Development Of Resistivity And Specific Heat Measurements Under Extreme Conditions, And Its Applications In Correlated Electron Materials

In strongly correlated electron systems, pressure and magnetic field are important tuning parameters which have been widely used to study the interplay between superconductivity and magnetism, charge density wave or structural phase transition. Measurements of physical properties under extreme conditions of low temperature, high pressure and strong magnetic field are highly important for elucidating the above problems, which may help reveal the mechanism of unconventional superconductivity and the universal behaviors of quantum criticlity. This dissertation is devoted to the developments of several experimental methods, in particular the heat capacitiy, under extreme conditions and its applications in strongly correlated electron systems. The main contents include:(1) We have developed measurements of the electrical resistivity and specific heat at low temperatures using different methods, including the ac and dc resistivity, the specific heat measurements based on the thermal relaxation method, the dual-slope method and the ac calorimetric method. We also successfully apply the ac resistivity and the ac calorimetric methods to high pressure and high magnetic field. These experimental developments have largely extended our capabilities to study the unusual physical properties emerging in strongly correlated electron systems.(2) CeIrIn5 is assumed to lie on the antiferromagnetic (AFM) threshold. The Ir/Cd subistution strengthens the magnetism and gives rise to a long-range AFM order, driving the system away from the quantum critical point (QCP). In this study, we have measured the electrical resistivity and heat capacity of 1% Cd-doped CelrIn5 under hydrostatic pressure up to 2.7 GPa, near where the long-range antiferromagnetic order is suppressed and bulk superconductivity suddenly reemerges. The pressure-induced Tc is close to that of pristine CeIrIn5 at 2.7 GPa, and no signatures of a quantum critical point under pressure support a local origin of the antiferromagnetic moments in Cd-CeIrIn5 at ambient pressure. Similarities between superconductors CeIrIn5 and CeCoIn5 in response to Cd substitutions suggest a common magnetic mechanism.(3) Ce2PdIn8 and the Ce-115 compounds belong to the same heavy fermion family CenMmIn3n+2m. In order to study the superconducting order parameter in this material, we have measured the angle dependence of the specific heat at low temperatures for Ce2PdIn8. It is found that the material shows a weak two-fold symmetry, which underlying reasons are discussed.(4) The recently discovered layer-compound EuBiS2F shows a charge-density-wave (CDW)-like transition around 270K, followed by a superconducting transition at Tc≈0.3K. By measuring the electrical resistivity and X-ray diffractions under pressure, we found that the superconducting transition temperature Tc of EuBiS2F undergoes a dramatic increase around pc≈1.5GPa, changing from Tc≈0.3 K at p=0 to Tc≈8.6 K at p>pc. Furthermore, a structural phase transition is found to take place at pc, which is accompanied by the disappearance of the CDW-like transition. These experimental results suggest that two distinct superconducting phases exist in EuBiS2F, corresponding to two different crystal structures. Our results also imply that this feature can be general to other BiS2-based superconductors.