Possible reordering of vortex matter near the end point of the second peak line in theYBa2Cu3O

Abstract

We report on the second peak line H sp and the possible phases of vortex matter near T c for a detwinned underdoped YBa 2 Cu 3 O 7Ϫ␦ single crystal. Our local ac and dc permeability measurements revealed that the second peak line H sp does not terminate either at the critical temperature or on the irreversibility line H irr . Pronounced hysteretic behavior is observed in the regime below the second peak line H sp . Below ͑above͒ a characteristic field the end point of the second peak differs from ͑coincides with͒ the irreversibility point, H end point H irr (H end point ϵH irr ). A possible reentrance of a dynamically ordered solid phase in the hightemperature regime near the irreversibility line is discussed.

From the second magnetization peak to peak effect. A study of superconducting properties in Nb films and MgB2bulk samples

“…First of all, we observe that the H irr (T ) data exhibit a slight upward curvature, which is reminiscent of the behavior observed in type-II high and low-T c [4,5,6,17,19], or even type-I [41] superconductors. As we clearly see, the irreversibility points T irr (H) as determined from isofield magnetic measurements as a function of temperature (solid triangles), do not coincide with the respective points H irr (T ) as determined from isothermal magnetic loop measurements (open triangles).…”

“…This behavior may be seen in fig. 3 for three representative temperatures T = 4.3, 5 and 6 K. The overall behavior resembles the SMP observed usually in high-T c superconductors [16,17,18,19,20]. For this reason we "loosely" refer to these characteristic fields as H′′ smp ′′ .…”

“…More specifically, questions on the importance of fluctuation effects [8] and the nature of the melting transition and/or an order-disorder transition is still under investigation in this type-II superconductor [9,10,11,12,13]. In addition, recent magnetic studies in Nb films [14,15] reported the existence of a structure that reminisces of the second magnetization peak (SMP) which is usually observed in high-T c superconductors [16,17,18,19,20]. These studies concluded that for the case of Nb films the "second magnetization peak" ("SMP") is motivated by thermomagnetic insta- ‡ Corresponding author (densta@ims.demokritos.gr) bilities (TMI) that occur in the low-temperature regime, far below the upper-critical field [14,15,21].…”

Relaxation measurements in the regime of the second magnetization peak in Nb films

“…As a result the magnetic curves are more regular. The overall behavior resembles the SMP observed usually in high-T c superconductors [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]. For this reason we "loosely" refer to these characteristic fields as H′′ smp ′′ .…”

“…Recent magnetic studies in Nb films [1,2,3] reported the existence of a structure that reminisces of the second magnetization peak (SMP) which is usually observed in high-T c superconductors [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]. These studies concluded that for the case of Nb films the "SMP" is probably motivated by thermomagnetic instabilities (TMIs) that occur in the low-temperature regime, far below the uppercritical field [1,2,3].…”