TY - JOUR
T1 - Superconducting 3 R-Ta1+ xSe2 with Giant In-Plane Upper Critical Fields
AU - Tanaka, Yuki
AU - Matsuoka, Hideki
AU - Nakano, Masaki
AU - Wang, Yue
AU - Sasakura, Sana
AU - Kobayashi, Kaya
AU - Iwasa, Yoshihiro
N1 - Funding Information:
We are grateful to T. Nojima, Y. Kashiwabara, S. Yoshida, M. Yoshida, Y. Nakagawa, M. Kawasaki, M. Uchida, and T. Fujita for experimental help and valuable discussions. This work was supported by Grants-in-Aid for Scientific Research (grant nos. 19H05602, 19H02593, 19H00653, 18K03540, and 15K21732) and the A3 Foresight Program from the Japan Society for the Promotion of Science (JSPS). M.N. was partially supported by The Murata Science Foundation. H.M. was supported by JSPS through the Program for Leading Graduate Schools (MERIT).
Publisher Copyright:
Copyright © 2020 American Chemical Society.
PY - 2020/3/11
Y1 - 2020/3/11
N2 - Molecular-beam epitaxy (MBE) enables the stabilization of a nonequilibrium material phase, providing a powerful approach to the exploration of emergent phenomena in condensed-matter research. Here we demonstrate that one of the metallic two-dimensional (2D) materials, TaSe2, grown by MBE crystallizes into the pure 3R phase with the self-intercalated Ta atoms, 3R-Ta1+xSe2, which is thermodynamically metastable and does not exist in nature as a pure material phase. Interestingly, the thick-enough 3R-Ta1+xSe2 film exhibits a superconducting (SC) critical temperature (Tc) of 3.0 K, which is the highest among all of the polymorphs in TaSe2. Thickness-dependence measurements reveal that Tc decreases with decreasing thickness, accompanied by the development of the charge-density wave phase. The 3R-Ta1+xSe2 films exhibit large in-plane upper critical fields (Hc2) in their SC states even in the thick-enough regime, most likely due to the suppression of the interlayer hopping associated with the unique 3R stacking. Moreover, the temperature dependence of the in-plane Hc2 evolves from linear to square-root behavior with decreasing thickness, indicating crossover behavior from anisotropic three-dimensional superconductivity to 2D superconductivity. Our results unveil intriguing SC properties of metastable 3R-Ta1+xSe2 distinct from those of thermodynamically stable 2H-TaSe2, demonstrating the essential importance of the MBE-based approach to the exploration of novel quantum phenomena in 2D materials research.
AB - Molecular-beam epitaxy (MBE) enables the stabilization of a nonequilibrium material phase, providing a powerful approach to the exploration of emergent phenomena in condensed-matter research. Here we demonstrate that one of the metallic two-dimensional (2D) materials, TaSe2, grown by MBE crystallizes into the pure 3R phase with the self-intercalated Ta atoms, 3R-Ta1+xSe2, which is thermodynamically metastable and does not exist in nature as a pure material phase. Interestingly, the thick-enough 3R-Ta1+xSe2 film exhibits a superconducting (SC) critical temperature (Tc) of 3.0 K, which is the highest among all of the polymorphs in TaSe2. Thickness-dependence measurements reveal that Tc decreases with decreasing thickness, accompanied by the development of the charge-density wave phase. The 3R-Ta1+xSe2 films exhibit large in-plane upper critical fields (Hc2) in their SC states even in the thick-enough regime, most likely due to the suppression of the interlayer hopping associated with the unique 3R stacking. Moreover, the temperature dependence of the in-plane Hc2 evolves from linear to square-root behavior with decreasing thickness, indicating crossover behavior from anisotropic three-dimensional superconductivity to 2D superconductivity. Our results unveil intriguing SC properties of metastable 3R-Ta1+xSe2 distinct from those of thermodynamically stable 2H-TaSe2, demonstrating the essential importance of the MBE-based approach to the exploration of novel quantum phenomena in 2D materials research.
KW - TaSe
KW - Transition-metal dichalcogenide
KW - molecular-beam epitaxy
KW - polymorphism
KW - superconductivity
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U2 - 10.1021/acs.nanolett.9b04906
DO - 10.1021/acs.nanolett.9b04906
M3 - Article
C2 - 32013454
AN - SCOPUS:85081944028
VL - 20
SP - 1725
EP - 1730
JO - Nano Letters
JF - Nano Letters
SN - 1530-6984
IS - 3
ER -