Strong electron correlation can induce Mott insulating behaviour and produce intriguing states of matter such as unconventional superconductivity and quantum spin liquids. Recent advances in van der Waals material synthesis enable the exploration of Mott systems in the two-dimensional limit. Here we report characterization of the local electronic properties of single- and few-layer 1T-TaSe2 via spatial- and momentum-resolved spectroscopy involving scanning tunnelling microscopy and angle-resolved photoemission. Our results indicate that electron correlation induces a robust Mott insulator state in single-layer 1T-TaSe2 that is accompanied by unusual orbital texture. Interlayer coupling weakens the insulating phase, as shown by reduction of the energy gap and quenching of the correlation-driven orbital texture in bilayer and trilayer 1T-TaSe2. This establishes single-layer 1T-TaSe2 as a useful platform for investigating strong correlation physics in two dimensions.
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The codes used in this study are available from the corresponding author upon reasonable request.
Imada, M., Fujimori, A. & Tokura, Y. Metal–insulator transitions. Rev. Mod. Phys. 70, 1039–1263 (1998).
Keimer, B. & Moore, J. E. The physics of quantum materials. Nat. Phys. 13, 1045–1055 (2017).
Kravchenko, S. Strongly Correlated Electrons in Two Dimensions (Pan Stanford, 2017).
Dagotto, E. Correlated electrons in high-temperature superconductors. Rev. Mod. Phys. 66, 763–840 (1994).
Lee, P. A., Nagaosa, N. & Wen, X.-G. Doping a Mott insulator: physics of high-temperature superconductivity. Rev. Mod. Phys. 78, 17–85 (2006).
Cao, Y. et al. Correlated insulator behaviour at half-filling in magic-angle graphene superlattices. Nature 556, 80–84 (2018).
Cao, Y. et al. Unconventional superconductivity in magic-angle graphene superlattices. Nature 556, 43–50 (2018).
Chen, G. et al. Evidence of a gate-tunable Mott insulator in a trilayer graphene moiré superlattice. Nat. Phys. 15, 237–241 (2019).
Chen, G. et al. Signatures of tunable superconductivity in a trilayer graphene moiré superlattice. Nature 572, 215–219 (2019).
Wilson, J. A. & Yoffe, A. D. The transition metal dichalcogenides discussion and interpretation of the observed optical, electrical and structural properties. Adv. Phys. 18, 193–335 (1969).
Fazekas, P. & Tosatti, E. Electrical, structural and magnetic properties of pure and doped 1T-TaS2. Philos. Mag. B 39, 229–244 (1979).
Perfetti, L. et al. Spectroscopic signatures of a bandwidth-controlled Mott transition at the surface of 1T-TaSe2. Phys. Rev. Lett. 90, 166401 (2003).
Colonna, S. et al. Mott phase at the surface of 1T-TaSe2 observed by scanning tunneling microscopy. Phys. Rev. Lett. 94, 036405 (2005).
Tosatti, E. & Fazekas, P. On the nature of the low-temperature phase of 1T-TaS2. J. Phys. Colloq. 37, 165–168 (1976).
Sipos, B. et al. From Mott state to superconductivity in 1T-TaS2. Nat. Mater. 7, 960–965 (2008).
Ritschel, T. et al. Orbital textures and charge density waves in transition metal dichalcogenides. Nat. Phys. 11, 328–331 (2015).
Ma, L. et al. A metallic mosaic phase and the origin of Mott-insulating state in 1T-TaS2. Nat. Commun. 7, 10956 (2016).
Cho, D. et al. Nanoscale manipulation of the Mott insulating state coupled to charge order in 1T-TaS2. Nat. Commun. 7, 10453 (2016).
Ritschel, T., Berger, H. & Geck, J. Stacking-driven gap formation in layered 1T-TaS2. Phys. Rev. B 98, 195134 (2018).
Lee, S.-H., Goh, J. S. & Cho, D. Origin of the insulating phase and first-order metal–insulator transition in 1T-TaS2. Phys. Rev. Lett. 122, 106404 (2019).
Ugeda, M. M. et al. Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor. Nat. Mater. 13, 1091–1095 (2014).
He, K. et al. Tightly bound excitons in monolayer WSe2. Phys. Rev. Lett. 113, 026803 (2014).
Qiu, D. Y., da Jornada, F. H. & Louie, S. G. Screening and many-body effects in two-dimensional crystals: monolayer MoS2. Phys. Rev. B 93, 235435 (2016).
Halperin, B. I. & Rice, T. M. Possible anomalies at a semimetal–semiconductor transistion. Rev. Mod. Phys. 40, 755–766 (1968).
Narozhny, B. N. & Levchenko, A. Coulomb drag. Rev. Mod. Phys. 88, 025003 (2016).
Nakata, Y. et al. Monolayer 1T-NbSe2 as a Mott insulator. NPG Asia Mater. 8, e321 (2016).
Nakata, Y. et al. Selective fabrication of Mott-insulating and metallic monolayer TaSe2. ACS Appl. Nano Mater. 1, 1456–1460 (2018).
Di Salvo, F. J., Maines, R. G., Waszczak, J. V. & Schwall, R. E. Preparation and properties of 1T-TaSe2. Solid State Commun. 14, 497–501 (1974).
Ryu, H. et al. Persistent charge-density-wave order in single-layer TaSe2. Nano Lett. 18, 689–694 (2018).
Sohrt, C., Stange, A., Bauer, M. & Rossnagel, K. How fast can a Peierls–Mott insulator be melted? Faraday Discuss. 171, 243–257 (2014).
Qiao, S. et al. Mottness collapse in 1T−TaS2−xSex transition-metal dichalcogenide: an interplay between localized and itinerant orbitals. Phys. Rev. X 7, 041054 (2017).
Brouwer, R. & Jellinek, F. The low-temperature superstructures of 1T-TaSe2 and 2H-TaSe2. Phys. B+C 99, 51–55 (1980).
Sanders, C. E. et al. Crystalline and electronic structure of single-layer TaS2. Phys. Rev. B 94, 081404 (2016).
Darancet, P., Millis, A. J. & Marianetti, C. A. Three-dimensional metallic and two-dimensional insulating behavior in octahedral tantalum dichalcogenides. Phys. Rev. B 90, 045134 (2014).
Yu, X.-L. et al. Electronic correlation effects and orbital density wave in the layered compound 1T-TaS2. Phys. Rev. B 96, 125138 (2017).
Moser, S. An experimentalist's guide to the matrix element in angle resolved photoemission. J. Electron Spectrosc. 214, 29–52 (2017).
Qiu, Z. et al. Giant gate-tunable bandgap renormalization and excitonic effects in a 2D semiconductor. Sci. Adv. 5, eaaw2347 (2019).
Yankowitz, M. et al. Dynamic band-structure tuning of graphene moiré superlattices with pressure. Nature 557, 404–408 (2018).
Tang, S. et al. Quantum spin Hall state in monolayer 1T'-WTe2. Nat. Phys. 13, 683–687 (2017).
Giannozzi, P. et al. QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials. J. Phys. Condens. Matter 21, 395502 (2009).
Liechtenstein, A. I., Anisimov, V. I. & Zaanen, J. Density-functional theory and strong interactions: orbital ordering in Mott–Hubbard insulators. Phys. Rev. B 52, R5467–R5470 (1995).
Dudarev, S. L., Botton, G. A., Savrasov, S. Y., Humphreys, C. J. & Sutton, A. P. Electron-energy-loss spectra and the structural stability of nickel oxide: an LSDA+U study. Phys. Rev. B 57, 1505–1509 (1998).
Hamann, D. R. Optimized norm-conserving Vanderbilt pseudopotentials. Phys. Rev. B 88, 085117 (2013).
Schlipf, M. & Gygi, F. Optimization algorithm for the generation of ONCV pseudopotentials. Comput. Phys. Commun. 196, 36–44 (2015).
Scherpelz, P., Govoni, M., Hamada, I. & Galli, G. Implementation and validation of fully relativistic GW calculations: spin–orbit coupling in molecules, nanocrystals, and solids. J. Chem. Theory Comput. 12, 3523–3544 (2016).
Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).
Medeiros, P. V. C., Stafström, S. & Björk, J. Effects of extrinsic and intrinsic perturbations on the electronic structure of graphene: retaining an effective primitive cell band structure by band unfolding. Phys. Rev. B 89, 041407 (2014).
Medeiros, P. V. C., Tsirkin, S. S., Stafström, S. & Björk, J. Unfolding spinor wave functions and expectation values of general operators: introducing the unfolding-density operator. Phys. Rev. B 91, 041116 (2015).
We thank P.A. Lee and D.-H. Lee for helpful discussions. This research was supported by the VdW Heterostructure programme (KCWF16) (STS measurements and DFT simulations) and the Advanced Light Source (sample growth and ARPES measurements) funded by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the US Department of Energy under contract no. DE-AC02-05CH11231. Support was also provided by National Science Foundation award DMR-1508412 (DFT + U simulations), award DMR-1926004 (theoretical STS and ARPES analyses), award DMR-1507141 (electrostatic analysis) and award EFRI-1433307 (CDW model development). The work at the Stanford Institute for Materials and Energy Sciences and Stanford University (sample growth) was supported by the DOE Office of Basic Energy Sciences, Division of Material Science. Low-energy electron diffraction measurements were supported by the National Natural Science Foundation of China (grant no. 11227902). S.T. acknowledges the support by the CPSF-CAS Joint Foundation for Excellent Postdoctoral Fellows. H.R. acknowledges fellowship support from NRF, Korea through Max Planck Korea/POSTECH Research Initiatives no. 2016K1A4A4A01922028. H.-Z.T. acknowledges fellowship support from the Shenzhen Peacock Plan (grant numbers 827-000113, KQJSCX20170727100802505 and KQTD2016053112042971).
The authors declare no competing interests.
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Chen, Y., Ruan, W., Wu, M. et al. Strong correlations and orbital texture in single-layer 1T-TaSe2. Nat. Phys. 16, 218–224 (2020). https://doi.org/10.1038/s41567-019-0744-9