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Distrontium ruthenate

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Distrontium ruthenate, also known as strontium ruthenate, is an oxide of strontium and ruthenium with the chemical formula Sr2RuO4. It was the first reported perovskite superconductor that did not contain copper. Strontium ruthenate is structurally very similar to the high-temperature cuprate superconductors, and in particular, is almost identical to the lanthanum doped superconductor (La, Sr)2CuO4. 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]

Distrontium 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)
  • InChI=1S/4O.Ru.2Sr/q4*-1;+4;2*+2
    Key: KWNWXODLYNPAJR-UHFFFAOYSA-N
  • [Sr+2].[Sr+2].[O-][Ru+4]([O-])([O-])[O-]
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).

Superconductivity edit

Superconductivity in SRO was first observed by Yoshiteru Maeno et al. Unlike the cuprate superconductors, SRO displays superconductivity in the absence of doping.[2] The superconducting order parameter in SRO exhibits signatures of time-reversal symmetry breaking,[3] 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.[4]

Early proposals 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.[5] This has led some to speculate that superconductivity arises dominantly from the α and β bands instead.[6] 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.[7] 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.[8][9]

Tc seems to increase under uniaxial compression[10] that pushes the van Hove singularity of the dxy orbital across the Fermi level.[11]

Evidence was reported for p-wave singlet state as in cuprates and conventional superconductors, instead of the conjectured more unconventional p-wave triplet state.[12][13] It has also been suggested that Strontium ruthenate superconductivity could be due to a Fulde–Ferrell–Larkin–Ovchinnikov phase.[14][15]

Strontium ruthenate behaves as a conventional Fermi liquid at temperatures below 25 K.[16]

In 2023, a team of researchers from the University of Illinois Urbana-Champaign confirmed the 67-year-old prediction of Pines' demon excitation in Sr2RuO4.[17]

See also edit

References edit

  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. 60 (9). AIP Publishing: 1138–1140. doi:10.1063/1.106432. ISSN 0003-6951.
  2. ^ a b Koster, Gertjan; Klein, Lior; Siemons, Wolter; Rijnders, Guus; Dodge, J. Steven; Eom, Chang-Beom; Blank, Dave H. A.; Beasley, Malcolm R. (2012). "Structure, Physical Properties, and Applications of SrRuO3 Thin Films". Reviews of Modern Physics. 84 (1): 253–298. Bibcode:2012RvMP...84..253K. doi:10.1103/RevModPhys.84.253.
  3. ^ Kapitulnik, Aharon; Xia, Jing; 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. arXiv:0906.2845. Bibcode:2009NJPh...11e5060K. doi:10.1088/1367-2630/11/5/055060. S2CID 43924082.
  4. ^ Mazin, I. I.; Singh, David J. (1997-07-28). "Ferromagnetic Spin Fluctuation Induced Superconductivity in Sr2RuO4". Physical Review Letters. 79 (4). American Physical Society (APS): 733–736. arXiv:cond-mat/9703068. Bibcode:1997PhRvL..79..733M. doi:10.1103/physrevlett.79.733. ISSN 0031-9007. S2CID 119434737.
  5. ^ Hicks, Clifford W.; et al. (2010). "Limits on superconductivity-related magnetization in Sr2RuO4 and PrOs4Sb12 from scanning SQUID microscopy". Physical Review B. 81 (21): 214501. arXiv:1003.2189. Bibcode:2010PhRvB..81u4501H. doi:10.1103/PhysRevB.81.214501. S2CID 26608198.
  6. ^ Raghu, S.; Marini, Aharon; Pankratov, Steve; Rubio, Angel (2010). "Hidden Quasi-One-Dimensional Superconductivity in Sr2RuO4". Physical Review Letters. 105 (13): 136401. arXiv:1003.3927. Bibcode:2010PhRvL.105b6401B. doi:10.1103/PhysRevLett.105.026401. PMID 20867720. S2CID 26117260.
  7. ^ 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. arXiv:1412.4592. Bibcode:2015PhRvB..91i4507H. doi:10.1103/physrevb.91.094507. ISSN 1098-0121.
  8. ^ 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. arXiv:1410.0377. Bibcode:2014PhRvB..90v4519H. doi:10.1103/physrevb.90.224519. ISSN 1098-0121. S2CID 118773764.
  9. ^ 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. arXiv:1409.7459. Bibcode:2015PhRvL.114s5301T. doi:10.1103/physrevlett.114.195301. ISSN 0031-9007. PMID 26024177. S2CID 3152887.
  10. ^ Steppke, Alexander; Zhao, Lishan; Barber, Mark E.; Scaffidi, Thomas; Jerzembeck, Fabian; Rosner, Helge; Gibbs, Alexandra S.; Maeno, Yoshiteru; Simon, Steven H.; Mackenzie, Andrew P.; Hicks, Clifford W. (2017-01-12). "Strong peak in Tc of Sr2RuO4 under uniaxial pressure" (PDF). Science. 355 (6321). American Association for the Advancement of Science (AAAS): eaaf9398. doi:10.1126/science.aaf9398. hdl:10023/10113. ISSN 0036-8075. PMID 28082534. S2CID 8197509.
  11. ^ Sunko, Veronika; Abarca Morales, Edgar; Marković, Igor; Barber, Mark E.; Milosavljević, Dijana; Mazzola, Federico; Sokolov, Dmitry A.; Kikugawa, Naoki; Cacho, Cephise; Dudin, Pavel; Rosner, Helge (2019-08-19). "Direct observation of a uniaxial stress-driven Lifshitz transition in Sr2RuO4". npj Quantum Materials. 4 (1): 46. arXiv:1903.09581. Bibcode:2019npjQM...4...46S. doi:10.1038/s41535-019-0185-9. ISSN 2397-4648. S2CID 85459284.
  12. ^ Chronister, Aaron; Pustogow, Andrej; Kikugawa, Naoki; Sokolov, Dmitry A.; Jerzembeck, Fabian; Hicks, Clifford W.; Mackenzie, Andrew P.; Bauer, Eric D.; Brown, Stuart E. (2021-06-22). "Evidence for even parity unconventional superconductivity in Sr2RuO4". Proceedings of the National Academy of Sciences. 118 (25). arXiv:2007.13730. Bibcode:2021PNAS..11825313C. doi:10.1073/pnas.2025313118. ISSN 0027-8424. PMC 8237678. PMID 34161272.
  13. ^ Lopatka, Alex (2021-08-05). "An unconventional superconductor isn't so odd after all". Physics Today. 2021: 0805a. doi:10.1063/PT.6.1.20210805a. S2CID 241654779.
  14. ^ 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". Science. 376 (6591): 397–400. Bibcode:2022Sci...376..397K. doi:10.1126/science.abb0332. ISSN 0036-8075. PMID 35446631. S2CID 248322696.
  15. ^ "Magnetic field induces spatially varying superconductivity". Physics Today. 2022 (1): 0613a. 2022-06-13. Bibcode:2022PhT..2022a.613.. doi:10.1063/PT.6.1.20220613a. S2CID 249659408.
  16. ^ Yanoff, Brian (2000). Temperature dependence of the penetration depth in the unconventional superconductor Sr2RuO4 (PDF). University of Illinois at Urbana-Champaign. Archived from the original (PDF) on 2012-09-16. Retrieved 2012-04-16.
  17. ^ Abbamonte, Peter (August 9, 2023). "Pines' demon observed as a 3D acoustic plasmon in Sr2RuO4". Nature. 45 (7977): 66–70. Bibcode:2023Natur.621...66H. doi:10.1038/s41586-023-06318-8. PMC 10482684. PMID 37558882.

Further reading edit

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