36 research outputs found
Effect of the Orbital Level Difference in Doped Spin-1 Chains
Doping of a two-orbital chain with mobile S=1/2 Fermions and strong Hund's
rule couplings stabilizing the S=1 spins strongly depends on the presence of a
level difference among these orbitals. By DMRG methods we find a finite spin
gap upon doping and dominant pairing correlations without level-difference,
whereas the presence of a level difference leads to dominant charge density
wave (CDW) correlations with gapless spin-excitations. The string correlation
function also shows qualitative differences between the two models.Comment: 4 pages, 4 figure
Doped two orbital chains with strong Hund's rule couplings - ferromagnetism, spin gap, singlet and triplet pairings
Different models for doping of two-orbital chains with mobile
fermions and strong, ferromagnetic (FM) Hund's rule couplings stabilizing the
S=1 spins are investigated by density matrix renormalization group (DMRG)
methods. The competition between antiferromagnetic (AF) and FM order leads to a
rich phase diagram with a narrow FM region for weak AF couplings and strongly
enhanced triplet pairing correlations. Without a level difference between the
orbitals, the spin gap persists upon doping, whereas gapless spin excitations
are generated by interactions among itinerant polarons in the presence of a
level difference. In the charge sector we find dominant singlet pairing
correlations without a level difference, whereas upon the inclusion of a
Coulomb repulsion between the orbitals or with a level difference, charge
density wave (CDW) correlations decay slowest. The string correlation functions
remain finite upon doping for all models.Comment: 9pages, 9figure
Structure of end states for a Haldane Spin Chain
Inelastic neutron scattering was used to probe edge states in a quantum spin
liquid. The experiment was performed on finite length antiferromagnetic spin-1
chains in Y_2BaNi_{1-x}Mg_xO_5. At finite fields, there is a Zeeman resonance
below the Haldane gap. The wave vector dependence of its intensity provides
direct evidence for staggered magnetization at chain ends, which decays
exponentially towards the bulk (xi = 8(1) at T=0.1K). Continuum contributions
to the chain end spectrum indicate inter-chain-segment interactions. We also
observe a finite size blue shift of the Haldane gap.Comment: 4 pages RevTex, 3 figure
Mid-Infrared Conductivity from Mid-Gap States Associated with Charge Stripes
The optical conductivity of La(2-x)Sr(x)NiO(4) has been interpreted in
various ways, but so far the proposed interpretations have neglected the fact
that the holes doped into the NiO(2) planes order in diagonal stripes, as
established by neutron and X-ray scattering. Here we present a study of optical
conductivity in La(2)NiO(4+d) with d=2/15, a material in which the charge
stripes order three-dimensionally. We show that the conductivity can be
decomposed into two components, a mid-infrared peak that we attribute to
transitions from the filled valence band into empty mid-gap states associated
with the stripes, and a Drude peak that appears at higher temperatures as
carriers are thermally excited into the mid-gap states. The shift of the mid-IR
peak to lower energy with increasing temperature is explained in terms of the
Franck-Condon effect. The relevance of these results to understanding the
optical conductivity in the cuprates is discussed.Comment: final version of paper (minor changes from previous version
Freezing of a Stripe Liquid
The existence of a stripe-liquid phase in a layered nickelate,
La(1.725)Sr(0.275)NiO(4), is demonstrated through neutron scattering
measurements. We show that incommensurate magnetic fluctuations evolve
continuously through the charge-ordering temperature, although an abrupt
decrease in the effective damping energy is observed on cooling through the
transition. The energy and momentum dependence of the magnetic scattering are
parametrized with a damped-harmonic-oscillator model describing overdamped
spin-waves in the antiferromagnetic domains defined instantaneously by charge
stripes.Comment: 4 2-col pages, including 5 figures; Final version, to be published in
PR
Co-regulation map of the human proteome enables identification of protein functions
This is the author accepted manuscript. The final version is available from Nature Research via the DOI in this recordData availability:
All mass spectrometry raw files generated in-house have been deposited in the ProteomeXchange Consortium (http://proteomecentral.proteomexchange.org) via the PRIDE partner repository36 with the dataset identifier PXD008888. The co-regulation map is hosted on our website at www.proteomeHD.net, and pair-wise co-regulation scores are available through STRING (https://string-db.org). A network of the top 0.5% co-regulated protein pairs can be explored interactively on NDEx (https://doi.org/10.18119/N9N30Q).Code availability:
Data analysis was performed in R 3.5.1. R scripts and input files required to reproduce the results of this manuscript are available in the following GitHub repository: https://github.com/Rappsilber-Laboratory/ProteomeHD. R scripts related specifically to the benchmarking of the treeClust algorithm using synthetic data are available in the following GitHub repository: https://github.com/Rappsilber-Laboratory/treeClust-benchmarking. The R package data.table was used for fast data processing. Figures were prepared using ggplot2, gridExtra, cowplot and viridis.Note that the title of the AAM is different from the published versionThe annotation of protein function is a longstanding challenge of cell biology that
suffers from the sheer magnitude of the task. Here we present ProteomeHD, which
documents the response of 10,323 human proteins to 294 biological perturbations,
measured by isotope-labelling mass spectrometry. We reveal functional associations
between human proteins using the treeClust machine learning algorithm, which we
show to improve protein co-regulation analysis due to robust selectivity for close
linear relationships. Our co-regulation map identifies a functional context for many
uncharacterized proteins, including microproteins that are difficult to study with
traditional methods. Co-regulation also captures relationships between proteins
which do not physically interact or co-localize. For example, co-regulation of the
peroxisomal membrane protein PEX11ÎČ with mitochondrial respiration factors led us
to discover a novel organelle interface between peroxisomes and mitochondria in
mammalian cells. The co-regulation map can be explored at www.proteomeHD.net .Biotechnology & Biological Sciences Research Council (BBSRC)European Commissio