[20a-E201-1~10] 17.3 Layered materials

[20a-E201-2] Angle dependence of Pauli-paramagnetic limit in 2D superconductor NbSe₂

〇(DC)Hideki Matsuoka¹, Masaki Nakano^1,2, Yoshimitsu Kohama^1,3, Yue Wang¹, Yuta Kashiwabara¹, Satoshi Yoshida¹, Kazuki Matsui³, Takashi Shitaokoshi³, Takumi Ouchi⁴, Kyoko Ishizaka^1,2, Tsutomu Nojima⁴, Masashi Kawasaki^1,2, Yoshihiro Iwasa^1,2 (1.Dept. of Appl. Phys., Univ.of Tokyo, 2.RIKEN CEMS, 3.ISSP, Univ. of Tokyo, 4.IMR, Tohoku Univ.)

Keywords:superconductivity, transition metal dichalcogenide, molecular beam epitaxy

Transition metal dichalcogenides (TMDs) are layered materials of abundant variety, providing the emergence of two-dimensional (2D) physical phenomena such as 2D superconductivity in NbSe₂. Main fabrication methods of TMDs have been mechanical exfoliation and chemical-vapor deposition, but alternative method is molecular-beam epitaxy (MBE), which leads to design broad platform for solid-state physics research. In fact some groups have succeeded in growing superconducting NbSe₂ thin films by MBE, while the superconducting critical temperatures (T_c) were relatively low presumably those films were grown on conducting graphene substrates. Here we report layer-by-layer MBE growth of NbSe₂ thin films on insulating sapphire substrates, achieving relatively high T_c comparable to that of bulk in the thick-enough regime. With reducing thickness, superconducting properties turned out to exhibit 2D-like behavior, realizing Ising superconductivity with large-area samples. In this presentation, we report the results of the angle dependence measurements on H_c2 at low temperature in the bilayer film. We observed cusp-like angle dependence of H_c2 even far below T_c, which could be well explained by the Pauli-paramagnetic limit within the Ginzburg-Landau formalism for 2D superconductors.