Metastability and hysteretic vortex pinning near the order-disorder transition in NbSe2 : Interplay between plastic and elastic energy barriers

Abstract

We studied thermal and dynamic history effects in the vortex lattice (VL) near the order-disorder transition in clean NbSe2 single crystals. Comparing the evolution of the effective vortex pinning and the bulk VL structure, we observed metastable superheated and supercooled VL configurations that coexist with a hysteretic effective pinning response due to thermal cycling of the system. A novel scenario, governed by the interplay between (lower) elastic and (higher) plastic energy barriers, is proposed as an explanation for our observations: Plastic barriers, which prevent the annihilation or creation of topological defects, require dynamic assistance to be overcome and to achieve a stable VL at each temperature. Conversely, thermal hysteresis in the pining response is ascribed to low energy barriers, which inhibit rearrangement within a single VL correlation volume and are easily overcome as the relative strength of competing interactions changes with temperature.

Thermal hysteresis of the Campbell response as a probe for bulk pinning landscape spectroscopy

“…This paper is organized as follows: We revisit in section II the key ingredients to describe the Campbell response in the framework of strong vortex pinning and derive a set of rules governing its evolution upon changing temperature or applying a shaking field. In section III, we summarize experimental studies on NbSe 2 [24][25][26][27] and interpret the findings within the strong-pinning picture. In section IV, we show how the hysteresis in the Campbell response-as caused by thermal cycling-may be used to extract the temperature evolution of characteristic pinned parameters (force and length).…”

“…We first review the experimental signatures of thermal and dynamic history effects in NbSe 2 with a particular focus on the results reported in Ref. [24][25][26][27]. Hysteresis in the response of ac-driven vortex systems have been observed in many superconductors, including traditional BCS materials [29][30][31] , high T c cuprates 44,45 , and other non-conventional superconductors 21 .…”

“…The necessary tuning knobs-temperature and ac field shaking-to exploit this spectroscopic tool have recently been used [24][25][26][27] to investigate the linear ac susceptibility of NbSe 2 single crystals; a superconductor with a scarce distribution of structural defects * and where dynamic and thermal effects in vortex matter have been studied extensively [24][25][26][27][29][30][31][32] . In Refs.…”

“…In Refs. [26,27], joint small-angle neutron scattering (SANS) and in-situ ac susceptibility measurements have been used to investigate the vortex lattice structure and its response to ac magnetic perturbations. Various cooling and warming protocols have revealed a strong hysteresis in the ac response of this material.…”

Thermal creep induced by cooling a superconducting vortex lattice

“…Actually, 2H-NbSe 2 is among the materials with lowest creep rates, close to MgB 2 67 . Creep between metastable vortex states that occur near the order-disorder transition of the vortex lattice in 2H-NbSe 2 or related to domain formation of lattices with different orientations in MgB 2 has been reported [68][69][70] . Motion then appears when modifying the relative strength of competing interactions, and it might well occur that the equilibrium configuration at some particular locations is influenced by temperature.…”