1,378 research outputs found
Room-temperature superparamagnetism due to giant magnetic anisotropy in Mo defected single-layer MoS
Room-temperature superparamagnetism due to a large magnetic anisotropy energy
(MAE) of a single atom magnet has always been a prerequisite for nanoscale
magnetic devices. Realization of two dimensional (2D) materials such as
single-layer (SL) MoS, has provided new platforms for exploring magnetic
effects, which is important for both fundamental research and for industrial
applications. Here, we use density functional theory (DFT) to show that the
antisite defect (Mo) in SL MoS is magnetic in nature with a
magnetic moment of of 2 and, remarkably, exhibits an
exceptionally large atomic scale
MAE of 500 meV. Our
calculations reveal that this giant anisotropy is the joint effect of strong
crystal field and significant spin-orbit coupling (SOC). In addition, the
magnetic moment can be tuned between 1 and 3 by varying
the Fermi energy , which can be achieved either by changing
the gate voltage or by chemical doping. We also show that MAE can be raised to
1 eV with n-type doping of the MoS:Mo sample. Our systematic
investigations deepen our understanding of spin-related phenomena in SL
MoS and could provide a route to nanoscale spintronic devices.Comment: 7 pages, 7 figure
Two-dimensional Fermionic Hong-Ou-Mandel Interference with Weyl Fermions
We propose a two-dimensional Hong-Ou-Mandel (HOM) type interference
experiment for Weyl fermions in graphene and 3D topological insulators. Since
Weyl fermions exhibit linear dispersion, similar to photons in vacuum, they can
be used to obtain the HOM interference intensity pattern as a function of the
delay time between two Weyl fermions. We show that while the Coulomb
interaction leads to a significant change in the angle dependence of the
tunneling of two identical Weyl fermions incident from opposite sides of a
potential barrier, it does not affect the HOM interference pattern, in contrast
to previous expectations. We apply our formalism to develop a Weyl fermion
beam-splitter (BS) for controlling the transmission and reflection
coefficients. We calculate the resulting time-resolved correlation function for
two identical Weyl fermions scattering off the BS.Comment: 4 pages, 3 figure
Reply to the comment of Chudnovsky&Garanin on "Spin relaxation in Mn12-acetate"
Reply to the comment of E.M. Chudnovsky and D.A. Garanin on Europhys. Lett.
46, 692 (1999).Comment: 2 pages, Latex (europhys.sty
Optical signatures of states bound to vacancy defects in monolayer MoS
We show that pristine MoS single layer (SL) exhibits two bandgaps
eV and eV for the optical in-plane and
out-of-plane susceptibilities and , respectively.
In particular, we show that odd states bound to vacancy defects (VDs) lead to
resonances in inside in MoS SL with VDs. We use
density functional theory, the tight-binding model, and the Dirac equation to
study MoS SL with three types of VDs: (i) Mo-vacancy, (ii) S-vacancy,
and (iii) 3MoS quantum antidot. The resulting optical spectra
identify and characterize the VDs.Comment: 5 pages, 5 figure
Electronic and Optical Properties of Vacancy Defects in Transition Metal Dichalcogenides
A detailed first-principle study has been performed to evaluate the
electronic and optical properties of single-layer (SL) transition metal
dichalcogenides (TMDCs) (MX; M= transition metal such as Mo, W and X= S,
Se, Te), in the presence of vacancy defects (VDs). Defects usually play an
important role in tailoring electronic, optical, and magnetic properties of
semiconductors. We consider three types of VDs in SL TMDCs i) -vacancy,
-vacancy, and iii) -vacancy. We show that VDs lead to localized
defect states (LDS) in the band structure, which in turn give rise to sharp
transitions in in-plane and out-of-plane optical susceptibilities,
and . The effects of spin orbit coupling (SOC)
are also considered. We find that SOC splitting in LDS is directly related to
the atomic number of the transition metal atoms. Apart from electronic and
optical properties we also find magnetic signatures (local magnetic moment of
) in MoSe in the presence of Mo vacancy, which breaks the
time reversal symmetry and therefore lifts the Kramers degeneracy. We show that
a simple qualitative tight binding model (TBM), involving only the hopping
between atoms surrounding the vacancy with an on-site SOC term, is sufficient
to capture the essential features of LDS. In addition, the existence of the LDS
can be understood from the solution of the 2D Dirac Hamiltonian by employing
infinite mass boundary conditions. In order to provide a clear description of
the optical absorption spectra, we use group theory to derive the optical
selection rules between LDS for both and .Comment: 14 pages, 11 figure
A new Viola (Violaceae) from the Argentinian Andes
Viola beati, a hitherto unknown species of V. sect. Andinium (Violaceae) is described and illustrated. It is an inconspicuous, diminutive, perennial forb currently known from only one locality in NW Argentina. We draw attention to its morphology, ecology, rarity and endemism. The differences between V. beati and its apparently only close relative, V. singularis J. M. Watson & A. R. Flores, are defined
Dirac electrons in the presence of matrix potential barrier: application to graphene and topological insulators
Scattering of a 2D Dirac electrons on a rectangular matrix potential barrier
is considered using the formalism of spinor transfer matrices. It is shown, in
particular, that in the absence of the mass term, the Klein tunneling is not
necessarily suppressed but occurs at oblique incidence. The formalism is
applied to studying waveguiding modes of the barrier, which are supported by
the edge and bulk states. The condition of existence of the uni-directionality
property is found. We show that the band of edge states is always finite with
massless excitations, while the spectrum of the bulk states, depending on
parameters of the barrier, may consist of the infinite or finite band with
both, massive and massless, low-energy excitations. The effect of the Zeeman
term is considered and the condition of appearance of two distinct energy
dependent directions corresponding to the Klein tunneling is found.Comment: published versio
Dynamics of large anisotropic spin in a sub-ohmic dissipative environment close to a quantum-phase transition
We investigate the dynamics of a large anisotropic spin whose easy-axis
component is coupled to a bosonic bath with a spectral function J(\w)\propto
\omega^s. Such a spin complex might be realized in a single-molecular magnet.
Using the non-perturbative renormalization group, we calculate the line of
quantum-phase transitions in the sub-ohmic regime (). These quantum-phase
transitions only occur for integer spin . For half-integer , the low
temperature fixed-point is identical to the fixed-point of the spin-boson model
without quantum-tunneling between the two levels. Short-time coherent
oscillations in the spin decay prevail even into the localized phase in the
sub-ohmic regime. The influence of the reorganization energy and the recurrence
time on the decoherence in the absence of quantum-tunneling is discussed.Comment: 14 pages,7 figure
Carbon Isotope Constraints on the Deglacial CO2 Rise from Ice Cores
The stable carbon isotope ratio of atmospheric CO2 (d13Catm) is a key parameter in deciphering past carbon cycle changes. Here we present d13Catm data for the past 24,000 years derived from three independent records from two Antarctic ice cores. We conclude that a pronounced 0.3 per mil decrease in d13Catm during the early deglaciation can be best explained by upwelling of old, carbon-enriched waters in the Southern Ocean. Later in the deglaciation, regrowth of the terrestrial biosphere, changes in sea surface temperature, and ocean circulation governed the d13Catm evolution. During the Last Glacial Maximum, d13Catm and atmospheric CO2 concentration were essentially constant, which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then
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