Effects of Pb substitution on the vortex state of oxygen-overdoped Bi2Sr2CaCu2O8+δ single crystal

Abstract

We show that excessive Pb substitution of Bi in oxygen-overdoped BSCCO-2212 single crystal further reduces the anisotropy ( c / a ratio͒ of the system in addition to enhancing disorder in its vortex system. These effects have led to the suppression of first-order vortex melting as well as a peculiar second-peak effect exhibiting a sensitive temperature dependence over an unusually broad temperature range. Our experimental data further reveal, in a Bi-based system, the presence of a disentangled vortex liquid phase separating the solid vortex from the entangled vortex liquid phase in the H-T diagram constructed from the transport and magnetization data. INTRODUCTIONThe unusually rich variety of vortex phases in the H-T phase diagram is one of the most remarkable features distinguishing the new copper oxide superconductors from the conventional type-II superconductors. The appearance of a vortex liquid phase over a large area in the H-T diagram initiated intensive research on the structure and characteristics of the liquid phase as well as the true nature of the related thermodynamical transition across its boundary with the solid phase. It has now been established theoretically 1-5 and confirmed experimentally 6-12 that vortex melting in a clean sample is a first-order transition, while the presence of disorder is likely to change its character into a more gradual or second-order process.It is also well known that the traditional picture of the solid vortex phase has been greatly modified by the presence of disorder and anisotropy. It has been found necessary to include, in addition to the ordered vortex lattice state at low H and T, the less ordered or disordered glassy state at the higher H-T regime. This is further complicated by the occurrence of dimensional crossover at a certain boundary within the solid phase. 2,8,13-15 Studies on second-peak effects in BSCCO-2212 superconductors also suggest further complications of the solid vortex phase. 16,17 No less complicated is the vortex liquid phase where a multiphase structure emerges as a result of the intricate interplay among the thermal fluctuation effect, the pinning, and Lorentz forces as well as the plastic response of the vortex lines in highly anisotropic superconductors. The BSCCO-2212 superconductor, among others, offers a particularly rich and novel phenomenology of the vortex system due to its high T c and strongly layered structure. It has thus become one of the most intensely studied systems to date. It is theoretically predicted that apart from the metal-like viscous liq-

Intrinsic percolative superconductivity in heavily overdoped high-temperature superconductors

“…500 • C ), T c drops from 95 K to 72 K and the central peak becomes much smaller. Similar data were published recently [12] although no clear reasons have been given. It would be very interesting to see whether this central peak will vanish completely when further doping Bi-2212 to heavily overdoped regime.…”

Growth and superconducting properties of Bi2Sr2Ca2Cu3O10single crystals

“…Its position in the H -T plane depends on the competition between the elasticity of the lattice and the amount of disorder in the crystal. Furthermore, the temperature range over which the SP can be observed gives a good indication of the amount of disorder in the crystal [18]. In the inset of figure 5 we show an m(H ) loop acquired at T = 40 K from a Bi-2223 crystal.…”

Peak effects and the solid vortex phase of aT*-phaseSmLa0.8Sutjahja1, Nugroho2, Tjia3 et al. 2001Phys. Rev. B6030View full textAdd to dashboardCite

“…11͒ and (Bi,Pb) 2 Sr 2 CaCu 2 O 8ϩ␦ . 24 On the other hand, our data in the temperature range of 4 -20 K are much better fitted by an exponential function of H on (T)ϭH a exp(T a /T), with H a ϭ50 Oe and T a ϭ11 K. It is worth noting that this curve extrapolates at both ends of the temperature range toward the H SP field at temperatures where the peak effect is supposed to disappear completely. We recall that this is precisely the phenomenon depicted in Fig.…”

“…50 It must be stressed nevertheless, that the lower-temperature part of the second peak data (Tр5 K͒ is better described by an exponential function of H SP (T)ϭ5500 exp(ϪT/4) in conformity with the expression H SP (T)ϭH SP (0)exp(Ϫ␣T/T c ) as adopted in the previous analysis of Tl-based single crystal 26,28 and (Bi,Pb) 2 Sr 2 CaCu 2 O 8ϩ␦ single crystal. 24 This different behavior in the lower-temperature region (Tр5 K͒ is most likely a manifestation of a different pinning mechanism as a consequence of diminishing role of thermal energy.…”

“…1 One of the long standing research issues regarding the vortex ensemble in the cuprate superconductor is the physical mechanism underlying the anomalous increase of magnetization with increasing magnetic field applied parallel to the c axis above the lower critical field H c1 , the so called peakeffect or fishtail effect. This phenomenon has been observed in a relatively clean and high quality single crystals of YBa 2 Cu 3 O 7Ϫ␦ ͑YBCO͒, 2-7 Nd 1.85 Ce 0.15 CuO 4Ϫ␦ ͑NCCO͒, [8][9][10][11] (La 1Ϫx Sr x ) 2 CuO 4Ϫ␦ ͑LSCO͒, 12-14 Bi 2 Sr 2 CaCu 2 O 8 ͑BSCCO͒, [15][16][17][18][19][20][21] (Bi,Pb) 2 Sr 2 CaCu 2 O 8 ͑BPSCCO͒, [22][23][24] Tl-based compounds, 15,[25][26][27][28] and HgBa 2 CuO 4 ͑HBCO͒. 29 The same effect has also been reported for the low-temperature superconductor ͑LTS͒ of 2H-NbSe 2 , 30 intermetallic compound of CeRu 2 , 31 as well as organic materials such as -(BEDT-TTF) 2 Cu(NCS) 2 ͑Refs.…”