Freestanding\nCubic ZrN Single-Crystalline Films with\nTwo-Dimensional Superconductivity

Abstract

The successful fabrication\nof freestanding two-dimensional (2D)\ncrystals that exhibit unprecedented high crystal quality and macroscopic\ncontinuity renovates the conventional cognition that 2D long-range\ncrystalline order cannot stably exist at finite temperatures. Current\nprogresses are primarily limited to van der Waals (vdW) layered materials,\nwhile studies on how to obtain 2D materials from nonlayered bulk crystals\nremain sparse. Herein, we report the experimental realization of vdW-like\ncubic ZrN single crystal and emphasize the significant role of confined\nelectrons in stabilizing the atomic structure at the 2D limit. Furthermore,\nthe exfoliated ZrN single-crystal films with a few nanometers thick\nexhibit dimensional crossover effect of emerging 2D superconductivity\nwith the unconventional upper critical field beyond Pauli paramagnetic\nlimit, which suggests a dimensional effect in the pairing mechanism\nof dimensionally confined superconductors.