Negative differential resistance state in the free-flux-flow regime of driven vortices in a single crystal of 2H-NbS2

Article

关键词: CHARGE-DENSITY WAVES;    VORTEX;    DYNAMICS;    SUPERCONDUCTIVITY;    PHASE;    MAGNETIZATION;    METASTABILITY;    LATTICES;    MEDIA;   

DOI  :  10.1103/PhysRevB.104.184510

来源: SCIE

【 摘 要 】

Time series measurements [G. Shaw et al., Phys. Rev. B 85, 174517 (2012); B. Bag et al., Sci. Rep. 7, 5531 (2017)] in 2H-NbS2 crystal had unraveled a drive-induced transition wherein the critical current (I-c) changes from a low to a high I-c jammed vortex state, via a negative differential resistance (NDR) transition. Here, using multiple current-voltage (I-V ) measurement cycles, we explore the statistical nature of observing the NDR (or a quasi-NDR in reversing I measurements) transition in the free-flux-flow (FF) regime in a single crystal of 2H-NbS2. Prior to the occurrence of the NDR transition, the pristine full I-V curve exhibits a featureless smooth depinning from the low I-c state. With subsequent current cycling, the NDR transition appears in the I-V curve. Post-NDR, the full I-V curve is seen to be noisy with depinning commencing from the higher I-c state. The probability of observing the NDR transition always remains finite for a vortex state created with either fast or slow rate of magnetic field, B. The probability of observing the NDR transition in the FF regime is found to systematically increase with magnetic field (B) in weak collective pinning regime. In the strong pinning regime, the said probability becomes field independent. Retaining of a nonzero probability for the occurrence of the NDR transition under all conditions, the observed new data shows that the I-V branch with higher I-c is the more stable compared to the lower I-c branch. We show that the higher I-c state, generated via the NDR transition, is unique and cannot be accessed via any conventional route, in particular, by preparing the static vortex state with a different thermomagnetic history. While the I-V curves do not distinguish between zero field cooled (ZFC) and field cooled (FC) modes of preparing the vortex state, the probability for observing an NDR transition has different B dependences for the vortex matter prepared in the ZFC and FC modes. We find that the NDR transition occurs in a high dissipation regime, where the flow resistivity is well above the theoretical value expected in the FF regime. We understand our results on the basis of a rapid drop in vortex viscosity at high drives in 2H-NbS2, which triggers a rapid increase in the vortex velocity and reorganization in the moving vortex matter leading to a dynamical unstable vortex flow. This dynamical instability leads to the NDR transition into a high entropy vortex state with high I-c.

【 授权许可】

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