Chemistry:Strontium ruthenate

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Strontium ruthenate
strontium ruthenate unit cell
The unit cell of the layered perovskite structure of strontium ruthenate. Ruthenium ions are red, strontium ions are blue, and oxygen ions are green.
Identifiers
3D model (JSmol)
Properties
Sr2RuO4
Structure[1]
K2NiF4 structure (body-centered tetragonal)
a = 387 pm, c = 1274 pm
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references
Tracking categories (test):

Strontium ruthenate (SrO) is an oxide of strontium and ruthenium with the chemical formula Sr2RuO4. It was the first reported perovskite superconductor that did not contain copper.[2][3] Strontium ruthenate is structurally very similar to the high-temperature cuprate superconductors,[4] and in particular, is almost identical to the lanthanum doped superconductor (La, Sr)2CuO4.[5] However, the transition temperature for the superconducting phase transition is 0.93 K (about 1.5 K for the best sample), which is much lower than the corresponding value for cuprates.[2]

High-quality crystals of strontium ruthenate are synthesized using a floating zone method in a controlled atmosphere with ruthenium as flux. The perovskite structure can be deduced based on powder x-ray diffraction measurements. Strontium ruthenate behaves as a conventional Fermi liquid at temperatures below 25 K.[3]

Superconductivity

Superconductivity in SRO was first observed by Yoshiteru Maeno and his group in 1994 when they were looking for high temperature superconductors with structures similar to the cuprates. Unlike the cuprates, SRO displays superconductivity even in the absence of doping.[4] The superconducting order parameter in SRO has been shown to exhibit signatures of time-reversal symmetry breaking,[6] and hence, it can be classified as an unconventional superconductor.

Sr2RuO4 is believed to be a fairly two-dimensional system, with superconductivity occurring primarily on the Ru-O plane. The electronic structure of Sr2RuO4 is characterized by three bands derived from the Ru t2g 4d orbitals, namely, α, β and γ bands, of which the first is hole-like while the other two are electron-like. Among them, the γ band arises mainly from the dxy orbital, while the α and β bands emerge from the hybridization of dxz and dyz orbitals. Due to the two-dimensionality of Sr2RuO4, its Fermi surface consists of three nearly two-dimensional sheets with little dispersion along the crystalline c-axis and that the compound is nearly magnetic.[7]

Early proposals have suggested that superconductivity is dominant in the γ band. In particular, the candidate chiral p-wave order parameter in the momentum space exhibits k-dependence phase winding which is characteristic of time-reversal symmetry breaking. This peculiar single-band superconducting order is expected to give rise to appreciable spontaneous supercurrent at the edge of the sample. Such an effect is closely associated with the topology of the Hamiltonian describing Sr2RuO4 in the superconducting state, which is characterized by a nonzero Chern number. However, scanning probes have so far failed to detect expected time-reversal symmetry breaking fields generated by the supercurrent, off by orders of magnitude.[8] This has led some to speculate that superconductivity arises dominantly from the α and β bands instead.[9] Such a two-band superconductor, although having k-dependence phase winding in its order parameters on the two relevant bands, is topologically trivial with the two bands featuring opposite Chern numbers. Therefore, it could possibly give a much reduced if not completely cancelled supercurrent at the edge. However, this naive reasoning was later found not to be entirely correct: the magnitude of edge current is not directly related to the topological property of the chiral state.[10] In particular, although the non-trivial topology is expected to give rise to protected chiral edge states, due to U(1) symmetry-breaking the edge current is not a protected quantity. In fact, it has been shown that the edge current vanishes identically for any higher angular momentum chiral pairing states which feature even larger Chern numbers, such as chiral d-, f-wave etc.[11][12]

Tc seems to increase under uniaxial compression[13] that pushes the van Hove singularity of the dxy orbital across the Fermi level.[14]

In August 2021 evidence was reported for p-wave singlet state as in cuprates and conventional superconductors, instead of the conjectured more unconventional p-wave triplet state.[15][16] It has also been suggested that Strontium ruthenate superconductivity could be due to a Fulde–Ferrell–Larkin–Ovchinnikov phase.[17][18]

References

  1. ↑ Lichtenberg, F.; Catana, A.; Mannhart, J.; Schlom, D. G. (1992-03-02). "Sr2RuO4: A metallic substrate for the epitaxial growth of YBa2Cu3O7−δ". Applied Physics Letters (AIP Publishing) 60 (9): 1138–1140. doi:10.1063/1.106432. ISSN 0003-6951. 
  2. ↑ 2.0 2.1 Yoshiteru Maeno et al. (1994). "Superconductivity in a layered perovskite without copper". Nature 372 (6506): 532–534. doi:10.1038/372532a0. Bibcode: 1994Natur.372..532M. 
  3. ↑ 3.0 3.1 Yanoff, Brian (2000). Temperature dependence of the penetration depth in the unconventional superconductor Sr2RuO4. University of Illinois at Urbana-Champaign. http://groups.mrl.uiuc.edu/dvh/theses/yanoff.pdf. 
  4. ↑ 4.0 4.1 Wooten, Rachel. "Strontium Ruthenate". University of Tennessee-Knoxville. https://docs.google.com/viewer?a=v&q=cache:DgnknpjYbx4J:sces.phys.utk.edu/~dagotto/condensed/HW2_2008/Strontium_Ruthenate.ppt+&hl=en&gl=us&pid=bl&srcid=ADGEESjZ7iZGRQSADAb7Z1s_9eAna1xiWVss132uKFgZzdWLT0aMoimFedsvEYqudjD3jQQnZj0ttTougqs1felMdAWruV20EbFHDcoyabxp8gHZE7bmi1WI28B0Y5qLzU42RqJuuJwO&sig=AHIEtbTQVVf6y8oDl63wDTUkXKH9NrNEug&pli=1. 
  5. ↑ Yoshiteru Maeno; Maurice Rice; Manfred Sigrist (2001). "The intriguing superconductivity of Strontium Ruthenate". Physics Today 54 (1): 42. doi:10.1063/1.1349611. Bibcode: 2001PhT....54a..42M. http://www.physics.mcmaster.ca/~imai/PhysicsToday_2001.pdf. Retrieved 16 April 2012. 
  6. ↑ Aharon Kapitulnik; Jing Xia; Elizabeth Schemm Alexander Palevski (May 2009). "Polar Kerr effect as probe for time-reversal symmetry breaking in unconventional superconductors". New Journal of Physics 11 (5): 055060. doi:10.1088/1367-2630/11/5/055060. Bibcode: 2009NJPh...11e5060K. 
  7. ↑ Mazin, I. I.; Singh, David J. (1997-07-28). "Ferromagnetic Spin Fluctuation Induced Superconductivity in Sr2RuO4". Physical Review Letters (American Physical Society (APS)) 79 (4): 733–736. doi:10.1103/physrevlett.79.733. ISSN 0031-9007. Bibcode: 1997PhRvL..79..733M. 
  8. ↑ Hicks, Clifford W. (2010). "Limits on superconductivity-related magnetization in Sr2RuO4 and PrOs4Sb12 from scanning SQUID microscopy". Physical Review B 81 (21): 214501. doi:10.1103/PhysRevB.81.214501. Bibcode: 2010PhRvB..81u4501H. 
  9. ↑ Raghu, S.; Marini, Aharon; Pankratov, Steve; Rubio, Angel (2010). "Hidden Quasi-One-Dimensional Superconductivity in Sr2RuO4". Physical Review Letters 105 (13): 136401. doi:10.1103/PhysRevLett.105.026401. PMID 20867720. Bibcode: 2010PhRvL.105b6401B. http://prl.aps.org/abstract/PRL/v105/i13/e136401. 
  10. ↑ Huang, Wen; Lederer, Samuel; Taylor, Edward; Kallin, Catherine (2015-03-12). "Nontopological nature of the edge current in a chiralp-wave superconductor". Physical Review B 91 (9): 094507. doi:10.1103/physrevb.91.094507. ISSN 1098-0121. Bibcode: 2015PhRvB..91i4507H. 
  11. ↑ Huang, Wen; Taylor, Edward; Kallin, Catherine (2014-12-19). "Vanishing edge currents in non-p-wave topological chiral superconductors". Physical Review B 90 (22): 224519. doi:10.1103/physrevb.90.224519. ISSN 1098-0121. Bibcode: 2014PhRvB..90v4519H. 
  12. ↑ Tada, Yasuhiro; Nie, Wenxing; Oshikawa, Masaki (2015-05-13). "Orbital Angular Momentum and Spectral Flow in Two-Dimensional Chiral Superfluids". Physical Review Letters 114 (19): 195301. doi:10.1103/physrevlett.114.195301. ISSN 0031-9007. PMID 26024177. Bibcode: 2015PhRvL.114s5301T. 
  13. ↑ Steppke, Alexander; Zhao, Lishan; Barber, Mark E.; Scaffidi, Thomas; Jerzembeck, Fabian; Rosner, Helge; Gibbs, Alexandra S.; Maeno, Yoshiteru et al. (2017-01-12). "Strong peak in Tc of Sr2RuO4 under uniaxial pressure". Science (American Association for the Advancement of Science (AAAS)) 355 (6321): eaaf9398. doi:10.1126/science.aaf9398. ISSN 0036-8075. PMID 28082534. http://pure-oai.bham.ac.uk/ws/files/102786770/Hicks_2017_Science.pdf. 
  14. ↑ Sunko, Veronika; Abarca Morales, Edgar; Marković, Igor; Barber, Mark E.; Milosavljević, Dijana; Mazzola, Federico; Sokolov, Dmitry A.; Kikugawa, Naoki et al. (2019-08-19). "Direct observation of a uniaxial stress-driven Lifshitz transition in Sr2RuO4" (in en). NPJ Quantum Materials 4 (1): 46. doi:10.1038/s41535-019-0185-9. ISSN 2397-4648. Bibcode: 2019npjQM...4...46S. https://www.nature.com/articles/s41535-019-0185-9. 
  15. ↑ Chronister, Aaron; Pustogow, Andrej; Kikugawa, Naoki; Sokolov, Dmitry A.; Jerzembeck, Fabian; Hicks, Clifford W.; Mackenzie, Andrew P.; Bauer, Eric D. et al. (2021-06-22). "Evidence for even parity unconventional superconductivity in Sr2RuO4" (in en). Proceedings of the National Academy of Sciences 118 (25). doi:10.1073/pnas.2025313118. ISSN 0027-8424. PMID 34161272. Bibcode: 2021PNAS..11825313C. 
  16. ↑ Lopatka, Alex (2021-08-05). "An unconventional superconductor isn't so odd after all" (in en). Physics Today 2021: 0805a. doi:10.1063/PT.6.1.20210805a. https://physicstoday.scitation.org/do/10.1063/PT.6.1.20210805a/abs/. 
  17. ↑ Kinjo, K.; Manago, M.; Kitagawa, S.; Mao, Z. Q.; Yonezawa, S.; Maeno, Y.; Ishida, K. (2022-04-22). "Superconducting spin smecticity evidencing the Fulde-Ferrell-Larkin-Ovchinnikov state in Sr 2 RuO 4" (in en). Science 376 (6591): 397–400. doi:10.1126/science.abb0332. ISSN 0036-8075. https://www.science.org/doi/10.1126/science.abb0332. 
  18. ↑ "Magnetic field induces spatially varying superconductivity" (in en). Physics Today 2022 (1): 0613a. 2022-06-13. doi:10.1063/PT.6.1.20220613a. https://physicstoday.scitation.org/do/10.1063/PT.6.1.20220613a/full. 

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