2,338 research outputs found
Dirac nodal line metal for topological antiferromagnetic spintronics
Topological antiferromagnetic (AFM) spintronics is an emerging field of
research, which exploits the N\'eel vector to control the topological
electronic states and the associated spin-dependent transport properties. A
recently discovered N\'eel spin-orbit torque has been proposed to electrically
manipulate Dirac band crossings in antiferromagnets; however, a reliable AFM
material to realize these properties in practice is missing. Here, we predict
that room temperature AFM metal MnPd allows the electrical control of the
Dirac nodal line by the N\'eel spin-orbit torque. Based on first-principles
density functional theory calculations, we show that reorientation of the
N\'eel vector leads to switching between the symmetry-protected degenerate
state and the gapped state associated with the dispersive Dirac nodal line at
the Fermi energy. The calculated spin Hall conductivity strongly depends on the
N\'eel vector orientation and can be used to experimentally detect the
predicted effect using a proposed spin-orbit torque device. Our results
indicate that AFM Dirac nodal line metal MnPd represents a promising
material for topological AFM spintronics
Spin-torque switching of noncollinear antiferromagnetic antiperovskites
Antiferromagnetic (AFM) spintronics exploits the Néel vector as a state variable for novel electronic devices. Recent studies have demonstrated that the Néel vector can be switched by a spin-orbit torque. These studies however are largely limited to collinear antiferromagnets of proper magnetic space-group symmetry. There is, however, a large group of high-temperature noncollinear antiferromagnets, which are suitable for such switching. Here, we predict that spin torque can be efficiently used to switch a noncollinear AFM order in antiperovskite materials. Based on first-principles calculations and atomistic spin-dynamics modeling, we show that in antiperovskites ANMn3 (A = Ga, Ni, etc.) with the AFM Γ4g ground state, the AFM order can be switched on the picosecond timescale using a spin torque generated by a spin current. The threshold switching current density can be tuned by the ANMn3 stoichiometry engineering, changing the magnetocrystalline anisotropy. The Γ4g AFM phase supports a sizable anomalous Hall effect, which can be used to detect the spin-torque switching of the AFM order. The predicted ultrafast switching dynamics and the efficient detection of the AFM order state make noncollinear magnetic antiperovskites a promising material platform for AFM spintronics
Two-dimensional antiferroelectric tunnel junction
Ferroelectric tunnel junctions (FTJs), which consist of two metal electrodes
separated by a thin ferroelectric barrier, have recently aroused significant
interest for technological applications as nanoscale resistive switching
devices. So far, most of existing FTJs have been based on perovskite-oxide
barrier layers. The recent discovery of the two-dimensional (2D) van der Waals
ferroelectric materials opens a new route to realize tunnel junctions with new
functionalities and nm-scale dimensions. Due to the weak coupling between the
atomic layers in these materials, the relative dipole alignment between them
can be controlled by applied voltage. This allows transitions between
ferroelectric and antiferroelectric orderings, resulting in significant changes
of the electronic structure. Here, we propose to realize 2D antiferroelectric
tunnel junctions (AFTJs), which exploit this new functionality, based on
bilayer InX (X = S, Se, Te) barriers and different 2D electrodes. Using
first-principles density functional theory calculations, we demonstrate that
the InX bilayers exhibit stable ferroelectric and antiferroelectric
states separated by sizable energy barriers, thus supporting a non-volatile
switching between these states. Using quantum-mechanical modeling of the
electronic transport, we explore in-plane and out-of-plane tunneling across the
InS van der Waals bilayers, and predict giant tunneling
electroresistance (TER) effects and multiple non-volatile resistance states
driven by ferroelectric-antiferroelectric order transitions. Our proposal opens
a new route to realize nanoscale memory devices with ultrahigh storage density
using 2D AFTJs
Two-Dimensional Antiferroelectric Tunnel Junction
Ferroelectric tunnel junctions (FTJs), which consist of two metal electrodes separated by a thin ferroelectric barrier, have recently aroused significant interest for technological applications as nanoscale resistive switching devices. So far, most existing FTJs have been based on perovskite-oxide barrier layers. The recent discovery of the two-dimensional (2D) van der Waals ferroelectric materials opens a new route to realize tunnel junctions with new functionalities and nm-scale dimensions. Because of the weak coupling between the atomic layers in these materials, the relative dipole alignment between them can be controlled by applied voltage. This allows transitions between ferroelectric and antiferroelectric orderings, resulting in significant changes of the electronic structure. Here, we propose to realize 2D antiferroelectric tunnel junctions (AFTJs), which exploit this new functionality, based on bilayer In2X3 (X = S, Se, Te) barriers and different 2D electrodes. Using first-principles density functional theory calculations, we demonstrate that the In2X3 bilayers exhibit stable ferroelectric and antiferroelectric states separated by sizable energy barriers, thus supporting a nonvolatile switching between these states. Using quantum-mechanical modeling of the electronic transport, we explore in-plane and out-of-plane tunneling across the In2S3 van der Waals bilayers, and predict giant tunneling electroresistance effects and multiple nonvolatile resistance states driven by ferroelectric-antiferroelectric order transitions. Our proposal opens a new route to realize nanoscale memory devices with ultrahigh storage density using 2D AFTJs
Electrical Detection of Ferroelectric-like Metals through Nonlinear Hall Effect
Ferroelectric-like metals are a relatively rare class of materials that have
ferroelectric-like distortion and metallic conductivity. LiOsO is the first
demonstrated and the most investigated ferroelectric-like metal. The presence
of free carriers makes them difficult to be studied by traditional
ferroelectric techniques. In this paper, using the symmetry analysis and
first-principles calculations, we demonstrate that the ferroelectric-like
transition of LiOsO can be probed by a kind of electrical transport method
based on nonlinear Hall effect. The Berry curvature dipole exists in the
ferroelectric-like phase, and it can lead to a measurable nonlinear Hall
conductance with a conventional experimental setup. However, the symmetry of
the paraelectric-like phase LiOsO vanishes the Berry curvature dipole. The
Berry curvature dipole shows a strong dependence on the polar displacement,
which might be helpful for the detection of polar order. The nonlinear Hall
effect provides an effective method for the detection of phase transition in
the study of the ferroelectric-like metals and promotes them to be applied in
the ferroelectric-like electronic devices
Friedel oscillations in graphene gapped by breaking \u3ci\u3eƤ\u3c/i\u3e and \u3ci\u3eT\u3c/i\u3e symmetries: Topological and geometrical signatures of electronic structure
The measurement of Friedel oscillations (FOs) is conventionally used to recover the energy dispersion of electronic structure. Besides the energy dispersion, the modern electronic structure also embodies other key ingredients such as the geometrical and topological properties; it is one promising direction to explore the potential of FOs for the relevant measurement. Here, we present a comprehensive study of FOs in substrate-supported graphene under off-resonant circularly polarized light, in which a valley-contrasting feature and topological phase transition occur due to the combined breaking of inversion (Ƥ) and time reversal (T) symmetries. Depending on the position of the Fermi level, FOs may be contributed by electronic backscattering in one single valley or two valleys. In the single-valley regime, the oscillation periods of FOs can be used to determine the topological phase boundary of electronic structure, while the amplitudes of FOs distinguish trivial insulators and topological insulators in a quantitative way. In the two-valley regime, the unequal Fermi surfaces lead to a beating pattern (robust two-wave-front dislocations) of FOs contributed by intravalley (intervalley) scattering. This study implies the great potential of FOs in characterizing topological and geometrical properties of the electronic structure of two-dimensional materials
Electrical detection of ferroelectriclike metals through the nonlinear Hall effect
Ferroelectriclike metals are a relatively rare class of materials that have ferroelectriclike distortion and metallic conductivity. LiOsO3 is the first demonstrated and the most investigated ferroelectriclike metal. The presence of free carriers makes them difficult to be studied by traditional ferroelectric techniques. In this paper, using symmetry analysis and first-principles calculations, we demonstrate that the ferroelectriclike transition of LiOsO3 can be probed by a kind of electrical transport method based on nonlinear Hall effect. The Berry curvature dipole exists in the ferroelectriclike phase and it can lead to a measurable nonlinear Hall conductance with a conventional experimental setup. However, the symmetry of the paraelectriclike phase LiOsO3 vanishes the Berry curvature dipole. The Berry curvature dipole shows a strong dependence on the polar displacement, which might be helpful for the detection of polar order. The nonlinear Hall effect provides an effective method for the detection of phase transition in the study of the ferroelectriclike metals and promotes them to be applied in ferroelectriclike electronic devices
Anomalous Hall Conductivity of a Non-Collinear Magnetic Antiperovskite
The anomalous Hall effect (AHE) is a well-known fundamental property of
ferromagnetic metals, commonly associated with the presence of a net
magnetization. Recently, an AHE has been discovered in non-collinear
antiferromagnetic (AFM) metals. Driven by non-vanishing Berry curvature of AFM
materials with certain magnetic space group symmetry, anomalous Hall
conductivity (AHC) is very sensitive to the specific type of magnetic ordering.
Here, we investigate the appearance of AHC in antiperovskite GaNMn as a
representative of broader materials family ANMn (A is a main group
element), where different types of non-collinear magnetic ordering can emerge.
Using symmetry analyses and first-principles density-functional theory
calculations, we show that with almost identical band structure, the nearly
degenerate non-collinear AFM and phases of
GaNMn have zero and finite AHC, respectively. In a non-collinear
ferrimagnetic -1 phase, GaNMn exhibits a large AHC due to the presence
of a sizable net magnetic moment. In the non-collinear antiperovskite magnets,
transitions between different magnetic phases, exhibiting different AHC states,
can be produced by doping, strain, or spin transfer torque, which makes these
materials promising for novel spintronic applications
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