scholarly journals Two-dimensional higher-order topology in monolayer graphdiyne

2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Eunwoo Lee ◽  
Rokyeon Kim ◽  
Junyeong Ahn ◽  
Bohm-Jung Yang
Keyword(s):  
Tight Binding ◽  
Three Dimensional ◽  
Higher Order ◽  
Order Topology ◽  
Two Dimensional ◽  
First Principles Calculations ◽  
Charge Accumulation ◽  
Binding Model ◽  
Nodal Lines ◽  
Bulk Band

AbstractBased on first-principles calculations and tight-binding model analysis, we propose monolayer graphdiyne as a candidate material for a two-dimensional higher-order topological insulator protected by inversion symmetry. Despite the absence of chiral symmetry, the higher-order topology of monolayer graphdiyne is manifested in the filling anomaly and charge accumulation at two corners. Although its low energy band structure can be properly described by the tight-binding Hamiltonian constructed by using only the pz orbital of each atom, the corresponding bulk band topology is trivial. The nontrivial bulk topology can be correctly captured only when the contribution from the core levels derived from px,y and s orbitals are included, which is further confirmed by the Wilson loop calculations. We also show that the higher-order band topology of a monolayer graphdyine gives rise to the nontrivial band topology of the corresponding three-dimensional material, ABC-stacked graphdiyne, which hosts monopole nodal lines and hinge states.

scholarly journals Cobalt-based magnetic Weyl semimetals with high-thermodynamic stabilities

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Wei Luo ◽  
Yuma Nakamura ◽  
Jinseon Park ◽  
Mina Yoon
Keyword(s):  
Tight Binding ◽  
Three Dimensional ◽  
Interlayer Coupling ◽  
First Principles Calculation ◽  
Optimization Approach ◽  
Binding Model ◽  
Nodal Lines ◽  
Weyl Semimetal ◽  
Topological Quantum ◽  
First Time

AbstractRecent experiments identified Co3Sn2S2 as the first magnetic Weyl semimetal (MWSM). Using first-principles calculation with a global optimization approach, we explore the structural stabilities and topological electronic properties of cobalt (Co)-based shandite and alloys, Co3MM’X2 (M/M’ = Ge, Sn, Pb, X = S, Se, Te), and identify stable structures with different Weyl phases. Using a tight-binding model, for the first time, we reveal that the physical origin of the nodal lines of a Co-based shandite structure is the interlayer coupling between Co atoms in different Kagome layers, while the number of Weyl points and their types are mainly governed by the interaction between Co and the metal atoms, Sn, Ge, and Pb. The Co3SnPbS2 alloy exhibits two distinguished topological phases, depending on the relative positions of the Sn and Pb atoms: a three-dimensional quantum anomalous Hall metal, and a MWSM phase with anomalous Hall conductivity (~1290 Ω−1 cm−1) that is larger than that of Co2Sn2S2. Our work reveals the physical mechanism of the origination of Weyl fermions in Co-based shandite structures and proposes topological quantum states with high thermal stability.

scholarly journals Two-dimensional Weyl points and nodal lines in pentagonal materials and their optical response

Nanoscale ◽  
2021 ◽  
Author(s):  
Sergio Bravo ◽  
M. Pacheco ◽  
V. Nuñez ◽  
J. D. Correa ◽  
Leonor Chico
Keyword(s):  
First Principles ◽  
Optical Response ◽  
Symmetry Analysis ◽  
Two Dimensional ◽  
First Principles Calculations ◽  
Nodal Lines

A symmetry analysis combined with first-principles calculations of two-dimensional pentagonal materials (PdSeTe, PdSeS, InP5 and GeBi2) based on the Cairo tiling reveal nontrivial spin textures, nodal lines and Weyl points.

scholarly journals Scalable Majorana vortex modes in iron-based superconductors

2020 ◽  
Vol 6 (9) ◽  
pp. eaay0443 ◽  
Author(s):  
Ching-Kai Chiu ◽  
T. Machida ◽  
Yingyi Huang ◽  
T. Hanaguri ◽  
Fu-Chun Zhang
Keyword(s):  
Tight Binding ◽  
Three Dimensional ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Zero Energy ◽  
Binding Model ◽  
Zero Bias ◽  
Iron Based Superconductors ◽  
Iron Based ◽  
Important Indication

The iron-based superconductor FeTexSe1−x is one of the material candidates hosting Majorana vortex modes residing in the vortex cores. It has been observed by recent scanning tunneling spectroscopy measurement that the fraction of vortex cores having zero-bias peaks decreases with increasing magnetic field on the surface of FeTexSe1−x. The hybridization of two Majorana vortex modes cannot simply explain this phenomenon. We construct a three-dimensional tight-binding model simulating the physics of over a hundred Majorana vortex modes in FeTexSe1−x. Our simulation shows that the Majorana hybridization and disordered vortex distribution can explain the decreasing fraction of the zero-bias peaks observed in the experiment; the statistics of the energy peaks off zero energy in our Majorana simulation are in agreement with the experiment. These agreements lead to an important indication of scalable Majorana vortex modes in FeTexSe1−x. Thus, FeTexSe1−x can be one promising platform having scalable Majorana qubits for quantum computing.

scholarly journals Three-dimensional superconductors with hybrid higher-order topology

2019 ◽  
Vol 99 (12) ◽  
Author(s):  
Nick Bultinck ◽  
B. Andrei Bernevig ◽  
Michael P. Zaletel
Keyword(s):  
Three Dimensional ◽  
Higher Order ◽  
Order Topology

Energetics of AlN Epitaxial Wetting Layers on SiC (0001)

1996 ◽  
Vol 449 ◽  
Author(s):  
R. Di Felice ◽  
J. E. Northrup ◽  
J. Neugebauer
Keyword(s):  
First Principles ◽  
Three Dimensional ◽  
Layer Growth ◽  
Layer By Layer ◽  
Two Dimensional ◽  
Charge Accumulation ◽  
Wetting Layer ◽  
Interface Charge ◽  
Wetting Layers

ABSTRACTWe present a first-principles characterization of the initial stages of formation of AlN films on c-plane SiC substrates. Studying the competition between two-dimensional films and three-dimensional islands as a function of Al and N abundances, we find that a two-dimensional film can wet the surface in N-rich conditions. Ordered layer-by-layer growth can proceed to some extent on this wetting layer, and is improved by the formation of an atomically mixed interface which eliminates interface charge accumulation. Our results indicate that the stable AlN films grow in the (0001) orientation on the Si-terminated SiC(0001) substrate.

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