Study On Chromium - Based, Manganese - Based Superconductors And Its Physical Properties

Recently, the discovery of superconductivity in CrAs and MnP via the application of high pressure makes CrAs and MnP the first Cr-based and Mn-based superconductor. The superconductivity of CrAs and MnP exist near a quantum critical point, which suggests an unconventional pairing mechanism. Many experimental techniques like ARPES and STM that could reveal the microscopic pairing mechanism of a superconductor cannot be carried out under high pressure.Therefore, to explore for superconductivity in CrAs、MnP and related materials by chemical doping is highly desire.In this paper, we report the growth and the low temperature physical properties measurements results for phosphorus doped CrAs1-xPx and MnP0.8B0.2 single crystals, and compare with the previous results on CrAs and MnP under high pressure.This paper is organized as follow:.Section I first briefly introduces the basic physical properties and the discovery of superconductivity for CrAs single crystal. And then we report a systematically study of resistivity and specific heat on phosphorus doped CrAs1-xPx single crystals with x=0 to 0.2. Non-fermi liquid behavior and quantum criticality phenomenon are observed from low temperature resistivity around critical doping with xc0.05 where the long-range antiferromagnetic ordering is completely suppressed. The electronic specific heat coefficient y also indicating the existence of quantum critical phenomenon around the critical doping. Section II first introduces the discovery of superconductivity on the border of long-range magnetic order in the itinerant-electron helimagnet MnP via the application of high pressure. And then we report low temperature results of the resistivity,heat capacity and magnetic susceptibility measurements for MnP0.sB0.2 single crystal and compare with the previous results of high pressure experiment on MnP. Below 100 K, a magnetic transition can beobserved from magnetic susceptibility measurement. Considering the small ordered moments, large anisotropic magnetization, and large positive magnetoresistance for MnP0.8B0.2, we suggest that the magnetic state below 100K could be a canted antiferromagnetc ordered state or a spiral magnetic ordered state. Neutron scattering experiment need to be carried out to reveal magnetic structure of this material in the future. The behavior of low temperature resistivity for MnP0.8B0.2 resemble that of MnP under 4-6 GPa. Section III summarizes the current work and presents several unsolved problems and feasible research direction in the future.