Florian Kämpfer

Systematic low-energy effective theory for magnons and charge carriers in an antiferromagnet

Abstract By electron or hole doping quantum antiferromagnets may turn into high-temperature superconductors. The low-energy dynamics of antiferromagnets are governed by their Nambu–Goldstone bosons—the magnons—and are described by an effective field theory analogous to chiral perturbation theory for the pions in strong interaction physics. In analogy to baryon chiral perturbation theory—the effective theory for pions and nucleons—we construct a systematic low-energy effective theory for magnons and electrons or holes in an antiferromagnet. The effective theory is universal and makes model-independent predictions for the entire class of antiferromagnetic cuprates. We present a detailed analysis of the symmetries of the Hubbard model and discuss how these symmetries manifest themselves in the effective theory. A complete set of linearly independent leading contributions to the effective action is constructed. The coupling to external electromagnetic fields is also investigated.

Homogeneous versus spiral phases of hole-doped antiferromagnets : A systematic effective field theory investigation

Using the low-energy effective field theory for magnons and holes--the condensed matter analog of baryon chiral perturbation theory for pions and nucleons in QCD--we study different phases of doped antiferromagnets. We systematically investigate configurations of the staggered magnetization that provide a constant background field for doped holes. The most general configuration of this type is either constant itself or represents a spiral in the staggered magnetization. Depending on the values of the low-energy parameters, a homogeneous phase, a spiral phase, or an inhomogeneous phase is energetically favored. The reduction of the staggered magnetization upon doping is also investigated.

Monte Carlo determination of the low-energy constants of a spin-1/2 Heisenberg model with spatial anisotropy

Motivated by the possible mechanism for the pinning of the electronic liquid crystal direction in YBa{sub 2}Cu{sub 3}O{sub 6.45} as proposed by Pardini et al. [Phys. Rev. B 78, 024439 (2008)], we use the first-principles Monte Carlo method to study the spin-(1/2) Heisenberg model with antiferromagnetic couplings J{sub 1} and J{sub 2} on the square lattice. In particular, the low-energy constants spin stiffness {rho}{sub s}, staggered magnetization M{sub s}, and spin wave velocity c are determined by fitting the Monte Carlo data to the predictions of magnon chiral perturbation theory. Further, the spin stiffnesses {rho}{sub s1} and {rho}{sub s2} as a function of the ratio J{sub 2}/J{sub 1} of the couplings are investigated in detail. Although we find a good agreement between our results with those obtained by the series expansion method in the weakly anisotropic regime, for strong anisotropy we observe discrepancies.

Systematic low-energy effective field theory for electron-doped antiferromagnets

In contrast to hole-doped systems which have hole pockets centered at

Magnon-mediated binding between holes in an antiferromagnet

(\ifmmode\pm\else\textpm\fi{}\frac{\ensuremath{\pi}}{2a},\ifmmode\pm\else\textpm\fi{}\frac{\ensuremath{\pi}}{2a})

Nested cluster algorithm for frustrated quantum antiferromagnets.

, in lightly electron-doped antiferromagnets the charged quasiparticles reside in momentum space pockets centered at

Loop-cluster simulation of the zero- and one-hole sectors of the t-J model on the honeycomb lattice

(\frac{\ensuremath{\pi}}{a},0)

Systematic low-energy effective field theory for magnons and holes in an antiferromagnet on the honeycomb lattice

or

Microscopic model versus systematic low-energy effective field theory for a doped quantum ferromagnet

(0,\frac{\ensuremath{\pi}}{a})

Systematic effective field theory investigation of spiral phases in hole-doped antiferromagnets on the honeycomb lattice

. This has important consequences for the corresponding low-energy effective field theory of magnons and electrons which is constructed in this paper. In particular, in contrast to the hole-doped case, the magnon-mediated forces between two electrons depend on the total momentum