Electronically driven spin-reorientation transition of the correlated polar metal Ca3Ru2O7

Igor Marković; Matthew D. Watson; Oliver J. Clark; Federico Mazzola; Edgar Abarca Morales; Chris A. Hooley; Helge Rosner; Craig M. Polley; Thiagarajan Balasubramanian; Saumya Mukherjee; Naoki Kikugawa; Dmitry A. Sokolov; Andrew P. Mackenzie; Phil D.C. King

doi:10.1073/pnas.2003671117

Electronically driven spin-reorientation transition of the correlated polar metal Ca₃Ru₂O₇

Igor Marković, Matthew D. Watson, Oliver J. Clark, Federico Mazzola, Edgar Abarca Morales, Chris A. Hooley, Helge Rosner, Craig M. Polley, Thiagarajan Balasubramanian, Saumya Mukherjee, Naoki Kikugawa, Dmitry A. Sokolov, Andrew P. Mackenzie, Phil D.C. King^*

^*Corresponding author for this work

Physics and Astronomy

Research output: Contribution to journal › Article › peer-review

17 Citations (Scopus)

Abstract

The interplay between spin-orbit coupling and structural inversion symmetry breaking in solids has generated much interest due to the nontrivial spin and magnetic textures which can result. Such studies are typically focused on systems where large atomic number elements lead to strong spin-orbit coupling, in turn rendering electronic correlations weak. In contrast, here we investigate the temperature-dependent electronic structure of Ca₃Ru₂O₇, a 4d oxide metal for which both correlations and spin-orbit coupling are pronounced and in which octahedral tilts and rotations combine to mediate both global and local inversion symmetry-breaking polar distortions. Our angle-resolved photoemission measurements reveal the destruction of a large hole-like Fermi surface upon cooling through a coupled structural and spinreorientation transition at 48 K, accompanied by a sudden onset of quasiparticle coherence. We demonstrate how these result from band hybridization mediated by a hidden Rashba-type spin- orbit coupling. This is enabled by the bulk structural distortions and unlocked when the spin reorients perpendicular to the local symmetry-breaking potential at the Ru sites. We argue that the electronic energy gain associated with the band hybridization is actually the key driver for the phase transition, reflecting a delicate interplay between spin-orbit coupling and strong electronic correlations and revealing a route to control magnetic ordering in solids.

Original language	English
Pages (from-to)	15524-15529
Number of pages	6
Journal	Proceedings of the National Academy of Sciences of the United States of America
Volume	117
Issue number	27
DOIs	https://doi.org/10.1073/pnas.2003671117
Publication status	Published - 7 Jul 2020

Bibliographical note

Funding Information:
7. D. Puggioni, J. M. Rondinelli, Designing a robustly metallic noncenstrosymmet-ric ruthenate oxide with large thermopower anisotropy. Nat. Commun. 5, 3432 (2014). Materials and Methods Single-Crystal Growth. Single crystals of Ca3Ru2O7 were grown using a floating-zone method in a mirror furnace (Canon Machinery; model SCI-MDH) (38). The crystal growth was performed in an atmosphere of a mixture of Ar and O2 (Ar : O2 = 85 : 15). In general, antiphase domains can be expected and are visible via contrast in polarized-light optical microscopy (SI Appendix, Fig. S4). We used this to select samples which are single domain over a scale of at least 500 × 500 µm2. The monodomain nature of our resulting samples is further evident in our measured Fermi surfaces, which show a clear twofold symmetry with no signatures of rotated features coming from different domains. Angle-Resolved Photoemission. ARPES measurements were performing using the Bloch beamline of the MAX IV synchrotron and the I05 beamline of Diamond Light Source. Measurements were performed using p-polarized 22-eV synchrotron light. Additional data measured using s-polarized light are shown in SI Appendix, Fig. S1. The samples were cleaved in situ and measured at temperatures between 6 and 70 K, as specified in Figs. 1 and 2. Temperature-dependent datasets were repeated on multiple samples and via both warming and recooling cycles, confirming that the changes shown in Fig. 2 are intrinsic and are not a result of sample aging upon temperature cycling. Density-Functional Theory. DFT calculations were performed using the local spin density approximation (LSDA) exchange-correlation functionals, as implemented in the full-potential local-orbital minimum-basis code (39–41). Additional calculations were performed with the Perdew–Burke–Ernzerhof (PBE) functional (42) and are shown and discussed in SI Appendix, Fig. S2. The experimental crystal structures were used in all cases (11), and spin–orbit coupling was included throughout. The Brillouin zone sampling employed a k mesh of at least 16 × 16 × 6 k points. Additional calculations were performed using WIEN2K (43) and gave consistent results. We employed ferromagnetic calculations, neglecting the antiferromagnetic coupling between neighboring bilayers. Given the ferromagnetic ordering within the bilayer and the weak coupling between bilayers, this does not affect any of the key conclusions drawn from our calculations, as confirmed by the broad agreement between our calculations and the experimentally measured electronic structure shown in Fig. 1E. Data Availability. The data that underpin the findings of this study are available from the University of St Andrews research portal: https://doi.org/ 10.17630/e8a98e0e-a6f3-4117-87c7-b1df1607dc81 (44). ACKNOWLEDGMENTS. We thank Erez Berg, Bernd Braunecker, Sean Hartnoll, Phil Lightfoot, Finlay Morrison, Roderich Moessner, Silvia Picozzi, Ulrich Rössler, Andreas Rost, and Veronika Sunko for useful discussions. We gratefully acknowledge support from the European Research Council (through the ERC-714193-QUESTDO project), the Royal Society, the UK Research and Innovation (via Grants EP/R031924/1 and EP/R025169/1), the Max-Planck Society, and the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) (JP17H06136 and JP18K04715) and the Japan Science and Technology Agency JST-Mirai Program (JPMJMI18A3). I.M. and E.A.M. acknowledge studentship support through the International Max-Planck Research School for the Chemistry and Physics of Quantum Materials. We thank Ulrike Nitzsche for technical support with the DFT calculations. We thank Diamond Light Source and MAX IV synchrotrons for access to beamlines I05 (Proposals SI21986 and SI25040) and Bloch (Proposal 20180399), respectively, that contributed to the results presented here. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. 8. N. A. Benedek, T. Birol, ‘Ferroelectric’ metals reexamined: Fundamental mecha-nisms and design considerations for new materials. J. Mater. Chem. C 4, 4000–4015 (2016). 9. T. H. Kim et al., Polar metals by geometric design. Nature 533, 68–72 (2016). 10. N. J. Laurita et al., Evidence for the weakly coupled electron mechanism in an Anderson-Blount polar metal. Nat. Commun. 10, 3217 (2019). 11. Y. Yoshida et al., Crystal and magnetic structure of Ca3Ru2O7. Phys. Rev. B 72, 054412 (2005). 12. S. Lei et al., Observation of quasi-two-dimensional polar domains and ferroelastic switching in a metal, Ca3Ru2O7. Nano Lett. 18, 3088–3095 (2018). 13. E. Bousquet et al., Improper ferroelectricity in perovskite oxide artificial superlattices. Nature 452, 732–736 (2008). 14. N. A. Benedek, C. J. Fennie, Hybrid improper ferroelectricity: A mechanism for controllable polarization-magnetization coupling. Phys. Rev. Lett. 106, 107204 (2011). 15. E. A. Nowadnick, C. J. Fennie, Domains and ferroelectric switching pathways in Ca3Ti2O7 from first principles. Phys. Rev. B 94, 104105 (2016). Downloaded at Elsevier Science London on July 8, 2020 16. Y. Yoshida et al., Quasi-two-dimensional metallic ground state of Ca3Ru2O7. Phys. Rev. B 69, 220411 (2004). 17. N. Kikugawa, A. W. Rost, C. W. Hicks, A. J. Schofield, A. P. Mackenzie, Ca3Ru2O7: Den-sity wave formation and quantum oscillations in the Hall resistivity. J. Phys. Soc. Jpn. 79, 024704 (2010). 18. B. Bohnenbuck et al., Magnetic structure and orbital state of Ca3Ru2O7 investigated by resonant x-ray diffraction. Phys. Rev. B 77, 224412 (2008). 19. W. Bao, Z. Q. Mao, Z. Qu, J. W. Lynn, Spin valve effect and magnetoresistivity in single crystalline Ca3Ru2O7. Phys. Rev. Lett. 100, 247203 (2008). 20. D. A. Sokolov et al., Metamagnetic texture in a polar antiferromagnet. Nat. Phys. 15, 671–677 (2019). 21. S. Nakatsuji, S.-I. Ikeda, Y. Maeno, Ca2RuO4: New Mott insulators of layered ruthenate. J. Phys. Soc. Jpn. 66, 1868–1871 (1997). 22. F. Baumberger et al., Nested Fermi surface and electronic instability in Ca3Ru2O7. Phys. Rev. Lett. 96, 107601 (2006). 23. M. Horio et al., Electron-driven C2-symmetric Dirac semimetal uncovered in Ca3Ru2O7. arXiv:1911.12163 (27 November 2019). 24. A. Tamai et al., High-resolution photoemission on Sr2RuO4 reveals correlation-enhanced effective spin-orbit coupling and dominantly local self-energies. Phys. Rev. X 9, 021048 (2019). 25. S. Acharya et al., Evening out the spin and charge parity to increase Tc in unconventional superconductor Sr2RuO4. Commun. Phys. 2, 163 (2019). 26. G. Cao et al., Observation of a metallic antiferromagnetic phase and metal to nonmetal transition in Ca3Ru2O7. Phys. Rev. Lett. 78, 1751 (1997). 27. E. Ohmichi et al., Colossal magnetoresistance accompanying a structural transition in a highly two-dimensional metallic state of Ca3Ru2O7. Phys. Rev. B 70, 104414 (2004). 28. Y. Yoshida, S.-I. Ikeda, N. Shirakawa, Hall effect in Ca3Ru2O7. J. Phys. Soc. Jpn. 76, 085002 (2007). 29. H. Xing et al., Existence of electron and hole pockets and partial gap opening in the correlated semimetal Ca3Ru2O7. Phys. Rev. B 97, 041113 (2018). 30. C. H. Mousatov, E. Berg, S. A. Hartnoll, Theory of the strange metal Sr3Ru2O7. Proc. Natl. Acad. Sci. U.S.A. 117, 2852–2857 (2020). 31. Y. A. Bychkov, E. I. Rashba, Properties of a 2d electron gas with lifted spectral degeneracy. JETP Lett. 39, 78–81 (1984). 32. X. Zhang, Q. Liu, J.-W. Luo, A. J. Freeman, A. Zunger, Hidden spin polarization in inversion-symmetric bulk crystals. Nat. Phys. 10, 387–393 (2014). 33. J. M. Riley et al., Direct observation of spin-polarized bulk bands in an inversion-symmetric semiconductor. Nat. Phys. 10, 835–839 (2014). 34. J. S. Lee et al., Pseudogap dependence of the optical conductivity spectra of Ca3Ru2O7: A possible contribution of the orbital flip excitation. Phys. Rev. Lett. 98, 097403 (2007). 35. M. P. Warusawithana, E. V. Colla, J. N. Eckstein, M. B. Weissman, Artificial dielec-tric superlattices with broken inversion symmetry. Phys. Rev. Lett. 90, 036802 (2003). 36. V. Sunko et al., Maximal Rashba-like spin splitting via kinetic-energy-coupled inversion-symmetry breaking. Nature 549, 492–496 (2017). 37. A. D. Caviglia et al., Tunable Rashba spin-orbit interaction at oxide interfaces. Phys. Rev. Lett. 104, 126803 (2010). 38. R. Perry, Y. Maeno, Systematic approach to the growth of high-quality single crystals of Sr3Ru2O7. J. Cryst. Growth 271, 134–141 (2004). 39. K. Koepernik, H. Eschrig, Full-potential nonorthogonal local-orbital minimum-basis band-structure scheme. Phys. Rev. B 59, 1743–1757 (1999). 40. I. Opahle, K. Koepernik, H. Eschrig, Full-potential band-structure calculation of iron pyrite. Phys. Rev. B 60, 14035–14041 (1999). 41. Institute for Theoretical Solid State Physics Dresden, FPLO package, Version 18.00-52. http://www.fplo.de. Accessed 10 June 2020. 42. J. P. Perdew, K. Burke, M. Ernzerhof, Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996). 43. P. Blaha, WIEN2k package, Version 10.1 (2010). http://www.wien2k.at. Accessed 10 June 2020. 44. I. Marković et al., Electronically driven spin-reorientation transition of the correlated polar metal Ca3Ru2O7 (dataset). University of St Andrews Research Portal. https:// doi.org/10.17630/e8a98e0e-a6f3-4117-87c7-b1df1607dc81. Deposited 1 June 2020. PHYSICS

Funding Information:
We thank Erez Berg, Bernd Braunecker, Sean Hartnoll, Phil Lightfoot, Finlay Morrison, Roderich Moessner, Silvia Picozzi, Ulrich R?ssler, Andreas Rost, and Veronika Sunko for useful discussions. We gratefully acknowledge support from the European Research Council (through the ERC-714193-QUESTDO project), the Royal Society, the UK Research and Innovation (via Grants EP/R031924/1 and EP/R025169/1), the Max-Planck Society, and the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) (JP17H06136 and JP18K04715) and the Japan Science and Technology Agency JST-Mirai Program (JPMJMI18A3). I.M. and E.A.M. acknowledge studentship support through the International Max-Planck Research School for the Chemistry and Physics of Quantum Materials. We thank Ulrike Nitzsche for technical support with the DFT calculations. We thank Diamond Light Source and MAX IV synchrotrons for access to beamlines I05 (Proposals SI21986 and SI25040) and Bloch (Proposal 20180399), respectively, that contributed to the results presented here. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020.

Funding Information:
ACKNOWLEDGMENTS. We thank Erez Berg, Bernd Braunecker, Sean Hartnoll, Phil Lightfoot, Finlay Morrison, Roderich Moessner, Silvia Picozzi, Ulrich Rössler, Andreas Rost, and Veronika Sunko for useful discussions. We gratefully acknowledge support from the European Research Council (through the ERC-714193-QUESTDO project), the Royal Society, the UK Research and Innovation (via Grants EP/R031924/1 and EP/R025169/1), the Max-Planck Society, and the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) (JP17H06136 and JP18K04715) and the Japan Science and Technology Agency JST-Mirai Program (JPMJMI18A3). I.M. and E.A.M. acknowledge studentship support through the International Max-Planck Research School for the Chemistry and Physics of Quantum Materials. We thank Ulrike Nitzsche for technical support with the DFT calculations. We thank Diamond Light Source and MAX IV synchrotrons for access to beamlines I05 (Proposals SI21986 and SI25040) and Bloch (Proposal 20180399), respectively, that contributed to the results presented here. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020.

Publisher Copyright:
© 2020 National Academy of Sciences. All rights reserved.

Keywords

Angle-resolved photoemission
Correlated oxide
Magnetism
Rashba spin-orbit
Ruthenate

ASJC Scopus subject areas

General

Access to Document

10.1073/pnas.2003671117

Cite this

Marković, I., Watson, M. D., Clark, O. J., Mazzola, F., Morales, E. A., Hooley, C. A., Rosner, H., Polley, C. M., Balasubramanian, T., Mukherjee, S., Kikugawa, N., Sokolov, D. A., Mackenzie, A. P., & King, P. D. C. (2020). Electronically driven spin-reorientation transition of the correlated polar metal Ca₃Ru₂O₇. Proceedings of the National Academy of Sciences of the United States of America, 117(27), 15524-15529. https://doi.org/10.1073/pnas.2003671117

@article{9318327a68b6405bb30ba1fac1e61ae9,

title = "Electronically driven spin-reorientation transition of the correlated polar metal Ca3Ru2O7",

abstract = "The interplay between spin-orbit coupling and structural inversion symmetry breaking in solids has generated much interest due to the nontrivial spin and magnetic textures which can result. Such studies are typically focused on systems where large atomic number elements lead to strong spin-orbit coupling, in turn rendering electronic correlations weak. In contrast, here we investigate the temperature-dependent electronic structure of Ca3Ru2O7, a 4d oxide metal for which both correlations and spin-orbit coupling are pronounced and in which octahedral tilts and rotations combine to mediate both global and local inversion symmetry-breaking polar distortions. Our angle-resolved photoemission measurements reveal the destruction of a large hole-like Fermi surface upon cooling through a coupled structural and spinreorientation transition at 48 K, accompanied by a sudden onset of quasiparticle coherence. We demonstrate how these result from band hybridization mediated by a hidden Rashba-type spin- orbit coupling. This is enabled by the bulk structural distortions and unlocked when the spin reorients perpendicular to the local symmetry-breaking potential at the Ru sites. We argue that the electronic energy gain associated with the band hybridization is actually the key driver for the phase transition, reflecting a delicate interplay between spin-orbit coupling and strong electronic correlations and revealing a route to control magnetic ordering in solids.",

keywords = "Angle-resolved photoemission, Correlated oxide, Magnetism, Rashba spin-orbit, Ruthenate",

author = "Igor Markovi{\'c} and Watson, {Matthew D.} and Clark, {Oliver J.} and Federico Mazzola and Morales, {Edgar Abarca} and Hooley, {Chris A.} and Helge Rosner and Polley, {Craig M.} and Thiagarajan Balasubramanian and Saumya Mukherjee and Naoki Kikugawa and Sokolov, {Dmitry A.} and Mackenzie, {Andrew P.} and King, {Phil D.C.}",

note = "Funding Information: 7. D. Puggioni, J. M. Rondinelli, Designing a robustly metallic noncenstrosymmet-ric ruthenate oxide with large thermopower anisotropy. Nat. Commun. 5, 3432 (2014). Materials and Methods Single-Crystal Growth. Single crystals of Ca3Ru2O7 were grown using a floating-zone method in a mirror furnace (Canon Machinery; model SCI-MDH) (38). The crystal growth was performed in an atmosphere of a mixture of Ar and O2 (Ar : O2 = 85 : 15). In general, antiphase domains can be expected and are visible via contrast in polarized-light optical microscopy (SI Appendix, Fig. S4). We used this to select samples which are single domain over a scale of at least 500 × 500 µm2. The monodomain nature of our resulting samples is further evident in our measured Fermi surfaces, which show a clear twofold symmetry with no signatures of rotated features coming from different domains. Angle-Resolved Photoemission. ARPES measurements were performing using the Bloch beamline of the MAX IV synchrotron and the I05 beamline of Diamond Light Source. Measurements were performed using p-polarized 22-eV synchrotron light. Additional data measured using s-polarized light are shown in SI Appendix, Fig. S1. The samples were cleaved in situ and measured at temperatures between 6 and 70 K, as specified in Figs. 1 and 2. Temperature-dependent datasets were repeated on multiple samples and via both warming and recooling cycles, confirming that the changes shown in Fig. 2 are intrinsic and are not a result of sample aging upon temperature cycling. Density-Functional Theory. DFT calculations were performed using the local spin density approximation (LSDA) exchange-correlation functionals, as implemented in the full-potential local-orbital minimum-basis code (39–41). Additional calculations were performed with the Perdew–Burke–Ernzerhof (PBE) functional (42) and are shown and discussed in SI Appendix, Fig. S2. The experimental crystal structures were used in all cases (11), and spin–orbit coupling was included throughout. The Brillouin zone sampling employed a k mesh of at least 16 × 16 × 6 k points. Additional calculations were performed using WIEN2K (43) and gave consistent results. We employed ferromagnetic calculations, neglecting the antiferromagnetic coupling between neighboring bilayers. Given the ferromagnetic ordering within the bilayer and the weak coupling between bilayers, this does not affect any of the key conclusions drawn from our calculations, as confirmed by the broad agreement between our calculations and the experimentally measured electronic structure shown in Fig. 1E. Data Availability. The data that underpin the findings of this study are available from the University of St Andrews research portal: https://doi.org/ 10.17630/e8a98e0e-a6f3-4117-87c7-b1df1607dc81 (44). ACKNOWLEDGMENTS. We thank Erez Berg, Bernd Braunecker, Sean Hartnoll, Phil Lightfoot, Finlay Morrison, Roderich Moessner, Silvia Picozzi, Ulrich R{\"o}ssler, Andreas Rost, and Veronika Sunko for useful discussions. We gratefully acknowledge support from the European Research Council (through the ERC-714193-QUESTDO project), the Royal Society, the UK Research and Innovation (via Grants EP/R031924/1 and EP/R025169/1), the Max-Planck Society, and the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) (JP17H06136 and JP18K04715) and the Japan Science and Technology Agency JST-Mirai Program (JPMJMI18A3). I.M. and E.A.M. acknowledge studentship support through the International Max-Planck Research School for the Chemistry and Physics of Quantum Materials. We thank Ulrike Nitzsche for technical support with the DFT calculations. We thank Diamond Light Source and MAX IV synchrotrons for access to beamlines I05 (Proposals SI21986 and SI25040) and Bloch (Proposal 20180399), respectively, that contributed to the results presented here. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. 8. N. A. Benedek, T. Birol, {\textquoteleft}Ferroelectric{\textquoteright} metals reexamined: Fundamental mecha-nisms and design considerations for new materials. J. Mater. Chem. C 4, 4000–4015 (2016). 9. T. H. Kim et al., Polar metals by geometric design. Nature 533, 68–72 (2016). 10. N. J. Laurita et al., Evidence for the weakly coupled electron mechanism in an Anderson-Blount polar metal. Nat. Commun. 10, 3217 (2019). 11. Y. Yoshida et al., Crystal and magnetic structure of Ca3Ru2O7. Phys. Rev. B 72, 054412 (2005). 12. S. Lei et al., Observation of quasi-two-dimensional polar domains and ferroelastic switching in a metal, Ca3Ru2O7. Nano Lett. 18, 3088–3095 (2018). 13. E. Bousquet et al., Improper ferroelectricity in perovskite oxide artificial superlattices. Nature 452, 732–736 (2008). 14. N. A. Benedek, C. J. Fennie, Hybrid improper ferroelectricity: A mechanism for controllable polarization-magnetization coupling. Phys. Rev. Lett. 106, 107204 (2011). 15. E. A. Nowadnick, C. J. Fennie, Domains and ferroelectric switching pathways in Ca3Ti2O7 from first principles. Phys. Rev. B 94, 104105 (2016). Downloaded at Elsevier Science London on July 8, 2020 16. Y. Yoshida et al., Quasi-two-dimensional metallic ground state of Ca3Ru2O7. Phys. Rev. B 69, 220411 (2004). 17. N. Kikugawa, A. W. Rost, C. W. Hicks, A. J. Schofield, A. P. Mackenzie, Ca3Ru2O7: Den-sity wave formation and quantum oscillations in the Hall resistivity. J. Phys. Soc. Jpn. 79, 024704 (2010). 18. B. Bohnenbuck et al., Magnetic structure and orbital state of Ca3Ru2O7 investigated by resonant x-ray diffraction. Phys. Rev. B 77, 224412 (2008). 19. W. Bao, Z. Q. Mao, Z. Qu, J. W. Lynn, Spin valve effect and magnetoresistivity in single crystalline Ca3Ru2O7. Phys. Rev. Lett. 100, 247203 (2008). 20. D. A. Sokolov et al., Metamagnetic texture in a polar antiferromagnet. Nat. Phys. 15, 671–677 (2019). 21. S. Nakatsuji, S.-I. Ikeda, Y. Maeno, Ca2RuO4: New Mott insulators of layered ruthenate. J. Phys. Soc. Jpn. 66, 1868–1871 (1997). 22. F. Baumberger et al., Nested Fermi surface and electronic instability in Ca3Ru2O7. Phys. Rev. Lett. 96, 107601 (2006). 23. M. Horio et al., Electron-driven C2-symmetric Dirac semimetal uncovered in Ca3Ru2O7. arXiv:1911.12163 (27 November 2019). 24. A. Tamai et al., High-resolution photoemission on Sr2RuO4 reveals correlation-enhanced effective spin-orbit coupling and dominantly local self-energies. Phys. Rev. X 9, 021048 (2019). 25. S. Acharya et al., Evening out the spin and charge parity to increase Tc in unconventional superconductor Sr2RuO4. Commun. Phys. 2, 163 (2019). 26. G. Cao et al., Observation of a metallic antiferromagnetic phase and metal to nonmetal transition in Ca3Ru2O7. Phys. Rev. Lett. 78, 1751 (1997). 27. E. Ohmichi et al., Colossal magnetoresistance accompanying a structural transition in a highly two-dimensional metallic state of Ca3Ru2O7. Phys. Rev. B 70, 104414 (2004). 28. Y. Yoshida, S.-I. Ikeda, N. Shirakawa, Hall effect in Ca3Ru2O7. J. Phys. Soc. Jpn. 76, 085002 (2007). 29. H. Xing et al., Existence of electron and hole pockets and partial gap opening in the correlated semimetal Ca3Ru2O7. Phys. Rev. B 97, 041113 (2018). 30. C. H. Mousatov, E. Berg, S. A. Hartnoll, Theory of the strange metal Sr3Ru2O7. Proc. Natl. Acad. Sci. U.S.A. 117, 2852–2857 (2020). 31. Y. A. Bychkov, E. I. Rashba, Properties of a 2d electron gas with lifted spectral degeneracy. JETP Lett. 39, 78–81 (1984). 32. X. Zhang, Q. Liu, J.-W. Luo, A. J. Freeman, A. Zunger, Hidden spin polarization in inversion-symmetric bulk crystals. Nat. Phys. 10, 387–393 (2014). 33. J. M. Riley et al., Direct observation of spin-polarized bulk bands in an inversion-symmetric semiconductor. Nat. Phys. 10, 835–839 (2014). 34. J. S. Lee et al., Pseudogap dependence of the optical conductivity spectra of Ca3Ru2O7: A possible contribution of the orbital flip excitation. Phys. Rev. Lett. 98, 097403 (2007). 35. M. P. Warusawithana, E. V. Colla, J. N. Eckstein, M. B. Weissman, Artificial dielec-tric superlattices with broken inversion symmetry. Phys. Rev. Lett. 90, 036802 (2003). 36. V. Sunko et al., Maximal Rashba-like spin splitting via kinetic-energy-coupled inversion-symmetry breaking. Nature 549, 492–496 (2017). 37. A. D. Caviglia et al., Tunable Rashba spin-orbit interaction at oxide interfaces. Phys. Rev. Lett. 104, 126803 (2010). 38. R. Perry, Y. Maeno, Systematic approach to the growth of high-quality single crystals of Sr3Ru2O7. J. Cryst. Growth 271, 134–141 (2004). 39. K. Koepernik, H. Eschrig, Full-potential nonorthogonal local-orbital minimum-basis band-structure scheme. Phys. Rev. B 59, 1743–1757 (1999). 40. I. Opahle, K. Koepernik, H. Eschrig, Full-potential band-structure calculation of iron pyrite. Phys. Rev. B 60, 14035–14041 (1999). 41. Institute for Theoretical Solid State Physics Dresden, FPLO package, Version 18.00-52. http://www.fplo.de. Accessed 10 June 2020. 42. J. P. Perdew, K. Burke, M. Ernzerhof, Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996). 43. P. Blaha, WIEN2k package, Version 10.1 (2010). http://www.wien2k.at. Accessed 10 June 2020. 44. I. Markovi{\'c} et al., Electronically driven spin-reorientation transition of the correlated polar metal Ca3Ru2O7 (dataset). University of St Andrews Research Portal. https:// doi.org/10.17630/e8a98e0e-a6f3-4117-87c7-b1df1607dc81. Deposited 1 June 2020. PHYSICS Funding Information: We thank Erez Berg, Bernd Braunecker, Sean Hartnoll, Phil Lightfoot, Finlay Morrison, Roderich Moessner, Silvia Picozzi, Ulrich R?ssler, Andreas Rost, and Veronika Sunko for useful discussions. We gratefully acknowledge support from the European Research Council (through the ERC-714193-QUESTDO project), the Royal Society, the UK Research and Innovation (via Grants EP/R031924/1 and EP/R025169/1), the Max-Planck Society, and the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) (JP17H06136 and JP18K04715) and the Japan Science and Technology Agency JST-Mirai Program (JPMJMI18A3). I.M. and E.A.M. acknowledge studentship support through the International Max-Planck Research School for the Chemistry and Physics of Quantum Materials. We thank Ulrike Nitzsche for technical support with the DFT calculations. We thank Diamond Light Source and MAX IV synchrotrons for access to beamlines I05 (Proposals SI21986 and SI25040) and Bloch (Proposal 20180399), respectively, that contributed to the results presented here. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. Funding Information: ACKNOWLEDGMENTS. We thank Erez Berg, Bernd Braunecker, Sean Hartnoll, Phil Lightfoot, Finlay Morrison, Roderich Moessner, Silvia Picozzi, Ulrich R{\"o}ssler, Andreas Rost, and Veronika Sunko for useful discussions. We gratefully acknowledge support from the European Research Council (through the ERC-714193-QUESTDO project), the Royal Society, the UK Research and Innovation (via Grants EP/R031924/1 and EP/R025169/1), the Max-Planck Society, and the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) (JP17H06136 and JP18K04715) and the Japan Science and Technology Agency JST-Mirai Program (JPMJMI18A3). I.M. and E.A.M. acknowledge studentship support through the International Max-Planck Research School for the Chemistry and Physics of Quantum Materials. We thank Ulrike Nitzsche for technical support with the DFT calculations. We thank Diamond Light Source and MAX IV synchrotrons for access to beamlines I05 (Proposals SI21986 and SI25040) and Bloch (Proposal 20180399), respectively, that contributed to the results presented here. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. Publisher Copyright: {\textcopyright} 2020 National Academy of Sciences. All rights reserved.",

year = "2020",

month = jul,

day = "7",

doi = "10.1073/pnas.2003671117",

language = "English",

volume = "117",

pages = "15524--15529",

journal = "Proceedings of the National Academy of Sciences of the United States of America",

issn = "0027-8424",

publisher = "National Academy of Sciences",

number = "27",

}

Marković, I, Watson, MD, Clark, OJ, Mazzola, F, Morales, EA, Hooley, CA, Rosner, H, Polley, CM, Balasubramanian, T, Mukherjee, S, Kikugawa, N, Sokolov, DA, Mackenzie, AP & King, PDC 2020, 'Electronically driven spin-reorientation transition of the correlated polar metal Ca₃Ru₂O₇', Proceedings of the National Academy of Sciences of the United States of America, vol. 117, no. 27, pp. 15524-15529. https://doi.org/10.1073/pnas.2003671117

TY - JOUR

T1 - Electronically driven spin-reorientation transition of the correlated polar metal Ca3Ru2O7

AU - Marković, Igor

AU - Watson, Matthew D.

AU - Clark, Oliver J.

AU - Mazzola, Federico

AU - Morales, Edgar Abarca

AU - Hooley, Chris A.

AU - Rosner, Helge

AU - Polley, Craig M.

AU - Balasubramanian, Thiagarajan

AU - Mukherjee, Saumya

AU - Kikugawa, Naoki

AU - Sokolov, Dmitry A.

AU - Mackenzie, Andrew P.

AU - King, Phil D.C.

N1 - Funding Information: 7. D. Puggioni, J. M. Rondinelli, Designing a robustly metallic noncenstrosymmet-ric ruthenate oxide with large thermopower anisotropy. Nat. Commun. 5, 3432 (2014). Materials and Methods Single-Crystal Growth. Single crystals of Ca3Ru2O7 were grown using a floating-zone method in a mirror furnace (Canon Machinery; model SCI-MDH) (38). The crystal growth was performed in an atmosphere of a mixture of Ar and O2 (Ar : O2 = 85 : 15). In general, antiphase domains can be expected and are visible via contrast in polarized-light optical microscopy (SI Appendix, Fig. S4). We used this to select samples which are single domain over a scale of at least 500 × 500 µm2. The monodomain nature of our resulting samples is further evident in our measured Fermi surfaces, which show a clear twofold symmetry with no signatures of rotated features coming from different domains. Angle-Resolved Photoemission. ARPES measurements were performing using the Bloch beamline of the MAX IV synchrotron and the I05 beamline of Diamond Light Source. Measurements were performed using p-polarized 22-eV synchrotron light. Additional data measured using s-polarized light are shown in SI Appendix, Fig. S1. The samples were cleaved in situ and measured at temperatures between 6 and 70 K, as specified in Figs. 1 and 2. Temperature-dependent datasets were repeated on multiple samples and via both warming and recooling cycles, confirming that the changes shown in Fig. 2 are intrinsic and are not a result of sample aging upon temperature cycling. Density-Functional Theory. DFT calculations were performed using the local spin density approximation (LSDA) exchange-correlation functionals, as implemented in the full-potential local-orbital minimum-basis code (39–41). Additional calculations were performed with the Perdew–Burke–Ernzerhof (PBE) functional (42) and are shown and discussed in SI Appendix, Fig. S2. The experimental crystal structures were used in all cases (11), and spin–orbit coupling was included throughout. The Brillouin zone sampling employed a k mesh of at least 16 × 16 × 6 k points. Additional calculations were performed using WIEN2K (43) and gave consistent results. We employed ferromagnetic calculations, neglecting the antiferromagnetic coupling between neighboring bilayers. Given the ferromagnetic ordering within the bilayer and the weak coupling between bilayers, this does not affect any of the key conclusions drawn from our calculations, as confirmed by the broad agreement between our calculations and the experimentally measured electronic structure shown in Fig. 1E. Data Availability. The data that underpin the findings of this study are available from the University of St Andrews research portal: https://doi.org/ 10.17630/e8a98e0e-a6f3-4117-87c7-b1df1607dc81 (44). ACKNOWLEDGMENTS. We thank Erez Berg, Bernd Braunecker, Sean Hartnoll, Phil Lightfoot, Finlay Morrison, Roderich Moessner, Silvia Picozzi, Ulrich Rössler, Andreas Rost, and Veronika Sunko for useful discussions. We gratefully acknowledge support from the European Research Council (through the ERC-714193-QUESTDO project), the Royal Society, the UK Research and Innovation (via Grants EP/R031924/1 and EP/R025169/1), the Max-Planck Society, and the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) (JP17H06136 and JP18K04715) and the Japan Science and Technology Agency JST-Mirai Program (JPMJMI18A3). I.M. and E.A.M. acknowledge studentship support through the International Max-Planck Research School for the Chemistry and Physics of Quantum Materials. We thank Ulrike Nitzsche for technical support with the DFT calculations. We thank Diamond Light Source and MAX IV synchrotrons for access to beamlines I05 (Proposals SI21986 and SI25040) and Bloch (Proposal 20180399), respectively, that contributed to the results presented here. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. 8. N. A. Benedek, T. Birol, ‘Ferroelectric’ metals reexamined: Fundamental mecha-nisms and design considerations for new materials. J. Mater. Chem. C 4, 4000–4015 (2016). 9. T. H. Kim et al., Polar metals by geometric design. Nature 533, 68–72 (2016). 10. N. J. Laurita et al., Evidence for the weakly coupled electron mechanism in an Anderson-Blount polar metal. Nat. Commun. 10, 3217 (2019). 11. Y. Yoshida et al., Crystal and magnetic structure of Ca3Ru2O7. Phys. Rev. B 72, 054412 (2005). 12. S. Lei et al., Observation of quasi-two-dimensional polar domains and ferroelastic switching in a metal, Ca3Ru2O7. Nano Lett. 18, 3088–3095 (2018). 13. E. Bousquet et al., Improper ferroelectricity in perovskite oxide artificial superlattices. Nature 452, 732–736 (2008). 14. N. A. Benedek, C. J. Fennie, Hybrid improper ferroelectricity: A mechanism for controllable polarization-magnetization coupling. Phys. Rev. Lett. 106, 107204 (2011). 15. E. A. Nowadnick, C. J. Fennie, Domains and ferroelectric switching pathways in Ca3Ti2O7 from first principles. Phys. Rev. B 94, 104105 (2016). Downloaded at Elsevier Science London on July 8, 2020 16. Y. Yoshida et al., Quasi-two-dimensional metallic ground state of Ca3Ru2O7. Phys. Rev. B 69, 220411 (2004). 17. N. Kikugawa, A. W. Rost, C. W. Hicks, A. J. Schofield, A. P. Mackenzie, Ca3Ru2O7: Den-sity wave formation and quantum oscillations in the Hall resistivity. J. Phys. Soc. Jpn. 79, 024704 (2010). 18. B. Bohnenbuck et al., Magnetic structure and orbital state of Ca3Ru2O7 investigated by resonant x-ray diffraction. Phys. Rev. B 77, 224412 (2008). 19. W. Bao, Z. Q. Mao, Z. Qu, J. W. Lynn, Spin valve effect and magnetoresistivity in single crystalline Ca3Ru2O7. Phys. Rev. Lett. 100, 247203 (2008). 20. D. A. Sokolov et al., Metamagnetic texture in a polar antiferromagnet. Nat. Phys. 15, 671–677 (2019). 21. S. Nakatsuji, S.-I. Ikeda, Y. Maeno, Ca2RuO4: New Mott insulators of layered ruthenate. J. Phys. Soc. Jpn. 66, 1868–1871 (1997). 22. F. Baumberger et al., Nested Fermi surface and electronic instability in Ca3Ru2O7. Phys. Rev. Lett. 96, 107601 (2006). 23. M. Horio et al., Electron-driven C2-symmetric Dirac semimetal uncovered in Ca3Ru2O7. arXiv:1911.12163 (27 November 2019). 24. A. Tamai et al., High-resolution photoemission on Sr2RuO4 reveals correlation-enhanced effective spin-orbit coupling and dominantly local self-energies. Phys. Rev. X 9, 021048 (2019). 25. S. Acharya et al., Evening out the spin and charge parity to increase Tc in unconventional superconductor Sr2RuO4. Commun. Phys. 2, 163 (2019). 26. G. Cao et al., Observation of a metallic antiferromagnetic phase and metal to nonmetal transition in Ca3Ru2O7. Phys. Rev. Lett. 78, 1751 (1997). 27. E. Ohmichi et al., Colossal magnetoresistance accompanying a structural transition in a highly two-dimensional metallic state of Ca3Ru2O7. Phys. Rev. B 70, 104414 (2004). 28. Y. Yoshida, S.-I. Ikeda, N. Shirakawa, Hall effect in Ca3Ru2O7. J. Phys. Soc. Jpn. 76, 085002 (2007). 29. H. Xing et al., Existence of electron and hole pockets and partial gap opening in the correlated semimetal Ca3Ru2O7. Phys. Rev. B 97, 041113 (2018). 30. C. H. Mousatov, E. Berg, S. A. Hartnoll, Theory of the strange metal Sr3Ru2O7. Proc. Natl. Acad. Sci. U.S.A. 117, 2852–2857 (2020). 31. Y. A. Bychkov, E. I. Rashba, Properties of a 2d electron gas with lifted spectral degeneracy. JETP Lett. 39, 78–81 (1984). 32. X. Zhang, Q. Liu, J.-W. Luo, A. J. Freeman, A. Zunger, Hidden spin polarization in inversion-symmetric bulk crystals. Nat. Phys. 10, 387–393 (2014). 33. J. M. Riley et al., Direct observation of spin-polarized bulk bands in an inversion-symmetric semiconductor. Nat. Phys. 10, 835–839 (2014). 34. J. S. Lee et al., Pseudogap dependence of the optical conductivity spectra of Ca3Ru2O7: A possible contribution of the orbital flip excitation. Phys. Rev. Lett. 98, 097403 (2007). 35. M. P. Warusawithana, E. V. Colla, J. N. Eckstein, M. B. Weissman, Artificial dielec-tric superlattices with broken inversion symmetry. Phys. Rev. Lett. 90, 036802 (2003). 36. V. Sunko et al., Maximal Rashba-like spin splitting via kinetic-energy-coupled inversion-symmetry breaking. Nature 549, 492–496 (2017). 37. A. D. Caviglia et al., Tunable Rashba spin-orbit interaction at oxide interfaces. Phys. Rev. Lett. 104, 126803 (2010). 38. R. Perry, Y. Maeno, Systematic approach to the growth of high-quality single crystals of Sr3Ru2O7. J. Cryst. Growth 271, 134–141 (2004). 39. K. Koepernik, H. Eschrig, Full-potential nonorthogonal local-orbital minimum-basis band-structure scheme. Phys. Rev. B 59, 1743–1757 (1999). 40. I. Opahle, K. Koepernik, H. Eschrig, Full-potential band-structure calculation of iron pyrite. Phys. Rev. B 60, 14035–14041 (1999). 41. Institute for Theoretical Solid State Physics Dresden, FPLO package, Version 18.00-52. http://www.fplo.de. Accessed 10 June 2020. 42. J. P. Perdew, K. Burke, M. Ernzerhof, Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996). 43. P. Blaha, WIEN2k package, Version 10.1 (2010). http://www.wien2k.at. Accessed 10 June 2020. 44. I. Marković et al., Electronically driven spin-reorientation transition of the correlated polar metal Ca3Ru2O7 (dataset). University of St Andrews Research Portal. https:// doi.org/10.17630/e8a98e0e-a6f3-4117-87c7-b1df1607dc81. Deposited 1 June 2020. PHYSICS Funding Information: We thank Erez Berg, Bernd Braunecker, Sean Hartnoll, Phil Lightfoot, Finlay Morrison, Roderich Moessner, Silvia Picozzi, Ulrich R?ssler, Andreas Rost, and Veronika Sunko for useful discussions. We gratefully acknowledge support from the European Research Council (through the ERC-714193-QUESTDO project), the Royal Society, the UK Research and Innovation (via Grants EP/R031924/1 and EP/R025169/1), the Max-Planck Society, and the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) (JP17H06136 and JP18K04715) and the Japan Science and Technology Agency JST-Mirai Program (JPMJMI18A3). I.M. and E.A.M. acknowledge studentship support through the International Max-Planck Research School for the Chemistry and Physics of Quantum Materials. We thank Ulrike Nitzsche for technical support with the DFT calculations. We thank Diamond Light Source and MAX IV synchrotrons for access to beamlines I05 (Proposals SI21986 and SI25040) and Bloch (Proposal 20180399), respectively, that contributed to the results presented here. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. Funding Information: ACKNOWLEDGMENTS. We thank Erez Berg, Bernd Braunecker, Sean Hartnoll, Phil Lightfoot, Finlay Morrison, Roderich Moessner, Silvia Picozzi, Ulrich Rössler, Andreas Rost, and Veronika Sunko for useful discussions. We gratefully acknowledge support from the European Research Council (through the ERC-714193-QUESTDO project), the Royal Society, the UK Research and Innovation (via Grants EP/R031924/1 and EP/R025169/1), the Max-Planck Society, and the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) (JP17H06136 and JP18K04715) and the Japan Science and Technology Agency JST-Mirai Program (JPMJMI18A3). I.M. and E.A.M. acknowledge studentship support through the International Max-Planck Research School for the Chemistry and Physics of Quantum Materials. We thank Ulrike Nitzsche for technical support with the DFT calculations. We thank Diamond Light Source and MAX IV synchrotrons for access to beamlines I05 (Proposals SI21986 and SI25040) and Bloch (Proposal 20180399), respectively, that contributed to the results presented here. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. Publisher Copyright: © 2020 National Academy of Sciences. All rights reserved.

PY - 2020/7/7

Y1 - 2020/7/7

N2 - The interplay between spin-orbit coupling and structural inversion symmetry breaking in solids has generated much interest due to the nontrivial spin and magnetic textures which can result. Such studies are typically focused on systems where large atomic number elements lead to strong spin-orbit coupling, in turn rendering electronic correlations weak. In contrast, here we investigate the temperature-dependent electronic structure of Ca3Ru2O7, a 4d oxide metal for which both correlations and spin-orbit coupling are pronounced and in which octahedral tilts and rotations combine to mediate both global and local inversion symmetry-breaking polar distortions. Our angle-resolved photoemission measurements reveal the destruction of a large hole-like Fermi surface upon cooling through a coupled structural and spinreorientation transition at 48 K, accompanied by a sudden onset of quasiparticle coherence. We demonstrate how these result from band hybridization mediated by a hidden Rashba-type spin- orbit coupling. This is enabled by the bulk structural distortions and unlocked when the spin reorients perpendicular to the local symmetry-breaking potential at the Ru sites. We argue that the electronic energy gain associated with the band hybridization is actually the key driver for the phase transition, reflecting a delicate interplay between spin-orbit coupling and strong electronic correlations and revealing a route to control magnetic ordering in solids.

AB - The interplay between spin-orbit coupling and structural inversion symmetry breaking in solids has generated much interest due to the nontrivial spin and magnetic textures which can result. Such studies are typically focused on systems where large atomic number elements lead to strong spin-orbit coupling, in turn rendering electronic correlations weak. In contrast, here we investigate the temperature-dependent electronic structure of Ca3Ru2O7, a 4d oxide metal for which both correlations and spin-orbit coupling are pronounced and in which octahedral tilts and rotations combine to mediate both global and local inversion symmetry-breaking polar distortions. Our angle-resolved photoemission measurements reveal the destruction of a large hole-like Fermi surface upon cooling through a coupled structural and spinreorientation transition at 48 K, accompanied by a sudden onset of quasiparticle coherence. We demonstrate how these result from band hybridization mediated by a hidden Rashba-type spin- orbit coupling. This is enabled by the bulk structural distortions and unlocked when the spin reorients perpendicular to the local symmetry-breaking potential at the Ru sites. We argue that the electronic energy gain associated with the band hybridization is actually the key driver for the phase transition, reflecting a delicate interplay between spin-orbit coupling and strong electronic correlations and revealing a route to control magnetic ordering in solids.

KW - Angle-resolved photoemission

KW - Correlated oxide

KW - Magnetism

KW - Rashba spin-orbit

KW - Ruthenate

UR - http://www.scopus.com/inward/record.url?scp=85088087025&partnerID=8YFLogxK

U2 - 10.1073/pnas.2003671117

DO - 10.1073/pnas.2003671117

M3 - Article

C2 - 32576687

AN - SCOPUS:85088087025

SN - 0027-8424

VL - 117

SP - 15524

EP - 15529

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

IS - 27

ER -