Josephson effect

Let’s start with a 4-terminal Josephson junction. The drain contact is connected to a MFLI lock-in via an AC-DC mixer. The AC current is sourced via the MFLI Voltage input, the DC current via the Auxiliary output 1 of the MFLI. The device is also exposed to an RF excitation, sourced from a R&S SMB 100A.

Initialisation

import mesoscopy
mesoscopy.init_db('../database_josephson.db')
station = mesoscopy.init_station(
     '4400', '4401',
     rf_addr='TCPIP::192.168.0.3::inst0::INSTR',
     triton_addr='192.168.0.2'
)

mesoscopy.init_lockin(
     station,
     freq=117,
     ampl=2,
     filterorder=8)

D.C. Josephson effect

We can start with the d.c. Josephson effect. At first, we initialise our experiment:

exp = mesoscopy.create_exp(
     experiment_name='d.c. Josephson effect',
     sample_name='test sample'
)

Then, we can do a 1D sweep:

xarray = mesoscopy.generate_lin_array(1, -1, num=201)

mesoscopy.sweep1d(
    station.mf4406.auxouts[0].offset,
    xarray,
    1.6,
    station.mf4400.demods[0].sample,
    station.mf4400.demods[2].sample,
    station.triton.B,
    station.triton.T8,
    exp=exp,
    measurement_name='Iac=2nA, Idc swept from 10 to -10nA',
    use_threads=True
)

From here, many other things can be measured with the use of mesoscopy.sweep1d and mesoscopy.sweep2d, for example Fraunhofer diagram, temperature dependence, etc.

A.C. Josephson effect

Let’s start by initialising our experiment.

exp = mesoscopy.create_exp(
     experiment_name='a.c. Josephson effect',
     sample_name='test sample'
)

At first, let’s generate 2 arrays to sweep within. mesoscoPy can take into account the attenuation within the line (assuming that you measured it with a VNA), and generate an array for constant RF voltage on the device.

xarray = mesoscopy.generate_lin_array(1,-1, num=101)
yarray = mesoscopy.generate_RF_array(15e-3,.1e-3,num=101, attenuation=42)

Here, our line has a -42dB attenuation. Now that this is generated, we can start the map.

mesoscopy.sweep2d(
    station.mf4406.auxouts[0].offset,
    xarray, 1.6,
    station.rf_source.power,
    yarray, .1,
    station.mf4400.demods[0].sample,
    station.mf4400.demods[2].sample,
    station.triton.T8,
    exp=exp,
    measurement_name='RF power dep, Id swept from 10nA to -10nA, Iac = 2nA,',
    use_threads=True,
    measure_retrace=False
)