Quantum phenomena in topological materials
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cember 2020 Vol. 63 No. 12: 127031 https://doi.org/10.1007/s11433-020-1627-4
Quantum phenomena in topological materials Jian Wang
*
International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China Received October 10, 2020; accepted October 16, 2020; published online October 26, 2020
Citation:
J. Wang, Quantum phenomena in topological materials, Sci. China-Phys. Mech. Astron. 63, 127031 (2020), https://doi.org/10.1007/s11433-020-1627-4
In 1980, the integer quantum Hall effect in two-dimensional (2D) systems was discovered under high magnetic field [1], which opened a door to the novel phase of matter. The concept of topology was then introduced into condensed matter physics to distinguish the intriguing phenomenon of quantum Hall effect by non-zero Chern number (C) [2]. The topological scenario suggests a new type of phase where the phase transition does not need symmetry breaking. In 2005, Z2 invariant was proposed to characterize the topological properties of time-reversal-invariant systems. In 2006, the HgTe quantum well was predicted to be a quantum spin Hall system with insulating bulk state and spin-orbit locking helical edge state, which was experimentally demonstrated in 2007 and called 2D topological insulator later on. Despite some debates on the evidence of the 2D topological insulator, the studies soon expanded to three-dimensional (3D) topological insulators. Further investigations also revealed topological semimetals and topological superconductors. The materials with topological nontrivial properties are collectively called topological materials. Nowadays, many topological materials have become wellknown and shown important quantum phenomena, such as Bi2Te3, Cd3As2, and ZrTe5. In 2018, a new class of quantum oscillations was reported in high-quality ZrTe5 crystals beyond the quantum limit under high magnetic field [3]. Different from the textbook works of Shubnikov-de Haas oscillations and Aharonov-Bohm effect, the observed resistance oscillations are periodic in logarithmic magnetic field (Figure 1(a)). Considering the Dirac relativistic quasi*Corresponding author (email: [email protected])
particles and Coulomb interaction, two-body quasi-bound states with discrete scale invariance feature were proposed to explain the observation. Moreover, the investigation of these peculiar quasi-bound states in topological materials can broaden our understanding of supercritical atomic collapse. The log-periodic quantum oscillations represent rare discrete scale invariance in quantum matter and may open a new chapter in the 90-year history of quantum oscillations. Actually, in many situations, symmetry protected topological properties are not robust enough, which might hinder the deep research and potential application of topological materials. However, when the correlation is brought into topological matter, topological protection could be very robust. A typical paradigm is the quantum anomalous Hall effect (QAHE) found in magnetic topological materials. In 1
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