27,512 research outputs found
Polarization and valley switching in monolayer group-IV monochalcogenides
Group-IV monochalcogenides are a family of two-dimensional puckered materials
with an orthorhombic structure that is comprised of polar layers. In this
article, we use first principles calculations to show the multistability of
monolayer SnS and GeSe, two prototype materials where the direction of the
puckering can be switched by application of tensile stress or electric field.
Furthermore, the two inequivalent valleys in momentum space, which are dictated
by the puckering orientation, can be excited selectively using linearly
polarized light, and this provides an additional tool to identify the
polarization direction. Our findings suggest that SnS and GeSe monolayers may
have observable ferroelectricity and multistability, with potential
applications in information storage
2D materials and van der Waals heterostructures
The physics of two-dimensional (2D) materials and heterostructures based on
such crystals has been developing extremely fast. With new 2D materials, truly
2D physics has started to appear (e.g. absence of long-range order, 2D
excitons, commensurate-incommensurate transition, etc). Novel heterostructure
devices are also starting to appear - tunneling transistors, resonant tunneling
diodes, light emitting diodes, etc. Composed from individual 2D crystals, such
devices utilize the properties of those crystals to create functionalities that
are not accessible to us in other heterostructures. We review the properties of
novel 2D crystals and how their properties are used in new heterostructure
devices
Probing the two-scale-factor universality hypothesis by exact rotation symmetry-breaking mechanism
We probe the two-scale factor universality hypothesis by evaluating, firstly
explicitly and analytically at the one-loop order, the loop quantum corrections
to the amplitude ratios for O() scalar field theories with
rotation symmetry-breaking in three distinct and independent methods in which
the rotation symmetry-breaking mechanism is treated exactly. We show that the
rotation symmetry-breaking amplitude ratios turn out to be identical in the
three methods and equal to their respective rotation symmetry-breaking ones,
although the amplitudes themselves, in general, depend on the method employed
and on the rotation symmetry-breaking parameter. At the end, we show that all
these results can be generalized, through an inductive process based on a
general theorem emerging from the exact calculation, to any loop level and
physically interpreted based on symmetry ideas.Comment: 17 pages, 3 figure
Controlling chaos in the quantum regime using adaptive measurements
The continuous monitoring of a quantum system strongly influences the
emergence of chaotic dynamics near the transition from the quantum regime to
the classical regime. Here we present a feedback control scheme that uses
adaptive measurement techniques to control the degree of chaos in the
driven-damped quantum Duffing oscillator. This control relies purely on the
measurement backaction on the system, making it a uniquely quantum control, and
is only possible due to the sensitivity of chaos to measurement. We quantify
the effectiveness of our control by numerically computing the quantum Lyapunov
exponent over a wide range of parameters. We demonstrate that adaptive
measurement techniques can control the onset of chaos in the system, pushing
the quantum-classical boundary further into the quantum regime
Spin-Orbit Dirac Fermions in 2D Systems
We propose a novel model for including spin-orbit interactions in buckled two
dimensional systems. Our results show that in such systems, intrinsic
spin-orbit coupling leads to a formation of Dirac cones, similar to Rashba
model. We explore the microscopic origins of this behaviour and confirm our
results using DFT calculations
Axial Multicentric Osteosarcoma in an English Cocker Spaniel
No abstract available
Two-dimensional square buckled Rashba lead chalcogenides
We propose the lead sulphide (PbS) monolayer as a two-dimensional semiconductor with a large Rashba-like spin-orbit effect controlled by the out-of-plane buckling. The buckled PbS conduction band is found to possess Rashba-like dispersion and spin texture at the M and Γ points, with large effective Rashba parameters of λ∼5 eV Å and λ∼1 eV Å, respectively. Using a tight-binding formalism, we show that the Rashba effect originates from the very large spin-orbit interaction and the hopping term that mixes the in-plane and out-of-plane p orbitals of Pb and S atoms. The latter, which depends on the buckling angle, can be controlled by applying strain to vary the spin texture as well as the Rashba parameter at Γ and M. Our density functional theory results together with tight-binding formalism provide a unifying framework for designing Rashba monolayers and for manipulating their spin properties.P.Z.H., H.S.P., and D.K.C. acknowledge the support of the Physics and Mechanical Engineering Department at Boston University. P.Z.H. is grateful for the hospitality of the NUS Centre for Advanced 2D Materials and Graphene Research Centre where this work was initiated. D.K.C. acknowledges the hospitality of the Aspen Center for Physics, which is supported by the US National Science Foundation Grant No. PHY-1607611. A.S.R., A.C.,and A.H.C.N. acknowledge support by the National Research Foundation, Prime Minister Office, Singapore, under its Medium Sized Centre Programme and CRP award "Novel 2D materials with tailored properties: Beyond graphene" (Grant No. R-144-000295-281). (Physics and Mechanical Engineering Department at Boston University; PHY-1607611 - US National Science Foundation; R-144-000295-281 - National Research Foundation, Prime Minister Office, Singapore, under its Medium Sized Centre Programme and CRP award "Novel 2D materials with tailored properties: Beyond graphene")Published versio
Holonomy Transformation in the FRW Metric
In this work we investigate loop variables in Friedman-Robertson-Walker
spacetime. We analyze the parallel transport of vectors and spinors in several
paths in this spacetime in order to classify its global properties. The band
holonomy invariance is analysed in this background.Comment: 8 page
Monitoramento da Entomofauna Epígea em pomar orgânico em processo inicial de transição agroecológica.
O estudo das relações entre diversidade e funcionamento do agroecossitema é importante no solo, por ser constituído de habitats diversos podendo-se prever mudanças no seu funcionamento em decorrência de alterações na sua diversidade (TILMAN, 1996). Nesse sentido, a utilização de insetos como bioindicadores de mudanças no ambiente pode fornecer informações úteis para o manejo e recuperação de ecossistemas degradados (ROSEMBERG et al., 1986, PARR; CHOWN, 2001)
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