Diamagnetism above the superconducting transition in underdoped La1.9Sr0.1CuO4

Abstract

The interplay between superconducting fluctuations and inhomogeneities presents a renewed interest due to recent works of different groups, which apparently support an intrinsically anomalous (beyond the conventional Gaussian-Ginzburg-Landau scenario) diamagnetism above T c in underdoped cuprates. This conclusion, mainly based in the observation of new anomalies in the isothermal magnetization curves at low-field amplitudes, is in contradiction with our earlier results in the underdoped La 1.9 Sr 0.1 CuO 4 [Phys. Rev. Lett. 84, 3157 (2000)]. These seemingly intrinsic anomalies are being presented in various influential works as a "thermodynamic evidence" for phase incoherent superconductivity in the pseudogap regime, this last being at present a central and debated issue of the cuprate superconductors' physics. To further probe the diamagnetism above T c in underdoped cuprates, here we have extended our magnetization measurements in La 1.9 Sr 0.1 CuO 4 to two samples with the same nominal composition but, due to different growth procedures, with different chemical disorder, in one of the samples this disorder being close to the intrinsic-like one, associated with the unavoidable random distribution of the Sr ions (which will be then present even in an ideal La 1.9 Sr 0.1 CuO 4 crystal). For this sample, the corresponding T c inhomogeneities may be approximated as symmetric around the average T c . In contrast, the most disordered sample presents a pronounced asymmetric T c distribution. The comparison between the magnetization measured in both samples provides a crucial check of the chemical disorder origin of the observed diamagnetism anomalies, which are similar to those claimed as due to phase fluctuations by other authors. This conclusion applies also to the sample affected only by the intrinsic-like chemical disorder, providing then a further check that, for all applied magnetic field amplitudes, the intrinsic diamagnetism above the superconducting transition of underdoped cuprates is not affected by the opening of a pseudogap in the normal state. It is also shown here that once these disorder effects are overcome, the remaining precursor diamagnetism may be accounted at a quantitative level in terms of the Gaussian-Ginzburg-Landau approach under a total energy cutoff.

Evolution of superconducting correlations within magnetic-field-decoupled La2−xBaxCuOStegen1, Han2, Wu3 et al. 2013Phys. Rev. B338320View full textAdd to dashboardCite

“…Josephson coupling between the layers leads to the onset of three-dimensional (3D) superconductivity as soon as the correlation length for superconducting order within the layers becomes sizable. 18,19 The recent observations [12][13][14][15][16] that strong superconducting correlations appear only in a regime that is reasonably close to T c are consistent with the expectation that 3D order should appear as soon as 2D superconducting correlations become substantial. 18 In fact, in a previous study of La 2−x Ba x CuO 4 (LBCO) with x = 0.095, evidence was found indicating that superconducting correlations between layers start to develop locally before superconducting correlations diverge within the layers.…”

“…2-8 This work motivated theoretical suggestions 9-11 of a possible phase-disordered twodimensional (2D) superconducting state (2D vortex liquid) that might exist above T c . In contrast, recent studies of superconducting contributions to magnetoresistance 12 and low-frequency optical conductivity, 13,14 as well as further torque magnetometry studies, 15,16 indicate that strong superconducting correlations are found only within a relatively narrow range (∼10 K) above T c ; the response at higher temperatures is quite weak relative to expectations for a 2D vortex-liquid state. 17 There is general agreement that pairing interactions within the CuO 2 layers are responsible for the development of superconducting correlations in the cuprates.…”

Non-conventional superconducting fluctuations in Ba(Fe1−xRhx)2As2 iron-based superconductors

“…1, we exclude the possibility of an asymmetric distribution of T c . 27 After obtaining T c (0), the magnetization has been measured as a function of the field (isotherm) at different temperatures: high resolution scans have been performed for several isotherms, above T c , generally by 0.03 K increments, in steps of 2 Oe, up to 1000 Oe. Additional scans at a temperature well above T c allow to determine the paramagnetic signal of the normal state, and the background contributions from the sample holder.…”

Probing the connections between superconductivity, stripe order, and structure in La1.905Ba0.095CuWen1, Xu2, Xu3 et al. 2012Phys. Rev. B256380View full textAdd to dashboardCite

“…They find that the ratio is off by almost an order of magnitude just above T c . In a recent study of diamagnetism above T c in LSCO x = 0.1, Mosqueira et al 133 have argued that their observations can be explained by chemical disorder plus fluctuations in the pairing amplitude. At minimum, these results cast doubt on a picture of the normal state involving decoupled layers with superconductivity limited only by phase fluctuations.…”