Figure 1

Transmission spectroscopy of VOPc sample #4 in the weak coupling regime at different temperatures. The resonant frequency at zero field is 7.66 GHz (Res #2). (a) Sketch of the resonator with a VOPc pellet (purple) on it. Transparent light blue area represents the fundamental resonant MW mode and the green arrows indicate the path of the microwaves. The red arrow shows the direction of the static magnetic field, B₀. Yellow cylinders represent the antennas for the injection and the collection of the MW signal. The light blue scale bar corresponds to 3 mm. A sketch of the VOPc molecular structure is reported in the inset. (b) Easy Spin simulation of the energy levels for a VOPc molecule with the static magnetic field applied along the z direction (i.e along the V = O bond) based on the values reported in²⁵. The blue arrows represents the eight |−m _S, m _I> → |-m _S+1, m _I> parallel transitions at a probing frequency of 7.7 GHz. Labels help in the identification of the transitions. (c) Normalized frequency shift δν/ν₀ dependence as a function of the magnetic field. (d) Plot of the normalized transmission as a function of the magnetic field. (e) Easy Spin simulation of the CW-ESR powder spectrum at 7.66 GHz based on the parameters given in²⁵. Black dashed lines help in recognizing the transitions.