Fluctuating diamagnetism in underdoped high-temperature superconductors

Abstract

The fluctuation induced diamagnetism of underdoped high temperature superconductors is studied in the framework of the Lawrence-Doniach model. By taking into account the fluctuations of the phase of the order parameter only, the latter reduces to a layered XY-model describing a liquid of vortices which can be either thermally excited or induced by the external magnetic field. The diamagnetic response is given by a current-current correlation function which is evaluated using the Coulomb gas analogy. Our results are then applied to recent measurements of fluctuation diamagnetism in underdoped YBCO. They allow to understand both the observed anomalous temperature dependence of the zero-field susceptibility and the two distinct regimes appearing in the magnetic field dependence of the magnetization.

Diamagnetism above the superconducting transition in underdoped La1.9Sr0.1CuO4Mosqueira1, Dancausa2, Vidal3 2011Phys. Rev. B167290View full textAdd to dashboardCite

“…The strong sensitivity of the precursor diamagnetism to the presence of T c inhomogeneities, together with the fact that their doping makes most of the HTSC intrinsically inhomogeneous, would explain why an anomalous diamagnetism was observed above T c in a wide number of HTSC families and doping levels. [9][10][11][12][13][14][15][16][17][18][19] Note also that, although these inhomogeneity effects were already predicted up to ε inh in Ref. 13 (see the Fig.…”

“…Indirectly, these last results also support recent proposals that the large Nernst signal observed in the normal state in LSCO is not associated with superconducting fluctuations. 23,24 Nevertheless, the relevance that is being given at present to the precise location of T c in underdoped cuprates, and to the seeming disagreements between the values inferred from transport or magnetic measurements, 11,[17][18][19][20][21][22]39 make particularly desirable to extend our present magnetization measurements to the high reduced-temperature regime of cuprates with different dopings. For this task, our present results suggest the way to separate the intrinsic fluctuation effects from those due to a, symmetric or not, T c distribution.…”

“…The dashed lines in these figures are fits to Eq. (11), and lead to z values between 0.55 and 0.75. This effect was claimed to be an evidence of the unconventional nature of the superconducting transition of these materials.…”

“…The anomalies observed since then by various groups in different HTSC, including the La 1.9 Sr 0.1 CuO 4 compound, 9,10 fueled different theoretical proposals of unconventional (non-GGL) precursor diamagnetism, in some cases seemingly confirming the popular scenario of phase incoherent superconductivity up to the pseudogap temperature. [9][10][11][12] However, these anomalies were later easily explained in terms of T c inhomogeneities with long characteristic lengths associated to chemical disorder, which do not directly affect the superconducting transition's own nature. [13][14][15] In fact, as the diamagnetism in the superconducting state is orders of magnitude stronger than the one associated with fluctuating superconducting pairs, even the T c inhomogeneities inherent to the unavoidable random distribution of dopants could have a dramatic influence on the measurements.…”

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

“…The early interpretative attempts were due to Sewer and Beck [18] who described this phenomenology in terms of phase instabilities due to the formation of a vortex liquid, which can be either thermally excited, or induced by the magnetic field. Later on, following this idea, and by taking into account the initially neglected terms of the free energy functional, the model was extended [16,17] and the upturn in |M f l | at low field was justified from a phenomenological point of view.…”