R esearch E xperience for U ndergraduates

1. Research Experience for Undergraduates Sahara D. Hernandez Smith College Millikelvin Lab and C108

2. CeCoIn5 • Heavy fermion superconductor • Building block structure • First reported 2001 • Discovered at NHMFL • Single crystal layered material • CeIn3 and CoIn2 make up 1 unit cell CoIn2 CeIn3

3. Cantilever Technique • The cantilever magnetometry method measures the magnetization of the sample • Bottom fixed plate made of Copper and top plate (cantilever) made of Beryllium Copper • Both plates act like a capacitor, measured with a capacitance bridge • Capacitance ~ Torque

4. Cantilever Graph

5. TDO Technique • Tunnel Diode Oscillator (TDO) method measures the penetration depth of the sample • The penetration depth is proportional to the resonance frequency, so it’s measured on the frequency counter • The coil is connected to a TDO board with a tunnel diode • When TDO board is properly biased, then it’s a self resonant circuit (100-200 MHz)

6. TDO Graph

7. Tunnel Diode Oscillator • My goal is to observe and measure the penetration depth of an ac field on a superconductor at a fixed temperature as a function of the magnetic field. • In an attempt to increase productivity by 100%, we would like to combine both the cantilever and TDO technique.

8. Frequency Counter Power Source TDO Circuit Components On/Off Switch for TDO

9. Oscilloscope Multi-Meter Frequency Generator

10. TDO Board Coaxial Wire Resistors Tunnel Diode Coaxial Wire Capacitors

11. Sample Coils • Wire # 38 • Mandril 100 has a diameter of 2.5 mm • Mandril 125 has a diameter of 3 mm • Each coil has either 3 turns or 6 turns • The same four coils are also made with a #44 wire

12. Sample Cantilevers • The coil is glued to the cantilever with GE Varnish • The GE Varnish can be removed by dipping it in a 1 to 1 ratio of Ethanol and Toluene for a couple of minutes • Wire # 38

13. Making a Coil Mandril • Thinner wire has a bigger AWG number and thicker wire has a smaller AWG number

14. Soldering the Coil • The TDO board is exposed to 600 degrees Fahrenheit every time a component is soldered • This can cause the lifespan of the TDO components to malfunction • One bad solder joint can cause an open circuit

15. Resistance Check • When there is no coil connected, the voltmeter should read 602Ω (for our TDO board) • When a coil is connected, the voltmeter should read 460Ωand 477Ω when the polarity is changed (for our TDO board)

16. Dipping the Sample • The TDO board has to be completely covered by the liquid nitrogen • Temperature changes from 300 K to 77 K every time the TDO board is dipped

17. Taking Data • Fundamental Frequency • Amplitude • Bias Range • The number of Harmonics FM radio(Rap station) Mysterious signal (162 MHz)

20. Conclusions • Positive effect: cantilever damps the circuit and decreases the number of harmonics • Negative effect: massive interference of the cantilever on the circuit causing two #44 wire signals not to be visible due to eddy currents • 3 turns yields better amplitudes then 6 turns • Parameters need to be selected carefully due to two counter acting effects • Next step would be to mount a sample inside the coil to see the effects

21. Acknowledgments Dr. Stan Tozer Dr. Eric Palm Mr. Glover Jones Dr. Henri Radovan Mr. Tim Murphy

22. Acknowledgments Ms. Gina LaFrazza Amanda UnderwoodSoon Young Kim (RET) Dr. Pat Dixon Ms. Stacy Vanderlaan Mr. Carlos Villa Mr. Dave Sheaffer

23. Acknowledgments National High Magnetic Field Laboratory & National Science Foundation

24. Thank You.Any Questions?