Speaker
Description
As one of the lightest elements, beryllium exhibits high-frequency lattice vibrations, a condition for achieving superconductivity (SC) with a sizeable critical temperature. Yet, paradoxically, its $T_c = 0.026$ K is so low, that its SC is often overlooked. Clearly, $T_c$ is affected also by other factors, notably the electron-phonon coupling strength and the density of states (DOS) at the Fermi level $N(\varepsilon_{\mathrm{F}})$ (rather low in pure Be). Recently, computational searches have shown that SC is more likely to occur in $p^0$- and $d^1$ metals with low-lying empty orbitals. Their electronic properties are predicted to be highly sensitive to structural details, thus resulting in stronger electron-phonon interactions and higher $N(\varepsilon_{\mathrm{F}})$ [1]. Based on this intuition, Be-rich alloys may achieve a much higher $T_c$ than elementary Be itself, a prediction which turns out to be true for ReBe$_{22}$, whose $T_c \sim 9.6$ K [2] exceeds by almost 400(!) times that of Be. Here, we report on an extensive study of the physical properties in the normal- and superconducting state of ReBe$_{22}$, by using a series of experimental techniques, in particular muon-spin rotation/relaxation ($\mu$SR), as well as numerical density-functional-theory (DFT) band-structure calculations [3]. Our results not only explain the origin of the formidable increase of $T_c$ in ReBe$_{22}$, but also predict exciting developments in case of chemical substitution (of Re with Mo or W) or under high-pressure conditions.
- D. V. Semenok, A. G. Kvashnin, I. A. Kruglov, and A. R. Oganov, J. Phys. Chem. Lett. 9, 1920 (2018).
- E. Bucher and C. Palmy, Phys. Lett. A 24, 340 (1967).
- T. Shang et al., New J. Phys. 21, 073034 (2019).
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