Charge correlations in the weakly doped model calculated by projection technique

Abstract

We study frequency-and wave-vector dependent charge correlations in weakly doped antiferromagnets using Mori-Zwanzig projection technique. The system is described by the two-dimensional t-J model. The ground state is expressed within a cumulant formalism which has been successfully applied to study magnetic properties of the weakly doped system. Within this approach the ground state contains independent spin-bag quasiparticles (magnetic polarons). We present results for the charge-density response function and for the optical conductivity at zero temperature for different values of t/J. They agree well with numerical results calculated by exact diagonalization techniques. The density response function for intermediate and large momenta shows a broad continuum on energy scales of order of several t whereas the optical conductivity for ω > 0 is dominated by low energy excitations (at 1.5-2J). We show that these weak-doping properties can be well understood by transitions between excited states of spin-bag quasiparticles.

Phase boundaries of power-law Anderson and Kondo models: A poor man's scaling study

“…However, in Sec. III C we briefly consider the range −1 < r < 0 describing bands with a generalized Van Hove singularity at the Fermi energy [22,23].…”

“…Coupling a Kondo impurity to a fermionic density of states that diverges at the Fermi level in a manner described by Eq. (9) with r < 0 has been shown to yield rich physics including nontrivial quantum phase transitions occurring for ferromagnetic exchange couplings J < 0 [22,23]. The poor man's scaling analysis of the spinanisotropic Kondo model applies also to cases r < 0.…”

“…Several theoretical techniques that have proved powerful for describing quantum impurities in metallic hosts, including the Bethe ansatz, bosonization, and conformal field theory, cannot be applied for a power-law density of states. However, power-law variants of the Kondo impurity model and the corresponding Anderson model have been extensively studied using other techniques such as perturbative scaling [19][20][21][22][23], large-N approaches [19,[24][25][26][27], the NRG [22,[28][29][30][31][32][33][34][35], the perturbative RG [36][37][38], and the local-moment approach [39][40][41]. Due to the depletion of the conduction-band density of states near arXiv:1702.06515v2 [cond-mat.str-el] 30 Jun 2017 the Fermi energy, these pseudogap models feature quantum phase transitions [19] between a local-moment phase for weak impurity-band couplings, in which the impurity spin survives unscreened down to zero temperature, and one or more strong-coupling Kondo phases in which the impurity spin undergoes complete or partial manybody screening (depending on the presence or absence of particle-hole symmetry) [31].…”

Charge dynamics and optical conductivity of thet−Jmodel

“…Similar features of the density response have been previously observed in exact diagonalization studies of small clusters. 7 Recently, the charge correlations in the AFM phase of the t − J model has been investigated by commulant version of projection technique 8 .…”

Spin-anisotropic magnetic impurity in a Fermi gas: Integration of poor man's scaling equations

“…In particular, graphene, where the Kondo effect was observed recently 8 , is considered as a typical realization of this model. More generally, one is interested in Kondo problem for spin coupled to electrons with the pseudogap or diverging DOS [9][10][11][12][13][14][15] .…”