3,346 research outputs found
Quantum phase transitions in three-leg spin tubes
We investigate the properties of a three-leg quantum spin tube using several
techniques such as the density matrix renormalization group method, strong
coupling approaches and the non linear sigma model. For integer spins S, the
model proves to exhibit a particularly rich phase diagram consisting of an
ensemble of 2S phase transitions. They can be accurately identified by the
behavior of a non local string order parameter associated to the breaking of a
hidden symmetry in the Hamiltonian. The nature of these transitions are further
elucidated within the different approaches. We carry a detailed DMRG analysis
in the specific cases S = 1. The numerical data confirm the existence of two
Haldane phases with broken hidden symmetry separated by a trivial singlet
state. The study of the gap and of the von Neumann entropy suggest a first
order phase transition but at the close proximity of a tricritical point
separating a gapless and a first order transition line in the phase diagram of
the quantum spin tube.Comment: 20 pages, 18 figure
Combined analytical and numerical approach to magnetization plateaux in one-dimensional spin tube antiferromagnets
In this paper, we investigate the properties of frustrated three-leg spin
tubes under a magnetic field. We concentrate on two kind of geometries for
these tubes, one of which is relevant for the compound
. We combine an analytical path integral
approach with a strong coupling approach, as well as large-scale Density Matrix
Renormalization Groups (DMRG) simulations, to identify the presence of plateaux
in the magnetization curve as a function of the value of spin . We also
investigate the issue of gapless non-magnetic excitations on some plateaux,
dubbed chirality degrees of freedom for both tubes.Comment: 17 page
Surface excitations in the modelling of electron transport for electron- beam-induced deposition experiments
The aim of the present overview article is to raise awareness of an essential
aspect that is usually not accounted for in the modelling of electron transport
for focused-electron-beam-induced deposition (FEBID) of nanostructures: surface
excitations are on the one hand responsible for a sizeable fraction of the
intensity in reflection-electron-energy-loss spectra for primary electron
energies of up to a few keV and, on the other hand, they play a key role in the
emission of secondary electrons from solids, regardless of the primary energy.
In this overview work we present a general perspective of recent works on the
subject of surface excitations and on low-energy electron transport,
highlighting the most relevant aspects for the modelling of electron transport
in FEBID simulations.Comment: 17 pages, 5 figure
Selection of factorizable ground state in a frustrated spin tube: Order by disorder and hidden ferromagnetism
The interplay between frustration and quantum fluctuation in magnetic systems
is known to be the origin of many exotic states in condensed matter physics. In
this paper, we consider a frustrated four-leg spin tube under a magnetic field.
This system is a prototype to study the emergence of a nonmagnetic ground state
factorizable into local states and the associated order parameter without
quantum fluctuation, that appears in a wide variety of frustrated systems. The
one-dimensional nature of the system allows us to apply various techniques: a
path-integral formulation based on the notion of order by disorder,
strong-coupling analysis where magnetic excitations are gapped, and
density-matrix renormalization group. All methods point toward an interesting
property of the ground state in the magnetization plateaus, namely, a quantized
value of relative magnetizations between different sublattices (spin imbalance)
and an almost perfect factorization of the ground state
Electron supersurface scattering on polycrystalline Au
Supersurface electron scattering, i.e., electron energy losses and associated deflections in vacuum above the surface of a medium, is shown to contribute significantly to electron spectra. We have obtained experimental verification (in absolute units) of theoretical predictions that the angular distribution of the supersurface backscattering probability exhibits strong oscillations which are anticorrelated with the generalized Ramsauer-Townsend minima in the backscattering probability. We have investigated 500-eV electron backscattering from an Au surface for an incidence angle of 70° and scattering angles between 37° and 165°. After removing the contribution of supersurface scattering from the experimental data, the resulting angular and energy distribution agrees with the Landau-Goudsmit-Saunderson (LGS) theory, which was proposed about 60 years ago, while the raw data are anticorrelated with LGS theory. This result implies that supersurface scattering is an essential phenomenon for quantitative understanding of electron spectra
Magnetization plateaux in the classical Shastry-Sutherland lattice
We investigated the classical Shastry-Sutherland lattice under an external
magnetic field in order to understand the recently discovered magnetization
plateaux in the rare-earth tetraborides compounds RB. A detailed study of
the role of thermal fluctuations was carried out by mean of classical spin
waves theory and Monte-Carlo simulations. Magnetization quasi-plateaux were
observed at 1/3 of the saturation magnetization at non zero temperature. We
showed that the existence of these quasi-plateaux is due to an entropic
selection of a particular collinear state. We also obtained a phase diagram
that shows the domains of existence of different spin configurations in the
magnetic field versus temperature plane.Comment: 4 pages, proceedings of HFM200
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