Superconductivity in a Hole-Doped Mott-Insulating Triangular Adatom Layer on a Silicon Surface

Abstract

The discovery of high-temperature superconductivity in doped copper-oxide (cuprate) materials 1 triggered an enormous interest in the relation between Mott physics, magnetism, and superconductivity 2 . Undoped cuprates are antiferromagnetic Mott insulators, where the Coulomb repulsion between electrons occupying the same atomic orbital prevents carriers from moving through the crystal. The introduction of electron vacancies or 'holes' into these materials, however, leads to the formation of Cooper pairs and their condensation into a macroscopically coherent superconducting quantum state. Now several decades later, there still is no consensus regarding the precise mechanism of cuprate superconductivity. Progress in this field would greatly benefit from discoveries of superconductivity in other Mottinsulating materials 3 . Here, we show that adsorption of only 1/3 monolayer of Sn atoms on a heavily boron-doped silicon (111) substrate 4 produces a strictly two-dimensional superconductor with a critical temperature 𝑻 𝐜 of 4.7 ± 0.3 K that rivals that of NaxCoO2•yH2O 5,6 Both systems can be viewed as close but very rare realizations of the triangular-lattice spin-1/2 Heisenberg antiferromagnet, which is a strong candidate for hosting exotic magnetism 7 and chiral superconductivity 8-11 . These findings point to 'cupratelike' physics in a simple sp-bonded non-oxide system and suggest the possibility of exploring unconventional superconductivity using a conventional semiconductor platform.

Experimental observation of pseudogap in a modulation-doped Mott insulator: Sn/Si(111)-($\sqrt{3}\times \sqrt{3}$)-R30$^\textrm{o}$

“…By extrapolating the linear relationship of the PG depth versus temperature to the point where the gap depth is equal to zero, the transition temperature, T * , is estimated to be around 99 K. We further compare the spectral weight of IGS relative to LHB and UHB, and therefore obtain the hole doping level of at most 8.5% for our samples investigated. This value is lower than the threshold doping level of 10% required for the emergent superconductivity [27]. This suggests that the √ 3-Sn samples studied here lie in the underdoped regions, which happens to match with the experimental observation of PG.…”

“…This hints that it has nothing to do with superconductivity. Indeed, the gap magnitude of ∼ 20 meV turns out to be unrealistically larger than the specific superconducting gap of ∼ 1.5 meV identified in this system [27]. Figure 2(b) plots the dependence of the site-specific tunneling dI/dV spectra on temperature ranging from 4.2 K to 77 K. At elevated temperatures, the gap gets gradually suppressed.…”

“…3)R30 o (hereinafter referred to as √ 3-Sn) on chemical doping by employing heavily boron-doped Si substrates [27]. Such a charge transfer mechanism has been well known as modulation doping in semiconductor heterostructures [28][29][30] and recently evidenced in cuprates [31,32], thereby calling for further investigation of possible commonalities and distinctions between the doped √ 3-Sn and cuprates.…”

Superconductivity in Shear Strained Semiconductors

“…These results underscore excellent prospects for inducing vigorous superconducting states in elastically deformed semiconductors. These superior Tc values under tunable shear strains are well above those achieved in semiconducting or conducting films under fixed tensile strains by lattice mismatch [11][12][13][14], making shear-strain tuning a desirable approach.…”

“…The resulting electrically conducting states couple to another degree of freedom, e.g., lattice vibration (i.e., phonon), to generate superconductivity in chemically (doping) or physically (pressure) modulated semiconductors. In recent years, strain engineering has been employed to induce superconductivity at surfaces or thin films via adatom adsorption or interfacial lattice mismatch [11][12][13][14][15]. This approach is effective, but lacks flexibility of tuning the resulting superconducting states, since the strains are fixed once the surface or substrate conditions are set.…”