Debye temperature, electron-phonon coupling constant, and microcrystalline strain in highly-compressed La3_3Ni2_2O7−δ_{7-\delta}

Recently Sun et al (Nature 621, 493 (2023)) reported on the discovery of high-temperature superconductivity in highly-compressed La$_3$Ni$_2$O$_{7-\delta}$. In addition to ongoing studies of the phase structural transition, pairing mechanism, and other properties/parameters in this highly-pressurized nickelate, here explore a possibility for the electron-phonon pairing mechanism in the La$_3$Ni$_2$O$_{7-\delta}$. To do this, we analyzed experimental data on temperature dependent resistance, $R(T)$, and extracted pressure dependent Debye temperature, $\Theta_D$, for the $Fmmm$-phase (high-pressure phase). Derived ballpark value is $\Theta_D(P = 25 GPa) = 550$ $K$. We also estimated the electron-phonon coupling constant, $\lambda_{e-ph}(P=22.4 GPa) = 1.75$, for La$_3$Ni$_2$O$_{7-\delta}$ sample exhibited zero-resistance transition. Performed analysis of XRD data showed that the crystal lattice strain, $\epsilon(P)$, is higher in the $Fmmm$-phase in comparison with the $Amam$-phase (low-pressure phase). Based on performed $\epsilon(P)$ analysis, we proposed possible reason for the presence/absence of the zero-resistance state in La$_3$Ni$_2$O$_{7-\delta}$.Comment: 19 pages, 9 figures, 96 reference

The Glacier Complexes of the Mountain Massifs of the North-West of Inner Asia and their Dynamics

The subject of this paper is the glaciation of the mountain massifs Mongun-Taiga, Tavan-Boghd-Ola, Turgeni- Nuru, and Harhira-Nuru. The glaciation is represented mostly by small forms that sometimes form a single complex of domeshaped peaks. According to the authors, the modern glaciated area of the mountain massifs is 21.2 km2 (Tavan-Boghd-Ola), 20.3 km2 (Mongun-Taiga), 42 km2 (Turgeni- Nuru), and 33.1 km2 (Harhira-Nuru). The area of the glaciers has been shrinking since the mid 1960’s. In 1995–2008, the rate of reduction of the glaciers’ area has grown considerably: valley glaciers were rapidly degrading and splitting; accumulation of morainic material in the lower parts of the glaciers accelerated. Small glaciers transformed into snowfields and rock glaciers. There has been also a degradation of the highest parts of the glaciers and the collapse of the glacial complexes with a single zone of accumulation into isolated from each other glaciers. Reduced snow cover area has led to a rise in the firn line and the disintegration of a common accumulation area of the glacial complex. In the of the Mongun-Taiga massif, in 1995– 2008, the firn line rose by 200–300 m. The reduction of the glaciers significantly lagged behind the change in the position of the accumulation area boundary. In the past two years, there has been a significant recovery of the glaciers that could eventually lead to their slower degradation or stabilization of the glaciers in the study area