Layer-by-layer material engineering has produced interesting quantum phenomena such as interfacial superconductivity and the quantum anomalous Hall effect. However, probing electronic states layer by layer remains challenging. This is exemplified by the difficulty in understanding the layer origins of topological electronic states in magnetic topological insulators. Here we report a layer-encoded frequency-domain photoemission experiment on the magnetic topological insulator (MnBi2Te4)(Bi2Te3) that characterizes the origins of its electronic states. Infrared laser excitations launch coherent lattice vibrations with the layer index encoded by the vibration frequency. Photoemission spectroscopy then tracks the electron dynamics, where the layer information is carried in the frequency domain. This layer–frequency correspondence shows wavefunction relocation of the topological surface state from the top magnetic layer into the buried second layer, reconciling the controversy over the vanishing broken-symmetry energy gap in (MnBi2Te4)(Bi2Te3) and its related compounds. The layer–frequency correspondence can be harnessed to disentangle electronic states layer by layer in a broad class of van der Waals superlattices.
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We acknowledge very helpful discussions with J. Sobota and P. Kirchmann from SLAC National Accelerator Laboratory, and with S. King, J. Park, P. Littlewood and S. Guha from the University of Chicago. The optimization of the static µ-ARPES set-up was partially supported by the US National Science Foundation (NSF) through grant no. DMR-2145373. The trARPES work was supported by the US Department of Energy (grant no. DE-SC0022960). The financial support for a part of sample preparation by S.H.L. was provided by the NSF through the Penn State 2D Crystal Consortium-Materials Innovation Platform (2DCC-MIP) under NSF cooperative agreement DMR-2039351. The sample synthesis efforts by Y.G. were supported by the US Department of Energy under grant DE-SC0019068. C.L. and R.M. acknowledge support from the Penn State MRSEC Center for Nanoscale Science through NSF grant no. DMR-2011839. B.Y. acknowledges financial support by the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant no. 815869).
The authors declare no competing interests.
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Lee, W., Fernandez-Mulligan, S., Tan, H. et al. Layer-by-layer disentanglement of Bloch states. Nat. Phys. (2023). https://doi.org/10.1038/s41567-023-02008-4
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