Average kinetic energy density of Cooper pairs aboveTcinYBa2Cu3

S. Salem‐Sugui

¹

,

Mauro M. Doria

²

,

A. D. Alvarenga

³

et al.

Abstract

We have obtained isofield curves for the square root of the average kinetic energy density of the superconducting state for three single crystals of underdoped YBa 2 Cu 3 O 7−x , an optimally doped single crystal of Bi 2 Sr 2 CaCu 2 O 8+␦ , and Nb. These curves, determined from isofield magnetization versus temperature measurements and the virial theorem of superconductivity, probe the order parameter amplitude near the upper critical field. The striking differences between the Nb and the high-T c curves clearly indicate for the latter cases the presence of a unique superconducting condensate below and above T c .

Diamagnetic fluctuations inYBa2Cu3O7−xand

“…7 Isofield magnetization curves, M vs T, were obtained for YBaCuO crystals with the magnetic field, H, applied parallel and perpendicular to the c axis while for Bi2212 we used previous obtained magnetization curves for H ʈ c axis. 11 The YBaCuO crystals data complement a previous study performed in the vicinity of T c on two deoxygenated samples 12 and verify ͑by studying another samples with T c =92 K͒ a result obtained in Ref. 12 for an optimally doped sample, where no phase correlations were observed above T c .…”

“…These theoretical works of Refs. 7-9 do not consider an applied magnetic field, but most of the superconducting phenomena observed above T c in these underdoped systems depend on the application of a magnetic field 2,4,5,10,11 and the common thought regarding fluctuations above T c is the existence of a state with vortices with no phase coherence. [4][5][6] In a recent work, 12 which include some of us, it was shown that the asymptotic behavior of isofield ͱ −M vs T curves near T c in two deoxygenated YBaCuO crystals supports the existence of a superconducting state with phase coherence persisting above T c as predicted in Ref.…”

Superconducting fluctuations in the reversible magnetization of the iron-pnictideBa1−xKxFe2As

“…This rounding effect is reminiscent of magnetization curves obtained in high-T c superconductors [21,22,23,39,40]. In the case of cuprate superconductors, superconducting activity above T c appears to be related with the so called pseudo-gap [41,42] which is not considered in the theories for layered systems [43] . Despite some similarities between iron-pnictides and cuprates in what concerns for instance the existence of magnetic fluctuations and magnetic order (AF anomaly) in the non-superconductor precursors [34], most likely there is no such pseudo-gap phase in iron -pnictides [44] .…”

Structural andTcinhomogeneities inherent to doping inLa2−xSrxMosqueira1, Cabo2, Vidal3 2009Phys. Rev. B2811670View full textAdd to dashboardCite

“…4,[16][17][18][19][20][21][22][23][24][25][26] Nevertheless, these authors propose very different origins for such anomalous precursor diamagnetism, including the presence of superconducting phase fluctuations up to the pseudogap temperature or the existence in the bulk of intrinsic inhomogeneities with short characteristic lengths, as those observed by using surface probes.…”