g-factor-enhanced upper critical field in Superconducting PdTe2 due to qauntum confinement.

PdTe2 is reported to be a Type-II Ising superconductor. In ultra-thin flakes, its upper critical field can exceed the Pauli limit by more than 7 times. [1] In weak coupling BCS theory, it is known that the Pauli limit is derived by equating the condensation energy of superconducting energy and free energy of spin paramagnetic effect with g-factor being 2. Here we report the enhancement of the upper critical field of thin films of PdTe2 of intermediate thickness, ranging from 30nm to 19nm . The films are grown by chemical vapor deposition. We have conducted magnetotransport measurements down to 20mK and extracted both the in-plane and out-of-plane upper critical field. We have seen the enhancement of the in-plane critical field by more than 20 times with decreasing thickness. We attribute this enhancement to a thickness-dependent change in effective g-factor, due to quantum confinement in the PdTe2, which drives an enhancement of the Pauli limit. We rule out a potential origin of Hc2 enhancement related to impurities by studying the residual resistivity ratio and the lateral grain size of films of different thickness.