List of Tables

• Selected properties of some of the high- T_c superconductors. dagger indicates a single-crystal measurement. The coherence length quoted for ceramic sample is an average one. NR means that the parameter was not reported in the cited reference.
• T_c values for C₈KHg as reported by several research groups. There is almost universal agreement on T_c 1.9 K.
• T_c values for C₄KHg as reported by several research groups. There is a great deal of scatter in the values, which seem to fall primarily into two groups, with most likely values being about 0.8 and 1.5 K. ^dagger indicates a broad superconducting transition. ^ddagger indicates a liquid-nitrogen quenched sample.[58]
• Parameters obtained from fits to the C₄KHg neutron diffraction data. N_Hg is the number of Hg atoms per 4 carbon atoms. Additional parameters for the hydrogenated sample: hydrogen position = 3.9 Å; hydrogen/carbon ratio = 1.0. The parameters reported for the hydrogenated sample are not well constrained since the residual in this case is considerably higher than for the other diffraction patterns.
• Stoichiometries of the KHg-GIC's as determined from various experiments. ND = not determined by this experiment; NR = not reported by the authors of the cited reference.
• Transition temperatures T_c and reduced widths Delta T_c/T_c for a sampling of C₄KHg specimens.
• Calculated values of kappa for selected C₄KHg samples. The H_c2(0) numbers come from linear extrapolation of the H_c2(T) data (see Section ), and so are independent of the H_c2(theta) measurements.
• H_c(t) values for C₄KHg obtained from fits to Eqn. . For comparison, H_c(t) calculated from the specific heat data for a T_c = 1.53 K sample is also included. The samples' H_c2(theta) data are shown in Figs. , , and .
• Residuals for fits to H_c2(theta) using the AGL formula and the Tinkham formula, both with and without type I behavior. The residual index cal R is defined in Eqn. , the AGL formula is Eqn. , and the Tinkham formula is Eqn. . Eqn. shows how each of these formulae was modified to account for possible type I superconductivity.
• Parameters obtained from least-squares fits of Eqn. to C₄KHg H_c2(T) data. The individual specimens are labeled by the value of T_c obtained from the zero-field sweeps. The other parameters, including the ``fit'' T_c, are obtained from the least-squares linear fits to the critical field data that are shown in Figure . The residual cal R is calculated using Eqn. . NR denotes that the parameter was not reported in the cited reference.
• Comparison of the anisotropy parameter epsilon as obtained from H_c2(T) and H_c2(theta) fits. The H_c2(T) epsilon numbers were obtained from the ratio of the slopes. The H_c2(theta) numbers were obtained from fits using Eqns. (AGL) and (Tinkham's formula), with type I superconductivity allowed for small theta. In each case, the TF fits had lower residuals than the AGL fits (see Table ). NA indicates that a TF fit was not performed on this data; NR denotes information that was not reported in the cited reference.
• Values of the KLB parameter r for the GIC superconductors. means that the value of r was calculated from parameters in the cited references.
• Comparison for C₄KHg of two different methods for determination of Maki's alpha parameter.[262] The orientation indicated is that of the applied magnetic field. In parentheses it is noted which of the two halves of Eqn. was used.
• Values of Lambda_ep, the electron-phonon coupling parameter, for GIC superconductors. T_c = 0.73 K[120] is used for C₄KHg since no transition was observed down to 0.8 K during the specific-heat measurement.[8] Values of Lambda_ep for the KH-GIC's are gathered in Table .
• A summary of the known differences between the pink and gold C₄KHg. The numbers here are representative of a typical sample of its type, although some variation was observed from sample to sample. Lambda_ep is McMillan's electron-phonon coupling parameter.[165] kappa is the Ginzburg-Landau parameter discussed in Section ; kappa ;SPM_lt; 1/sqrt2 indicates type I superconductivity. The density of states, N(0), shown here was calculated in Section from the H_c2(theta) data. NA means not applicable.
• Superconducting transition temperatures of the KH-GIC's and C₈K. Two methods of preparation are possible: direct intercalation of KH powder into graphite,[76] and intercalation of K into graphite to form C₈K, followed by hydrogen chemisorption.[78] Single-phase specimens are difficult to obtain because of slow hydrogen sorption kinetics.[231,78]
• Parameters relevant to superconductivity in the KH- and RbH-GIC's. Adapted from Ref. [78]. The density of states has been corrected for the electron-phonon coupling. ^dagger means a calculated parameter; ? means not measured.
• Effect of hydrogenation on T_c in KHg-GIC's. All the T_c's are for C₄KHg, except for the blue 1.879 K sample, which was C₈KHg. ^dagger indicates the second hydrogenation of a previously hydrogenated sample. ^* indicates that deuterium rather than hydrogen was added. ^S indicates that the remeasurement of a transition one year after hydrogenation.
• Superconducting transition temperatures of the MBi-GIC's and related alloys. For Ref.[36], the volume fraction column actually contains the effective areal fraction of superconductivity, as explained in Section . NR=Not reported. NA=Not applicable.
• Electronic parameters for selected superconducting GIC's. The stage and phase of each compound are listed in parentheses. The compounds are listed in order of increasing superconducting transition temperature. Omega_p is the unscreened plasma frequency.
• Two tables prepared by McRae and Marêché[166] which list the c-axis resistivity and resistivity anisotropy of many GIC's, both donors and acceptors. A== rho_c/rho_a. Correct sources for these numbers are given in Ref. [166].

5em

Abbreviations and Symbols

Abbreviations and Symbols Used in This Work

1em