Dependence of the superconducting transition temperature of single and polycrystalline MgB2 on hydrostatic pressure

Abstract

The dependence of T c for MgB 2 on purely hydrostatic or nearly hydrostatic pressure has been determined to 23 GPa for single-crystalline and to 32 GPa for polycrystalline samples, and found to be in good agreement. T c decreases from 39 K at ambient pressure to 15 K at 32 GPa with an initial slope dT c /dP ≃ -1.11(2) K/GPa. Evidence is presented that the differing values of dT c /dP reported in the literature result primarily from shear-stress effects in nonhydrostatic pressure media and not differences in the samples. Although comparison of these results with theory supports phonon-mediated superconductivity, a critical test of theory must await volume-dependent calculations based on the solution of the anisotropic Eliashberg equations.

Carbon-substituted MgB2 single crystals

“…Extrapolating the experimental data for the lower C -content samples by linear dependence, the actual carbon content for C7 is about 15%, in excellent agreement with the solubility limit of C in MgB 2 determined from XRD data. Comparing the rates of T c suppression with the change in lattice volume (V/Vo) by Csubstitution and by applying hydrostatic pressure [17] (inset Fig.4b), we can conclude that the effect of lattice contraction on T c suppression by C -substituted MgB 2 is quite modest.…”

Pressure effect on the magnetic penetration depth inMgB2

“…The first hydrostatic measurement of T c (p) up to 0.7 GPa, reveals that T c decreases reversibly under hydrostatic pressure at the rate dT c /dp = − 1.11(2) K/GPa. 4 The behavior of T c (p) with pressure in MgB 2 was attributed to the pressure induced lattice stiffening (increase of the phonon frequency), 5,6 rather than to the decrease in the electronic density of states N(E F ), that is only moderately affected by pressure. 7 Comparison with theoretical calculations supported the view that MgB 2 is a BCS superconductor with moderately strong electron-phonon coupling.…”

Response of Critical Temperature of the Superconducting Transition and Energy Gaps of MgB$_2$ to the Hydrostatic Compression

“…Величина T c определялась по середине перехода на зависимости R(T). Значение dT c /dP = =−1,1 ± 0,1 К/ÃПа, полученное из этих измерений, соответствует ли-тературным данным по влиянию давления на критическую темпе-ратуру сверхпроводящего перехода MgB 2 [29].…”

“…С другой стороны, при низких температурах обычные передающие давление среды не обеспечивают полную гидростатику в камере вы-сокого давления [47,48] (исключение, жидкий гелий). Поэтому в стандартной камере [28] на образце всегда сохраняется влияние ка-сательных (сдвиговых) напряжений, составляющих ≅ 5% от при-ложенного давления 10-15 кбар.…”

“…Îтметим, что наблюдаемое (рис. 1) смеще-ние T c под давлением соответствовало литературным данным для монокристаллов [47]. Îднако при этом ширина резистивного пере-хода …”