen with fluorine improved the compound — it became superconductive at 26 kelvins, the team reports in the March 19, 2008 Journal of the American Chemical Society. Subsequent research from other groups suggests that replacing the lanthanum in LaOFeAs with other rare earth elements such as cerium, samarium, neodymium and praseodymium leads to superconductors that work at 52 kelvin.
—[2]

Compounds such as Sr2ScFePO3 (discovered in 2009) are referred to as the `22426' family. (as FePSr2ScO3) [7]

In 2009, it was shown that undoped iron pnictides had a magnetic quantum critical point deriving from competition between electronic localization and itinerancy.[citation needed]

Contents

Superconductivity

Superconducting transition temperatures:

oxypnictide Tc (K) non-oxypnictide Tc (K)
LaO0.89F0.11FeAs 26[8] Ba0.6K0.4Fe2As2 38[9]
LaO0.9F0.2FeAs 28.5[10] Ca0.6Na0.4Fe2As2 26[11]
CeFeAsO0.84F0.16 41[8] CaFe0.9Co0.1AsF 22[12]
SmFeAsO0.9F0.1 43[8] Sr0.5Sm0.5FeAsF 56[13]
La0.5Y0.5FeAsO0.6 43.1[14] LiFeAs <18[15][16]
NdFeAsO0.89F0.11 52[8] NaFeAs 9-25[17][18]
PrFeAsO0.89F0.11 52[19] FeSe* <27[20][21]
GdFeAsO0.85 53.5[22]
SmFeAsO~0.85 55[23]

*with small off-stoichiometry or tellurium doping

Mechanism of superconductivity

Modern conventional superconductors work at temperatures between absolute zero and 100 kelvins; by comparison, certain cuprates became superconductive at temperatures exceeding 163 kelvin. Some people have speculated that in cuprate superconductors the electrons are paired due to spin fluctuations that occur around the copper ions however other models have also been proposed and at this time there is no consensus on the actual mechanism for cuprate superconductivity. There are claims that in iron based superconductors orbital fluctuations are far more essential. However, as in the cuprates the mechanism for high temperature superconductivity remains unknown at this time.

On the other hand, the spin fluctuations that could glue together cuprate electrons might not be enough for those in the iron-based materials. Instead orbital fluctuations — or variations in the location of electrons around atoms — might also prove crucial, Haule speculates. In essence, the iron-based materials give more freedom to electrons than cuprates do when it comes to how electrons circle around atoms. Orbital fluctuations might play important roles in other unconventional superconductors as well, such as ones based on uranium or cobalt, which operate closer to absolute zero, Haule conjectures. Because the iron-based superconductors work at higher temperatures, such fluctuations may be easier to research. However, spectroscopic measurements have shown that Haule's calculations do not describe these materials accurately. In particular the correlated approach that he used predicts a Hubbard band that is not seen. Further work is needed to unravel the properties of these materials.[2]

References

  1. ^ T C Ozawa and S M Kauzlarich (2008). "Chemistry of layered d-metal pnictide oxides and their potential as candidates for new superconductors" (free-download review). Sci. Technol. Adv. Mater. 9: 033003. doi:10.1088/1468-6996/9/3/033003. 
  2. ^ a b c "Iron Exposed as High-Temperature Superconductor": Scientific American. June 2008
  3. ^ Barbara I. Zimmer, Wolfgang Jeitschko, Jörg H. Albering, Robert Glaum and Manfred Reehuis (1995). "The rate earth transition metal phosphide oxides LnFePO, LnRuPO and LnCoPO with ZrCuSiAs type structure". Journal of Alloys and Compounds 229 (2): 238–242. doi:10.1016/0925-8388(95)01672-4. 
  4. ^ Yoichi Kamihara, Hidenori Hiramatsu, Masahiro Hirano, Ryuto Kawamura, Hiroshi Yanagi, Toshio Kamiya, and Hideo Hosono (2006). "Iron-Based Layered Superconductor: LaOFeP". J. Am. Chem. Soc. 128 (31): 10012–10013. doi:10.1021/ja063355c. PMID 16881620. 
  5. ^ H. Hosono et al. (2006) Magnetic semiconductor material European Patent Application EP1868215
  6. ^ Johannes, Michelle (2008). "The iron age of superconductivity". Physics 1: 28. doi:10.1103/Physics.1.28. 
  7. ^ http://www.iop.org/EJ/article/0953-2048/23/2/022001/sust10_2_022001.html "Evidence for nodal superconductivity in Sr2ScFePO3" 2009
  8. ^ a b c d K. Ishida et al (2009). "To What Extent Iron-Pnictide New Superconductors Have Been Clarified: A Progress Report". J. Phys. Soc. Jpn. 78: 062001. doi:10.1143/JPSJ.78.062001. 
  9. ^ Marianne Rotter, Marcus Tegel, and Dirk Johrendt (2008). "Superconductivity at 38 K in the Iron Arsenide (Ba1-xKx)Fe2As2". Physical Review Letters 101 (10): 107006. doi:10.1103/PhysRevLett.101.107006. PMID 18851249. 
  10. ^ Prakash, J. (2008). "Potassium fluoride doped LaOFeAs multi-band superconductor: Evidence of extremely high upper critical field". EPL (Europhysics Letters) 84: 57003. doi:10.1209/0295-5075/84/57003. 
  11. ^ Shirage, Parasharam Maruti (2008). "Superconductivity at 26 K in (Ca1-xNax)Fe2As2". Applied Physics Express 1: 081702. doi:10.1143/APEX.1.081702. 
  12. ^ Satoru Matsuishi, Yasunori Inoue, Takatoshi Nomura, Hiroshi Yanagi, Masahiro Hirano and Hideo Hosono (2008). "Superconductivity Induced by Co-Doping in Quaternary Fluoroarsenide CaFeAsF". J. Am. Chem. Soc. 2008: 14428–14429. doi:10.1021/ja806357j. http://pubs.acs.org/doi/abs/10.1021/ja806357j. 
  13. ^ G. Wu, Y. L. Xie, H. Chen, M. Zhong, R. H. Liu, B. C. Shi, Q. J. Li, X. F. Wang, T. Wu, Y. J. Yan, J. J. Ying, and X. H. Chen (2008). "Superconductivity at 56 K in Samarium-doped SrFeAsF". http://arxiv.org/abs/0811.0761. 
  14. ^ Shirage, Parasharam M. (2008). "Superconductivity at 43 K at ambient pressure in the iron-based layered compound La1‑xYxFeAsOy". Physical Review B 78: 172503. doi:10.1103/PhysRevB.78.172503. Bibcode: 2008PhRvB..78q2503S. 
  15. ^ Michael J. Pitcher et al. (2008). "Structure and superconductivity of LiFeAs". Chem. Commun. 2008: 5918–5920. doi:10.1039/b813153h. 
  16. ^ Joshua H. Tapp et al. (2008). "LiFeAs: An intrinsic FeAs-based superconductor with Tc=18 K". Physical Review B 78: 060505(R). doi:10.1103/PhysRevB.78.060505. 
  17. ^ C. W. Chu et al. (2009). "The Synthesis and Characterization of LiFeAs and NaFeAs". http://arxiv.org/abs/0902.0806. 
  18. ^ Dinah R. Parker, Michael J. Pitcher, and Simon J. Clarke (2008). "Structure and superconductivity of the layered iron arsenide NaFeAs". http://arxiv.org/abs/0810.3214. 
  19. ^ Ren, Z. A. (2008). "Superconductivity at 52 K in iron based F doped layered quaternary compound Pr[O1–xFx]FeAs". Materials Research Innovations 12: 105. doi:10.1179/143307508X333686. 
  20. ^ Fong-Chi Hsu et al. (2008). "Superconductivity in the PbO-type structure α-FeSe". PNAS 105 (38): 14262–14264. doi:10.1073/pnas.0807325105. PMID 18776050. 
  21. ^ Yoshikazu Mizuguchi, Fumiaki Tomioka, Shunsuke Tsuda, Takahide Yamaguchi, and Yoshihiko Takano (2008). "Superconductivity at 27 K in tetragonal FeSe under high pressure". Appl. Phys. Lett. 93: 152505. doi:10.1063/1.3000616. 
  22. ^ Yang, Jie (2008). "Superconductivity at 53.5 K in GdFeAsO1−δ". Superconductor Science and Technology 21: 082001. doi:10.1088/0953-2048/21/8/082001. 
  23. ^ Ren, Zhi-An (2008). ""Superconductivity and phase diagram in iron-based arsenic-oxides ReFeAsO1−δ (Re = rare-earth metal) without fluorine doping". EPL (Europhysics Letters) 83: 17002. doi:10.1209/0295-5075/83/17002. 

Further reading

See also


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