Structure-induced Negative Resistance Phenomena in Highly Aligned NbN–CNT Superconducting Sheets

We fabricated planar NbN–CNT sheets by sputtering NbN films onto aligned CNT sheets and measured them in a four-probe configuration, confirming negative-resistance phenomena. The phenomenon is the same as that reported in twisted NbN–CNT yarns ^[1], but here it is reproduced in an untwisted, planar sheet. In this NbN–CNT sheet, temperature-dependent transport shows a superconducting transition near 11.5 K, where the resistance becomes transiently negative and then returns to zero. By varying temperature, magnetic field, and bias current, we mapped the parameter window for this behavior. SEM reveals an electrode–sheet coupling imbalance. This indicates that imbalanced internal connectivity and in-plane anisotropy within the NbN–CNT sheet can create a misaligned superconducting connection between the current and voltage paths, thereby inverting the measured potential difference. These results show that sputtered, highly aligned NbN–CNT sheets can exhibit pronounced nonlinear I–V characteristics rooted in their internal connectivity.



References

[1] Kim et al., ACS Nano 14, 3337 (2020).