Ar. Abanov

Quantum-critical theory of the spin-fermion model and its application to cuprates: normal state analysis

We present the full analysis of the normal state properties of the spin-fermion model near the antiferromagnetic instability in two dimensions. The model describes low-energy fermions interacting with their own collective spin fluctuations, which soften at the antiferromagnetic transition. We argue that in 2D, the system has two typical energies—an effective spin-fermion interaction g¯ and an energy ωsf below which the system behaves as a Fermi liquid. The ratio of the two determines the dimensionless coupling constant for spin-fermion interaction λ2 ∝ g¯/ωsf. We show that λ scales with the spin correlation length and diverges at criticality. This divergence implies that the conventional perturbative expansion breaks down. We develop a novel approach to the problem—the expansion in either the inverse number of hot spots in the Brillouin zone, or the inverse number of fermionic flavours—which allows us to explicitly account for all terms which diverge as powers of λ, and treat the remaining, O(log λ) terms in the RG formalism. We apply this technique to study the properties of the spin-fermion model in various frequency and temperature regimes. We present the results for the fermionic spectral function, spin susceptibility, optical conductivity and other observables. We compare our results in detail with the normal state data for the cuprates, and argue that the spin-fermion model is capable of explaining the anomalous normal state properties of the high T c materials. We also show that the conventional {4 theory of the quantum-critical behaviour is inapplicable in 2D due to the singularity of the {4 vertex.

A Relation between the Resonance Neutron Peak and ARPES Data in Cuprates

We argue that the resonant peak observed in neutron scattering experiments on superconducting cuprates and the peak/dip/hump features observed in ARPES measurements are byproducts of the same physical phenomenon. We argue that both are due to feedback effects on the damping of spin fluctuations in a

Spin-Fermion Model near the Quantum Critical Point: One-Loop Renormalization Group Results

d-

Current driven magnetization dynamics in ferromagnetic nanowires with a Dzyaloshinskii-Moriya interaction.

wave superconductor. We consider the spin-fermion model at strong coupling, solve a set of coupled integral equations for fermionic and bosonic propagators and show that the dynamical spin susceptibility below

Neutron Resonance in the Cuprates and its Effect on Fermionic Excitations

T_c

Holey topological thermoelectrics

possesses the resonance peak at

Minimization of Ohmic losses for domain wall motion in a ferromagnetic nanowire.

\Omega_{res} \propto \xi^{-1}

Coherent vs. incoherent pairing in 2D systems near magnetic instability

. The scattering of these magnetic excitations by electrons gives rise to a peak/dip/hump behavior of the electronic spectral function, the peak-dip separation is exactly

Large thermoelectric figure of merit for three-dimensional topological Anderson insulators via line dislocation engineering

\Omega_{res}

Fingerprints of spin mediated pairing in cuprates

.