TY - JOUR
T1 - Landau quantization and highly mobile fermions in an insulator
AU - Wang, Pengjie
AU - Yu, Guo
AU - Jia, Yanyu
AU - Onyszczak, Michael
AU - Cevallos, F. Alexandre
AU - Lei, Shiming
AU - Klemenz, Sebastian
AU - Watanabe, Kenji
AU - Taniguchi, Takashi
AU - Cava, Robert J.
AU - Schoop, Leslie M.
AU - Wu, Sanfeng
N1 - Funding Information:
Acknowledgements S.W. is indebted to N. P. Ong and A. Yazdani for their support for his new laboratory and their encouragement and discussions regarding this work. We acknowledge discussions with B. A. Bernevig, D. Cobden, F. D. M. Haldane, P. Jarillo-Herrero, P. A. Lee, T. Senthil, I. Sodemann, S. Sondhi and X. Xu. This research was supported primarily by NSF through the Princeton University Materials Research Science and Engineering Center (DMR-1420541) and a CAREER award to S.W. (DMR-1942942). Early measurements were performed at the National High Magnetic Field Laboratory, which is supported by NSF Cooperative Agreement no. DMR-1644779 and the State of Florida. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, grant no. JPMXP0112101001, JSPS KAKENHI grant no. JP20H00354 and the CREST (JPMJCR15F3), JST. F.A.C. and R.J.C. acknowledge support from the ARO MURI on Topological Insulators (grant W911NF1210461). S.L, S.K. and L.M.S. acknowledge support from the Arnold and Mabel Beckman Foundation through a Beckman Young Investigator grant awarded to L.M.S and the Gordon and Betty Moore Foundation through grant GBMF9064 to L.M.S.
Publisher Copyright:
© 2020, The Author(s), under exclusive licence to Springer Nature Limited.
PY - 2021/1/14
Y1 - 2021/1/14
N2 - In strongly correlated materials, quasiparticle excitations can carry fractional quantum numbers. An intriguing possibility is the formation of fractionalized, charge-neutral fermions—for example, spinons1 and fermionic excitons2,3—that result in neutral Fermi surfaces and Landau quantization4,5 in an insulator. Although previous experiments in quantum spin liquids1, topological Kondo insulators6–8 and quantum Hall systems3,9 have hinted at charge-neutral Fermi surfaces, evidence for their existence remains inconclusive. Here we report experimental observation of Landau quantization in a two-dimensional insulator, monolayer tungsten ditelluride (WTe2), a large-gap topological insulator10–13. Using a detection scheme that avoids edge contributions, we find large quantum oscillations in the material’s magnetoresistance, with an onset field as small as about 0.5 tesla. Despite the huge resistance, the oscillation profile, which exhibits many periods, mimics the Shubnikov–de Haas oscillations in metals. At ultralow temperatures, the observed oscillations evolve into discrete peaks near 1.6 tesla, above which the Landau quantized regime is fully developed. Such a low onset field of quantization is comparable to the behaviour of high-mobility conventional two-dimensional electron gases. Our experiments call for further investigation of the unusual ground state of the WTe2 monolayer, including the influence of device components and the possible existence of mobile fermions and charge-neutral Fermi surfaces inside its insulating gap.
AB - In strongly correlated materials, quasiparticle excitations can carry fractional quantum numbers. An intriguing possibility is the formation of fractionalized, charge-neutral fermions—for example, spinons1 and fermionic excitons2,3—that result in neutral Fermi surfaces and Landau quantization4,5 in an insulator. Although previous experiments in quantum spin liquids1, topological Kondo insulators6–8 and quantum Hall systems3,9 have hinted at charge-neutral Fermi surfaces, evidence for their existence remains inconclusive. Here we report experimental observation of Landau quantization in a two-dimensional insulator, monolayer tungsten ditelluride (WTe2), a large-gap topological insulator10–13. Using a detection scheme that avoids edge contributions, we find large quantum oscillations in the material’s magnetoresistance, with an onset field as small as about 0.5 tesla. Despite the huge resistance, the oscillation profile, which exhibits many periods, mimics the Shubnikov–de Haas oscillations in metals. At ultralow temperatures, the observed oscillations evolve into discrete peaks near 1.6 tesla, above which the Landau quantized regime is fully developed. Such a low onset field of quantization is comparable to the behaviour of high-mobility conventional two-dimensional electron gases. Our experiments call for further investigation of the unusual ground state of the WTe2 monolayer, including the influence of device components and the possible existence of mobile fermions and charge-neutral Fermi surfaces inside its insulating gap.
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U2 - 10.1038/s41586-020-03084-9
DO - 10.1038/s41586-020-03084-9
M3 - Article
C2 - 33398136
AN - SCOPUS:85098790694
SN - 0028-0836
VL - 589
SP - 225
EP - 229
JO - Nature
JF - Nature
IS - 7841
ER -