Abstract：After decades of explorations, suffering from the subtle nature and sample quality, whether a metallic ground state exists in a two-dimensional system (2D) beyond Anderson localization is still a mystery. Our work reveals how quantum phase coherence evolves across bosonic superconductor-metal-insulator transitions via magneto-conductance quantum oscillations in high-Tc superconducting films with patterned nanopores. A robust intervening anomalous metallic state characterized by both resistance and oscillation amplitude saturations in the low temperature regime is detected, which suggests that the saturation of phase coherence plays a prominent role in the formation of the anomalous metallic state. [1] Furthermore, we carried out a systematic transport study on the macro-size ambient-stable ultrathin crystalline PdTe2 films grown by molecular beam epitaxy. Remarkably, in perpendicular magnetic field, the film undergoes the quantum phase transition from quantum metal to weakly localized metal with the presence of intermediate quantum Griffiths singularity. Our findings lead to a global phase diagram of 2D superconducting system with strong spin-orbit coupling. [2]

The quantum Hall effect (QHE) without Landau levels (LLs) has become a long-pursuit research topic since the QHE was discovered around 40 years ago. Previous theoretical proposals and experiments based on two dimensional (2D) topological systems with time-reversal symmetry broken have revealed the QHE without LLs with Chern number C=1 at ultralow temperatures. Now the key issues of the QHE without LLs are how to increase the working temperature and realize high Chern number with more dissipationless chiral edge states (C>1) for emerging physics and low-dissipation electronics. We discovered the high Chern number (C=2) QHE without LLs in the nine-septuple-layer magnetic MnBi2Te4 nano-device and C=1 Chern insulator state in the seven-septuple-layer nano-device displaying nearly quantized Hall resistance plateau at record-high temperatures up to 60 K. [3] The thickness-dependent topological quantum phase transition from C=2 to C=1 is uncovered. To our knowledge, this is the first work to report high Chern number QHE without LLs above the liquid helium temperature and this is also the first time that the nearly quantized Hall resistance plateau is detected at the temperature up to 60 K for QHE without LLs.

References:

[1] arXiv: 1901.07706

[2] arXiv:1904.12719

[3] arXiv:1907.09947