Single-hole dispersion relation for the real CuO2 plane

Linear and nonlinear temperature-dependent transmission/absorption characteristics of cadmium telluride crystal for terahertz generation

This paper reports on the temperature-dependent investigation of linear and nonlinear transmission/absorption characteristics of CdTe crystal in the 300-408 K range using 780-970 nm tunable wavelengths of 140 fs pulses obtained from a Ti:Sapphire laser at 80 MHz repetition rate. The same pulses were also used for terahertz generation. The linear transmission/absorption properties were measured using a specially improvised temperature-tuned spectrophotometer in the 500-1500 nm wavelength range. The linear absorption of 750 nm wavelength gradually increases with respect to a rise in the temperature, and transmission becomes zero at 408 K. Nonlinear absorption induced by femtosecond pulses shows a sudden drop of 18% in transmission above the 800 nm range, due to electron-phonon interaction, which affects the strength of the terahertz signal. It is also responsible for change in the temperature along with the linear shift in the refractive index of the crystal.

Differences between the insulating limit quasiparticles of one-band and three-band cuprate models

We study the charge dynamics of the quasiparticle that forms when a single hole is doped in a two-dimensional antiferromagnet as described by the one-band t-t'-t"-J model, using a variational approximation that includes spin fluctuations in the vicinity of the hole. We explain why the spin fluctuations and the longer range hopping have complementary contributions to the quasiparticle dynamics, and thus why both are essential to obtain a dispersion in agreement with that measured experimentally. This is very different from the three-band Emery model in the strongly-correlated limit, where the same variational approximation shows that spin fluctuations have a minor effect on the quasiparticle dynamics. This difference proves that these one-band and three-band models describe qualitatively different quasiparticles in the insulating limit, and therefore that they cannot both be suitable to describe the physics of very underdoped cuprates.

Calculated momentum dependence of Zhang-Rice states in transition metal oxides

Using a combination of local density functional theory and cluster exact diagonalization based dynamical mean field theory, we calculate many-body electronic structures of several Mott insulating oxides including undoped high T(c) materials. The dispersions of the lowest occupied electronic states are associated with the Zhang-Rice singlets in cuprates and with doublets, triplets, quadruplets, and quintets in more general cases. Our results agree with angle resolved photoemission experiments including the decrease of the spectral weight of the Zhang-Rice band as it approaches k=0.

Nonlocal composite spin-lattice polarons in high temperature superconductors

The nonlocal nature of the polaron formation in t - t '- t'' - J model is studied in large lattices up to 64 sites by developing a new numerical method. We show that the effect of longer-range hoppings t' and t'' is a large anisotropy of the electron-phonon interaction (EPI) leading to a completely different influence of EPI on the nodal and antinodal points in agreement with the experiments. Furthermore, nonlocal EPI preserves polaron's quantum motion, which destroys the antiferromagnetic order effectively, even in the strong coupling regime, although the quasiparticle weight in angle-resolved-photoemission spectroscopy is strongly suppressed.

Low-energy spectra in t-J-type models at low doping levels

Based on a variational approach, we propose that there are two kinds of low-energy states in the t-J-type models at low doping. In a quasiparticle state an unpaired spin bound to a hole with a well-defined momentum can be excited with spin waves. The resulting state shows a suppression of antiferromagnetic order around the hole with the profile of a spin bag. These spin-bag states with spin and charge or hole separated form a continuum of low-energy excitations. Very different properties predicted by these two kinds of states explain a number of anomalous results observed in the exact diagonalization studies on small clusters up to 32 sites.

Stripes in doped antiferromagnets: single-particle spectral weight

Recent angle-resolved photoemission spectroscopy (ARPES) experiments on cuprate superconductors provide important guidelines for a theory of electronic excitations in the stripe phase. Using a cluster perturbation theory, where short-distance effects are accounted for by exact cluster diagonalization and long-distance effects by perturbation (in the hopping), we calculate the single-particle Green's function for a striped t-J model. The data obtained quantitatively reproduce salient (ARPES) features and may serve to rule out "bond-centered" in favor of "site-centered" stripes.

Doped stripes in models for the cuprates emerging from the one-hole properties of the insulator

The extended and standard t-J models are computationally studied on ladders and planes, with emphasis on the small J/t region. At couplings compatible with photoemission results for undoped cuprates, half-doped stripes separating pi-shifted antiferromagnetic (AF) domains are found, as in Tranquada's interpretation of neutron experiments. Our main result is that the elementary stripe "building block" resembles the properties of one hole at small J/t, with robust AF correlations across the hole induced by the local tendency of the charge to separate from the spin. This suggests that the seed of half-doped stripes already exists in the unusual properties of the insulating parent compound.