We present a theory that is a non-Fermi-liquid counterpart of the Abrikosov-Gor'kov pair-breaking theory due to paramagnetic impurities in superconductors. To this end we analyze a model of interacting electrons and phonons that is a natural generalization of the Sachdev-Ye-Kitaev-model. In the limit of large numbers of degrees of freedom, the Eliashberg equations of superconductivity become exact and emerge as saddlepoint equations of a field theory with fluctuating pairing fields. In its normal state the model is governed by two non-Fermi liquid fixed points, characterized by distinct universal exponents. At low temperatures a superconducting state emerges from the critical normal state. We study the role of pair-breaking on T c , where we allow for disorder that breaks time-reversal symmetry. For small Bogoliubov quasi-particle weight, relevant for systems with strongly incoherent normal state, T c drops rapidly as function of the pair breaking strength and reaches a small but finite value before it vanishes at a critical pair-breaking strength via an essential singularity. The latter signals a breakdown of the emergent conformal symmetry of the non-Fermi liquid normal state.Keywords: Eliashberg Theory, Superconductivity, Non-Fermi Liquid, Sachdev-Ye-Kitaev Model, Pair Breaking IntroductionThe dynamical theory of phonon-mediated superconductivity was formulated by Gerasim Matveevich Eliashberg in a pioneering tour de force of quantum many-body theory [1,2]. Considering the regime where phonon frequencies are much smaller than the Fermi energy of the electrons, electrons follow the lattice motion almost instantly. In this limit, Migdal had shown that electron-phonon vertex corrections become small [3]. Then a complicated intermediate-coupling problem suddenly becomes tractable. A closed, selfconsistent dynamical theory emerges that is not limited to the regime of weak electron-phonon interactions. The Eliashberg formalism follows the Gor'kov-Nambu description of superconductivity [4,5], reflecting the broken global U (1) symmetry, associated with charge conservation. The propagation of particles and the conversion of particles into holes are described by two self energies Σ (ω) and Φ (ω), respectively. Using the Eliashberg theory, important advances were made in understanding the physical properties of superconductors with a dimensionless electron-phonon coupling of order unity [6][7][8][9][10][11][12].The Eliashberg formalism has been applied to study superconductivity in problems that go significantly beyond the original electron-phonon problem [13][14][15][16][17][18][19][20][21][22][23]. When an electronic system becomes quantum critical, soft degrees of freedom emerge. The retarded nature of the coupling to such soft excitations makes an analysis in the spirit Eliashberg's approach, with a dynamical pairing field Φ (ω), natural. Since realistic models of quantum critical pairing usually possess no natural small parameter, a controlled approach that leads to an Eliashberg-like formalism is highly desirable....

We determine the information scrambling rate λL due to electron-electron Coulomb interaction in graphene. λL characterizes the growth of chaos and has been argued to give information about the thermalization and hydrodynamic transport coefficients of a many-body system. We demonstrate that λL behaves for strong coupling similar to transport and energy relaxation rates. A weak coupling analysis, however, reveals that scrambling is related to dephasing or single particle relaxation. Furthermore, λL is found to be parametrically larger than the collision rate relevant for hydrodynamic processes, such as electrical conduction or viscous flow, and the rate of energy relaxation, relevant for thermalization. Thus, while scrambling is obviously necessary for thermalization and quantum transport, it does generically not set the time scale for these processes. In addition we derive a quantum kinetic theory for information scrambling that resembles the celebrated Boltzmann equation and offers a physically transparent insight into quantum chaos in many-body systems.

We show that the antiferromagnetic state commonly observed in the phase diagrams of the ironbased superconductors necessarily triggers loop currents characterized by charge transfer between different Fe 3d orbitals. This effect is rooted on the glide-plane symmetry of these materials and on the existence of an atomic spin-orbit coupling that couples states at the X and Y points of the 1-Fe Brillouin zone. In the particular case in which the magnetic moments are aligned parallel to the magnetic ordering vector direction which is the moment configuration most commonly found in the iron-based superconductors these loop currents involve the dxy orbital and either the dyz orbital (if the moments point along the y axis) or the dxz orbitals (if the moments point along the x axis). We show that the two main manifestations of the orbital loop currents are the emergence of magnetic moments in the pnictide/chalcogen site and an orbital-selective band splitting in the magnetically ordered state, both of which could be detected experimentally. Our results highlight the unique intertwining between orbital and spin degrees of freedom in the iron-based superconductors, and reveal the emergence of an unusual correlated phase that may impact the normal state and superconducting properties of these materials.

The ubiquity of ever-connected smartphones has lead to new sensing paradigms that promise environmental monitoring in unprecedented temporal and spatial resolution. Everyday people may use low-cost sensors to collect environmental data. However, measurement errors increase over time, especially with low-cost air quality sensors. Therefore, regular calibration is important. On a larger scale and in participatory sensing, this needs be done in-situ. Since for this step, personal sensor data, time and location need to be exchanged, privacy implications arise. This paper presents a novel privacy-preserving multi-hop sensor calibration scheme, that combines Private Proximity Testing and an anonymizing MIX network with cross-sensor calibration based on rendezvous. Our evaluation with simulated ozone measurements and real-world taxicab mobility traces shows that our scheme provides privacy protection while maintaining competitive overall data quality in dense participatory sensing networks.

In this work, we determine states of electronic order of small-angle twisted bilayer graphene. Ground states are determined for weak and strong couplings which are representatives for varying distances of the twist-angle from its magic value. In the weak-coupling regime, charge density waves emerge which break translational and C 3-rotational symmetry. In the strong coupling-regime, we find rotational and translational symmetry breaking Mott insulating states for all commensurate moiré band fillings. Depending on the local occupation of superlattice sites hosting up to four electrons, global spin-(ferromagnetic) and valley symmetries are also broken which may give rise to a reduced Landau level degeneracy as observed in experiments for commensurate band fillings. The formation of those particular electron orders is traced back to the important role of characteristic non-local interactions which connect all localized states belonging to one hexagon formed by the AB- and BA-stacked regions of the superlattice.