1. Measuring Electrical Transport Joseph Graves Nathaniel Odell Mark Sikora

2. Objectives Construct apparatus and data acquisition system Model temperature dependence of resistance of various classes of materials down to 77 K Semiconductor Super-conductor

3. Thermometry 4 wire measurement on a platinum resistor Calibrated based on data provided by manufacturer Why platinum? Almost linear temperature dependence of resistance Precise calibration

4. 4 Wire Measurement Necessary for accurately measuring small resistances (ie super-conductors) by eliminating resistances of wires and contacts. 2 current wires, 2 voltage wires

5. Experimental Considerations Create environment where thermometer and sample are in good thermal contact Prevent convection: air-tight indium seal Regulate temperature: adiabatic cooling to ensure sample and thermometer are at the same temperature

6. Data Acquisition Use 2 simultaneous 4 wire measurements with 2 multimeters Write software to provide side by side display of thermometer and sample resistance as a function of temperature in real time Multimeter output read through GPIB interface > LabView program to record data Origin to plot/fit data conductor.viC:\Documents and Settings\student\Desktop\Conductors\conductor.viLast modified on 3/6/2006 at 5:03 PMPrinteon 4/30/2006 at 8:39 PM18200timeout ms (488.2 global) 3SAMPLEREAD?error out 31000Elapsed Time0TIME500TIMESignalsScaled SignalsScaling andMapping1 [0..1]stopnitrotest.txtcreate or replacefunction (open:0)conductor.viC:\Documents and Settings\student\Desktop\Conductors\conductor.viLast modified on 3/6/2006 at 5:03 PMPrinteon 4/30/2006 at 8:39 PM18200timeout ms (488.2 global) 3SAMPLEREAD?error out 31000Elapsed Time0TIME500TIMESignalsScaled SignalsScaling andMapping1 [0..1]stopnitrotest.txtcreate or replacefunction (open:0)

7. Results/Analysis Carbon Resistor Behaves like a semiconductor Did not find any equations modeling the resistance in this temperature range (77K-300K) R = Aexp(B/T + C/T^2)

8. Results/Analysis Diode Linear response

9. Results/Analysis Superconductor YBCO sample Was not compatible with existing apparatus > no temperature control Superconductivity was observed

10. Future Operational apparatus and data acquisition Once a permanent sample is put in place, the lab is ready Need to work on modifying the super conducting sample to fit in the probe