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Abstract:
We report a combined study of external pressure and Cu-substitution on
BaFe2As2 single crystals grown by the in-flux technique. At ambient
pressure, the Cu-substitution is known to suppress the spin density wave
(SDW) phase in pure BaFe2As2 (T-SDW approximate to 140 K) and to induce
a superconducting (SC) dome with a maximum transition temperature
T-c(max) similar or equal to 4.2 K. This T-c(max) is much lower than the
T-c similar to 15-28 K achieved in the case of Ru, Ni and Co
substitutions. Such a lower T-c is attributed to a Cu2+ magnetic
pair-breaking effect. The latter is strongly suppressed by applied
pressure, as shown herein, T-c can be significantly enhanced by applying
high pressures. In this work, we investigated the pressure effects on
Cu2+ magnetic pair-breaking in the BaFe2-xCuxAs2 series. Around the
optimal concentration (x(opd) = 0.11), all samples showed a substantial
increase of T-c as a function of pressure. Yet for those samples with a
slightly higher doping level (over-doped regime), T-c presented a
dome-like shape with maximum T-c similar or equal to 8K. Remarkably
interesting, the under-doped samples, e.g. x = 0.02 display a maximum
pressure induced T-c similar or equal to 30 K which is comparable to the
maximum T-c's found for the pure compound under external pressures.
Furthermore, the magnetoresistance effect as a function of pressure in
the normal state of the x = 0.02 sample also presented an evolution
consistent with the screening of the Cu2+ local moments. These findings
demonstrate that the Cu2+ magnetic pair-breaking effect is completely
suppressed by applying pressure in the low concentration regime of Cu2+
substituted BaFe2As2.
