Nodal-line semimetals are topological semimetals in which band touchings form nodal lines or rings. Around a loop that encloses a nodal line, an electron can accumulate a nontrivial π Berry phase, so ...the phase shift in the Shubnikov-de Haas (SdH) oscillation may give a transport signature for the nodal-line semimetals. However, different experiments have reported contradictory phase shifts, in particular, in the WHM nodal-line semimetals (W=Zr/Hf, H=Si/Ge, M=S/Se/Te). For a generic model of nodal-line semimetals, we present a systematic calculation for the SdH oscillation of resistivity under a magnetic field normal to the nodal-line plane. From the analytical result of the resistivity, we extract general rules to determine the phase shifts for arbitrary cases and apply them to ZrSiS and Cu_{3}PdN systems. Depending on the magnetic field directions, carrier types, and cross sections of the Fermi surface, the phase shift shows rich results, quite different from those for normal electrons and Weyl fermions. Our results may help explore transport signatures of topological nodal-line semimetals and can be generalized to other topological phases of matter.
Graphitic-like ZnO bilayer films deposited on coinage metals Cu(111), Ag(111), and Au(111) have been studied by density functional theory calculations including dispersion corrections. The scope is ...to compare on an equal footing the properties of the three systems and in particular the nature of the metal/oxide interface. To this end we have considered the adsorption of a CO probe molecule and the vibrational shifts induced by adsorption on ZnO/Cu(111), ZnO/Ag(111), and ZnO/Au(111) compared to adsorption on the unsupported ZnO bilayer and on the wurtzite ZnO (101̅0) surface. We find that while the interaction of ZnO with Ag and Au supports is dominated by dispersion interactions with little or no charge transfer at the interface, in the case of Cu a moderate electron transfer occurs toward the ZnO bilayer. As a consequence, while the stretching frequency of CO on ZnO/Au is blue-shifted, that on ZnO/Cu is red-shifted compared to free CO. CO on ZnO/Ag is intermediate. In all three cases, however, the ZnO bilayer is almost flat, with a modest rumpling found in the case of Cu as a consequence of the stronger chemical interaction. The results fully explain the CO vibrational shifts of CO on ZnO/Cu(111) Schott, V. ; Angew. Chem. Int. Ed. 2013, 52, 1−6 without implying major distortions in the supported film.
Abstract
Two-dimensional layered semiconductors such as molybdenum disulfide (MoS
2
) at the quantum limit are promising material for nanoelectronics and optoelectronics applications. Understanding ...the interface properties between the atomically thin MoS
2
channel and gate dielectric is fundamentally important for enhancing the carrier transport properties. Here, we investigate the frequency dispersion mechanism in a metal-oxide-semiconductor capacitor (MOSCAP) with a monolayer MoS
2
and an ultra-thin HfO
2
high-
k
gate dielectric. We show that the existence of sulfur vacancies at the MoS
2
-HfO
2
interface is responsible for the generation of interface states with a density (
D
it
) reaching ~7.03 × 10
11
cm
−2
eV
−1
. This is evidenced by a deficit S:Mo ratio of ~1.96 using X-ray photoelectron spectroscopy (XPS) analysis, which deviates from its ideal stoichiometric value. First-principles calculations within the density-functional theory framework further confirms the presence of trap states due to sulfur deficiency, which exist within the MoS
2
bandgap. This corroborates to a voltage-dependent frequency dispersion of ~11.5% at weak accumulation which decreases monotonically to ~9.0% at strong accumulation as the Fermi level moves away from the mid-gap trap states. Further reduction in
D
it
could be achieved by thermally diffusing
S
atoms to the MoS
2
-HfO
2
interface to annihilate the vacancies. This work provides an insight into the interface properties for enabling the development of MoS
2
devices with carrier transport enhancement.
Two-dimensional layered semiconductors such as molybdenum disulfide (MoS
) at the quantum limit are promising material for nanoelectronics and optoelectronics applications. Understanding the ...interface properties between the atomically thin MoS
channel and gate dielectric is fundamentally important for enhancing the carrier transport properties. Here, we investigate the frequency dispersion mechanism in a metal-oxide-semiconductor capacitor (MOSCAP) with a monolayer MoS
and an ultra-thin HfO
high-k gate dielectric. We show that the existence of sulfur vacancies at the MoS
-HfO
interface is responsible for the generation of interface states with a density (D
) reaching ~7.03 × 10
cm
eV
. This is evidenced by a deficit S:Mo ratio of ~1.96 using X-ray photoelectron spectroscopy (XPS) analysis, which deviates from its ideal stoichiometric value. First-principles calculations within the density-functional theory framework further confirms the presence of trap states due to sulfur deficiency, which exist within the MoS
bandgap. This corroborates to a voltage-dependent frequency dispersion of ~11.5% at weak accumulation which decreases monotonically to ~9.0% at strong accumulation as the Fermi level moves away from the mid-gap trap states. Further reduction in D
could be achieved by thermally diffusing S atoms to the MoS
-HfO
interface to annihilate the vacancies. This work provides an insight into the interface properties for enabling the development of MoS
devices with carrier transport enhancement.
The introduction of superconductivity to the Dirac surface states of a topological insulator leads to a topological superconductor, which may support topological quantum computing through Majorana ...zero modes
. The development of a scalable material platform is key to the realization of topological quantum computing
. Here we report on the growth and properties of high-quality (Bi,Sb)
Te
/graphene/gallium heterostructures. Our synthetic approach enables atomically sharp layers at both hetero-interfaces, which in turn promotes proximity-induced superconductivity that originates in the gallium film. A lithography-free, van der Waals tunnel junction is developed to perform transport tunnelling spectroscopy. We find a robust, proximity-induced superconducting gap formed in the Dirac surface states in 5-10 quintuple-layer (Bi,Sb)
Te
/graphene/gallium heterostructures. The presence of a single Abrikosov vortex, where the Majorana zero modes are expected to reside, manifests in discrete conductance changes. The present material platform opens up opportunities for understanding and harnessing the application potential of topological superconductivity.
Chemically stable quantum‐confined 2D metals are of interest in next‐generation nanoscale quantum devices. Bottom‐up design and synthesis of such metals could enable the creation of materials with ...tailored, on‐demand, electronic and optical properties for applications that utilize tunable plasmonic coupling, optical nonlinearity, epsilon‐near‐zero behavior, or wavelength‐specific light trapping. In this work, it is demonstrated that the electronic, superconducting, and optical properties of air‐stable 2D metals can be controllably tuned by the formation of alloys. Environmentally robust large‐area 2D‐InxGa1−x alloys are synthesized byConfinement Heteroepitaxy (CHet). Near‐complete solid solubility is achieved with no evidence of phase segregation, and the composition is tunable over the full range of x by changing the relative elemental composition of the precursor. The optical and electronic properties directly correlate with alloy composition, wherein the dielectric function, band structure, superconductivity, and charge transfer from the metal to graphene are all controlled by the indium/gallium ratio in the 2D metal layer.
Air‐stable large‐area 2D‐InxGa1−x alloys with tunable composition and no evidence of phase segregation are realized by confinement heteroepitaxy. The optical and electronic properties directly correlate with alloy composition, wherein the dielectric function, band structure, superconductivity, and charge transfer from the metal to graphene are all controlled by the indium/gallium ratio in the 2D metal layer.
The introduction of superconductivity to the Dirac surface states of a topological insulator leads to a topological superconductor, which may support topological quantum computing through Majorana ...zero modes. The development of a scalable material platform is key to the realization of topological quantum computing. Here we report on the growth and properties of high-quality (Bi,Sb)2Te3/graphene/gallium heterostructures. Our synthetic approach enables atomically sharp layers at both hetero-interfaces, which in turn promotes proximity-induced superconductivity that originates in the gallium film. A lithography-free, van der Waals tunnel junction is developed to perform transport tunneling spectroscopy. We find a robust, proximity-induced superconducting gap formed in the Dirac surface states in 5-10 quintuple-layer (Bi,Sb)2Te3/graphene/gallium heterostructures. The presence of a single Abrikosov vortex, where the Majorana zero modes are expected to reside, manifests in discrete conductance changes. The present material platform opens up opportunities for understanding and harnessing the application potential of topological superconductivity.
Improving reactivity on an insulating surface is crucial due to their important applications in surface catalytic reactions. In this work, we carried out first-principles calculations to investigate ...the adsorption of O2 on a single-layer MgO(100) film deposited on metal substrate. The adsorption configurations, reaction pathways, molecular dynamics simulations, and electronic properties are reported. We reveal that O2 can completely dissociate on the surface, which is in sharp contrast to that on MgO(100) films thicker than one monolayer. The dissociated O2 tends to penetrate into the interfacial region, behaving like a switch to trigger subsequent chemical reactions. As an example, the interplay between water and the interfacial oxygen results in the formation of hydroxyl radicals. This study paves an avenue to accomplish the desired surface catalytic reactions, especially those involving oxygen.
Chemically stable quantum-confined 2D metals are of interest in next-generation nanoscale quantum devices. Bottom-up design and synthesis of such metals could enable the creation of materials with ...tailored, on-demand, electronic and optical properties for applications that utilize tunable plasmonic coupling, optical non-linearity, epsilon-near-zero behavior, or wavelength-specific light trapping. In this work, we demonstrate that the electronic, superconducting and optical properties of air-stable two-dimensional metals can be controllably tuned by the formation of alloys. Environmentally robust large-area two-dimensional InxGa1-x alloys are synthesized by Confinement Heteroepitaxy (CHet). Near-complete solid solubility is achieved with no evidence of phase segregation, and the composition is tunable over the full range of x by changing the relative elemental composition of the precursor. The optical and electronic properties directly correlate with alloy composition, wherein the dielectric function, band structure, superconductivity, and charge transfer from the metal to graphene are all controlled by the indium/gallium ratio in the 2D metal layer.
Nodal-line semimetals are topological semimetals in which band touchings form nodal lines or rings. Around a loop that encloses a nodal line, an electron can accumulate a nontrivial \(\pi\) Berry ...phase, so the phase shift in the Shubnikov-de Haas (SdH) oscillation may give a transport signature for the nodal-line semimetals. However, different experiments have reported contradictory phase shifts, in particular, in the WHM nodal-line semimetals (W=Zr/Hf, H=Si/Ge, M=S/Se/Te). For a generic model of nodal-line semimetals, we present a systematic calculation for the SdH oscillation of resistivity under a magnetic field normal to the nodal-line plane. From the analytical result of the resistivity, we extract general rules to determine the phase shifts for arbitrary cases and apply them to ZrSiS and Cu\(_3\)PdN systems. Depending on the magnetic field directions, carrier types, and cross sections of the Fermi surface, the phase shift shows rich results, quite different from those for normal electrons and Weyl fermions. Our results may help exploring transport signatures of topological nodal-line semimetals and can be generalized to other topological phases of matter.
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