New Results on the Anomalous Precursor Diamagnetism in the Underdoped La1.9Sr0.1CuO4 Superconductor

Abstract

The new results summarized here, including a brief comparison with the paraconductivity, further suggest that the anomalous precursor (above T c ) diamagnetism recently observed in the underdoped La 1.9 Sr 0.1 CuO 4 superconductor could be attributed to the presence, in addition to the conventional superconducting pair fluctuations, of T c -inhomogeneities with long characteristic lengths associated with chemical disorder .

The conductivity and the magnetization around T c in optimally-doped YBa2Cu3O7-δ revisited: quantitative analysis in terms of fluctuating superconducting pairs

“…These anomalous roundings concern not only the in-plane magnetization [38][39][40][41] and the dc in-plane electrical conductivity [42,43] 7 , but also other observables [44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60], particularly the Nernst effect [41,[45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60]. Although some of these anomalies could in fact be attributed to T c inhomogeneities associated with the presence of chemical disorder with long characteristic lengths (larger than the superconducting coherence length amplitude), unavoidable in non-stoichiometric compounds [61][62][63][64][65][66][67]…”

The conductivity and the magnetization around Tc in optimally-doped YBa$_2$Cu$_3$O$_{7-δ}$ revisited: quantitative analysis in terms of fluctuating superconducting pairs

“…These anomalous roundings concern not only the in-plane magnetization [44][45][46][47] and the dc in-plane electrical conductivity [48,49], but also other observables, as the Nernst effect [47,[50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66]. Although some of these anomalies could in fact be attributed to T c inhomogeneities, associated with the presence of chemical disorder with long characteristics lengths (larger than the superconducting coherence length amplitude), unavoidable in non-stoichiometric compounds [67][68][69][70][71][72][73], most of the works published since then on that issue still attribute the measured rounding effects above T c to the opening of a pseudogap in the normal state. In this last scenario, the most popular mechanism is based on phase disordering.…”

“…[68][69][70][71][72][73] In addition, the layered nature of the HTSC and the complexity of their chemistry increases the relevance of these T c -inhomogeneities, whose influence may be particularly dramatic in compounds with doping different from the optimal. [67][68][69][70][71][72][73] Indeed, in the case of the theoretical approaches associated with the opening of a pseudogap in the normal state, these difficulties are further enhanced by the scarcity until now of quantitative theoretical proposals for the observed effects, in contrast with the GL approaches for the fluctuations of superconducting pairs. [3][4][5][6][7][8][9][10][28][29][30][31][32] Moreover, in the temperature region where these superconducting fluctuations, thermodynamiclike, are always present (typically below 2T c ), the corresponding rounding effects should be taken into account when considering other possible effects.…”

“…Moreover, the interest of our present results, in particular the extensions of the theoretical GGL scenario to high reduced temperatures, is also enhanced by their usefulness in future analyses at a quantitative level of the rounding effects around T c in underdoped and overdoped samples. However, as also stressed above, the unavoidable presence of chemical inhomogeneities [37,67,73], that lead to important inhomogeneities of T c , and also the possible entanglement with the effects associated with the opening of a pseudogap well above the measured T c , will add further difficulties when performing these analyses. In turn, these last conclusions further enhance the relevance of the prototypical OPT Y-123 to probe the phenomenological descriptions of the superconducting transition in cuprates.…”

“…Examples of recent works using such a relationship are the second work in Ref [59],. and Refs [64,67]…”