137 research outputs found
Review of the Structural Stability, Electronic and Magnetic Properties of Nonmetal-Doped TiO from First-Principles Calculations
This paper reviews and summarizes the recent first-principles theoretical
studies of the structural stability, electronic structure, optical and magnetic
properties of nonmetal-doped TiO. The first section presents a comparison
study of the structural stability for X-anion and X-cation doped TiO (X=B,
C, Si, Ge, N, P, As, Sb, S, Se, Te, F, Cl, Br, and I), which reveals that the
sites of nonmetal dopants (i.e., at O sites or at Ti sites) in TiO are
determined by the growth condition of doped TiO and the dopants'
electronegativities. The next section reviews the electronic structure, optical
absorption and mechanism of the visible-light photocatalytic activity for
nonmetal-doped TiO. The third section summarizes the origin of the
spin-polarization and the magnetic coupling character in C- (N- and B-) doped
TiO.Comment: 21 pages, 24 figures, 3 table
Density functional characterization of the antiferromagnetism in oxygen-deficient anatase and rutile TiO2
We present theoretical evidence for local magnetic moments on Ti3+ ions in
oxygen-deficient anatase and rutile TiO2 observed in a recent experiment [S.
Zhou, et al., Phys. Rev. B 79, 113201 (2009)]. Results of our first-principles
GGA+U calculations reveal that an oxygen vacancy converts two Ti4+ ions to two
Ti3+ ions in anatase phase, which results in a local magnetic moment of 1.0
per Ti3+. The two Ti3+ ions, however, form a stable antiferromagnetic
state, and similar antiferromagnetism is also observed in oxygen-deficient
rutile phase TiO2. The calculated results are in good agreement with the
experimentally observed antiferromagnetic-like behavior in oxygen-deficient
Ti-O systems.Comment: 16 pages, 5 figure
Two-Dimensional Ferroelastic Topological Insulators in Single-Layer Janus Transition Metal Dichalcogenides MSSe (M=Mo, W)
Two-dimensional topological insulators and two-dimensional materials with
ferroelastic characteristics are intriguing materials and many examples have
been reported both experimentally and theoretically. Here, we present the
combination of both features - a two-dimensional ferroelastic topological
insulator that simultaneously possesses ferroelastic and quantum spin Hall
characteristics. Using first-principles calculations, we demonstrate Janus
single-layer MSSe (M=Mo, W) stable two-dimensional crystals that show the
long-sought ferroelastic topological insulator properties. The material
features low switching barriers and strong ferroelastic signals, beneficial for
applications in nonvolatile memory devices. Moreover, their topological phases
harbor sizeable nontrivial band gaps, which supports the quantum spin Hall
effect. The unique coexistence of excellent ferroelastic and quantum spin Hall
phases in single-layer MSSe provides extraordinary platforms for realizing
multi-purpose and controllable devices
Ferroelectric higher-order topological insulator in two dimensions
The interplay between ferroelectricity and band topology can give rise to a
wide range of both fundamental and applied research. Here, we map out the
emergence of nontrivial corner states in two-dimensional ferroelectrics, and
remarkably demonstrate that ferroelectricity and corner states are coupled
together by crystallographic symmetry to realize the electric control of
higher-order topology. Implemented by density functional theory, we identify a
series of experimentally synthesized two-dimensional ferroelectrics, such as
InSe, BN bilayers, and SnS, as realistic material candidates for the
proposed ferroelectric higher-order topological insulators. Our work not only
sheds new light on traditional ferroelectric materials but also opens an avenue
to bridge the higher-order topology and ferroelectricity that provides a
nonvolatile handle to manipulate the topology in next-generation electronic
devices
Intertwined Ferroelectricity and Topological State in Two-Dimensional Multilayer
The intertwined ferroelectricity and band topology will enable the
non-volatile control of the topological states, which is of importance for
nanoelectrics with low energy costing and high response speed. Nonetheless, the
principle to design the novel system is unclear and the feasible approach to
achieve the coexistence of two parameter orders is absent. Here, we propose a
general paradigm to design 2D ferroelectric topological insulators by sliding
topological multilayers on the basis of first-principles calculations. Taking
trilayer Bi2Te3 as a model system, we show that in the van der Waals multilayer
based 2D topological insulators, the in-plane and out-of-plane ferroelectricity
can be induced through a specific interlayer sliding, to enable the coexistence
of ferroelectric and topological orders. The strong coupling of the order
parameters renders the topological states sensitive to polarization flip,
realizing non-volatile ferroelectric control of topological properties. The
revealed design-guideline and ferroelectric-topological coupling not only are
useful for the fundamental research of the coupled ferroelectric and
topological physics in 2D lattices, but also enable novel applications in
nanodevices
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