Current noise and Keldysh vertex function of an Anderson impurity in the Fermi liquid regime

Abstract

We present a complete microscopic Fermi-liquid description for next-to-leading order transport through an Anderson impurity under a finite bias voltage $V$. It is applicable to multilevel quantum dots without particle-hole or time-reversal symmetry, and is constructed based on the nonequilibrium Keldysh formalism, taking into account the current conservation between electrons in the impurity levels and the conduction bands. Specifically, we derive the formula for the current noise generated in the steady flow up to terms of order $(eV{)}^3$ at zero temperature $T=0$. To this end, we calculate the Keldysh vertex functions ${\Gamma }_{\sigma {\sigma }^{\prime };{\sigma }^{\prime }\sigma }^{{\nu }_1{\nu }_2;{\nu }_3{\nu }_4}(\omega ,{\omega }^{\prime };{\omega }^{\prime },\omega )$, which depend on branches ${\nu }_1,{\nu }_2,{\nu }_3$ and ${\nu }_4$ of the time-loop contour and on spin degrees of freedom $\sigma$ and ${\sigma }^{\prime }$, up to linear-order terms with respect to $eV$, $T$, and frequencies $\omega$ and ${\omega }^{\prime }$. The coefficients of these linear-order terms are determined by a set of the parameters, defined with respect to the equilibrium ground state: the phase shift, static susceptibilities, and nonlinear three-body susceptibilities of the impurity electrons. The low-energy expressions of the vertex components are shown to satisfy the Ward identities with the Keldysh Green's functions expanded up to terms of order ${\omega }^2$, $(eV{)}^2$, and $T^2$. We also find that the imaginary part of the Ward identities can be described in terms of the $eV$-dependent collision integrals for a single-quasiparticle excitation and that for a single quasiparticle-quasihole pair excitation. These collision integrals ensure the current conservation of the next-to-leading order Fermi-liquid transport due to the quasiparticles with a finite damping rate.

43 pages, 10 figures, typos have been corrected

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• Role of bias and tunneling asymmetries in nonlinear Fermi-liquid transport through an SU($N$) quantum dot
• Testing the parquet equations and the U(1) Ward identity for real-frequency correlation functions from the multipoint numerical renormalization group
• Thermoelectric transport and current noise through a multilevel Anderson impurity: Three-body Fermi-liquid corrections in quantum dots and magnetic alloys
• Kondo Temperature Evaluated from Linear Conductance in Magnetic Fields
• Three-body Fermi liquid corrections for an infinite-$U$ SU($N$) Anderson impurity model
• Three-body Fermi-liquid corrections for Andreev transport through quantum dots
• Fractional shot noise of an SU(N) Kondo system