Download NHMFL 2014 Cell 12 Practical_v2

Data acquisition program
Cell 12 Magnet
Magnet control
Data Acquisition computer
unit: mm
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35.1 T, 32 mm bore
Available cryostats: He3 (0.3 – 60 K) or VTI (1.4 – 300 K)
Magnet/Power
supply status
monitoring
computer
System D Rotator Probe
Side A
Side B
Before mounting
Sample holder mounted on the probe
Sample holder : side A
side view
top view
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Sr2RuO4
Magnetic torque
Capacitance between the
two parallel plates
11.4 mm
Sample holder : side B
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SrMnBi2
Electrical transport
Resistance (Rxx)
0.25 mm
1.5 mm
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Hall sensor (THS 118: GaAs based)
Hall Resistance (Rxy)
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Ba2Fe2As2
Surface conductivity
TDO (Tunnel Diode Oscillator)
resonance freq. shift
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PdCoO2
Magnetic torque
Resistance change of
piezo-resistive device
Sr2RuO4
Triplet superconductor (Tc = 1.4 K)
Torque: Capacitance signal, T= 30 mK
C. Bergemann et al., Physica B 294, 371 (2001)
BaFe2As2
Parent compound of 122 pnictide superconductors
TDO frequency shift
30 mK
350 mK
D. E. Graf et al., PRB 85, 134503 (2012)
J. G. Analytis et al., PRB 80, 064507 (2009)
SrMnBi2
Dirac Fermion compound
SrMnBi2
CaMnBi2
K. Wang et al., PRB 85 041101(R) (2012)
J. Park et al., PRL 107 126402 (2011)
PdCoO2
Metallic triangular lattice compound
Torque signal (piezo-cantilever)
T=0.7 K
C. W. Hicks et al., PRL 109 116401 (2012)
Measurement techniques
Resistance measurements by instrumentation (Rxx, Rxy, piezo-cantilever)
principle: apply current (current source) and measure voltage (voltmeter)
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Conventional lock-in amplifier technique
• Oscillating current applied, phase sensitive detection of corresponding voltage
DC resistance measurement technique
• DC current with switching polarities to remove offset
AC resistance bridge
• Resistance determined by nulling or measuring unbalanced signal
Q: what is advantage/disadvantage of the lock-in technique compared to the DC technique?
Capacitance measurement for magnetic torque
• AH capacitance bridge: automatic balancing
• GR capacitance bridge: manual balancing
Q: what other physical properties can be measured by the
capacitance measurement device?
TDO resonance frequency measurement
Typical capacitance bridge
Exercises 1: Resistance measurement on the standard resistor
(hints given in the appendix)
Lock-in technique
• configure resistance measurement setup with 1 lock-in amplifier (SR 830)
• Change parameters (current, frequency, time constant, ..) and check the
voltage readings
DC technique
• Configure measurement setup with 1 DC current source (Keithley 6221) and 1
DC nanovoltmeter (Keithly 2182)
• Apply constant DC current ( < 10 mA) and monitor the voltage
• Setup the Delta mode and test with different parameters (current, delay
time,..)
Exercises 2: Capacitance measurement on the standard capacitor
(1) AH bridge : hook up coax cables to the decade capacitor box and press buttons
(2) GR bridge
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configure GR bridge and 1 lockin-amplifer for capacitance measurement
balance the GR bridge to find the capacitance value (should be similar to obtained from (1)
find the conversion factor between lock-in signal and capacitance
Exercises 3: Balancing the piezo-cantilever
• Build a measurement circuit with a given
bridge circuit box
• Balance the bridge
inside
cryostat
Demonstration 1: TDO measurement
Exercises 4: Setting up instruments for the real samples
(1) Setup instruments for the Hall sensor (DC resistance delta mode) and piezocantilever (lock-in technique). Refer to the breakout box diagram in the next page.
NOTE: Do not apply currents until further notice.
(2) Instructor will setup AC resistance bridge for the transport measurement
(3) Connect cables to the AH bridge for the capacitance measurement
(4) Using the data acquisition program, collect the data at zero field as a function of time
variable
resistor
can be used as pseudo-current source
setup when combined with lock-in
oscillator
NHMFL breakout box
Exercises 5: Data acquisition
(1) Collect data while sweeping magnetic field under different instrumentation setup
(2) Collect data at different temperatures
(3) Collect data at different angles
Exercise/Demonstration: Data analysis
(1) Plot the data using data analysis program
Q1) Plot the temperature vs. magnetic field. Why does temperature reading change with field?
Any way to circumvent the problem?
Q2) What is the oscillation frequency of the quantum oscillations?
Q3) Capacitance torque signal from Sr2RuO4 sample look different from the text book (sawtooth not sinusoidal). Why? (answer given in the appendix)
(2) Perform FFT with different settings (field range, different background, FFT windows, …)
Appendix I
Resistance measurement (Lock-in technique)
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Oscillator out to the current terminals with a large resistor connected in series
Connect voltage terminals to voltage input (A-B mode)
voltage input
osc. out
sample
Current limiting resistor (R)
I = V/(Rsample+R) ~ V/R (if R >> Rsample)
DC resistance measurement (delta mode)
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Configure Delta (picture above) : set I-high, I-low, Delay. ,,,,
Press Delta to arm
Press TRIG to start delta mode operation
Appendix II
Torque interaction analysis in Sr2RuO4 by Naoki Kikugawa
Sr2RuO4
T = 1.4 K
B // ~ c axis
Data taken at Cell
12 (May 21, 2014)
Remember:
The oscillation is
periodic in 1/B not
in 1/H
Raw data
(before de-torque)
FFT: 28 – 34.5T
De-torqued
FFT: 28 – 34.5 T