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Seminar: "2D Superconductors and Log-periodic Quantum Oscillations” (Lecture)

Friday 24 August 2018Add to my calendar
from 16:00
Prof. Jian Wang (International Center for Quantum Materials, Peking University, China)

prof. Jian WangBy direct transport and magnetic measurements, we provide fist direct evidence for high temperature superconductivity in the 1-UC FeSe films grown on insulating STO substrates with the onset Tc and critical current density much higher than those for bulk FeSe [1]. The investigation may pave the way to enhancing and tailoring superconductivity by interface engineering. Besides, quantum phase transition is one of most important topics in condensed matter physics. When we study the superconductor-metal transition in ultrathin crystalline Ga films grown on GaN substrate [2], for the first time quantum Griffiths singularity in two dimensional (2D) systems [3] is discovered as a new quantum phase transition in 2D superconductors. The coexistence of quantum Griffiths singularity and Ising (Zeeman-protected) superconductivity is further revealed in monolayer NbSe2 films [4]. We also demonstrate that by interface engineering Zeeman-protected superconductivity can be artificially induced in crystalline 2D superconducting heterostructures [5].

It is well known that there are two classes of quantum oscillations. One is magnetic field B periodic oscillations, such as Aharonov-Bohm effect for mesoscopic system and Little Parks oscillations for superconducting systems. The other one is 1/B periodic Shubnikov-deHaas and deHaas van-Alphen oscillations from quantized Landau levels. We discover a new class of quantum oscillations beyond quantum limit in high quality topological semimetals, which shows exotic log B periodic oscillations, i.e. discrete scale invariance [6].

[1] Chin. Phys. Lett. 31, 017401 (2014) (with a highlight: Science 343, 230 (2014))
[2] Physical Review Letters 114, 107003 (2015) (Editors’ Suggestion)
[3] Science 350, 542 (2015) (with a perspective article: Science 350, 509(2015))
[4] Nano Letters 17, 6802 (2017)
[5] Phys. Rev. X 8, 021002 (2018)
[6] arXiv:1704.00995

prof. Uli Zeitler