Ultrasonic studies of the electronic structure of hexagonal metal crystals II. Superconducting state in zinc and cadmium

1973 ◽  
Vol 334 (1598) ◽  
pp. 379-396 ◽  
Keyword(s):  
Electronic Structure ◽  
Simple Model ◽  
Temperature Dependence ◽  
Energy Gap ◽  
Realistic Model ◽  
Pure Zinc ◽  
The Third ◽  
Energy Gaps ◽  
Gap Parameter ◽  
Complicated Variation

Measurements have been made of the temperature dependence of the attenuation of longitudinal ultrasound in the superconducting states of pure zinc and cadmium for propagation along the and <0001>, <101 ¯ 0> and <112 ¯ 0> directions, at frequencies from 40 to 160 MHz. This temperature dependence has been interpreted in terms of an energy gap parameter A = 2∆(0)/ kT c . In zinc, for T < ½ T c , A was found to be 3.41 ± 0.1, 3.79 ± 0.1 and 3.64 ± 0.1 for the <0001>, <101 ¯ 0> and <122 ¯ 0> directions respectively. The corresponding values for cadmium were 3.29 ± 0.1, 2.80 ± 0.1 and 3.87 ± 0.1. A simple model proposed by Hays for the distribution of the energy gaps on the Fermi surface of zinc does not explain these results, and a more realistic model has been proposed. The main features of the proposed energy-gap distributions in zinc and cadmium are that the electrons on the third band lens have larger energy gaps than those on the second band monster, over which there is a large and complicated variation.

TUNNELING MEASUREMENTS ON SUPERCONDUCTORS WITH ISOTROPIC ENERGY GAPS

1967 ◽  
Vol 45 (4) ◽  
pp. 1541-1548 ◽  
Author(s):  
D. G. Walmsley ◽  
C. K. Campbell
Keyword(s):  
Thin Films ◽  
Temperature Dependence ◽  
Energy Gap ◽  
Pure Metal ◽  
Isotropic Energy ◽  
Bulk Superconductors ◽  
Energy Gaps ◽  
Gap Anisotropy ◽  
Gap Parameter

The energy-gap anisotropy found in bulk superconductors is considerably reduced in thin films whose thickness, d, is much less than the range of coherence, ξ0, of the pure metal from which they are fabricated. By preparing such thin films of tin, indium, and lead, we have been able to examine the temperature dependence of the energy gap in each above 1.2 °K, using the tunneling technique. Values of the energy-gap parameter 2Δ(0)/kTe are given as 3.67 ± 0.07 and 3.87 ± 0.08, for tin and indium respectively, while the energy gap for lead is estimated to be 2ΔPb(0) = 2.70 ± 0.02 meV.

Temperature dependence of the energy gap in superconducting Al–Al2O3–Al tunnel junctions

1968 ◽  
Vol 46 (2) ◽  
pp. 141-145 ◽  
Author(s):  
B. L. Blackford ◽  
R. H. March
Keyword(s):  
Temperature Dependence ◽  
Energy Gap ◽  
Tunnel Junctions ◽  
Small Deviation ◽  
Mean Value ◽  
Bcs Theory ◽  
Energy Gaps ◽  
The Mean ◽  
Gap Values

The most detailed measurements of the energy gap in Al by the tunneling technique have been made using Al–Al2O3-Pb junctions. Determination of the energy gaps from the I–V curves of these junctions is more precise than previous results using Al–Al2O3–Al tunnel junctions. The chief difficulty with the Al–Al2O3–Al junctions has been the lack of definition in the I–V curves, especially near Tc. Al–Al2O3–Al junctions, in which the energy-gap voltages can be read from the I-V curve with very little ambiguity up to T/Tc ≈ 0.99, are reported here. For the majority of the junctions studied, the temperature dependence of the normalized gap Δ(t)/Δ(0) shows very little scatter (T = 0.34 °K to T = Tc) and agrees closely with the BCS theory. However, a consistent small deviation is observed, with the measured gap values being slightly higher than the BCS prediction. The mean value of 2Δ(0)/kBTc obtained from 21 different junctions is 3.53 with an r.m.s. deviation of ± 0.02.

Energy Gaps Induced by a Semiconducting Substrate in the Epitaxial Graphene Density of States

2013 ◽  
Vol 740-742 ◽  
pp. 141-144
Author(s):  
Sergey Yu. Davydov ◽  
Alexander A. Lebedev ◽  
Sergey P. Lebedev
Keyword(s):  
Simple Model ◽  
Density Of States ◽  
Energy Gap ◽  
Epitaxial Graphene ◽  
Layer Graphene ◽  
Energy Gaps ◽  
The One ◽  
Semiconducting Substrate

The simple model for the one-layer graphene energy gaps induced by the substrate energy gap is pro-posed.

Ultrasonic attenuation in white tin crystals

1967 ◽  
Vol 297 (1450) ◽  
pp. 408-423 ◽  
Keyword(s):  
Fermi Surface ◽  
Energy Gap ◽  
Ultrasonic Attenuation ◽  
Propagation Direction ◽  
Frequency Range ◽  
Weighted Averages ◽  
Conduction Electrons ◽  
Energy Gaps ◽  
Surface Measurements ◽  
Gap Parameter

A detailed study of the temperature dependence of the longitudinal ultrasonic attenuation in single crystals of white tin is presented. Measurements have been made at temperatures from 0⋅8 to 4⋅2°K on pure and impure samples in the frequency range 40 to 290 Mc/s, corresponding to ql e values 0⋅45 to 90, where q is the ultrasonic wave vector and l e the free path of the conduction electrons. For high ql e an energy gap parameter A = 2∆(0)/ kT c is measured as an average over a narrow effective zone of the Fermi surface. For propagation along <001>, A = 3⋅15 ± 0⋅04; along <310>, A = 4⋅24 ± 0⋅04; along <100>, A = 3⋅55 ± 0⋅04; along <110>, A = 3⋅84 ± 0⋅07. The results are interpreted by assigning different energy gaps to different zones of the Fermi surface. Measurements with ql e ~ 0⋅5 yield A = 3⋅47 ± 0⋅06, independent of the propagation direction, showing that the effective zone extends to the whole Fermi surface for such low ql e . A simple two-gap model of a superconductor is used to show that the gaps measured here are weighted averages over an effective zone, and not minima. At lower temperatures the attenuation is shown to depend on the minimum gap, in agreement with the analysis of Privorotskii, but to be negligibly small for tin.

19F Nuclear Quadrupole Coupling in some Halomethanes

1986 ◽  
Vol 41 (1-2) ◽  
pp. 171-174 ◽  
Author(s):  
M. Frank ◽  
F. Gubitz ◽  
W. Ittner ◽  
W. Kreische ◽  
A. Labahn ◽  
...  
Keyword(s):  
Angular Distribution ◽  
Simple Model ◽  
Temperature Dependence ◽  
Coupling Constants ◽  
Temperature Dependent ◽  
Distribution Method ◽  
Quadrupole Coupling ◽  
Time Differential ◽  
Nuclear Quadrupole

The 19F quadrupole coupling constants in CF4, CHF3, CClF3 and CHClF2 are reported. The measurements were carried out temperature dependent using the time differential perturbed angular distribution method (TDPAD). The temperature dependence can be satisfactorily described in the framework of the Bayer-Kushida theory. A simple model is used to explain the appearance of H-F and Cl-F coupling constants in CHF3/CHClF2 and CClF3, respectively.

Temperature dependence of the electron energy gap of highTCsuperconductors studied by work function spectroscopy

1994 ◽  
Vol 64 (13) ◽  
pp. 1726-1728
Author(s):  
S. Westermeyr ◽  
R. Müller ◽  
J. Scholtes ◽  
H. Oechsner
Keyword(s):  
Temperature Dependence ◽  
Work Function ◽  
Electron Energy ◽  
Energy Gap

Temperature Dependence of Optical Energy Gap of Gallium Selenide

2001 ◽  
Vol 8 (3-4) ◽  
pp. 251-259 ◽  
Author(s):  
M. Kepinska ◽  
M. Nowak ◽  
Z. Kovalyuk ◽  
R. Murri
Keyword(s):  
Temperature Dependence ◽  
Energy Gap ◽  
Gallium Selenide ◽  
Optical Energy Gap ◽  
Optical Energy

Light-Emitting Diodes Based on Conjugated Polymers: Control of Colour and Efficiency

1992 ◽  
Vol 247 ◽  
Author(s):  
Paul L. Burn ◽  
A. B. Holmes ◽  
A. Kraft ◽  
A. R. Brown ◽  
D. D. C. Bradley ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Conjugated Polymers ◽  
Light Emitting Diodes ◽  
Fold Increase ◽  
Transport Layer ◽  
Electron Transport Layer ◽  
Metal Contacts ◽  
Light Emitting ◽  
Lithographic Patterning ◽  
Energy Gaps

ABSTRACTStudies of the effect of different electrode combinations on the device characteristics of simple three layer light-emitting diodes (LEDs) prepared with poly(ρ-phenylenevinylene) (PPV) as the emissive layer sandwiched between two metal contacts have shown that it is generally more difficult to inject electrons than holes. In order to improve the efficiency of such devices it is, therefore, necessary to develop methods to enhance the injection of electrons and we illustrate here one example where we have successfully achieved this by the introduction of a further, electron transport, layer. The result is an eight fold increase in efficiency over our best three layer PPV devices. The efficiency is also dependent on the details of the polymer electronic structure and using a family of copolymers we have been able to produce enhancements in efficiency to values of up to 30 times that of the corresponding PPV devices. Variations in the polymer electronic structure also affect the colour of emission and the same family of copolymers allow control of emission colour from blue/green to orange/red. Supramolecular control of the copolymer electronic structure can be achieved by lithographic patterning and we show that it is possible to produce regions within a single polymer film that possess different π-π* energy gaps.

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