TY - JOUR
T1 - Quantum Griffiths singularities in TiO superconducting thin films with insulating normal states
AU - Zhang, Chao
AU - Fan, Yunjie
AU - Chen, Qiaoling
AU - Wang, Tianyi
AU - Liu, Xiang
AU - Li, Qi
AU - Yin, Yuewei
AU - Li, Xiaoguang
N1 - Funding Information:
This work was supported by the National Natural Science Foundation of China (51790491, 51622209, and 21521001) and the National Key Research and Development Program of China (2016YFA0300103 and 2015CB921201), and the work performed at Penn State University was supported by the United States Department of Energy under Grant no. DE-FG02-08ER46531 (Q.L.). A portion of the sample preparation was performed at the USTC Center for Microscale and Nanoscale Research and Fabrication at the University of Science and Technology of China, Hefei, China.
Publisher Copyright:
© 2019, The Author(s).
PY - 2019/12/1
Y1 - 2019/12/1
N2 - A superconductor–metal transition (SMT) with an unconventional diverging dynamic critical exponent was recently discovered, and it drew tremendous attention because this signature of a quantum Griffiths singularity (QGS) was thought to be a common characteristic of low-disorder crystalline superconductors. However, because the QGS was observed only in limited materials with metallic normal states, the question of whether the QGS exists in other superconducting systems is still unanswered. In this paper, a superconductor–insulator transition (SIT) is observed in TiO thin films with insulating normal states, which offers a more universal platform for investigating the QGS. A thickness-tuned SIT is obtained when the magnetic field is zero. Importantly, a magnetic field-tuned SIT with a diverging dynamic critical exponent, which is direct evidence of a QGS, is observed in TiO thin films with different thicknesses. By constructing a comprehensive phase diagram, it is demonstrated that the critical magnetic field Hc tends to saturate as the temperature approaches 0 K, which is different from the upturn trend of Hc observed in SMT systems and probably due to the weaker Josephson coupling of the locally ordered superconducting islands (rare regions) in a weakly insulating normal state background. The results extend the QGS scenario from only SMT systems to SIT systems, and they provide vital evidence that QGSs are common in crystalline superconducting thin films, which has possible applications in quantum-computing devices.
AB - A superconductor–metal transition (SMT) with an unconventional diverging dynamic critical exponent was recently discovered, and it drew tremendous attention because this signature of a quantum Griffiths singularity (QGS) was thought to be a common characteristic of low-disorder crystalline superconductors. However, because the QGS was observed only in limited materials with metallic normal states, the question of whether the QGS exists in other superconducting systems is still unanswered. In this paper, a superconductor–insulator transition (SIT) is observed in TiO thin films with insulating normal states, which offers a more universal platform for investigating the QGS. A thickness-tuned SIT is obtained when the magnetic field is zero. Importantly, a magnetic field-tuned SIT with a diverging dynamic critical exponent, which is direct evidence of a QGS, is observed in TiO thin films with different thicknesses. By constructing a comprehensive phase diagram, it is demonstrated that the critical magnetic field Hc tends to saturate as the temperature approaches 0 K, which is different from the upturn trend of Hc observed in SMT systems and probably due to the weaker Josephson coupling of the locally ordered superconducting islands (rare regions) in a weakly insulating normal state background. The results extend the QGS scenario from only SMT systems to SIT systems, and they provide vital evidence that QGSs are common in crystalline superconducting thin films, which has possible applications in quantum-computing devices.
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U2 - 10.1038/s41427-019-0181-3
DO - 10.1038/s41427-019-0181-3
M3 - Article
AN - SCOPUS:85076894359
VL - 11
JO - NPG Asia Materials
JF - NPG Asia Materials
SN - 1884-4049
IS - 1
M1 - 76
ER -