Supporting Information
Superconducting molybdenum-rhenium electrodes for single-molecule
transport studies
R. Gaudenzi1, J. Island1, J. de Bruijckere, E. Burzuri, T. Klapwijk, H. S. J. van der Zant
Supporting Information Contents
1. Electromigration current-voltage characteristics
Figure S1: I-Vb of electromigration process
2. Three terminal measurement (I-Vb-Vg) of an SN-I-NS junction
Figure S2: I-Vb-Vg characteristics and 1D line cuts
3. Temperature and magnetic field dependence for a second characteristic device
Figure S3: dI/dV-Vb as a function of temperature and magnetic field
4. Estimation of the charging energy U and electrode coupling constant 
1. Electromigration current-voltage characteristics
Feedback controlled software is used to monitor and adjust the voltage across the gold
wire to steadily create a constriction at room temperature. Figure S1 shows the typical current
voltage characteristics recorded during the creation of a constriction. The voltage is ramped
up to > 1V at which point the resistance of the junction starts to change and the feedback
software decreases the voltage to arrest an avalanche breaking of the wire. This continues to
create a final constriction which is left to self-break at room temperature leaving a fewnanometer gap.
Figure S1: Current-voltage characteristics for the electromigration of a typical device.
2. Three terminal measurement (I-Vb-Vg) of an SN-I-NS junction
Figure S2 shows a three terminal measurement of an SN-I-NS junction taken at 100 mK
after the electromigration and self-breaking process. A numerical derivative is taken to plot
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The two authors contributed equally
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dI/dV versus bias and gate voltage. The conductance does not change over the accessible gate
voltage range (+-7V) indicating tunneling through a gate independent vacuum barrier.
Figure S2: Three terminal measurement of an SN-I-NS junction at low temperature (100 mK).
Current is measured as a function bias voltage and back-gate voltage. A numerical derivative
is taken to plot dI/dV-Vb-Vg.
3. Temperature and magnetic field dependence for a second characteristic device
Figure S3 shows the complete characteristics for a second device. This SN-I-NS junction
shows the same characteristics as the main text device. The softening of the proximity
induced gap with temperature is shown in Fig. S3(a). Again, a residual gap is present at 4.5K.
Figures 3(b) and (c) for the magnetic field dependence in the z and y-axis. Greater modulation
of the gap is found for fields in the z-axis direction.
Figure S3: (a) Temperature dependence of the SN-I-NS junctions. A numerical derivative is
plotted versus the applied bias voltage. (b) Magnetic field dependence of the junction with the
external field in the z-axis direction. (c) Magnetic field dependence of the junctions with the
external field in the y-axis direction.
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4. Estimation of the charging energy U and electrode coupling constant 
An estimation of the charging energy U can be obtained from the V vs. Vgate differential
conductance map according to U = Vgate, where is the gate coupling – obtained from
the slopes of the Coulomb edges of the same conductance maps – and Vgate is the
distance in gate voltage between two charge degeneracy points.
From figure S4, meV/V and Vgate ≥ 7.5 V, so that U ≥ 13 x 7.5 meV.
V (mV)
7.5
2.5
-2.5
-7.5
-4
-2
0
Vgate (V)
2
4
Figure S4: Coarse differential conductance map of an individual Fe4-SMM as a function of
gate and bias voltages. The selected voltage range is the maximum allowed by the gate oxide.
The molecule-electrode coupling constant is obtained from fitting the charge degeneracy
peak (V = 0V, B = 8T) shown in figure S5 to a lorentzian function. The FWHM of the
lorentzian extracted from the fit multiplied by the gate coupling yields 1meV. The high
magnetic field ensures a negligible influence of superconductivity on transport.
Figure S5: Normalized differential conductance zero-bias trace (charge degeneracy point) as
a function of gate voltage obtained at a magnetic field of 8T. At this field superconductivity is
completely lifted so that regular quasiparticle transport is restored. The molecule-electrode
coupling constant is obtained by fitting the trace to a lorentzian.
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