Observation of Two-Dimensional Type-II Superconductivity in Bulk 3R-TaSe2 by Scanning Tunneling Spectroscopy

Herewe report a low-temperature and vector-magnetic-field scanningtunneling microscopy/spectroscopy (STM/S) study on 3R-TaSe2. The sample surface was obtained by exfoliating a bulk 3R-TaSe2 single crystal in an ultrahigh-vacuum (UHV) chamber and thentransferred in situ to STM. It was observed thatthe topmost layer shows a 3 x 3 charge density wave pattern at T = 4.2 K with metallic character in STS. The electroniccharacterization study by variable-temperature and magnetic fieldSTS revealed that 3R-TaSe2 behaves as a type-II superconductor.More intriguingly, such superconductivity (SC) can survive under strongin-plane magnetic fields even up to 2.5 T and out-of-plane magneticfields up to 0.7 T, exhibiting an anisotropic superconducting property.Temperature-dependent STS showed that 3R-TaSe2 undergoesa transition above 0.58 K. Our results may be important for understandingthe intriguing SC properties of the 3R-phase van der Waals materials.