Orbital textures and charge density waves in transition metal dichalcogenides

Abstract

Low-dimensional electron systems, as realized in layered materials, often tend to spontaneously break the symmetry of the underlying nuclear lattice by forming so-called density waves1; a state of matter that at present attracts enormous attention2,3,4,5,6. Here we reveal a remarkable and surprising feature of charge density waves, namely their intimate relation to orbital order. For the prototypical material 1T-TaS2 we not only show that the charge density wave within the two-dimensional TaS2 layers involves previously unidentified orbital textures of great complexity. We also demonstrate that two metastable stackings of the orbitally ordered layers allow manipulation of salient features of the electronic structure. Indeed, these orbital effects provide a route to switch 1T-TaS2 nanostructures from metallic to semiconducting with technologically pertinent gaps of the order of 200 meV. This new type of orbitronics is especially relevant for the ongoing development of novel, miniaturized and ultrafast devices based on layered transition metal dichalcogenides7,8.

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Figure 1: The supercell structure of 1T-TaS2.
Figure 2: Different layer stackings and their impact on the band structure.
Figure 3: Real-space illustration of the electron density for the highest occupied band.
Figure 4: Device concept based on the switching between metastable orbital orders.

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Acknowledgements

This work was financially supported by the German Research Foundation under grant DFG-GRK1621. J.T. and J.G. gratefully acknowledge financial support by the German Research Foundation through the Emmy Noether program (grant GE 1647/2-1). Y.I.J. and P.A. were supported by US Department of Energy grant DE-FG02-06ER46285. We thank K. Rossnagel for fruitful discussions.

Author information

J.G. and P.A. conceived the research project on 1T-TaS2. T.R., J.T., Y.I.J., M.v.Z. and J.G. conducted the synchrotron experiments. H.B. grew the single crystals. T.R., J.T. and K.K. performed the DFT calculations. T.R., J.T. and J.G. analysed the results and developed the concept of orbitronics. T.R., J.T., K.K., M.v.Z., P.A., B.B. and J.G. prepared the manuscript.

Correspondence to T. Ritschel or J. Geck.

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Ritschel, T., Trinckauf, J., Koepernik, K. et al. Orbital textures and charge density waves in transition metal dichalcogenides. Nature Phys 11, 328–331 (2015). https://doi.org/10.1038/nphys3267

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