Matthias Vojta

Charge Order, Superconductivity, and a Global Phase Diagram of Doped Antiferromagnets

We investigate the interplay between lattice symmetry breaking and superconducting order in a two-dimensional model of doped antiferromagnets, with long-range Coulomb interactions and

Impurity in a d-Wave Superconductor: Kondo Effect and STM Spectra

\mathrm{Sp}(2N)

Quantum phase transitions in d-wave superconductors

spin symmetry, in the large-

Competing orders and quantum criticality in doped antiferromagnets

N

Quantum phase transitions in models of coupled magnetic impurities

limit. Our results motivate the outline of a global phase diagram for the cuprate superconductors. We describe the quantum transitions between the phases, the evolution of their fermion excitation spectrum, and the experimental implications.

Superconducting charge-ordered states in cuprates

We present a theory for recent STM studies of Zn impurities in the superconductor Bi2Sr2CaCu2O8+delta, using insights from NMR experiments which show that there is a net S = 1/2 moment on the Cu ions near the Zn. We argue that the Kondo spin dynamics of this moment is the origin of the low bias peak in the differential conductance, rather than a resonance in a purely potential scattering model. The spatial and energy dependence of the STM spectra of our model can also fit the experiments.

Magnetic properties and spin waves of bilayer magnets in a uniform field

Motivated by the strong, low temperature damping of nodal quasiparticles observed in some cuprate superconductors, we study quantum phase transitions in d(x(2)-y(2)) superconductors with a spin-singlet, zero momentum, fermion bilinear order parameter. We present a complete, group-theoretic classification of such transitions into seven distinct cases (including cases with nematic order) and analyze fluctuations by the renormalization group. We find that only two, the transitions to d(x(2)-y(2))+is and d(x(2)-y(2))+id(xy) pairing, possess stable fixed points with universal damping of nodal quasiparticles; the latter leaves the gapped quasiparticles along (1,0), (0,1) essentially undamped.

Longitudinal magnon in the tetrahedral spin system Cu 2 Te 2 O 5 Br 2 near quantum criticality

We use a number of large-N limits to explore the competition between ground states of square lattice doped antiferromagnets which break electromagnetic

RENORMALIZATION GROUP ANALYSIS OF QUANTUM CRITICAL POINTS IN d-WAVE SUPERCONDUCTORS

U(1),

Kondo effect of impurity moments in d-wave superconductors: Quantum phase transition and spectral properties

time-reversal, or square lattice space-group symmetries. Among the states we find are d-,