124 research outputs found
String order and adiabatic continuity of Haldane chains and band insulators
The ground state of spin-1 Haldane chains is characterized by the so-called
string order. We show that the same hidden order is also present in ordinary
one-dimensional band insulators. We construct a family of Hamiltonians which
connects adiabatically band insulators to two topologically non-equivalent spin
models, the Haldane chain and the antiferromagnetic spin-1/2 ladder. We observe
that the localized spin-1/2 edge-state characteristic of spin-1 chains is
smoothly connected to a surface-bound state of band insulators and its
emergence is not related to any bulk phase transition. Furthermore, we show
that the string order is absent in any dimensions higher than one.Comment: 6 pages, 7 figures. Appendix about charge string orders added.
Version as publishe
Universal alternating order around impurities in antiferromagnets
The study of impurities in antiferromagnets is of considerable interest in
condensed matter physics. In this paper we address the elementary question of
the effect of vacancies on the orientation of the surrounding magnetic moments
in an antiferromagnet. In the presence of a magnetic field, alternating
magnetic moments are induced, which can be described by a universal expression
that is valid in any ordered antiferromagnet and turns out to be independent of
temperature over a large range. The universality is not destroyed by quantum
fluctuation, which is demonstrated by quantum Monte Carlo simulations in the
two-dimensional Heisenberg antiferromagnet. Physical predictions for finite
doping are made, which are relevant for experiments probing Knight shifts and
the order parameter.Comment: 5 pages, 2 figures. The most recent version in PDF format can be
found at http://www.physik.uni-kl.de/eggert/papers
Fragility of String Orders
One-dimensional gapped systems are often characterized by a 'hidden'
non-local order parameter, the so-called string order. Due to the gap,
thermodynamic properties are robust against a weak higher-dimensional coupling
between such chains or ladders. To the contrary, we find that the string order
is not stable and decays for arbitrary weak inter-chain or inter-ladder
coupling. We investigate the vanishing of the order for three different
systems: spin-one Haldane chains, band insulators, and the transverse-field
Ising model. Using perturbation theory and bosonization, we show that the
fragility of the string order arises from non-local commutation relations
between the non-local order parameter and the perturbation.Comment: 7 pages, 3 figures. Published versio
Utility of heavy minerals distribution and granulometric analyses in the study of coastal dynamics: Application to the littoral between SanlĂșcar de Barrameda and Rota (Cadiz, southwest Iberian Peninsula)
The present paper deals with grain size and heavy minerals distribution in the sandy coastal sediments of the littoral between the cities of SanlĂșcar de Barrameda and Rota. We have related these distributions to the predominant southward littoral drift and the possible source contributions, mostly represented by the Guadalquivir and Guadalete Rivers. The littoral studied is composed of fine sand in the northern sector and medium sand in its central and southern sectors. Heavy minerals were identified using X-ray analysis: the most abundant in the study area are epidote and garnet. We found that their concentrations and sizes decrease from north to south according to the coastal drift, whereas the grain morphology and the mineralogical component generally remain constant.Este trabajo trata de las distribuciones granulomĂ©trica y de minerales pesados de los sedimentos arenosos del tramo de litoral comprendido entre las ciudades de SanlĂșcar de Barrameda y Rota (suroeste de la penĂnsula IbĂ©rica). Se han relacionado dichas distribuciones con la deriva litoral predominante hacia el Sur y con las fuentes de aporte de sedimentos constituidas por los rĂos Guadalquivir y Guadalete. El litoral estudiado se caracteriza por arena fina en su parte norte y arena media en su parte central y meridional. Los minerales pesados se han identificado mediante rayos X: los mĂĄs abundantes en el ĂĄrea estudiada son epidota y granate. Se ha deducido cĂłmo sus concentraciones y tamaños disminuyen de norte a sur de acuerdo con la deriva litoral, manteniĂ©ndose el conjunto mineralĂłgico y la morfologĂa de los granos constante.Instituto Español de OceanografĂ
Interaction effects between impurities in low dimensional spin-1/2 antiferromagnets
We are considering the interplay between several non-magnetic impurities in
the spin-1/2 Heisenberg antiferromagnet in chains, ladders and planes by
introducing static vacancies in numerical quantum Monte Carlo simulations. The
effective potential between two and more impurities is accurately determined,
which gives a direct measure of the quantum correlations in the systems. Large
effective interaction potentials are an indication of strong quantum
correlations in the system and reflect the detailed nature of the valence bond
ground states. In two-dimensions (2D) the interactions are smaller, but can
still be analyzed in terms of valence bonds.Comment: 8 pages, 6 figures, accepted by Europhys. Lett. The latest pdf file
is available at http://www.physik.uni-kl.de/eggert/papers/interact2d.pd
Low-energy local density of states of the 1D Hubbard model
We examine the local density of states (DOS) at low energies numerically and
analytically for the Hubbard model in one dimension. The eigenstates represent
separate spin and charge excitations with a remarkably rich structure of the
local DOS in space and energy. The results predict signatures of strongly
correlated excitations in the tunneling probability along finite quantum wires,
such as carbon nanotubes, atomic chains or semiconductor wires in scanning
tunneling spectroscopy (STS) experiments. However, the detailed signatures can
only be partly explained by standard Luttinger liquid theory. In particular, we
find that the effective boundary exponent can be negative in finite wires,
which leads to an increase of the local DOS near the edges in contrast to the
established behavior in the thermodynamic limit.Comment: 6 pages, 4 figures, more information can be found at
http://www.physik.uni-kl.de/eggert/papers/index.htm
Diverging thermal expansion of the spin-ladder system (CHN)CuBr
We present high-resolution measurements of the -axis thermal
expansion and magnetostriction of piperidinium copper bromide \hp. The
experimental data at low temperatures is well accounted for by a two-leg
spin-ladder Hamiltonian. The thermal expansion shows a complex behaviour with
various sign changes and approaches a divergence at the critical
fields. All low-temperature features are semi-quantitatively explained within a
free fermion model; full quantitative agreement is obtained with Quantum Monte
Carlo simulations.Comment: 4 pages, 5 figures; version 2 is slightly shortened and typos are
correcte
Seasonal comparison of beach litter on Mediterranean coastal sites (Alicante, SE Spain)
Presence of beach litter was assessed during spring and summer seasons 2018, at 56 sites along the coast of Alicante Province (SE Spain). Selected sites covered âremoteâ (9), âruralâ (10) âvillageâ (17) and âurbanâ (20) bathing areas. In an area of 201,700âŻm2, a total of 10,101 litter items (Avg: 0.062 items m-2) was counted in spring, and 20,857 (Avg: 0.116 items mâ2) in summer. The most significant seasonal evolution was observed in the cigarette butt, group which increased from 4607 to 12843 units. Plastic represented the dominant material in both seasons (82.6 and 83.5% respectively). Litter items increased greatly during the summer season despite the increasing frequency of cleaning operations and were essentially related to beach users activities. Secondarily, beach litter was related to wastewater discharges and fishing activities. Beach litter management along investigated sites must be based on plans to reduce litter sources. For that, it is necessary to consider beach typology along with the seasonal influx of visitors to define the most appropriate management actions, not forgetting the implementation of environmental education, essential in schools and media
A tunable nanoplatform of nanogold functionalised with Angiogenin peptides for anti-angiogenic therapy of brain tumours
Angiogenin (ANG), an endogenous protein that plays a key role in cell growth and survival, has been scrutinised here as promising nanomedicine tool for the modulation of pro-/anti-angiogenic processes in brain cancer therapy. Specifically, peptide fragments from the putative cell membrane binding domain (residues 60-68) of the protein were used in this study to obtain peptide-functionalised spherical gold nanoparticles (AuNPs) of about 10 nm and 30 nm in optical and hydrodynamic size, respectively. Different hybrid biointerfaces were fabricated by peptide physical adsorption (Ang60-68) or chemisorption (the cysteine analogous Ang60-68Cys) at the metal nanoparticle surface, and cellular assays were performed in the comparison with ANG-functionalised AuNPs. Cellular treatments were performed both in basal and in copper-supplemented cell culture medium, to scrutinise the synergic effect of the metal, which is another known angiogenic factor. Two brain cell lines were investigated in parallel, namely tumour glioblastoma (A172) and neuron-like differentiated neuroblastoma (d-SH-SY5Y). Results on cell viability/proliferation, cytoskeleton actin, angiogenin translocation and vascular endothelial growth factor (VEGF) release pointed to the promising potentialities of the developed systems as anti-angiogenic tunable nanoplaftforms in cancer cells treatment
Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, CĂĄdiz, SW Spain
An application of the grain size trend analysis
(GSTA) is used in an exploratory approach to characterize
sediment transport on Camposoto beach (CĂĄdiz, SW Spain).
In May 2009 the mesotidal beach showed a well-developed
swash bar on the upper foreshore, which was associated
with fair-weather conditions prevailing just before and during
the field survey. The results were tested by means of an
autocorrelation statistical test (index I of Moran). Two sedimentological
trends were recognized, i.e. development towards
finer, better sorted and more negatively skewed
sediment (FBâ), and towards finer, better sorted and less
negatively or more positively skewed sediment (FB+). Both
vector fields were compared with results obtained from
more classical approaches (sand tracers, microtopography
and current measurements). This revealed that both trends
can be considered as realistic, the FB+ trend being identified
for the first time in a beach environment. The data demonstrate
that, on the well-developed swash bar, sediment
transported onshore becomes both finer and better sorted
towards the coast. On the lower foreshore, which exhibits a
steeper slope produced by breaking waves, the higherenergy
processes winnow out finer particles and thereby
produce negatively skewed grain-size distributions. The upper
foreshore, which has a flatter and smoother slope, is
controlled by lower-energy swash-backwash and overwash
processes. As a result, the skewness of the grain-size distributions
evolves towards less negative or more positive
values. The skewness parameter appears to be distributed
as a function of the beach slope and, thus, reflects variations
in hydrodynamic energy. This has novel implications for
coastal management
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