Specific Heat of Granular Aluminum Films

Greene, R. L.; King, Christopher N.; Zubeck, R.; Hauser, J. J.

doi:10.1103/physrevb.6.3297

Cited by 56 publications

(18 citation statements)

References 27 publications

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“…In these respects the specimen is obviously much better than those for which heatcapacity results have been published previously. 8 * 10 We therefore have reason for considerable confidence in our method of specimen prepara- The other curves show that as p N increases T c (c) goes down and the heat-capacity transition diminishes. In another specimen, with 40xl0~3 Q, cm, the heat-capacity transition is too small to be observed in our experiment, i.e., less than about 15% of the BCS value.…”

Section: G Deutschermentioning

confidence: 88%

Heat-Capacity Measurements of the Critical Coupling between Aluminum Grains

1978

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We have measured the heat capacity of granular aluminum specimens with normalstate resistivities p N between 0.6xl0~3 and 40xl(T 3 fi cm. The specimens become superconducting with a heat-capacity transition which is BCS-like for the lowest p A , and then diminishes until it is no longer observable for the highest p Nm We conclude that the grains become decoupled such that, because of their small size, they do not exhibit bulk superconductivity when they are isolated.When aluminum is evaporated in the presence of oxygen it deposits in the form of metallic grains surrounded by insulating oxide. With increasing oxygen pressure the oxide barrier becomes thicker, the grains become increasingly decoupled, and the room-temperature normalstate resistivity p N of the specimen increases. For p N larger than 1(T 4 Q cm the grain size remains constant at about 30 A. 1 ' 2 We have made measurements on a series of granular aluminum films which show that the discontinuity in the heat capacity, which is characteristic of bulk superconductivity, is there to its full extent only in the specimen with the lowest value of p N (0.6 xlO" 3 £2 cm). In the specimens with greater p N the change in the heat capacity becomes smaller, and occurs at a lower temperature and over a wider temperature interval, until for the specimen with the highest value of p N (40 xlO" 3 £2 cm) it is no longer observable. We were thus able to show that when the grains are isolated they show no heat-capacity transition and that they are, therefore, smaller than the characteristic size below which bulk superconductivity cannot occur in isolated grains. 3 " 8 In addition, our results show that there is a rather narrow range of values of p N , corresponding to a small change in composition, 7 such that on one side of 316

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Section: G Deutschermentioning

confidence: 88%

Heat-Capacity Measurements of the Critical Coupling between Aluminum Grains

1978

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“…167 The superconducting density of states N s in the fluctuation region was determined from tunneling measurements. 198 and Filler et al 19 * 12. 49.…”

Section: )mentioning

confidence: 97%

Granular Metal Films

Abeles

1976

Applied Solid State Science

215

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“…The dimensionless GL parameter K12 is related to Pn' the normal-state electrical resistivity, by K=Ko +7.5XlO-3 y l12 Pn , (1) where Ko is an instrinsic material constant, y is the temperature coefficient of the electronic specific heat (ergs/cml °K2), and Pn is the electrical resistivity (;in cm). Thus, a spatial variation of the electrical resistivity P n , caused by a higher density of dislocations in the cell walls relative to the cells, results in a spatial variation in K by OK(X) = 7.5 X lO-ly 1I2oPn (x).…”

Section: Modelmentioning

confidence: 99%

Effects of plastic deformation on the superconducting specific-heat transition of niobium

Zubeck

Barbee

Geballe

et al. 1979

Journal of Applied Physics

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Effects of plastic deformation on the normal, zero-field, and mixed-state specific heat of the type-II superconductor niobium were experimentally investigated. A high-resolution ac calorimetry technique was developed and used to study the effects of plastic deformation on the specific-heat superconducting transition in fields up to 2750 Oe. A method for the analysis of high-resolution specific-heat data near the superconducting transition is presented and used to determine κ variations (within a material) caused by plastic deformation. The effects of plastic deformation on the bulk superconducting transition temperature and width are also shown. Measurements of the zero-field specific heat show a systematic increase in width of the specific-heat transition with increasing deformation as well as a small increase in Tc. Both κ and the κ variation increase with increasing plastic deformation. The analysis method allows the specific-heat data of the mixed state to be decomposed in a way consistent with previously reported anisotropy data for niobium.

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Specific Heat of Granular Aluminum Films

Cited by 56 publications

References 27 publications

Heat-Capacity Measurements of the Critical Coupling between Aluminum Grains

Heat-Capacity Measurements of the Critical Coupling between Aluminum Grains

Granular Metal Films

Effects of plastic deformation on the superconducting specific-heat transition of niobium

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