Superconducting NbC nanoparticles synthesized by laser ablation in a liquid

Abstract

Niobium carbide (NbC) is a high-field type II superconductor with a critical temperature (T_C) of 11.1 K, slightly exceeding that of pure Nb (T_C = 9 K). The reduction of NbC to the nanoparticle scale leads to significant changes in its critical field and/or the superconducting temperature. This study presents findings on superconducting NbC nanoparticles with T_C ≃ 10 K produced through laser ablation in acetone, where different conditions of laser fluence and centrifugation were studied. Analysis by X-ray diffraction confirmed the cubic NbC phase, while electron microscopy images displayed approximately 8 nm spherical particles, showing no noticeable size variation with laser fluence. Additionally, magnetization curves exhibited both magnetic and superconducting loops for all investigated samples. A decrease in laser fluence resulted in the suppression of diamagnetic behavior below T_C. Furthermore, all samples exhibited a weak electron spin resonance (ESR) Curie-like signal at g ≃ 2.0, probably linked to localized defects on the particle's surface. The simultaneous existence of superconductivity and magnetism in nanoparticles has recently garnered significant research attention. This intricate scenario and unique properties arise from the significant enhancement of the surface-to-volume ratio in these superconducting NbC nanoparticles, emphasizing the need for further investigation to unveil novel material properties and shed new light on our comprehension of the superconducting phenomenon in this particular morphology.