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IBM Journal of Research and Development

Issue 1 • Date Jan. 1962

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Displaying Results 1 - 25 of 31
  • Foreword to papers in this issue [Fundamental Research in Superconductivity]

    Publication Year: 1962 , Page(s): 2
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    Freely Available from IEEE
  • Review of the Present Status of the Theory of Superconductivity

    Publication Year: 1962 , Page(s): 3 - 11
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (741 KB)  

    Theory and experiment are compared for a number of phenomena in superconductors. While the agreement is generally good, there are some discrepancies for which there is no adequate explanation. View full abstract»

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  • On the Influence of Free Path on the Meissner Effect

    Publication Year: 1962 , Page(s): 12 - 13
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (302 KB)  

    The influence of impurities on the behaviour of a superconductor is computed by introducing a scattering potential and averaging over all positions of the scattering centers. This procedure only takes into account scattering and free path effects and neglects changes in the elastic constants and electron density due to actual impurities. Using perturbation theory, it is shown that the free energy and the static Meissner effect are not influenced by scattering. View full abstract»

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  • Solutions of the BCS Integral Equation and Deviations from the Law of Corresponding States

    Publication Year: 1962 , Page(s): 14 - 23
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (795 KB)  

    The BCS integral equation has been studied for nonseparable interactions of the Bardeen-Pines form, V(|εε’|). Numerical solutions were obtained using an IBM 7090 for a simple interaction of this form which included the effect of the Coulomb repulsion. The results for the ratio of the energy gap to the critical temperature and for the temperature dependence of the energy gap, the electronic specific heat, and the critical field in terms of the proper reduced quantities were rather insensitive to the form or strength of the interaction. This indicates that the BCS theory gives the law of corresponding states. The calculated ratio of energy gap to critical temperature varies with the ratio of critical temperature to the Debye temperature, and this variation is of the correct order of magnitude if the Coulomb interaction is included. The same model is used to study the isotope effect. With the plausible assumption that the Coulomb cutoff is independent of the ionic mass, there are deviations from the M−½ law that are larger for small TcD superconductors. View full abstract»

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  • Nuclear Spin Relaxation in Superconducting Cadmium

    Publication Year: 1962 , Page(s): 24 - 26
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (415 KB)  

    The nuclear spin-lattice relaxation time, T1, in superconducting cadmium has been measured in the range of 0.37°K to 0.6°K. A field-cycling method was used. The results are explained by the theory of Bardeen, Cooper, and Schrieffer, and give another confirmation of the theory. The temperature dependence of T1 in cadmium is identical to that in aluminum, which is surprising in view of the different crystal symmetry and band structure of the two metals. View full abstract»

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  • Experimental Work on Superconductivity

    Publication Year: 1962 , Page(s): 27 - 30
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (473 KB)  

    The high thermal conductivity in the superconductive state at low reduced critical temperatures has been used for the detection of metal imperfections, including those caused by radiation damage. A statistically disordered single crystal of Ta with 30% Nb has also been investigated. Work is described on specific heats, ultrasonic attenuation and on the behaviour of thin superconductive films. An experiment for observing quantization of persistent currents is described. View full abstract»

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  • The Kapitza Resistance of Metals in the Normal and Superconducting States

    Publication Year: 1962 , Page(s): 31 - 33
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (341 KB)  

    A calculation has been made of the transfer of heat across a metal-liquid helium interface. In the normal state an appreciable transfer of energy occurs directly from the conduction electrons to the phonons of the fluid. Three mechanisms have been considered: the phonon-electron interaction within the metal, the modulation of the position of the interface and the phonon-electron interaction of the electrons which have tunnelled into the helium. All appear to be important. In the superconducting state each of these becomes ineffective at temperatures appreciably below the transition temperature and, consequently, the heat flow is reduced. The effect is sensitive to band structure and to the anisotropy of the energy gap. View full abstract»

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  • Superconductivity and Electron Tunneling

    Publication Year: 1962 , Page(s): 34 - 43
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (776 KB)  

    Experiments on the tunneling of electrons through a thin dielectric layer separating two superconducting metals are reported. Data are presented for the pairs Al-Pb, Sn-Pb, and In-Sn. Particular attention is paid to the form of the tunneling current vs voltage characteristics and to the changes observed as a function of temperature. Experimental details relative to the measurement techniques, the preparation of the samples, and the preparation of the dielectric layers are presented. An analysis of the problem is presented which is based on the simple, one-dimensional model of the electron energy spectrum of a superconductor given by the theory of Bardeen, Cooper, and Schrieffer. Close quantitative agreement is obtained between the results of the calculations and the observed characteristics. View full abstract»

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  • Magnetic Field Dependence of the Superconducting Energy Gap in Ginzburg-Landau Theory with Application to Al

    Publication Year: 1962 , Page(s): 44 - 48
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (507 KB)  

    A theoretical calculation is given of the magnetic field dependence of the superconducting energy gap, using the Ginzburg-Landau theory. In addition to depending upon the size of the specimen, the field dependence of the energy gap depends quite strongly on the nature of the boundary conditions. For the usual case with the magnetic field equal on opposite sides of a film, the calculations show that for a ratio of thickness, d, to penetration depth, λ, less than √5, the energy gap goes smoothly to zero as the critical field is approached—a second-order phase transition. When d/λ > √5, the energy gap approaches a finite value as the critical field is approached—a first-order phase transition. Energy-gap measurements for aluminum agree very well with these calculations. When one changes the boundary conditions so that the magnetic field is constrained to be zero on one side of the film, the theory predicts a very different behavior. For this case, at all thicknesses, the energy gap approaches a finite value as the critical field is approached—a first-order phase transition. An experiment involving cylindrical films is proposed to test this latter case. It is shown that in this proposed experiment these boundary conditions are appropriate for predicting the current dependence of the energy gap. View full abstract»

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  • Dependence of the Energy Gap in Superconductors on Position and Magnetic Field

    Publication Year: 1962 , Page(s): 49 - 54
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (654 KB)  

    A review is given of work concerning the decrease of the energy gap in superconductors when a magnetic field is applied. The absence of any observable effect in previous spectroscopic work is explained, and conditions for large effects are outlined. Experimental measurements on thermal conductivity and microwave absorption in films in a magnetic field are described. The results show that in thin films, the gap can be depressed continuously to zero, yielding a second-order phase transition. In thicker films, the gap can be only partially depressed before the transition, and the transition is of first order. These results agree with those obtained theoretically by Douglass from the Ginzburg-Landau-Gor'kov theory, and experimentally, by electron tunnelling. An attempt to generalize the Ginzburg-Landau-Gor'kov theory to cope with the case when ε0/kT ≫ 1 is then indicated. In this phenomenological theory, the normalized gap ε(H)/ε(0) is taken as an order parameter ω, and the free energy is assumed to contain a term in ξ02 |∇ω|2 , as well as a free energy density f(ω) and magnetic energy κ(ω)H2. Some success is found. View full abstract»

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  • Far-Infrared Absorption in a Lead-Thallium Superconducting Alloy

    Publication Year: 1962 , Page(s): 55 - 57
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (394 KB)  

    Preliminary measurements have been made of the absorption of far-infrared radiation in the surface of a bulk superconducting alloy composed of lead with 10.0 atomic percent thallium at 1.4K. The results indicate that the gap edge is quite distinct, in contrast to previous results of Richards and Tinkham on other alloys. The sharpness of the gap edge is thought to be characteristic of alloys which are homogeneous and have no trapped magnetic flux. Alloying narrows the observed gap width by about the same ratio as the critical temperature, and by an amount which is much smaller than that predicted by Suhl and Matthias from a simplified model. The subsidiary absorption maximum below the gap edge, which has been seen previously in pure lead, is also present in the alloy. This lends support to other evidence that it is not due to crystalline anisotropy. View full abstract»

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  • Ultrasonic Attenuation in Superconductors

    Publication Year: 1962 , Page(s): 58 - 62
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    A brief review is given of the ultrasonic attenuation in metals arising from direct interaction of the elastic waves and conduction electrons, and the physical variables on which it depends. The drop in attenuation of longitudinal waves on entering the superconducting state is in good agreement with BCS theory, the various factors combining to make the relative attenuation, αsn, depend only on the energy gap; the measurements give evidence, however, for gap anisotropy or the presence of more than one gap. Recent measurements at Brown by Claiborne of shear wave attenuation in single-crystal Al, are in good agreement with a theory based on the Boltzmann and London equations. The steep drop at Tc is produced by shorting out of electromagnetic waves by supercurrents; the residual attenuation results from the effects of collision drag. View full abstract»

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  • The Magnetic Behavior of Superconductors of Negative Surface Energy

    Publication Year: 1962 , Page(s): 63 - 67
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (540 KB)  

    Abrikosov and the author have separately suggested that a new type of reversible magnetic behavior is to be expected in superconductors whose coherence length is small compared with their penetration depth. The treatments of these two authors are shown to lead to similar results for pure metals and to only slightly different results for alloys. The experimental evidence in favor of a new type of reversible magnetic behavior in superconductors is discussed. View full abstract»

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  • Effects of Electron Concentration and Mean Free Path on the Superconducting Behavior of Alloys

    Publication Year: 1962 , Page(s): 68 - 70
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (326 KB)  

    A brief review is given of the superconducting behaviour of solid-solution alloys. Intermetallic compounds are not considered but some reference is made to secondary solid solutions. Two topics are discussed: some factors affecting the transition temperature, and the role played by surface energy between normal and superconducting regions. View full abstract»

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  • Surface Energy Effects at the Boundary between a Superconductor and a Normal Conductor

    Publication Year: 1962 , Page(s): 71 - 74
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (375 KB)  

    Films of tin ranging from 500 to 1400 Å in thickness have been prepared in pairs by vacuum deposition onto rotating cylindrical glass and metal substrates. The temperature dependence of the critical fields has been measured. The critical temperatures of the films on metal substrates are all depressed. Their critical fields at absolute zero, however, are usually not depressed but can be higher than those of the corresponding films on glass. This increase can be explained by a negative surface energy arising from a short mean free path of the superconducting electrons in an incidental oxide layer at the surface of the metal. Most of the films on glass had an abnormally small value of the critical field at absolute zero. View full abstract»

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  • Some Elementary Theoretical Considerations Concerning Superconductivity of Superimposed Metallic Films

    Publication Year: 1962 , Page(s): 75 - 76
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (337 KB)  

    A microscopic theory of superconductivity of superimposed metallic films is proposed, based on the fact that the electron pair correlation function penetrates into a normal metal where the electron-electron interaction would not by itself produce a superconducting state. View full abstract»

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  • Thermodynamic Consistency of Magnetic and Calorimetric Measurements on Superconductors

    Publication Year: 1962 , Page(s): 77 - 81
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    Comparison of the entropy and specific heats of normal and superconducting tin and indium as computed from critical field and calorimetric measurements shows excellent consistency. Salient features of the comparison are briefly summarized. Some implications of the recently reported specific heat anomaly for indium are discussed. View full abstract»

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  • The Temperature and Pressure Dependence of Critical Field Curves

    Publication Year: 1962 , Page(s): 82 - 83
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    A brief discussion is given of the analysis of recent critical field measurements. In particular, a negative volume coefficient of thermal expansion is predicted for tin in the superconducting state. View full abstract»

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  • Mechanical Effects at the Superconducting Transition

    Publication Year: 1962 , Page(s): 84 - 88
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (497 KB)  

    Work in Zürich on the difference in size and in expansion coefficient between the normal and the superconducting states is summarized. The volume dependences of the critical temperature and of the electronic density of states at the Fermi surface are discussed. View full abstract»

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  • Variation of the Elastic Moduli at the Superconducting Transition

    Publication Year: 1962 , Page(s): 89 - 93
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    Using an ultrasonic technique capable of measuring changes in the elastic moduli as small as one part in 107, the small modulus changes associated with the normal-to-superconducting transition have been measured as a function of both temperature and magnetic field. Single-crystal specimens of the cubic metals Pb, V, Nb and Ta were used and all their elastic moduli measured so that changes in the bulk modulus and Debye θ could be computed. The results showed that changes in the zero-point energy of the lattice can be far from negligible. Furthermore, the shear moduli are the most changed by the appearance of superconductivity. View full abstract»

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  • First- and Second-Order Stress Effects on the Superconducting Transitions of Tantalum and Tin

    Publication Year: 1962 , Page(s): 94 - 111
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1398 KB)  

    The shift of critical field of a single-crystal wire under uniaxial tension is studied for Ta and Sn. For Ta the shift is nonlinear and gives both the first-order critical field-stress coefficient and a particular combination of second-order coefficients. By combining with other data, the three second-order constants are estimated. The smaller first-order coefficient of Sn is found to be considerably smaller than previous estimates. Both Ta and Sn are found to satisfy a similarity condition for the coefficients, but of a less restrictive form than usual. Similarity is used to predict the behavior of jumps in elastic constant moduli at the transition in Ta. The general formal theory of the first-and second-order coefficients is formulated and many special cases are given. The general thermodynamic relations at the transition between jumps in strain and elastic constants and the various coefficients, are derived. It is shown that BCS theory implies similarity. View full abstract»

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  • Thermal Conductivity of Dilute Indium-Mercury Superconducting Alloys

    Publication Year: 1962 , Page(s): 112 - 115
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (437 KB)  

    Thermal conductivities were measured for a series of polycrystalline alloys of indium containing 0.1 to 2.5 At.% mercury. Using theoretical models which relate the electronic thermal conductivity of a superconductor to its energy gap, the temperature and composition dependences of the energy gap have been calculated for these specimens. Estimates of the lattice thermal conduction were also obtained. View full abstract»

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  • The Superconductivity of Some Intermetallic Compounds

    Publication Year: 1962 , Page(s): 116 - 118
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (374 KB)  

    The W-Os, Re-W, Re-Mo, Re-Hf, and Mo-Hf binary systems were investigated for superconductivity down to 1°K. Several new superconducting regions were found with the most significant occurring in the primary and terminal solid-solution alloys. The occurrence of superconductivity in the β-phase field of the Re-Hf and Mo-Hf binaries indicates a possible explanation for the spurious superconducting effects sometimes observed in elemental hafnium. View full abstract»

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  • High-Field Superconductivity in Some bcc Ti-Mo and Nb-Zr Alloys

    Publication Year: 1962 , Page(s): 119 - 121
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (434 KB)  

    Zero electrical resistance at unusually high magnetic field strengths has been observed in the bcc alloys Ti-16 a/o (atomic percent) Mo, Nb-12 a/o Zr, and Nb-25 a/o Zr. The maximum high-field zero-resistance current density, Jc, in these alloys appears to be a sensitive function of temperature, the degree of cold-working, and the orientation of the applied transverse magnetic field. For cold-rolled alloy specimens in an applied transverse field, Jc is a maximum or minimum, according to whether the field is set respectively parallel or perpendicular to the rolled face of the specimen. In Ti-16 a/o Mo the zero-resistance condition is observed in fields at least a factor 35 greater than the bulk material critical field as inferred from calorimetric data. View full abstract»

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  • Anomalous Resistive Transitions and New Phenomena in Hard Superconductors

    Publication Year: 1962 , Page(s): 122 - 125
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (441 KB)  

    The value of the critical current (Ic)-critical field (Hc) of cold-worked Nb, Mo-Re and Nb-Zr wires at constant temperature is not a single-valued function of the field and current direction. The previous history of a specimen during an experiment plays an important role and a measurement of the critical field-critical current value can influence the response of the specimen to subsequent measurements. Anomalous resistive transitions are observed when Ic vs Hc curves are determined by proceeding from low to high fields which may not occur in measurements proceeding from high to low fields. Further, it is possible to condition a specimen to enable it to reach maximum values of the critical field and critical current. This phenomenon is also encountered in the operation of superconducting solenoids. The polarity of the field and current during this treatment is found to be significant. The effects of the rate increase of the current, of rotating the specimen in a transverse field, and of current density and temperature have also been studied. View full abstract»

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The IBM Journal of Research and Development is a peer-reviewed technical journal, published bimonthly, which features the work of authors in the science, technology and engineering of information systems.

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IBM T. J. Watson Research Center