To examine the electronic phase diagram of superconducting CuO double chains, we report the effect of external pressure on the magneto-transport properties in superconducting and nonsuperconducting polycrystalline samples of Pr2Ba4Cu7O 15−δ at low temperatures (1.8-40 K) under various magnetic fields (up to 14 T). In the as-sintered non-superconducting sample, the magnetoresistance (MR) follows a power law of H 3/2 at low temperatures, which is in no agreement with the H 2 dependence of MR in the PrBa2Cu4O8 system. The negative pressure dependence of the superconducting phase is qualitatively consistent with a theoretical prediction on the basis of the Tomonaga-Luttinger Liquid theory. The 48-h-reduced superconducting sample at ambient pressure exhibits no clear increase in MR for T > Tc,on = 26.5 K. In contrast, with the application of pressure to the superconducting sample, the MR effects reappear and are also well fitted by H 3/2 . The model of slightly warped Fermi surfaces explains not only the MR effect of the non-superconducting sample, but is also related to the reasons for the pressure-induced MR phenomena of the superconducting sample.
To examine the thermodynamic properties of Pr2Ba4Cu7O 15−δ compounds with metallic CuO double chains, we measured the specific heats of superconducting and non-superconducting polycrystalline samples at low temperatures (1.8-40 K) under various magnetic fields (up to 9 T). In the as-sintered non-superconducting sample, a λ−like enhancement in the specific heat measurement appeared near the antiferromagnetic transition temperature TN = 17 K. In contrast, the reduced superconducting sample with Tc,on = 26.5 K exhibited no obvious superconducting anomaly in its specific data, but a Schottky-like broad maximum appeared at low temperatures. The Schottky-like anomaly was attributed to low-lying quasi-triplet splitting of Pr 3+ ions under the crystal field effect.
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