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Semyon I. Polukeev

Publications and source records attributed to Semyon I. Polukeev.

2 recordsLinked to original sources

Lattice source for charge and spin inhomogeneity in 2D perovskite cuprates

In the work we highlight the structural features of 2D perovskite cuprates (tilted CuO$_6$ octahedra with different orientation with respect to spacer rocksalt layers), where sources of charge and spin inhomogeneity can be hidden. We used the impurity Anderson model with the Jahn-Teller(JT) local cells to show the charge inhomogeneity arises at any low doping concentration $x$, but disappears when the doping level exceeds threshold concentration $x_c$, and the lower the magnitudes $x_c$, the more JT region square. It is expected that spontaneous chiral symmetry breaking in the dynamic JT state of the stripe CuO$_2$ layer as a whole can lead to the appearance of the goldstone phonon mode. As consequence, the giant thermal Hall effect could be observed in the 2D perovskite cuprates with CuO$_6$ octahedra, rather than with CuO$_4$ squares, e.g. in Tl-based $n$ layer cuprates or cuprates based on the infinite-layer CaCuO$_2$ structure.

cond-mat.str-el

Cation spin and superexchange interaction in oxide materials below and above spin crossover under high pressure

We derived simple rules for the sign of superexchange interaction based on the multielectron calculations of the superexchange interaction in the transition metal oxides that are valid both below and above spin crossover under high pressure. The superexchange interaction between two cations in d$^n$ configurations is given by a sum of individual contributions related to the electron-hole virtual excitations to the different states of the d$^{n + 1}$ and d$^{n - 1}$ configurations. Using these rules, we have analyzed the sign of the superexchange interaction of a number of oxides with magnetic cations in electron configurations from d$^2$ till d$^8$: the iron, cobalt, chromium, nickel, copper and manganese oxides with increasing pressure. The most interesting result concerns the magnetic state of cobalt and nickel oxides CoO, Ni$_2$O$_3$ and also La$_2$CoO$_4$, LaNiO$_3$ isostructural to well-known high-T$_C$ and colossal magnetoresistance materials. These oxides have a spin $\frac{1}{2}$ at the high pressure. Change of the interaction from antiferromagnetic below spin crossover to ferromagnetic above spin crossover is predicted for oxide materials with cations in d$^5$(FeBO$_3$) and d$^7$(CoO) configurations, while for materials with the other d$^n$ configurations spin crossover under high pressure does not change the sign of the superexchange interaction.

cond-mat.mtrl-sci