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

Bio：Jian Wang, Changjiang Distinguished Professor of China's Ministry of Education, received his bachelor’s degree in Physics from Shandong University in 2001, and PhD degree in condensed matter physics from Institute of Physics, Chinese Academy of Sciences in 2007. From 2006 to 2011, he worked as a Postdoc and Research Associate at Penn State University, USA. He became a tenure-track Associate Professor and established a research group at Peking University in 2010. In 2017, Jian Wang was promoted to Professor. He was selected to Changjiang Distinguished Professor of China's Ministry of Education in 2016 and Chief Scientist for National Key R&D Program of China in 2018. He won Sir Martin Wood China Prize in 2015. His current research interests are quantum transport properties of low dimensional superconductors and topological materials. Jian Wang with collaborators discovered log-periodic quantum oscillations in a solid state system, quantum Griffiths singularity in 2D superconductors, and tip-induced unconventional superconductivity in topological materials. Furthermore, as the leader Jian Wang also for the first time revealed interface-modulated Ising superconductivity, demonstrated high Tc in one unit cell thick FeSe films by direct transport and Meissner evidences, and detected eletron-electron interaction in topological materials. In recent years, he has authored more than 80 SCI papers including around 60 corresponding author publications in Science, Science Advances, Nature Materials, Nature Physics, Nature Communications, PNAS, Physical Review X, Physical Review Letters, Nano Letters, Advanced Materials, and ACS nano etc. Jian Wang’s lab at Peking University possesses ultralow temperature-high magnetic field measurement systems and low temperature scanning tunneling microcopy/spectroscopy-molecular beam epitaxy combined ultrahigh vacuum system etc.

More details: http://www.phy.pku.edu.cn/icqmjianwanggroup/