{"id":1948,"date":"2015-07-05T23:25:31","date_gmt":"2015-07-06T06:25:31","guid":{"rendered":"http:\/\/physikon.net\/?p=1948"},"modified":"2022-06-22T09:48:51","modified_gmt":"2022-06-22T16:48:51","slug":"1948","status":"publish","type":"post","link":"http:\/\/physikon.net\/?p=1948","title":{"rendered":"Modeling Intercalated Group-4-Metal Nitride Halide Superconductivity with Interlayer Coulomb Coupling"},"content":{"rendered":"

<\/p>\n

\n

Modeling Intercalated Group-4-Metal Nitride Halide Superconductivity with Interlayer Coulomb Coupling<\/strong>, D. R. Harshman and A. T. Fiory [arXiv<\/a>]\n

Behavior consistent with Coulomb-mediated high-T<\/em>C<\/sub> superconductivity is shown to be present in the intercalated group-4-metal nitride halides A<\/em>x<\/sub>(S<\/em>)y<\/sub>M<\/em>NX<\/em>, where the M<\/em>NX<\/em> host (M<\/em> = Ti, Zr, Hf; X<\/em> = Cl, Br) is partially intercalated with cations A<\/em>x<\/sub> and optionally molecular species (S<\/em>)y<\/sub> in the van der Waals gap between the halide X<\/em> layers, expanding the basal-plane spacing d<\/em>. The optimal transition temperature is modeled by T<\/em>C0<\/sub> \u221d \u03b6\u20131<\/sup>(\u03c3\/A<\/em>)1\/2<\/sup>, where the participating fractional charge per area per formula unit \u03c3\/A<\/em> and the distance \u03b6, given by the transverse A<\/em>x<\/sub>–X<\/em> separation (\u03b6 < d<\/em>), govern the interlayer Coulomb coupling. From experiment results for \u03b2-form compounds based on Zr and Hf, in which concentrations x of A<\/em>x<\/sub> are varied, it is shown that \u03c3 = \u03b3[v(xopt<\/sub> \u2212 x0<\/sub>)], where xopt<\/sub> is the optimal doping, x0<\/sub> is the onset of superconducting behavior, v is the A<\/em>x<\/sub> charge state, and \u03b3 = 1\/8 is a factor determined by the model. Observations of T<\/em>C<\/sub> < T<\/em>C0<\/sub> in the comparatively more disordered \u03b1-Ax<\/sub>(S<\/em>)y<\/sub>TiNX<\/em> compounds are modeled as pair-breaking by remote Coulomb scattering from the A<\/em>x<\/sub> cations, which attenuates exponentially with increasing \u03b6. The T<\/em>C0<\/sub> values calculated for nine\u00a0A<\/em>x<\/sub>(S<\/em>)y<\/sub>M<\/em>NCl compounds, shown to be optimal, agree with the measured T<\/em>C<\/sub> to within experimental error. The model for T<\/em>C0<\/sub> is also found to be consistent with the absence of high-T<\/em>C<\/sub> characteristics for A<\/em>x<\/sub>M<\/em>NX<\/em> compounds in which a spatially separated intercalation layer is not formed.<\/p>\n\n\n\n\n\t\n\t
\"FIG1_JSNM\"<\/a>
\n

Plot of measured transition temperature T<\/em>C<\/sub> versus ζ−1<\/sup>[(1\/8) v(xopt<\/sub> − x0<\/sub>)\/A<\/em>]1\/2<\/sup> for the high-T<\/em>C<\/sub> compounds listed in Table 1 and compounds with α = 0 from Table 2. Interaction distance ζ is from Eq. (1), v(xopt<\/sub> − x0<\/sub>) is the optimal doping xopt<\/sub> relative to the superconductivity onset value x0<\/sub> and multiplied by valence v, and A<\/em> is basal area per formula unit. The line represents T<\/em>C0<\/sub> for optimal compounds from Eq. (6).<\/p><\/td>\n<\/tr>\n

\"FIG2-JSMN\"<\/a>
\n

Pair breaking parameter α from Table 2 normalized to alkali content x and plotted against interaction distance ζ for the α-form compounds, (a) A<\/em>x<\/sub>(S<\/em>)y<\/sub>TiNCl and (b) A<\/em>x<\/sub>(S<\/em>)y<\/sub>TiNBr. The curves represent the function of Eq. (5) fitted to the A<\/em>x<\/sub>(S<\/em>)y<\/sub>TiNCl compounds.<\/p><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n

Dale R. Harshman and Anthony T. Fiory, J. Supercond. Nov. Mater. 28<\/strong>, 2967 (2015)<\/a>.<\/p>\n

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