Structural andTcinhomogeneities inherent to doping inLa2−xSrx

Abstract

The inhomogeneities inherent to the random distribution of Sr dopants in La2−xSrxCuO4 superconductors are probed by measuring the x-ray diffraction linewidths and the Meissner transition widths, and then consistently explained on the grounds of a simple model in which the local Sr content is calculated by averaging over distances close to the in-plane electronic mean free path. By taking into account these intrinsic bulk inhomogeneities with long characteristic lengths (much larger than the superconducting coherence length amplitudes), the precursor diamagnetism measured above Tc, a fingerprint of the superconducting transition own nature, is then explained for all doping levels in terms of the conventional Gaussian-Ginzburg-Landau approach for layered superconductors. These results also suggest that the electronic inhomogeneities observed in the normal state by using surface probes overestimate the ones in the bulk.

Diamagnetism above the superconducting transition in underdoped La1.9Sr0.1CuO4Mosqueira1, Dancausa2, Vidal3 2011Phys. Rev. BSelf Cite167290View full textAdd to dashboardCite

“…On the other, the improved Sr distribution in sample 1 makes its diamagnetic transition much sharper than in sample 2, for sample 1, T c /T c ≈ 0.04 (which is close to the intrinsic value associated to the unavoidable random distribution of the Sr dopants, see Ref. 16), while T c /T c ≈ 0.25 for sample 2. In fact, as may be already observed in Fig.…”

“…Following a standard procedure described in detail elsewhere (see, e.g., Ref. 16 and references therein), both samples were prepared by reacting in air at 930 • C for 20 h stoichiometric proportions of thoroughly mixed powders of La 2 O 3 , SrCO 3 , and CuO (99.99% purity). Sample 1 was reacted up to ten times with intermediate grindings in an agate mortar.…”

“…Such a number of grind-react (G-R) processes was shown to be enough to attain a superconducting transition width close to the intrinsic one (associated to the random distribution of the Sr dopants). 16 However, to study the influence of the extrinsic structural and chemical inhomogeneities on the precursor diamagnetism, sample 2 was prepared in a slightly different way: on the one side, it has been subjected to only four G-R processes, so one may expect that this sample will have more chemical inhomogeneities and then more T c inhomogeneities. On the other hand, in order to obtain a smaller grain size, intermediate grindings were performed with a commercial grinder (Retsch, model PM 100).…”

“…The relevance of these intrinsic-like T c inhomogeneities on the measurements of the precursor diamagnetism was probed in recent experiments in the LSCO system. 16 The debate about the nature of the precursor diamagnetism in underdoped cuprates has been recently reopened by new measurements and analyses, some of which were again performed in LSCO compounds, which seemingly confirm the intrinsically anomalous behavior of their magnetization above T c . [17][18][19] These anomalies include a huge and fielddependent diamagnetism close to the average T c and an increase with the temperature of the so-called upturn magnetic field, H up , at which the differential magnetic susceptibility changes from negative to positive with increasing applied magnetic field, a behavior that cannot be explained by a Gaussian T c distribution.…”

“…20 The results summarized above stress the interest to further study the influence of different inhomogeneities on the precursor diamagnetism in underdoped cuprate superconductors, in particular complementing our previous works on that issue. [13][14][15][16] This is the central aim of our present paper where we will first present magnetization measurements in two underdoped granular samples of the same nominal composition, La 1.9 Sr 0.1 CuO 4 (LSCO-0.1), but with different structural and chemical disorder due to differences in the synthesis. These differences lead, in particular, to different x-ray diffraction linewidths and superconducting transition widths.…”