Triplet Superconductivity from Nonlocal Coulomb Repulsion in an Atomic Sn Layer Deposited onto a Si(111) Substrate

Abstract

Atomic layers deposited on semiconductor substrates introduce a platform for the realization of the extended electronic Hubbard model, where the consideration of electronic repulsion beyond the on-site term is paramount. Recently, the onset of superconductivity at 4.7 K has been reported in the hole-doped triangular lattice of tin atoms on a silicon substrate. Through renormalization group methods designed for weak and intermediate coupling, we investigate the nature of the superconducting instability in hole-doped Sn=Sið111Þ. We find that the extended Hubbard nature of interactions is crucial to yield triplet pairing, which is f-wave (p-wave) for moderate (higher) hole doping. In light of persisting challenges to tailor triplet pairing in an electronic material, our finding promises to pave unprecedented ways for engineering unconventional triplet superconductivity.

Topological Superconductivity in Sn/Si(111) driven by non-local Coulomb interactions

“…In addition, due to the lack of spatial inversion symmetry, an antisymmetric Rashba spin-orbit coupling (SOC) is induced [22]. However, previous local density approximation (LDA) calculations have revealed that this effect is very small and barely affects the band structure of the system [15]. Thus we will ignore Rashba SOC.…”

“…The non-interacting energy dispersion is then given by where the first neighbor hopping is set to t 1 = −52.7 meV. Relative to t 1 , the other hopping parameters are given by t 2 /t 1 = −0.389, t 3 /t 1 = 0.144, and t 4 /t 1 = −0.027 [14,15]. Besides, µ is the chemical potential, which varies with doping.…”

“…This half-filled elec-tronic state is subject to strong electron-electron interactions that can be modeled by the Hubbard model with a ( √ 3 × √ 3)R30 • structure [13,14]. The triangular lattice Hubbard model is a standard model to study the competition between strong electronic correlations and geometric frustration [15][16][17]. In addition, it has been suggested that non-local Coulomb interactions in Sn/Si(111) are important [15].…”

“…The triangular lattice Hubbard model is a standard model to study the competition between strong electronic correlations and geometric frustration [15][16][17]. In addition, it has been suggested that non-local Coulomb interactions in Sn/Si(111) are important [15]. In 2D atomic layers, it is possible to tune the hopping integrals, filling coefficients, and Coulomb repulsion parameters using impurities or by depositing adatoms on different substrates [18,19].…”

“…These studies found, on the one hand, the mixing of spin-singlet and triplet superconductivity [22], and, on the other hand, pure spin-singlet s-wave pairing [23]; results which are not consistent with each other. Besides, a recent theoretical investigation using functional renormalization group (FRG) and weak-coupling renormalization group (WCRG) approaches lead to a phase diagram for the superconducting instability of the system [15] consisting of chiral d-wave, chiral p-wave, and odd-parity spin-triplet f -wave pairings. These contradictory results lead us to believe that more work is required to understand the mechanism for the Cooper pairing in this system.…”