Magnetoresistance oscillations in superconducting granular niobium nitride nanowires

We report on magnetoresistance oscillations in superconducting ${\text{NbN}}_x$ nanowires synthesized through ammonia gas annealing of ${\text{NbSe}}_3$ precursor nanostructures. Even though the transverse dimensions of the nanowires are much larger than the superconducting coherence length, the voltage-current characteristics of these nanowires at low temperatures are reminiscent of one-dimensional superconductors where quantum phase slips are associated with the origin of dissipation. We show that both the magnetoresistance oscillations and voltage-current characteristics observed in this work result from the granular structure of our nanowires.

Figure 1

(Color online) $R\text{−}H$ curves of samples A $\left(I=2\mu \text{A}\right)$ and B $\left(I=0.5\mu \text{A}\right)$. Upper-left insets show expanded views of the low-field data at numerous fixed temperatures. The magnetic-field direction is perpendicular to the wire axis. Zero-field $R\text{−}T$ curves are given in the lower-right insets.

Figure 2

(Color online) (a) $R\text{−}H$ curves of sample A at 9.2 K and various applied currents. Inset shows an atomic force microscopy image of sample B. (b) FFT trace from $R_{\text{osc}}\text{−}H$ curve presented in the inset for sample A at 9.2 K, where $R_{\text{osc}}$ is the oscillatory part of the $R\text{−}H$ curve at $I=2\mu \text{A}$.

Figure 3

(Color online) Period of the dominant oscillation $\Delta H$ and the first peak field $H_1$ at various angles. The solid lines represent the inverse cosine relationship. The definitions of angles $\varphi$ and $\theta$ are given in the lower-right insets. $R\text{−}H$ curves at various angles are presented in the upper-left insets where the curves at angles other than $90°$ have been offset for clarity.

Figure 4

(Color online) $V\text{−}I$ characteristics at various temperatures in zero field. The inset in (a) gives the temperature dependence of the current $I^{\ast }$ at which the first voltage jump occurs, where the solid symbols and line are experimental data and the fit, respectively. Inset of (b) presents the zero-field $R\text{−}T$ curve of sample B with resistance in logarithmic scale.