Oct 29 – 30, 2019
FHNW Brugg
Europe/Zurich timezone

Why does an almost pure-beryllium alloy exhibit a hundred-fold increase in $T_c$?

Oct 30, 2019, 3:40 PM
20m
FHNW Brugg

FHNW Brugg

Oral presentation Contributed talks

Speaker

T. Shiroka (Paul Scherrer Institut)

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.

  1. D. V. Semenok, A. G. Kvashnin, I. A. Kruglov, and A. R. Oganov, J. Phys. Chem. Lett. 9, 1920 (2018).
  2. E. Bucher and C. Palmy, Phys. Lett. A 24, 340 (1967).
  3. T. Shang et al., New J. Phys. 21, 073034 (2019).
Position Scientist

Primary authors

T. Shiroka (Paul Scherrer Institut) T. Shang (Paul Scherrer Institut) A. Amon (MPI CPS) D. Kasinathan (MPI CPS) W. Xie (Zhejiang Univ.) M. Bobnar (MPI CPS) Y. Chen (Zhejiang Univ.) A. Wang (Zhejiang Univ.) M. Shi (Paul Scherrer Institut) M. Medarde (Paul Scherrer Institut) H.-Q. Yuan (Zhejiang Univ.)

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