Hidden phase in a two-dimensional Sn layer stabilized by modulation hole doping

Ming, Fangfei; Mulugeta, Daniel; Tu, Weisong; Smith, Tyler; Vilmercati, Paolo; Lee, Geunseop; Huang, Y. Y.; Diehl, Renee D.; Snijders, Paul C.; Weitering, Hanno H.

doi:10.1038/ncomms14721

Cited by 19 publications

(40 citation statements)

References 38 publications

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“…We monitored the evolution of the local density of states (LDOS) as a function of doping level by measuring the differential conductance with STM (𝑑𝐼/𝑑𝑉 ∝ LDOS), where we introduced valence band holes using heavily boron-doped silicon substrates 4 . This method is similar to the modulation doping approach widely used in semiconductor heterostructure engineering 26 . We estimated that the highest doping level achievable with this method is about ten percent, based on the measured spectral weight transfer (see below) 4 .…”

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confidence: 99%

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

Ming

Smith

et al. 2020

Phys. Rev. Lett.

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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.

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confidence: 99%

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

Ming

Smith

et al. 2020

Phys. Rev. Lett.

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“…To ensure the consistency of the results, we repeated the experiments on different Si(111) substrates, including heavily-doped n-type substrates (As-doped; 0.002 Ωcm), moderately doped p-type substrates (B-doped; 0.02 Ωcm), and heavily-doped p-type substrates (B-doped; 0.001 Ωcm). We generally find that the n-type substrates produce fewer defects while only p-type substrates provide reliable spectroscopy data at low temperature (19). The surfaces were studied using scanning tunneling microscopy and spectroscopy (STM/STS).…”

Section: Methodsmentioning

confidence: 99%

Coupled Sublattice Melting and Charge-Order Transition in Two Dimensions

et al. 2020

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Two-dimensional melting is one of the most fascinating and poorly understood phase transitions in nature. Theoretical investigations often point to a two-step melting scenario involving unbinding of topological defects at two distinct temperatures. Here we report on a novel melting transition of a charge-ordered K-Sn alloy monolayer on a silicon substrate. Melting starts with short-range positional fluctuations in the K sublattice while maintaining long-range order, followed by longer-range K diffusion over small domains, and ultimately resulting in a molten sublattice. Concomitantly, the charge-order of the Sn host lattice collapses in a multi-step process with both displacive and order-disorder transition characteristics. Our combined experimental and theoretical analysis provides a rare insight into the atomistic processes of a multi-step melting transition of a two-dimensional materials system.Main Text: Low-dimensional solids are fundamentally different from three-dimensional (3D) bulk solids. This difference is especially manifest in phase transitions and critical phenomena as the balance between energy and entropy is profoundly altered in low dimension. The melting transition arguably provides the most striking contrast. 3D melting is known to be a first order (i.e. discontinuous) phase transition. In 2D, on the other hand, continuous melting transitions are possible and they are believed to be topological in nature (1-5). Most structural phase transitions in quasi 2D systems such as surfaces and interfaces can be described within Landau's conceptual framework of spontaneous symmetry breaking where the ground state of the system no longer possesses the full symmetry of the high-temperature phase (6, 7). Symmetry and dimensionality are the quintessential ingredients of this theoretical framework.

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“…Using the modulation doping concept, we recently uncovered a novel equilibrium phase in a hole-doped bilayer of Sn on p-type Si(111) [17]. The holes originate from the boron dopants inside the bulk substrate.…”

Section: Introductionmentioning

confidence: 99%

“…Scanning Tunneling Microscopy (STM) images of the high-symmetry phase or Si(111)(23×23)R30⁰-Sn surface (henceforth denoted as the '23 phase') reveal a 2D hexagonal array of Sn tetramers where each tetramer consists of a bright 'up-dimer' and a dim 'down dimer' (Fig. 1; see also Ref [17]). The 23 surface has a rhombic unit cell with cm symmetry (2D space group no.…”

Section: Introductionmentioning

confidence: 99%

“…The 23 surface has a rhombic unit cell with cm symmetry (2D space group no. 5) [17] where the (23×23) supercell is rotated 30° degrees with respect to the (1×1) unit cell of the truncated Si(111) substrate. The broken symmetry phase, or Si(111)(43×23)R30⁰-Sn surface ('43 phase'), reveals a pattern in which the bright dimers are rotated 45° and form a staggered zig-zag pattern (Fig.…”

Section: Introductionmentioning

confidence: 99%

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Atomic and electronic structure of doped Si(111)(23×23)R30∘ -Sn interfaces

Ming

Huang

et al. 2018

Phys. Rev. B

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The hole doped Si(111)(23×23)R30⁰-Sn interface exhibits a symmetry-breaking insulator-insulator transition below 100 K that appears to be triggered by electron tunneling into the empty surface-state bands.No such transition is seen in electron-doped systems. To elucidate the nature and driving force of this phenomenon, the structure of the interface must be resolved. Here we report on an extensive experimental I INTRODUCTIONSurfaces and ultrathin metal/semiconductor interfaces are an interesting platform for studying phase transitions and emergent phenomena in two-dimensions (2D). In particular, adsorption of group III and group IV post-transition metal atoms on Si(111) and Ge(111) surfaces produces a variety of interesting phenomena such as Mott metal-insulator transitions [1-3], charge-ordering transitions [4][5][6][7][8], and even superconductivity [9][10][11][12][13]. Although the structural degrees of freedom of these systems are determined in large part by the underlying substrate, these systems are near-perfect 2D electron systems as the electronic interactions take place in one or several surface state bands that are generally decoupled from the 3D electronic structure of the underlying Si or Ge substrate.Notwithstanding their intellectual appeal, the electronic properties of surfaces and interfaces are difficult to control, other than through simple coverage control or change of substrate. For instance, strictly 3 2D systems such as exfoliated 2D materials, surfaces, and interfaces are all difficult to dope because the presence of dopants inevitably introduces structural disorder as the ionized dopant impurities, and the associated modulations of the potential energy landscape, become an integral part of the 2D electron system.In principle, this dilemma can be avoided by employing a modulation doping approach in which the chemical dopants are spatially separated from the 2D electron system [14], as is done in, e.g., semiconductor quantum well superlattices [14, 15] and layered perovskite materials [16]. In fact, most of the current emphasis on low-dimensional quantum matter phases involves mapping of the electronic phase diagrams of quasi 2D bulk materials as a function of doping level or chemical potential. However, efforts to systematically control the electronic properties of surfaces and interfaces are largely undeveloped, suggesting that many interesting 2D phases of matter are still awaiting experimental discovery.Using the modulation doping concept, we recently uncovered a novel equilibrium phase in a hole-doped bilayer of Sn on p-type Si(111) [17]. The holes originate from the boron dopants inside the bulk substrate.The formation of this broken symmetry phase appears to be triggered by electrons tunneling from the tip of a scanning tunneling microscope (STM) into the sample, and sets in below 100 K. No such transition is seen on n-type Si suggesting that the high-symmetry phase is the ground state for the n-type system. Scanning Tunneling Microscopy (STM) images of the high-symmetry phase orSi...

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Hidden phase in a two-dimensional Sn layer stabilized by modulation hole doping

Cited by 19 publications

References 38 publications

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

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

Coupled Sublattice Melting and Charge-Order Transition in Two Dimensions

Atomic and electronic structure of doped Si(111)(23×23)R30∘ -Sn interfaces

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