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It is known that some (BEDT-TTF) 2 X layered organic superconductors undergo a glassy transition near 80 K. Our purpose is to exploit quenched disorder to get new insights on both the superconducting state (T ≤ 12 K) and the glassy transition by studying the superconducting properties as functions of annealing time (t a ) and temperature (T a 1) The data can be described by a percolation cluster model. 2) At short time scales, the clusters grow with t a following a power law. 3) At large time scales the clusters grow toward a thermodynamic state following a stretched exponential law However, we emphasize that the low-temperature state contains some amount of quenched disorder that strongly depends on the anion, the applied pressure, the cooling conditions and, more importantly, on whether the ethylene groups are formed by hydrogen bonds (denoted H8-Br) or deuterium bonds (denoted D8-Br). This is why the exact nature of the 80 K anomaly and the associated low-temperature superconducting state are still not understood.)As a matter of fact, D8-Br exhibits several puzzling superconducting properties. Some of these properties were ascribed to the appearance of a magnetic transition at low temperature (10-20 K), the meaning of which is unclear: Several mechanisms have been proposed including spin-density waves 13 , spin canting 12 , or the suppression of superconductivity by dispersed magnetic ions associated with the persistent disorder 14 . Also, some authors 7,8 3 ascribed the decrease of the apparent superconducting volume to an increase in λ (the inplane penetration depth) through mean-free-path effect 7 .However none of these mechanisms is able to explain, even qualitatively, the following experimental facts: 1) The fact that the apparent magnetic critical current density j c (as deduced from the Bean model) always decreases as the degree of quenched disorder increases.2) The low-field susceptibility also decreases in the same experimental conditions.To account for such a decrease, one is led to assume that λ can reach unphysical values, as high as 0.1 mm [8] (and much more if applied to the present results). 3) Despite these large changes in the apparent j c and λ , T c stays almost constant. 4) As the quenched disorder is increased; one observes: firstly, the appearance of increasing irreversibilities at H << H c1 (for instance, H = 0.1 Oe and T = 2 K), secondly, a large broadening of the superconducting transition.One of the purposes of this work is to prove that all of these features can naturally be explained in the framework of a granular model and the associated weak links connecting the grains.We have investigated the ac magnetic susceptibility and the dc magnetization of the superconducting phase after performing a series of thermal treatments on a D8-Br singlecrystal of dimension ~ 1 × 1 × 0.25 mm 3 . To this end, we annealed the sample inside the SQUID cryostat at different fixed temperatures T a ranging from 65 to 110 K. Moreover, in order to carefully monitor the development of ethylene or...

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We report investigations of the low temperature (2 K < T < 15 K) ac susceptibility and the magnetization of the fully deuterated organic superconductor κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br. Our measurements were performed after successive annealing at high temperature in the region 65 K < T a < 110 K where the ethylene molecules undergo some kind of order disorder transition. The annealing time t a was varied from few seconds to about 2×10 6 s. The superconducting state can be described by a distribution of percolating clusters grown during annealing in the transition region. The spatial structure of such clusters and their relaxation times (in the transition region) obey essentially the same scaling laws and the same stretched exponential relaxation as in Ising spin glasses. The data are described by a granular model in which the grain radius r is equal to the average radius of the clusters. At the lowest fields and temperatures the clusters are coupled via Josephson junctions. 1 Introduction We report systematic investigations of the relationship between the superconducting properties (T c = 11.5 K) and the structural transition occurring around 80 K in the fully deuterated organic salt κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br. As it is known [1-13], organic conductors of this family behave like semi-conductors at high enough temperature and undergo a transition toward a metallic state at some intermediate temperature of order 70-80 K. On the other hand, at very high temperature the ethylene molecules oscillate rapidly and independently between two equivalent conformations. Upon cooling, these thermal fluctuations gradually slow down and simultaneously a long-range order among the ethylene groups builds up [7,8]. However, what is important to emphasize is the fact that the low temperature state (T < 50 K) is never completely ordered in laboratory realizable conditions. As a consequence, the persistent disorder strongly controls the magnetic and the transport properties. In addition, the remnant disorder strongly depends on whether the ethylene groups are formed by hydrogen bonds (denoted H8-Br here) or deuterium bonds (denoted D8-Br). Note that due to the lack of space we shall limit the present study to D8-Br. To help clarify this complicated situation, we therefore exploit the extreme sensitivity of the superconducting properties to any type of disorder. However, to take advantage of this disorder we must first identify its exact nature. We can indeed consider two limiting disordered structures having opposite effects on the superconducting state:(1) The most usual, the most referred to in the literature on superconductivity and the simplest disorder is exemplified by columnar defects, precipitates or punctual defects diluted in a perfect crystal. This kind of

Despite its appearance in physics around the 1850th, the second law of thermodynamics is still attracting more efforts to be clarified. More specifically, fifteen years later (1865) after its definition and introduction, entropy has been the subject of various interpretations. Hence, in physical sciences and notably in different education levels, its concept seems to be relatively tough to unambiguous decipher. In this work, we reintroduce the notion of entropy from classical, quantum and information theories viewpoints. The controversial over entropy and a measure of disorder misconception, stated by many scientists, is addressed as well to come up with less confusing physical interpretation of entropy. Hence, over time, an increase of entropy, a quantitative quantity, is most often associated to a rising of disorder, a non-quantitative quantity and no value-returning mathematical equation, rather than a continuously increasing of hidden data. In other words, linking disorder to hidden data is typically raising more confusion than clarification. Here, we shed more light on both concepts to find out an acceptable interpretation of entropy.