Strain to alter the covalency and superconductivity in transition metal diborides

Abstract

Among layered metal diborides, MB2, only MgB2 is a superconductor. However, a strategically applied mechanical stress that removes metal–boron covalency can turn ScB2 into a superconductor with the same mechanism.

Progress, Challenges, and Opportunities in the Synthesis, Characterization, and Application of Metal-Boride-Derived Two-Dimensional Nanostructures

“…Bekaert et al found that surface states in thin MgB 2 layers also support superconductivity . Various authors have highlighted how strain can greatly increase T C in nanosheets. , The largest predicted T C of ∼100 K was calculated by Bekaert et al for atomically thin MgB 2 and a combination of hydrogenation and biaxial strain.…”

“…In this Perspective, we summarize the history, chemical bonding, and crystal structure of both bulk metal borides and the corresponding 2D nanostructures. ,− We emphasize various strategies proposed to synthesize metal-boride-derived 2D nanostructures and ultrathin films. − ,,,, We also present newly developed insights upon revisiting the chemistry of AlB 2 -type metal diborides. ,,,,, Synthetic challenges toward nanostructures of metal diborides, pseudo-metal diborides, MAB phases, and 2D MBenes are summarized and discussed in detail. ,,,,− Later, attention is drawn towards the effect of nanoscaling on catalytic, electrochemical, transport, optical, and mechanical properties. ,,,,,,,,,− Our emphasis is not only on the synthesis and properties, but also on diverse potential applications, such as energy storage in batteries, ,,− hydrogen storage and production, ,,,,− sensors, ,,− propellants, combustion and fuels, and biomedicine. , Finally, this Perspective summarizes and presents an outlook on the intriguing aspects, missing links, and some of the remaining challenges and opportunities in the field of metal-boride-derived 2D nanostru...…”

The effect of strain and pressure on the electron-phonon coupling and superconductivity in MgB2—Benchmark of theoretical methodologies and outlook for nanostructure design

“…Bekaert et al 22 used DFPT to study strained MgB 2 monolayers and found that reducing in-plane Mg-Mg distances with 4.5% biaxial compressive strain reduces T c by 11 K, from 20 K of the relaxed single monolayer, while 4.5% tensile strain boosts it up to 53 K. It is noted that the response to strain is much higher in MgB 2 than in superconducting graphene. 22 Zhai et al 23 studied how strain alters the covalency in transition metal diborides and discussed implications for superconductivity. They note how stretching uniaxially along the c-axis can raise the energy of the σ-band and favorably reduce the frequency of the E 2g phonon.…”

“…The study is the only one showing such pressure behavior. Moreover, the effect of anisotropic strain on MgB 2 superconductivity has been explored experimentally [18][19][20] and theoretically, [21][22][23] out of which only Ref. 22 treats EPC from first principles (for a monolayer).…”

High-temperature phonon-mediated superconductivity in monolayer Mg2B4C2

“…Pickett and co-workers proposed that one can, in principle, achieve a much higher T c (than 39 K) by designing a MgB 2 -like stable material which has a similar Fermi surface as in MgB 2 , and in which more than two phonon modes couple to the electronic states near the Fermi level, thereby, resulting in a sizable total el-ph coupling [25,43,44]. This idea has been employed for the rational design of new bulk superconductors with a good success rate [53][54][55][56][57][58][59][60][61][62][63][64]. The high-pressure superconductivity observed at 250 K in lanthanum hydride is one such example [65][66][67][68].…”