Evolution of Electron Spin Resonance through a Metallic Quantum Critical Phase Diagram

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Abstract
In the heavy-fermion metal YbRh 2 Si 2 , quantum criticality at a suppressed antiferromagnetic order is governed by the interplay of local magnetic moments and itinerant conduction electrons. We demonstrate how this can be investigated by a new experimental approach that enables the observation of electron spin resonance (ESR) across a broad range of frequencies and fields at very low temperatures. This allowed us to cover a large part of the phase diagram from the paramagnetic Fermi-liquid phase to the phase with antiferromagnetic order and including the quantum-critical regime. Both the ESR g factor and the linewidth present distinct behaviors in these three regimes, providing further insight into the physics across a quantum critical point. Notably, when cooling down at a field directly toward the quantum critical point, both g factor and linewidth continuously decrease. Furthermore, we observe a very good matching of the g -factor behavior upon field tuning and temperature tuning toward the quantum-critical point. We analyze and discuss the results in the context of present theories on ESR in strongly correlated electron systems.
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Funding Information
  • Deutsche Forschungsgemeinschaft (SCHE 1580/2-1)
  • Deutsche Forschungsgemeinschaft (SI 1339/1-1)
  • Deutsche Forschungsgemeinschaft (A3)
  • Deutsche Forschungsgemeinschaft (422213477)
  • Deutsche Forschungsgemeinschaft (A03)
  • Volkswagen Foundation (I/84689)

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