Sabine Andergassen (University of Vienna)
The non-equilibrium electron transport through mesoscopic systems dominated by spin fluctuations is affected by the relaxation and decoherence processes resulting from the coupling of the spin to its environment. The understanding of their origin and their impact on the transport properties is of fundamental importance. We here study the finite-frequency noise of a quantum dot in the Kondo regime in presence of a magnetic field by using the real-time renormalization group in frequency space . Based on a systematic expansion in the reservoir system coupling, we integrate out the reservoir degrees of freedom and provide an analytic solution of the resulting two-loop RG equations in the weak-coupling regime. In particular, the relaxation and decoherence rates characterizing the non-equilibrium transport of mesoscopic systems emerge during the RG flow. We extend the approach of Ref.  to derive analytic expressions for the finite-frequency noise in the stationary state, as well as the real and imaginary part of the ac conductance. We find a singularity in the finite-frequency noise in presence of a magnetic field which is not featured in the ac conductance and discuss the results in reference to recent experiments .
 H. Schoeller, Eur. Phys. J. Special Topics 168, 179 (2009)
 D. Schuricht and H. Schoeller, Phys. Rev. B 80, 075120 (2009)
 J. Basset et al., Phys. Rev. Lett. 108, 046802 (2012)
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