We investigate Anomalous High-Harmonic Generation (AHHG) within a model undergoing a transition from a Weyl semimetal with broken time-reversal symmetry to a semi-Dirac regime. The latter represents a gapless semimetal with a parabolic dispersion in one direction and conical dispersion in the other two. We highlight the broadening of the distribution of excitations in the Brillouin zone and peaks in the AHHG response, observed as a function of the parameter governing the separation of Weyl nodes, as the frequency of the laser pulse increases. Furthermore, we explain the splitting of these peaks upon an increase in the frequency when multiple semi-Dirac points coexist in the Brillouin zone.
Normal and superconducting state spectral properties of cuprates are theoretically described within the extended t-J model. The method is based on the equations of motion for projected fermionic operators and the mode-coupling approximation for the self-energy matrix. The dynamical spin susceptibility at various doping is considered as an input, extracted from experiments. The analysis shows that the onset of superconductivity is dominated by the spin-fluctuation contribution. The coupling to spin fluctuations directly involves the next-nearest-neighbor hopping t', hence Tc shows a pronounced dependence on t'. The latter can offer an explanation for the variation of Tc among different families of hole-doped cuprates. A formula for maximum Tc is given and it is shown that optimum doping, where maximum Tc is reached, is with increasing -t' progresively increased.
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