Dicalcium ruthenate

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Dicalcium ruthenate
Identifiers
3D model (JSmol)
  • InChI=1S/2Ca.O4Ru/c;;1-5(2,3)4/q2*+2;-4
  • Key: JWAHTWBBWFKEMH-UHFFFAOYSA-N
  • [Ca+2].[Ca+2].[O-][Ru]([O-])([O-])[O-]
Properties
Ca2O4Ru
Molar mass 245.22 g·mol−1
Related compounds
Other cations
Distrontium ruthenate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Dicalcium ruthenate, with the chemical formula Ca2RuO4, is a stoichiometric oxide compound that hosts a multi-orbital (band) Mott insulating ground state as it exhibits strong coupling between lattice, spin and orbital degrees of freedom [1] . For this reason, Ca2RuO4 serves as an important "meeting-point" between conceptual developments [2] [3] of strongly correlated multi-band physics and advanced experimental spectroscopies. [4] [5] Its electronic structure and also orbital magnetism are therefore subjects of experimental and theoretical scrutiny. Ca₂RuO₄ belongs to the Ruddlesden–Popper family of layered perovskites (n = 1), consisting of RuO₆ octahedral sheets separated by rock-salt CaO layers [6] .

Contents

Electronic, Structural, and Magnetic Properties

Ca₂RuO₄ undergoes a first-order metal–insulator transition near 357 K that coincides with a structural change from a long-c (L-Pbca) to a short-c (S-Pbca) orthorhombic phase. The transition features an abrupt distortion of the RuO₆ octahedra, where the in-plane Ru–O bonds lengthen and the apical bond shortens, producing a flattened octahedron with an enhanced tilt [7] . 'Pbca' refers to an orthorhombic space group (No. 61) [8] . The transition displays a large hysteresis (~20 K) indicating that it is a first order phase transition. Negative thermal expansion has also been reported in conjunction with this c-axis compression. [9] The metal insulator transition is sensitive to electrical current. [10] [11]

Below 110-115 K, it develops a long-range anti-ferromagnetic ordering [12] . The magnetic structure has B-centered magnetic order similar to La₂NiO₄ .The easy axis for magnetization is parallel to the a or b axis in the Ru-O plane [13] . Spin direction aligns with the octahedral tilt axis, not with bond elongation, highlighting strong magneto-elastic and spin–orbit coupling [7] .

As Sr replaces Ca in Ca₂₋ₓSrₓRuO₄, the strong RuO₆ octahedral tilt and flattening are progressively reduced, which suppresses the Mott insulating S-Pbca phase and drives the system metallic. For x ≳ 0.15–0.2 the metal–insulator transition disappears, and long-range antiferromagnetism vanishes. At higher Sr content, only rotational distortions remain (I4₁/acd symmetry), producing a correlated metal [7] .Ca1.8Sr0.2RuO4 has been proposed as a candidate system for orbital selective Mott physics. [14] The bilayer compound Ca3Ru2O7 is metallic, but display a sequence of electronic transitions below 60 K. Finally, Sr2RuO4 hosts an unconventional superconducting state. [15]

References

  1. ↑ Cuono, Giuseppe; Forte, Filomena; Romano, Alfonso; Noce, Canio (2025-02-03). "Emerging new phases in correlated Mott insulator Ca 2 RuO 4". Journal of Physics: Condensed Matter. 37 (5): 053002. doi:10.1088/1361-648X/ad906d. ISSN   0953-8984.
  2. ↑ Gorelov, E.; Karolak, M.; Wehling, T. O.; Lechermann, F.; Lichtenstein, A. I.; Pavarini, E. (2010-06-01). "Nature of the Mott Transition in Ca2RuO4". Physical Review Letters. 104 (22) 226401. arXiv: 1001.4705 . doi: 10.1103/PhysRevLett.104.226401 . ISSN   0031-9007. PMID   20867184.
  3. ↑ Han, Qiang; Millis, Andrew (2018-08-08). "Lattice Energetics and Correlation-Driven Metal-Insulator Transitions: The Case of Ca2RuO4". Physical Review Letters. 121 (6) 067601. arXiv: 1801.06215 . doi: 10.1103/PhysRevLett.121.067601 . ISSN   0031-9007. PMID   30141680.
  4. ↑ Jain, A.; Krautloher, M.; Porras, J.; Ryu, G. H.; Chen, D. P.; et al. (2017-03-27). "Higgs mode and its decay in a two-dimensional antiferromagnet". Nature Physics. 13 (7). Springer Science and Business Media LLC: 633–637. arXiv: 1705.00222 . Bibcode:2017NatPh..13..633J. doi: 10.1038/nphys4077 . ISSN   1745-2473.
  5. ↑ Sutter, D.; Fatuzzo, C. G.; Moser, S.; Kim, M.; Fittipaldi, R.; et al. (2017-05-05). "Hallmarks of Hunds coupling in the Mott insulator Ca2RuO4" (PDF). Nature Communications. 8 (1) 15176. Springer Science and Business Media LLC. doi: 10.1038/ncomms15176 . ISSN   2041-1723. PMC   5424259 . PMID   28474681.
  6. ↑ González, J. W.; León, A. M.; González-Fuentes, C.; Gallardo, R. A. (2025-02-20). "Altermagnetism in two-dimensional Ca2RuO4 perovskite". Nanoscale. 17 (8): 4796–4807. doi:10.1039/D4NR04053H. ISSN   2040-3372.
  7. 1 2 3 Friedt, O.; Braden, M.; André, G.; Adelmann, P.; Nakatsuji, S.; Maeno, Y. (2001-04-12). "Structural and magnetic aspects of the metal-insulator transition in Ca 2 − x Sr x RuO 4". Physical Review B. 63 (17). doi:10.1103/PhysRevB.63.174432. ISSN   0163-1829.
  8. ↑ "Space Group 61: Pbca; P b c a". img.chem.ucl.ac.uk. Retrieved 2025-12-08.
  9. ↑ Takenaka, Koshi; Okamoto, Yoshihiko; Shinoda, Tsubasa; Katayama, Naoyuki; Sakai, Yuki (2017-01-10). "Colossal negative thermal expansion in reduced layered ruthenate" (PDF). Nature Communications. 8 (1) 14102. Bibcode:2017NatCo...814102T. doi: 10.1038/ncomms14102 . ISSN   2041-1723. PMC   5234094 . PMID   28071647.
  10. ↑ Curcio, Davide; Sanders, Charlotte E.; Chikina, Alla; Lund, Henriette E.; Bianchi, Marco; et al. (2023-10-16). "Current-driven insulator-to-metal transition without Mott breakdown in Ca 2 RuO 4". Physical Review B. 108 (16). arXiv: 2303.00662 . doi: 10.1103/PhysRevB.108.L161105 . ISSN   2469-9950.
  11. ↑ Suen, C. T.; Marković, I.; Zonno, M.; Heinsdorf, N.; Zhdanovich, S.; et al. (2024). "Electronic response of a Mott insulator at a current-induced insulator-to-metal transition". Nature Physics. 20 (11): 1757–1763. arXiv: 2308.05803 . Bibcode:2024NatPh..20.1757S. doi: 10.1038/s41567-024-02629-3 . ISSN   1745-2473.
  12. ↑ Braden, M.; André, G.; Nakatsuji, S.; Maeno, Y. (1998-07-01). "Crystal and magnetic structure of Ca 2 RuO 4 : Magnetoelastic coupling and the metal-insulator transition". Physical Review B. 58 (2): 847–861. doi:10.1103/PhysRevB.58.847. ISSN   0163-1829.
  13. ↑ Cao, G.; McCall, S.; Shepard, M.; Crow, J. E.; Guertin, R. P. (1997-08-01). "Magnetic and transport properties of single-crystal Ca 2 RuO 4 : Relationship to superconducting Sr 2 RuO 4". Physical Review B. 56 (6): R2916 –R2919. doi:10.1103/PhysRevB.56.R2916. ISSN   0163-1829.
  14. ↑ Koga, Akihisa; Kawakami, Norio; Rice, T. M.; Sigrist, Manfred (2004-05-28). "Orbital-Selective Mott Transitions in the Degenerate Hubbard Model". Physical Review Letters. 92 (21) 216402. arXiv: cond-mat/0401223 . Bibcode:2004PhRvL..92u6402K. doi: 10.1103/PhysRevLett.92.216402 . ISSN   0031-9007. PMID   15245300.
  15. ↑ Mackenzie, Andrew Peter; Maeno, Yoshiteru (2003-05-01). "The superconductivity of Sr 2 RuO 4 and the physics of spin-triplet pairing". Reviews of Modern Physics. 75 (2): 657–712. doi:10.1103/RevModPhys.75.657. ISSN   0034-6861.
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