- Physical Review Journals
All JournalsPhysics Magazine

Physical Review Materials

Reuse & Permissions

It is not necessary to obtain permission to reuse this article or its components as it is available under the terms of the Creative Commons Attribution 4.0 International license. This license permits unrestricted use, distribution, and reproduction in any medium, provided attribution to the author(s) and the published article's title, journal citation, and DOI are maintained. Please note that some figures may have been included with permission from other third parties. It is your responsibility to obtain the proper permission from the rights holder directly for these figures.

Export citation

Export citation

Choose format for download:

Download Citation
  • Open Access

Mott insulating state of IrO6 honeycomb monolayer structured in ilmenite-type oxide superlattice

Masamichi Negishi1,2,*, Kohei Fujiwara1,3, Seong-Hoon Jang1,4, Yi-Feng Zhao4,5, Shun Sasano6, Ryo Ishikawa6, Naoya Shibata6,7, Daisuke Shiga8, Hiroshi Kumigashira8 et al.

Yuto Nakamura9, Hideo Kishida9, Yukitoshi Motome4, and Atsushi Tsukazaki1,4,10,11,†

  • *Contact author: masamichi.negishi@tohoku.ac.jp
  • †Contact author: tsukazaki@ap.t.u-tokyo.ac.jp
PDF

Phys. Rev. Materials 9, 086202 – Published 12 August, 2025

DOI: https://doi.org/10.1103/gz4v-8mds

Abstract

Quantum magnetism based on the Kitaev honeycomb model has been intensively studied both by theoretical material design and experimental materialization. In contrast to the considerable progress of theoretical modeling and experiments on bulk crystals, it is still difficult to find a candidate material applicable to thin films and devices toward future quantum computation. Here we clearly demonstrate a Mott insulating state of IrO6 honeycomb monolayer structured in ilmenite-type Mg−Ir−O/MgTiO3 superlattices, which is a good candidate of the Kitaev honeycomb magnet applicable to devices. Electronic states detected by photoelectron spectroscopy agree well with those in theoretical band calculations. The stabilized superlattice with the Mott gap state is a promising platform to examine the device physics of the Majorana fermions and the Z2 fluxes in the Kitaev honeycomb model, suggesting the thin-film techniques are quite beneficial for triggering the exploration of quantum computation in designable and evolvable heterostructures.

View figure in article

Physics Subject Headings (PhySH)

Article Text

Supplemental Material

References (67)

  1. A. Kitaev, Anyons in an exactly solved model and beyond, Ann. Phys. 321, 2 (2006).
  2. G. Jackeli and G. Khaliullin, Mott insulators in the strong spin-orbit coupling limit: From Heisenberg to a quantum compass and Kitaev models, Phys. Rev. Lett. 102, 017205 (2009).
  3. H. Takagi, T. Takayama, G. Jackeli, G. Khaliullin, and S. E. Nagler, Concept and realization of Kitaev quantum spin liquids, Nat. Rev. Phys. 1, 264 (2019).
  4. Y. Motome and J. Nasu, Hunting Majorana fermions in Kitaev magnets, J. Phys. Soc. Jpn. 89, 012002 (2020).
  5. L. Savary and L. Balents, Quantum spin liquids: A review, Rep. Prog. Phys. 80, 016502 (2017).
  6. Y. Singh and P. Gegenwart, Antiferromagnetic Mott insulating state in single crystals of the honeycomb lattice material Na2IrO3, Phys. Rev. B 82, 064412 (2010).
  7. K. Kitagawa, T. Takayama, Y. Matsumoto, A. Kato, R. Takano, Y. Kishimoto, S. Bette, R. Dinnebier, G. Jackeli, and H. Takagi, A spin-orbital-entangled quantum liquid on a honeycomb lattice, Nature (London) 554, 341 (2018).
  8. P. Lampen-Kelley, S. Rachel, J. Reuther, J.-Q. Yan, A. Banerjee, C. A. Bridges, H. B. Cao, S. E. Nagler, and D. Mandrus, Anisotropic susceptibilities in the honeycomb Kitaev system α−RuCl3, Phys. Rev. B 98, 100403(R) (2018).
  9. F. Freund, S. C. Williams, R. D. Johnson, R. Coldea, P. Gegenwart, and A. Jesche, Single crystal growth from separated educts and its application to lithium transition-metal oxides, Sci. Rep. 6, 35362 (2016).
  10. H. B. Cao, A. Banerjee, J.-Q. Yan, C. A. Bridges, M. D. Lumsden, D. G. Mandrus, D. A. Tennant, B. C. Chakoumakos, and S. E. Nagler, Low-temperature crystal and magnetic structure of α−RuCl3, Phys. Rev. B 93, 134423 (2016).
  11. A. Banerjee, J. Yan, J. Knolle, C. A. Bridges, M. D. Stone, D. G. Mandrus, D. A. Tennant, R. Moessner, and S. E. Nagler, Neutron scattering in the proximate quantum spin liquid α−RuCl3, Science 356, 1055 (2017).
  12. L. J. Sandilands, Y. Tian, K. W. Plumb, Y.-J. Kim, and K. S. Burch, Continuum and possible fractionalized excitations in α−RuCl3, Phys. Rev. Lett. 114, 147201 (2015).
  13. J. Nasu, J. Knolle, D. L. Kovrizhin, Y. Motome, and R. Moessner, Fermionic response from fractionalization in an insulating two-dimensional magnet, Nat. Phys. 12, 912 (2016).
  14. Y. Kasahara, T. Ohnishi, Y. Mizukami, O. Tanaka, S. Ma, K. Sugii, N. Kurita, H. Tanaka, J. Nasu, Y. Motome, T. Shibauchi, and Y. Matsuda, Majorana quantization and half-integer thermal quantum Hall effect in a Kitaev spin liquid, Nature (London) 559, 227 (2018).
  15. L. E. Chern, E. Z. Zhang, and Y. B. Kim, Sign structure of thermal Hall conductivity and topological magnons for in-plane field polarized Kitaev magnets, Phys. Rev. Lett. 126, 147201 (2021).
  16. E. Z. Zhang, L. E. Chern, and Y. B. Kim, Topological magnons for thermal Hall transport in frustrated magnets with bond-dependent interactions, Phys. Rev. B 103, 174402 (2021).
  17. T. Minakawa, Y. Murakami, A. Koga, and J. Nasu, Majorana-mediated spin transport in Kitaev quantum spin liquids, Phys. Rev. Lett. 125, 047204 (2020).
  18. J. Nasu, Y. Murakami, and A. Koga, Scattering phenomena for spin transport in a Kitaev spin liquid, Phys. Rev. B 106, 024411 (2022).
  19. T. Misawa, J. Nasu, and Y. Motome, Interedge spin resonance in the Kitaev quantum spin liquid, Phys. Rev. B 108, 115117 (2023).
  20. Y. Kato, J. Nasu, M. Sato, T. Okubo, T. Misawa, and Y. Motome, Spin Seebeck effect as a probe for Majorana fermions in Kitaev spin liquids, Phys. Rev. X 15, 011050 (2025).
  21. M. Carrega, I. J. Vera-Marun, and A. Principi, Tunneling spectroscopy as a probe of fractionalization in two-dimensional magnetic heterostructures, Phys. Rev. B 102, 085412 (2020).
  22. J. Feldmeier, W. Natori, M. Knap, and J. Knolle, Local probes for charge-neutral edge states in two-dimensional quantum magnets, Phys. Rev. B 102, 134423 (2020).
  23. R. G. Pereira and R. Egger, Electrical access to Ising anyons in Kitaev spin liquids, Phys. Rev. Lett. 125, 227202 (2020).
  24. E. J. König, M. T. Randeria, and B. Jäck, Tunneling spectroscopy of quantum spin liquids, Phys. Rev. Lett. 125, 267206 (2020).
  25. M. Udagawa, S. Takayoshi, and T. Oka, Scanning tunneling microscopy as a single Majorana detector of Kitaev's chiral spin liquid, Phys. Rev. Lett. 126, 127201 (2021).
  26. D. Weber, L. M. Schoop, V. Doppel, J. M. Lippmann, J. Nuss, and B. V. Lotsch, Magnetic properties of restacked 2D spin 1/2 honeycomb RuCl3 nanosheets, Nano Lett. 16, 3578 (2016).
  27. M. Grönke, P. Schmidt, M. Valldor, S. Oswald, D. Wolf, A. Lubk, B. Büchner, and S. Hampel, Chemical vapor growth and delamination of α−RuCl3 nanosheets down to the monolayer limit, Nanoscale 10, 19014 (2018).
  28. B. Zhou, Y. Wang, G. B. Osterhoudt, P. Lampen-Kelley, D. Mandrus, R. He, K. S. Burch, and E. A. Henriksen, Possible structural transformation and enhanced magnetic fluctuations in exfoliated α−RuCl3, J. Phys. Chem. Solids 128, 291 (2019).
  29. S. Mashhadi, Y. Kim, J. Kim, D. Weber, T. Taniguchi, K. Watanabe, N. Park, B. Lotsch, J. H. Smet, M. Burghard, and K. Kern, Spin-split band hybridization in graphene proximitized with α−RuCl3 nanosheets, Nano Lett. 19, 4659 (2019).
  30. B. Zhou, J. Balgley, P. Lampen-Kelley, J.-Q. Yan, D. G. Mandrus, and E. A. Henriksen, Evidence for charge transfer and proximate magnetism in graphene−α−RuCl3 heterostructures, Phys. Rev. B 100, 165426 (2019).
  31. D. J. Rizzo, B. S. Jessen, Z. Sun, F. L. Ruta, J. Zhang, J.-Q. Yan, L. Xian, A. S. McLeod, M. E. Berkowitz, K. Watanabe, T. Taniguchi, S. E. Nagler, D. G. Mandrus, A. Rubio, M. M. Fogler, A. J. Millis, J. C. Hone, C. R. Dean, and D. N. Basov, Charge-transfer plasmon polaritons at graphene/α−RuCl3 interfaces, Nano Lett. 20, 8438 (2020).
  32. D. Hirai, J. Matsuno, and H. Takagi, Fabrication of (111)-oriented Ca0.5Sr0.5IrO3/SrTiO3 superlattices—A designed playground for honeycomb physics, APL Mater. 3, 041508 (2015).
  33. K. Miura, K. Fujiwara, K. Nakayama, R. Ishikawa, N. Shibata, and A. Tsukazaki, Stabilization of a honeycomb lattice of IrO6 octahedra by formation of ilmenite-type superlattices in MnTiO3, Commun. Mater. 1, 55 (2020).
  34. K. Nakazawa, Y. Kato, and Y. Motome, Asymmetric modulation of Majorana excitation spectra and nonreciprocal thermal transport in the Kitaev spin liquid under a staggered magnetic field, Phys. Rev. B 105, 165152 (2022).
  35. Y.-F. Zhao, S.-H. Jang, and Y. Motome, Spin-orbit coupled insulators and metals on the verge of Kitaev spin liquids in ilmenite heterostructures, arXiv:2403.09112v1.
  36. B. J. Kim, H. Jin, S. J. Moon, J.-Y. Kim, B.-G. Park, C. S. Leem, J. Yu, T. W. Noh, C. Kim, S.-J. Oh, J.-H. Park, V. Durairaj, G. Cao, and E. Rotenberg, Novel Jeff=1/2 Mott state induced by relativistic spin-orbit coupling in Sr2IrO4, Phys. Rev. Lett. 101, 076402 (2008).
  37. W. Witczak-Krempa, G. Chen, Y. B. Kim, and L. Balents, Correlated quantum phenomena in the strong spin-orbit regime, Ann. Rev. Cond. Matter Phys. 5, 57 (2013).
  38. R. Comin, G. Levy, B. Ludbrook, Z.-H. Zhu, C. N. Veenstra, J. A. Rosen, Y. Singh, P. Gegenwart, D. Stricker, J. N. Hancock, D. van der Marel, I. S. Elfimov, and A. Damascelli, Na2IrO3 as a novel relativistic Mott insulator with a 340-meV gap, Phys. Rev. Lett. 109, 266406 (2012).
  39. Y. Haraguchi, C. Michioka, A. Matsuo, K. Kindo, H. Ueda, and K. Yoshimura, Magnetic ordering with an XY-like anisotropy in the honeycomb lattice iridates ZnIrO3 and MgIrO3 synthesized via a metathesis reaction, Phys. Rev. Mater. 2, 054411 (2018).
  40. M. Negishi, K. Fujiwara, and A. Tsukazaki, Composition tuning of Mg/Ir ratio and crystallization of a spinel-related structure in Mg-Ir-O films by pulsed-laser deposition, Thin. Solid. Films 769, 139740 (2023).
  41. M. Negishi, K. Fujiwara, and A. Tsukazaki, Formation of ilmenite-type single-crystalline MgTiO3 thin films by pulsed-laser deposition, AIP Adv. 11, 125125 (2021).
  42. P. Giannozzi, O. Andreussi, T. Brumme, O. Bunau, M. B. Nardelli, M. Calandra, R. Car, C. Cavazzoni, D. Ceresoli, M. Cococcioni, N. Colonna, I. Carnimeo, A. D. Corso, D. de Gironcoli, P. Delugas, R. A. DiStasio, Jr., A. Ferretti, A. Floris, G. Fratesi, G. Fugallo et al., Advanced capabilities for materials modelling with quantum espresso, J. Phys.: Condens. Matter 29, 465901 (2017).
  43. A. I. Liechtenstein, V. I. Anisimov, and J. Zaanen, Density-functional theory and strong interactions: Orbital ordering in Mott-Hubbard insulators, Phys. Rev. B 52, R5467 (1995).
  44. N. Marzari and D. Vanderbilt, Maximally localized Wannier functions for composite energy bands, Phys. Rev. B 56, 12847 (1997).
  45. I. Souza, N. Marzari, and D. Vanderbilt, Maximally localized Wannier functions for entangled energy bands, Phys. Rev. B 65, 035109 (2001).
  46. A. A. Mostofi, J. R. Yates, G. Pizzi, Y.-S. Lee, I. Souza, D. Vanderbilt, and N. Marzari, An updated version of Wannier90: A tool for obtaining maximally-localized Wannier functions, Comput. Phys. Commun. 185, 2309 (2014).
  47. S.-H. Jang and Y. Motome, Electronic and magnetic properties of iridium ilmenites AIrO3 (A=Mg, Zn, and Mn), Phys. Rev. Mater. 5, 104409 (2021).
  48. G. Kresse and J. Hafner, Ab initio molecular dynamics for liquid metals, Phys. Rev. B 47, 558(R) (1993).
  49. G. Kresse and J. Hafner, Ab initio molecular-dynamics simulation of the liquid-metal–amorphous-semiconductor transition in germanium, Phys. Rev. B 49, 14251 (1994).
  50. G. Kresse and J. Furthmüller, Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set, Comput. Mater. Sci. 6, 15 (1996).
  51. G. Kresse and J. Furthmüller, Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set, Phys. Rev. B 54, 11169 (1996).
  52. G. Kresse and D. Joubert, From ultrasoft pseudopotentials to the projector augmented-wave method, Phys. Rev. B 59, 1758 (1999).
  53. S. P. Ong, L. Wang, B. Kang, and G. Ceder, The Li−Fe−P−O2 phase diagram from first principles calculations, Chem. Mater. 20, 1798 (2008).
  54. S. P. Ong, A. Jain, G. Hautier, B. Kang, and G. Ceder, Thermal stabilities of delithiated olivine MPO4 (M=Fe, Mn) cathodes investigated using first principles calculations, Electrochem. Commun. 12, 427 (2002).
  55. R. Ishikawa, A. R. Lupini, S. D. Findlay, and S. J. Pennycook, Quantitative annular dark field electron microscopy using single electron signals, Microsc. Microanal. 20, 99 (2014).
  56. See Supplemental Material at http://link.aps.org/supplemental/10.1103/gz4v-8mds for the list of samples and experiments performed for them; the calculated total and projected DOS-s of ilmenite MgIrO3 and monolayer; the ADF and ABF images around Mg-Ir-O layer; the x-ray diffraction patterns of the Mg−Ir−O/MgTiO3 superlattice and the Mg−Ir−O/MgTiO3 heterostructure; the AFM image of a MgTiO3 film on α−Al2O3(001) substrate; the XPS survey scan of the Mg−Ir−O/MgTiO3 heterostructure; the XPS of the Mg−Ir−O/MgTiO3 heterostructure measured with pass energy of 200 and 100 eV; the calclated DOS of MgIrO3 monolayer and ilmenite bulk and valence band XPS of the Mg-Ir-O film on MgTiO3 buffer; and a summary of the results on optical spectroscopy.
  57. A. Jain, S. P. Ong, G. Hautier, W. Chen, W. D. Richards, S. Dacek, S. Cholia, D. Gunter, D. Skinner, G. Ceder, and A. K. Persson, The Materials Project: A materials genome approach to accelerating materials innovation, APL Mater. 1, 011002 (2013).
  58. A. Jain, G. Hautier, S. P. Ong, C. Moore, C. Fischer, K. Persson, and G. Ceder, Formation enthalpies by mixing GGA and GGA + U calculations, Phys. Rev. B 84, 045115 (2011).
  59. S. J. Pennycook and L. A. Boatner, Chemically sensitive structure-imaging with a scanning transmission electron microscope, Nature (London) 336, 565 (1988).
  60. NIST X-ray Photoelectron Spectroscopy Database, NIST Standard Reference Database Number 20, National Institute of Standards and Technology, Gaithersburg, MD (2000), DOI: https://dx.doi.org/10.18434/T4T88K (retrieved May 30, 2023).
  61. V. Pfeifer, T. E. Jones, J. J. Velasco Vélez, C. Massué, R. Arrigo, D. Teschner, F. Girgsdies, M. Scherzer, M. T. Greiner, J. Allan, M. Hashagen, G. Weinberg, S. Piccinin, M. Hävecker, A. Knop-Gericke, and R. Schlögl, The electronic structure of iridium and its oxides, Surf. Interface Anal. 48, 261 (2016).
  62. K. Morikawa, T. Mizokawa, A. Fujimori, Y. Taguchi, and Y. Tokura, Photoemission spectral weight distribution in Y1−xCaxTiO3, Phys. Rev. B 54, 8446 (1996).
  63. J.  M. Kahk, C. G. Poll, F. E. Oropeza, J. M. Ablett, D. Céolin, J.-P. Rueff, S. Agrestini, Y. Utsumi, K. D. Tsuei, Y. F. Liao, F. Borgatti, G. Panaccione, A. Regoutz, R. G. Egdell, B. J. Morgan, D. O. Scanlon, and D. J. Payne, Understanding the electronic structure of IrO2 using hard-x-ray photoelectron spectroscopy and density-functional theory, Phys. Rev. Lett. 112, 117601 (2014).
  64. S. Nair, Z. Yang, K. Storr, and B. Jalan, High-mobility carriers in epitaxial IrO2 films grown using hybrid molecular beam epitaxy, Nano Lett. 24, 10850 (2024).
  65. C. H. Sohn, H.-S. Kim, T. F. Qi, D. W. Jeong, H. J. Park, H. K. Yoo, H. H. Kim, J.-Y. Kim, T. D. Kang, D.-Y. Cho, G. Cao, J. Yu, S. J. Moon, and T. W. Noh, Mixing between Jeff=1/2 and 3/2 orbitals in Na2IrO3: A spectroscopic and density functional calculation study, Phys. Rev. B 88, 085125 (2013).
  66. K. Miura, K. Fujiwara, J. Shiogai, T. Nojima, and A. Tsukazaki, Electrical detection of the antiferromagnetic transition in MnTiO3 ultrathin films by spin Hall magnetoresistance, J. Appl. Phys. 127, 103903 (2020).
  67. K. Yoshimatsu, H. Mashiko, N. Umezawa, K. Horiba, and A. Ohtomo, Electronic structures and photoanodic properties of ilmenite-type MTiO3 epitaxial films (M=Mn, Fe, Co, Ni), J. Phys. Chem. C 121, 18717 (2017).

Outline

Information

Phys. Rev. Materials 9, 086202– Published 12 August, 2025
  • Received 3 November 2024
  • Accepted 23 June 2025
Crossmark - Check for updates button
Creative Commons Logo

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Sign In to Your Journals Account

Filter

Filter

Article Lookup

Enter a citation