Superconductivity in Compression-Shear Deformed Diamond

Diamond is a prototypical ultrawide band gap semiconductor, but turns into a superconductor with a critical temperature $T_c\approx 4\mathrm{K}$ near 3% boron doping [E. A. Ekimov et al., Nature (London) 428, 542 (2004)]. Here we unveil a surprising new route to superconductivity in undoped diamond by compression-shear deformation that induces increasing metallization and lattice softening with rising strain, producing phonon mediated $T_c$ up to 2.4–12.4 K for a wide range of Coulomb pseudopotential ${\mu }^{*}=0.15–0.05$. This finding raises intriguing prospects of generating robust superconductivity in strained diamond crystal, showcasing a distinct and hitherto little explored approach to driving materials into superconducting states via strain engineering. These results hold promise for discovering superconductivity in normally nonsuperconductive materials, thereby expanding the landscape of viable nontraditional superconductors and offering actionable insights for experimental exploration.

Figure 1

(a) The semiconducting, conducting, and superconducting stages of electronic evolution in deformed diamond indicated on the (11-2)[111] CS stress-strain curve. (b) Strain dependence of $T_c$ for a selected range of ${\mu }^{*}$. (c)–(e) Strain evolution of logarithmically averaged phonon frequency ${\omega }_{\log }$, electronic density of states at the Fermi energy $N_{E_F}$, and electron-phonon coupling parameter $\lambda$.

Figure 2

(a)–(d) Electronic band structure and density of states (EDOS, in states/eV/spin) at selected CS strains. (e) Tetrahedrally bonded structural unit with total charge in stable diamond lattice at minimal ($\epsilon =0.000$) and maximal ($\epsilon =0.566$) CS strains in the indicated crystallographic direction. (f) Left panel: a local view of conduction charge distribution from integrated EDOS in $[-0.3,0.3]\mathrm{eV}$ around the Fermi level at $\epsilon =0.000$ and 0.566 along the indicated crystallographic orientation; right panel: the same charge distribution presented in an extended view to showcase the global pattern of conduction charge in crystal planes relative to the strain weakened bonds in the [111] (marked red) and [11-1] (blue) directions.

Figure 3

(a)–(d) Phonon dispersion curves with the strength of $q$-resolved EPC parameter ${\lambda }_q$, indicated by the size of red circles (left panels) and spectral function ${\alpha }^{2}F(\omega )/\omega$ and $\lambda (\omega )$ (right panels) at selected strains. (e) Vibrational modes of the two lowest-frequency branches at $A$, modes $A1$ and $A2$, at CS strain $\epsilon =0.566$ with polarization vectors ${\mathit{e}}_{\mathit{q}j}$ pointed in the [11-1] and [111] directions as indicated by the arrows, which are aligned with the most charge depleted bonds that set the directions of the crystal potential gradients $\nabla V_{\mathit{q}}$.