g-Factor-Enhanced Upper Critical Field in Superconducting PdTe2 due to Quantum Confinement
Kota Yoshimura, Tzu-Chi Hsieh, Huiyang Ma, Dmitry V. Chichinadze, Shan Zou, Michael Stuckert, David Graf, Robert Nowell, Muhsin Abdul Karim, Daichi Kozawa, Ryo Kitaura, Bence G. Márkus, László Forró, Xiaolong Liu, Dafei Jin, Xinyu Liu, Cyprian Lewandowski, Yi-Ting Hsu, Badih A. AssafAbstract
The Pauli limiting field imposed by the Zeeman effect bounds the upper critical field of weak-coupling superconductivity. It is determined by setting the condensation energy equal to the paramagnetic energy and scales inversely with the effective g-factor. Here, we demonstrate that in a few-layer-thick van der Waals superconductor, PdTe2, quantum confinement can tune the effective g-factor causing the Pauli limit to become thickness-dependent. We experimentally probe the in-plane upper critical field, Hc2∥, of PdTe2 at multiple intermediate thicknesses down to 20 mK. We find that Hc2∥ is enhanced by more than an order of magnitude as the thickness is reduced from 50 nm down to 17 nm. We model the temperature- and thickness-dependent Hc2||, revealing a thickness-dependent spin Zeeman depairing mechanism impacting its value. Our findings reveal how quantum confinement drives a reduction in g that enhances the Pauli limiting field and allows the measured enhancement of Hc2∥. A violation of the Pauli limit is often associated with unconventional pairing symmetry in superconductors. Our work demonstrates that this simple association is difficult without knowledge of the g-factor, particularly in layered materials.