High-temperature superconductors exhibit superconducting behavior, e.g., the Meissner effect, zero resistance, etc., at temperatures which can be attained using liquid nitrogen. Below the critical temperature, the superconducting state may be destroyed by applying a large enough current or magnetic field. This occurs at the critical current density or the critical magnetic field, respectively.

Equipment

• Colorado Superconductor setup and experiment guide
• DC current source
• Two digital multimeters
• Magnet
• Hall probe
• Dewar (and liquid nitrogen)

There are two superconducting disks in this experiment, made of YBCO or BSCCO. They are encased in an enclosure that includes 6 leads: 2 are thermocouple leads (blue and red), 2 are used to measure the voltage drop across the sample (yellow), and the other 2 are used to provide a current across the sample (black). There is also a magnet that can be used to demonstrate the Meissner effect.

The purpose of this experiment is to determine the values of the critical temperature, current density and magnetic field for the samples provided. The critical temperature may be determined in two ways, using the Meissner effect or the zero resistance of the superconductor. Determine the critical current as a function of temperature. Compare your results to the theoretical relationship for the critical current J_c/J_c(0) ~ (1-T/T_c)^3/2 .

Read carefully the sections of the experiment guide which relate to the handling of superconductors and liquid nitrogen. You should also read about the construction of the 4-point probe and should familiarize yourself with the experimental setup and operation. Follow the experiment guide and complete as many experiments (Part III) as you can.