Degenerate topological line surface phonons in quasi-1D double helix crystal SnIP

AbstractDegenerate points/lines in the band structures of crystals have become a staple of the growing number of topological materials. The bulk-boundary correspondence provides a relation between bulk topology and surface states. While line degeneracies of bulk excitations have been extensively characterised, line degeneracies of surface states are not well understood. We show that SnIP, a quasi-one-dimensional van der Waals material with a double helix crystal structure, exhibits topological nodal rings/lines in both the bulk phonon modes and their corresponding surface states. Using a combination of first-principles calculations, symmetry-based indicator theories and Zak phase analysis, we find that two neighbouring bulk nodal rings form doubly degenerate lines in their drumhead-like surface states, which are protected by the combination of time-reversal symmetry $${{{\mathcal{T}}}}$$ T and glide mirror symmetry $${\bar{M}}_{y}$$ M ¯ y . Our results indicate that surface degeneracies can be generically protected by symmetries such as $${{{\mathcal{T}}}}{\bar{M}}_{y}$$ T M ¯ y , and phonons provide an ideal platform to explore such degeneracies.

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Obvious Surface States Connecting to the Projected Triple Points in NaCl’s Phonon Dispersion

Frontiers in Chemistry ◽

10.3389/fchem.2021.789522 ◽

2021 ◽

Vol 9 ◽

Author(s):

Li Zhang ◽

Fang Fang ◽

Lixin Cheng ◽

Huiming Lin ◽

Kai Wang

Keyword(s):

Computer Technology ◽

Triple Point ◽

First Principles ◽

Phonon Dispersion ◽

Surface States ◽

Theoretical Chemistry ◽

First Principles Calculations ◽

Nodal Lines ◽

Topological Materials ◽

Speed And Accuracy

With the development of computer technology and theoretical chemistry, the speed and accuracy of first-principles calculations have significantly improved. Using first-principles calculations to predict new topological materials is a hot research topic in theoretical and computational chemistry. In this work, we focus on a well-known material, sodium chloride (NaCl), and propose that the triple point (TP), quadratic contact triple point (QCTP), linear and quadratic nodal lines can be found in the phonon dispersion of NaCl with Fm3¯ m type structure. More importantly, we propose that the clear surface states connected to the projected TP and QCTP are visible on the (001) surface. It is hoped that further experimental investigation and verification for these properties as mentioned above.

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Interface-induced sign reversal of the anomalous Hall effect in magnetic topological insulator heterostructures

Nature Communications ◽

10.1038/s41467-020-20349-z ◽

2021 ◽

Vol 12 (1) ◽

Cited By ~ 1

Author(s):

Fei Wang ◽

Xuepeng Wang ◽

Yi-Fan Zhao ◽

Di Xiao ◽

Ling-Jie Zhou ◽

...

Keyword(s):

Hall Effect ◽

Electric Fields ◽

First Principles ◽

Berry Phase ◽

Condensed Matter ◽

Anomalous Hall Effect ◽

First Principles Calculations ◽

Sign Reversal ◽

Berry Curvature ◽

Topological Materials

AbstractThe Berry phase picture provides important insights into the electronic properties of condensed matter systems. The intrinsic anomalous Hall (AH) effect can be understood as the consequence of non-zero Berry curvature in momentum space. Here, we fabricate TI/magnetic TI heterostructures and find that the sign of the AH effect in the magnetic TI layer can be changed from being positive to negative with increasing the thickness of the top TI layer. Our first-principles calculations show that the built-in electric fields at the TI/magnetic TI interface influence the band structure of the magnetic TI layer, and thus lead to a reconstruction of the Berry curvature in the heterostructure samples. Based on the interface-induced AH effect with a negative sign in TI/V-doped TI bilayer structures, we create an artificial “topological Hall effect”-like feature in the Hall trace of the V-doped TI/TI/Cr-doped TI sandwich heterostructures. Our study provides a new route to create the Berry curvature change in magnetic topological materials that may lead to potential technological applications.

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Magnetism and Half-Metallicity in (100) Surface of Inverse Heusler Mn2CoSb

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1015.377 ◽

2014 ◽

Vol 1015 ◽

pp. 377-380

Author(s):

Tao Chen ◽

Ying Chen ◽

Yin Zhou ◽

Hong Chen

Keyword(s):

Density Functional Theory ◽

Magnetic Properties ◽

First Principles ◽

Heusler Alloy ◽

Density Functional ◽

Magnetic Moments ◽

Surface States ◽

First Principles Calculations ◽

Half Metallicity ◽

Functional Theory

Using the first-principles calculations within density functional theory (DFT), we investigated the electronic and magnetic properties of (100) surface of inverse Heusler alloy Mn2CoSb with five different terminations. Our work reveals that the surface Mn atom moves to vacuum while surface Co atom moves to slab. Moreover, duo to the reason that the surface atom lost half of the nearest atoms with respect to the bulk phase, resulting in the decrease of hybridization, the atom-resolved spin magnetic moments of surface atoms are enhanced. Further investigation on DOS and PDOS showed that half-metallicity was preserved only in SbSb-termination while was destroyed in MnCo-, MnSb-, MnMn-, and CoCo-termination due to the appearance of surface states.

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One-dimensional transition metal dihalide nanowires as robust bipolar magnetic semiconductors

Nanoscale ◽

10.1039/c9nr10849a ◽

2020 ◽

Vol 12 (16) ◽

pp. 8942-8948

Author(s):

Xingyi Tan ◽

Lili Liu ◽

Hui Xiang ◽

Gui-Fang Du ◽

Ao Lou ◽

...

Keyword(s):

Transition Metal ◽

First Principles ◽

Magnetic Semiconductors ◽

First Principles Calculations ◽

One Dimensional ◽

New Family

Herein, a new family of 1D transition metal dihalide (TMCl2) nanowires are proposed by using first-principles calculations.

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Theoretical Study of Atoms Filled in Carbon Nanotubes

Journal of Computational and Theoretical Nanoscience ◽

10.1166/jctn.2016.5655 ◽

2016 ◽

Vol 13 (10) ◽

pp. 6974-6977

Author(s):

Shuwen Cui ◽

Weiwei Liu ◽

Xiaosong Wang

Keyword(s):

Carbon Nanotubes ◽

First Principles ◽

Density Functional ◽

Theoretical Study ◽

Local Density ◽

First Principles Calculations ◽

Functional Theory ◽

One Dimensional ◽

Local Density Functional Theory ◽

Foreign Materials

The nano-sized quasi-one dimensional hollow cores of carbon nanotubes make it possible for them to be filled with and wetted by foreign materials. With C, S and Se atoms as example, we have studied the filling and wetting of these atoms into carbon nanotubes from local density functional theory in first principles calculations. The results suggest that the effect of nanotube length is negligible when it exceeds 3.6 Å, there is a relation between nanotube diameter and filling and wetting. Our studies would be important implications for the further use of carbon nanotubes.

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Metal–insulator-like transition, superconducting dome and topological electronic structure in Ga-doped Re3Ge7

npj Quantum Materials ◽

10.1038/s41535-021-00372-z ◽

2021 ◽

Vol 6 (1) ◽

Author(s):

Yanwei Cui ◽

Siqi Wu ◽

Qinqing Zhu ◽

Guorui Xiao ◽

Bin Liu ◽

...

Keyword(s):

Phase Transition ◽

First Principles ◽

Hole Doping ◽

First Principles Calculations ◽

Metal Insulator ◽

Topological Materials ◽

Maximum Value ◽

Fermi Surface Nesting ◽

Ga Doping ◽

Rare Opportunity

AbstractSuperconductivity frequently appears by doping compounds that show a collective phase transition. So far, however, this has not been observed in topological materials. Here we report the discovery of superconductivity induced by Ga doping in orthorhombic Re3Ge7, which undergoes a second-order metal–insulator-like transition at ~58 K and is predicted to have a nontrivial band topology. It is found that the substitution of Ga for Ge leads to hole doping in Re3Ge7−xGax. As a consequence, the phase transition is gradually suppressed and disappears above x = 0.2. At this x value, superconductivity emerges and Tc exhibits a dome-like doping dependence with a maximum value of 3.37 K at x = 0.25. First principles calculations suggest that the phase transition in Re3Ge7 is associated with an electronic instability driven by Fermi-surface nesting and the nontrival band topology is preserved after Ga doping. Our results indicate that Ga-doped Re3Ge7 provides a rare opportunity to study the interplay between superconductivity and competing electronic states in a topologically nontrivial system.

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