Observation of Floquet-Bloch States on the Surface of a Topological Insulator

By Y. Wang, H. Steinberg, P. Jarillo-Herrero, N. Gedik. Science, 2013

1,077 citations recorded by the source corpus.

Topological Replicas When a periodic perturbation couples strongly to electrons in a solid, replicas of the original electronic levels are predicted to develop at certain energies—the so-called Floquet-Bloch states. Such conditions can be achieved by shining light on a solid, but the effect is challenging to observe. Wang et al. (p. 453) used time- and angle-resolved photoemission spectroscopy to photoexcite Bi2Se3 and observe its dispersion at various delay times. The replicas were seen at expected energy shifts, along with the gaps predicted to occur at the new energy-level crossings caused by the appearance of the replicas. Because Bi2Se3 is a topological insulator, the breaking of the time-reversal symmetry caused by circularly polarized light resulted in the appearance of an energy gap at the Dirac point, indicating an interesting route toward manipulating electronic states in such materials. Time- and angle-resolved photoemission spectroscopy is used to observe coherent coupling of light with electronic states. The unique electronic properties of the surface electrons in a topological insulator are protected by time-reversal symmetry. Circularly polarized light naturally breaks time-reversal symmetry, which may lead to an exotic surface quantum Hall state. Using time- and angle-resolved photoemission spectroscopy, we show that an intense ultrashort midinfrared pulse with energy below the bulk band gap hybridizes with the surface Dirac fermions of a topological insulator to form Floquet-Bloch bands. These photon-dressed surface bands exhibit polarization-dependent band gaps at avoided crossings. Circularly polarized photons induce an additional gap at the Dirac point, which is a signature of broken time-reversal symmetry on the surface. These observations establish the Floquet-Bloch bands in solids and pave the way for optical manipulation of topological quantum states of matter.

Subfields: Atomic and Molecular Physics, and Optics, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/cd2e914aa3f90c6f519cb233b763c5cc54447528

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In Atomic and Molecular Physics, and Optics

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Citations in the corpus

Angle-resolved photoemission studies of quantum materials (2020, neutral): “25(a)) (Chen et al., 2009a; Kasahara et al., 2010; Nandi et al., 2010; Parker et al., 2010; Wang et al., 2013a).”
Anomalous Floquet-Anderson Insulator as a Nonadiabatic Quantized Charge Pump (2015, background): “, driven system analogues of topological insulators [1–22] in a variety of solid-state [23], atomic, and optical contexts [24,25].”
Floquet topological transitions in a driven one-dimensional topological insulator (2015, methodology): “The opening of laser-induced bandgaps has already been observed [16] and new experiments [17–19] and theories are being developed to unveil the states’ fingerprint of their topology [8, 20–23], e.”
Colloquium: Nonthermal pathways to ultrafast control in quantum materials (2021, methodology): “…Vol. 93, No. 4, October–December 2021 041002-12 wave driving, experimental results obtained using laser pulses with multiple optical cycles have nevertheless been well described using this framework (Wang et al., 2013; Kim et al., 2014; Sie et al., 2015; Mahmood et al., 2016; McIver et al., 2020).”
Perspective on topological states of non-Hermitian lattices (2019, background): “Along this new avenue for topological states, studies have focused on diverse materials and systems including normal insulators, [14], graphene [131, 132, 133, 134], other twodimensional materials [135, 136, 137], Rashba wires [138], ultracold matter [139], and topological insulators [140, 130, 141,”
Classification of Interacting Topological Floquet Phases in One Dimension (2016, background): “, to produce new Floquet-Bloch band structures [2,3] or understand nonlinear optical phenomena [4].”
Time- and Site-Resolved Dynamics in a Topological Circuit (2013, background): “Such a time-reversal asymmetric terms require something beyond inductors and capacitors (or equivalently, waveguides) to implement; possible approaches include periodic modulation [24, 33, 34, 51, 52] and coupling to materials with handed susceptibility induced by real magnetic ﬁelds [20].”