ALT On the top is a graph of the overall phase diagram with extremely heavy Landau fermi liquid regimes showing antiferromagnetic order and metallic paramagnetism as well as the temperature line. Circles indicate the electron spin resonance resonance field for different microwave frequencies obtained by temperature-dependent electron spin resonance measurements. The pronounced evolution of these resonance fields as a function of temperature clearly differs for the different regimes and directly reflects the temperature-dependent g-factor. Below are exemplary electron spin resonance spectra for three resonance frequencies for three temperatures each. Key observations upon cooling are, shown from left to right, broadening and back-shift in the AFL phase, monotonous shift and narrowing in the quantum-critical regime, and temperature-independent resonance field in the PFL regime.