Theoretical studies of single magnetic impurities on the surface of semiconductors and topological insulators

2013 ◽  
Vol 1564 ◽  
Author(s):  
M. R. Mahani ◽  
A. Pertsova ◽  
C.M. Canali ◽  
M. F. Islam ◽  
A.H. MacDonald
Keyword(s):  
Topological Insulators ◽  
Tight Binding ◽  
Three Dimensional ◽  
Magnetic Coupling ◽  
Magnetic Impurities ◽  
Theoretical Studies ◽  
Acceptor State ◽  
Binding Model ◽  
Deep Acceptor ◽  
Antisite Defects

ABSTRACTWe present results of theoretical studies of transition metal dopants in GaAs, based on microscopic tight-binding model and ab-initio calculations. We focus in particular on how the vicinity of surface affects the properties of the hole-acceptor state, its magnetic anisotropy and its magnetic coupling to the magnetic dopant. In agreement with STM experiments, Mn substitutional dopants on the (110) GaAs surface give rise to a deep acceptor state, whose wavefunction is localized around the Mn center. We discuss a refinement of the theory that introduces explicitly the d-levels for the TM dopant. The explicit inclusion of d-levels is particularly important for addressing recent STM experiments on substitutional Fe in GaAs. In the second part of the paper we discuss an analogous investigation of single dopants in Bi2Se3 three-dimensional topological insulators, focusing in particular on how substitutional impurities positioned on the surface affect the electronic structure in the gap. We present explicit results for BiSe antisite defects and compare with STM experiments.

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 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 Tight-binding model for the band dispersion in rhombohedral topological insulators over the whole Brillouin zone

2018 ◽  
Vol 98 (3) ◽  
Author(s):  
Carlos Mera Acosta ◽  
Matheus P. Lima ◽  
Antônio J. R. da Silva ◽  
A. Fazzio ◽  
C. H. Lewenkopf
Keyword(s):  
Brillouin Zone ◽  
Topological Insulators ◽  
Tight Binding ◽  
Tight Binding Model ◽  
Binding Model ◽  
Band Dispersion

scholarly journals Experimental demonstration of acoustic semimetal with topologically charged nodal surface

2020 ◽  
Vol 6 (8) ◽  
pp. eaav2360 ◽  
Author(s):  
Meng Xiao ◽  
Liping Ye ◽  
Chunyin Qiu ◽  
Hailong He ◽  
Zhengyou Liu ◽  
...  
Keyword(s):  
Momentum Space ◽  
Phononic Crystal ◽  
Tight Binding ◽  
Three Dimensional ◽  
Binding Model ◽  
Experimental Realization ◽  
Nodal Surface ◽  
Full Wave ◽  
Protected Surface ◽  
Topological Charges

Weyl points are zero-dimensional band degeneracy in three-dimensional momentum space that has nonzero topological charges. The presence of the topological charges protects the degeneracy points against perturbations and enables a variety of fascinating phenomena. It is so far unclear whether such charged objects can occur in higher dimensions. Here, we introduce the concept of charged nodal surface, a two-dimensional band degeneracy surface in momentum space that is topologically charged. We provide an effective Hamiltonian for this charged nodal surface and show that such a Hamiltonian can be implemented in a tight-binding model. This is followed by an experimental realization in a phononic crystal. The measured topologically protected surface arc state of such an acoustic semimetal reproduces excellently the full-wave simulations. Creating high-dimensional charged geometric objects in momentum space promises a broad range of unexplored topological physics.

scholarly journals Spin fluctuations and superconductivity in a three-dimensional tight-binding model forBaFe2As2

2010 ◽  
Vol 81 (21) ◽  
Author(s):  
S. Graser ◽  
A. F. Kemper ◽  
T. A. Maier ◽  
H.-P. Cheng ◽  
P. J. Hirschfeld ◽  
...  
Keyword(s):  
Tight Binding ◽  
Three Dimensional ◽  
Spin Fluctuations ◽  
Tight Binding Model ◽  
Binding Model

scholarly journals Electron Transport in Carbon Nanotubes with Adsorbed Chromium Impurities

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 524 ◽  
Author(s):  
Stanislav Repetsky ◽  
Iryna Vyshyvana ◽  
Yasuhiro Nakazawa ◽  
Sergei Kruchinin ◽  
Stefano Bellucci
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Cluster Size ◽  
Density Functional ◽  
Tight Binding ◽  
Electrical Current ◽  
Magnetic Impurities ◽  
Binding Model ◽  
Strong Electron ◽  
Electron Phonon Coupling

We employ Green’s function method for describing multiband models with magnetic impurities and apply the formalism to the problem of chromium impurities adsorbed onto a carbon nanotube. Density functional theory is used to determine the bandstructure, which is then fit to a tight-binding model to allow for the subsequent Green’s function description. Electron–electron interactions, electron–phonon coupling, and disorder scattering are all taken into account (perturbatively) with a theory that involves a cluster extension of the coherent potential approximation. We show how increasing the cluster size produces more accurate results and how the final calculations converge as a function of the cluster size. We examine the spin-polarized electrical current on the nanotube generated by the magnetic impurities adsorbed onto the nanotube surface. The spin polarization increases with both increasing concentration of chromium impurities and with increasing magnetic field. Its origin arises from the strong electron correlations generated by the Cr impurities.

scholarly journals A three-dimensional tight-binding model and magnetic instability of iron selenide KFe2Se2

2012 ◽  
Vol 407 (7) ◽  
pp. 1139-1145 ◽  
Author(s):  
Da-Yong Liu ◽  
Ya-Min Quan ◽  
Zhi Zeng ◽  
Liang-Jian Zou
Keyword(s):  
Tight Binding ◽  
Three Dimensional ◽  
Tight Binding Model ◽  
Binding Model ◽  
Magnetic Instability ◽  
Iron Selenide

scholarly journals Possible Three-Dimensional Topological Insulator in Pyrochlore Oxides

Symmetry ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1076
Author(s):  
Izumi Hase ◽  
Takashi Yanagisawa
Keyword(s):  
Band Structure ◽  
Topological Insulator ◽  
Nearest Neighbor ◽  
Tight Binding ◽  
Three Dimensional ◽  
Tight Binding Model ◽  
Coupling Constant ◽  
Binding Model ◽  
Effective Spin ◽  
Pyrochlore Oxides

A Kene–Mele-type nearest-neighbor tight-binding model on a pyrochlore lattice is known to be a topological insulator in some parameter region. It is an important task to realize a topological insulator in a real compound, especially in an oxide that is stable in air. In this paper we systematically performed band structure calculations for six pyrochlore oxides A2B2O7 (A = Sn, Pb, Tl; B = Nb, Ta), which are properly described by this model, and found that heavily hole-doped Sn2Nb2O7 is a good candidate. Surprisingly, an effective spin–orbit coupling constant λ changes its sign depending on the composition of the material. Furthermore, we calculated the band structure of three virtual pyrochlore oxides, namely In2Nb2O7, In2Ta2O7 and Sn2Zr2O7. We found that Sn2Zr2O7 has a band gap at the k = 0 (Γ) point, similar to Sn2Nb2O7, though the band structure of Sn2Zr2O7 itself differs from the ideal nearest-neighbor tight-binding model. We propose that the co-doped system (In,Sn)2(Nb,Zr)2O7 may become a candidate of the three-dimensional strong topological insulator.

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