Laura Classen

Interplay between Magnetism, Superconductivity, and Orbital Order in 5-Pocket Model for Iron-Based Superconductors: Parquet Renormalization Group Study

We report the results of the parquet renormalization group (RG) analysis of the phase diagram of the most general 5-pocket model for Fe-based superconductors. We use as an input the orbital structure of excitations near the five pockets made out of d_{xz}, d_{yz}, and d_{xy} orbitals and argue that there are 40 different interactions between low-energy fermions in the orbital basis. All interactions flow under the RG, as one progressively integrates out fermions with higher energies. We find that the low-energy behavior is amazingly simple, despite the large number of interactions. Namely, at low energies the full 5-pocket model effectively reduces either to a 3-pocket model made of one d_{xy} hole pocket and two electron pockets or a 4-pocket model made of two d_{xz}/d_{yz} hole pockets and two electron pockets. The leading instability in the effective 4-pocket model is a spontaneous orbital (nematic) order, followed by s^{+-} superconductivity. In the effective 3-pocket model, orbital fluctuations are weaker, and the system develops either s^{+-} superconductivity or a stripe spin-density wave. In the latter case, nematicity is induced by composite spin fluctuations.

Competing instabilities, orbital ordering, and splitting of band degeneracies from a parquet renormalization group analysis of a four-pocket model for iron-based superconductors: Application to FeSe

We report the results of a parquet renormalization group (RG) study of competing instabilities in the full 2D four pocket, three orbital low-energy model for iron-based superconductors. We derive and analyze the RG flow of the couplings, which describe all symmetry-allowed interactions between low-energy fermions. Despite that the number of the couplings is large, we argue that there are only two stable fixed trajectories of the RG flow and one weakly unstable fixed trajectory with a single unstable direction. Each fixed trajectory has a finite basin of attraction in the space of initial system parameters. On the stable trajectories, either interactions involving only

Competition of density waves and quantum multicritical behavior in Dirac materials from functional renormalization

d_{xz}

Interaction-induced charge and spin pumping through a quantum dot at finite bias

and

Three-Dimensional Non-Fermi-Liquid Behavior from One-Dimensional Quantum Critical Local Moments

d_{yz}

Ground-state phase diagram of the half-filled bilayer Hubbard model

or only

Fluctuation-induced continuous transition and quantum criticality in Dirac semimetals

d_{xy}

Mott multicriticality of Dirac electrons in graphene

orbital components on the electron pockets dominate, while on the weakly unstable trajectory interactions involving

Instabilities on graphene's honeycomb lattice with electron-phonon interactions

d_{xz}

3D non-Fermi liquid behavior from 1D quantum critical local moments.

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