Hendrik Meier

Cascade of phase transitions in the vicinity of a quantum critical point

We study the timely issue of charge order checkerboard patterns observed in a variety of cuprate superconductors. We suggest a minimal model in which strong quantum fluctuations in the vicinity of a single antiferromagnetic quantum critical point generate the complexity seen in the phase diagram of cuprates superconductors and, in particular, the evidenced charge order. The Fermi surface is found to fractionalize into hotspots and antinodal regions, where physically different gaps are formed. In the phase diagram, this is reflected by three transition temperatures for the formation of pseudogap, charge density wave, and superconductivity (or quadrupole density wave if a sufficiently strong magnetic field is applied). The charge density wave is characterized by modulations along the bonds of the CuO lattice with wave vectors connecting points of the Fermi surface in the antinodal regions. These features, previously observed experimentally, are so far unique to the quantum critical point in two spatial dimensions and shed a new light on the interplay between strongly fluctuating critical modes and conduction electrons in high-temperature superconductors.

Anomalous Hall effect in granular ferromagnetic metals and effects of weak localization.

We theoretically investigate the anomalous Hall effect in a system of dense-packed ferromagnetic grains in the metallic regime. Using the formalism recently developed for the conventional Hall effect in granular metals, we calculate the residual anomalous Hall conductivity

Effect of magnetic field on the competition between superconductivity and charge order below the pseudogap state

{\ensuremath{\sigma}}_{xy}

Exact bosonization for an interacting fermi gas in arbitrary dimensions.

and resistivity

Fluxonium-Based Artificial Molecule with a Tunable Magnetic Moment

{\ensuremath{\rho}}_{xy}

Vortices and charge order in high-

and weak localization corrections to them for both skew-scattering and side-jump mechanisms. We find that the scaling relation between

T_{c}

{\ensuremath{\rho}}_{xy}

superconductors

and the longitudinal resistivity

Pairing gaps near ferromagnetic quantum critical points

{\ensuremath{\rho}}_{xx}

Low-energy excitations and singular contributions in the thermodynamics of clean Fermi liquids

of the array does not hold, regardless of whether it is satisfied for the specific resistivities of the grain material or not. The weak localization corrections, however, are found to be in agreement with those for homogeneous metals. We discuss recent experimental data on the anomalous Hall effect in polycrystalline iron films in view of the obtained results.