The layered transition metal dichalcogenides (TMDs) have raised considerable interest in the past decades for both fundamental physics and low-dimensional nanodevice applications. Recently, intriguing phenomena of Ising superconductivity and quantum metallic state have been reported in two-dimensional (2D) 4Ha-TaSe₂ nanodevices. Here, we report the magnetic field induced superconductor–metal transition (SMT) in mechanical exfoliated 4Ha-TaSe₂ nanodevices with thickness down to 2.5 nm. We observe the quantum Griffiths singularity (QGS) of SMT in thin 4Ha-TaSe₂ nanodevices by performing ultralow temperature transport measurements and activated scaling analysis. With increasing the thickness of TaSe₂ nanodevice to 10.6 nm, the signature of magnetoresistance crossing region can hardly be detected, revealing the thickness dependence of SMT. In this procedure, the disorder strength plays a dominant role. This work enriches the platform for studying QGS and may stimulate further investigations on the correlation between different novel quantum phenomena in the same 2D superconducting system.

Topological insulators are insulating in the bulk but possess spin-momentum locked metallic surface states protected by time-reversal symmetry. The existence of these surface states has been confirmed by angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM). Detecting these surface states by transport measurements, which might at first appear to be the most direct avenue, was shown to be much more challenging than expected. Here, we report a detailed electronic transport study in high quality Bi₂Se₃ topological insulator thin films. Interestingly, measurements under an in-plane magnetic field, along and perpendicular to the bias current show anomalous opposite magnetoresistance.