108 research outputs found
Chebyshev matrix product state approach for time evolution
We present and test a new algorithm for time-evolving quantum many-body
systems initially proposed by Holzner et al. [Phys. Rev. B 83, 195115 (2011)].
The approach is based on merging the matrix product state (MPS) formalism with
the method of expanding the time-evolution operator in Chebyshev polynomials.
We calculate time-dependent observables of a system of hardcore bosons quenched
under the Bose-Hubbard Hamiltonian on a one-dimensional lattice. We compare the
new algorithm to more standard methods using the MPS architecture. We find that
the Chebyshev method gives numerically exact results for small times. However,
the reachable times are smaller than the ones obtained with the other
state-of-the-art methods. We further extend the new method using a
spectral-decomposition-based projective scheme that utilizes an effective
bandwidth significantly smaller than the full bandwidth, leading to longer
evolution times than the non-projective method and more efficient information
storage, data compression, and less computational effort.Comment: 14 pages, 8 figure
Strongly interacting bosons on a three-leg ladder in the presence of a homogeneous flux
We perform a density-matrix renormalization-group study of strongly
interacting bosons on a three-leg ladder in the presence of a homogeneous flux.
Focusing on one-third filling, we explore the phase diagram in dependence of
the magnetic flux and the inter-leg tunneling strength. We find several phases
including a Meissner phase, vortex liquids, a vortex lattice, as well as a
staggered-current phase. Moreover, there are regions where the chiral current
reverses its direction, both in the Meissner and in the staggered-current
phase. While the reversal in the latter case can be ascribed to spontaneous
breaking of translational invariance, in the first it stems from an effective
flux increase in the rung direction. Interactions are a necessary ingredient to
realize either type of chiral-current reversal
Entanglement spectroscopy of SU(2)-broken phases in two dimensions
In magnetically ordered systems, the breaking of SU(2) symmetry in the thermodynamic limit is associated with the appearance of a special type of low-lying excitations in finite-size energy spectra, the so-called tower of states (TOS). In the present work, we numerically demonstrate that there is a correspondence between the SU(2) tower of states and the lower part of the ground-state entanglement spectrum (ES). Using state-of-the-art density matrix renormalization group (DMRG) calculations, we examine the ES of the 2D antiferromagnetic J(1)-J(2) Heisenberg model on both the triangular and kagome lattice. At large ferromagnetic J(2), the model exhibits a magnetically ordered ground state. Correspondingly, its ES contains a family of low-lying levels that are reminiscent of the energy tower of states. Their behavior (level counting, finite-size scaling in the thermodynamic limit) sharply reflects TOS features, and is characterized in terms of an effective entanglement Hamiltonian that we provide. At large system sizes, TOS levels are divided from the rest by an entanglement gap. Our analysis suggests that (TOS) entanglement spectroscopy provides an alternative tool for detecting and characterizing SU(2)-broken phases using DMRG
Phase diagram of the J1-J2 Heisenberg model on the kagome lattice
We perform an extensive density matrix renormalization group (DMRG) study of
the ground-state phase diagram of the spin-1/2 J_1-J_2 Heisenberg model on the
kagome lattice. We focus on the region of the phase diagram around the kagome
Heisenberg antiferromagnet, i.e., at J_2=0. We investigate the static spin
structure factor, the magnetic correlation lengths, and the spin gaps. Our
results are consistent with the absence of magnetic order in a narrow region
around J_2\approx 0, although strong finite-size effects do not allow us to
accurately determine the phase boundaries. This result is in agreement with the
presence of an extended spin-liquid region, as it has been proposed recently.
Outside the disordered region, we find that for ferromagnetic and
antiferromagnetic J_2 the ground state displays signatures of the magnetic
order of the \sqrt{3}\times\sqrt{3} and the q=0 type, respectively. Finally, we
focus on the structure of the entanglement spectrum (ES) in the q=0 ordered
phase. We discuss the importance of the choice of the bipartition on the
finite-size structure of the ES.Comment: 9 pages, 10 figures. Figure added, minor modifications, as publishe
Role of Correlation and Exchange for Quasi-particle Spectra of Magnetic and Diluted Magnetic Semiconductors
Theoretical foundation and application of the generalized spin-fermion (sp-d)
exchange lattice model to magnetic and diluted magnetic semiconductors are
discussed. The capabilities of the model to describe spin quasi-particle
spectra are investigated. The main emphasis is made on the dynamic behavior of
two interacting subsystems, the localized spins and spin density of itinerant
carriers. A nonperturbative many-body approach, the Irreducible Green Functions
(IGF) method, is used to describe the quasi-particle dynamics. Scattering
states are investigated and three branches of magnetic excitations are
calculated in the regime, characteristic of a magnetic semiconductor. For a
simplified version of the model (Kondo lattice model) we study the spectra of
quasi-particle excitations with special attention given to diluted magnetic
semiconductors. For this, to include the effects of disorder, modified mean
fields are determined self-consistently. The role of the Coulomb correlation
and exchange is clarified by comparing of both the cases.Comment: 34 page
Evolution of the Ace-1 and Gste2 Mutations and Their Potential Impact on the Use of Carbamate and Organophosphates in IRS for Controlling Anopheles gambiae s.l., the Major Malaria Mosquito in Senegal
Widespread of insecticide resistance amongst the species of the Anopheles gambiae complex continues to threaten vector control in Senegal. In this study, we investigated the presence and evolution of the Ace-1 and Gste2 resistance genes in natural populations of Anopheles gambiae s.l., the main malaria vector in Senegal. Using historical samples collected from ten sentinel health districts, this study focused on three different years (2013, 2017, and 2018) marking the periods of shift between the main public health insecticides families (pyrethroids, carbamates, organophosphates) used in IRS to track back the evolutionary history of the resistance mutations on the Ace-1 and Gste2 loci. The results revealed the presence of four members of the Anopheles gambiae complex, with the predominance of An. arabiensis followed by An. gambiae, An. coluzzii, and An. gambiae-coluzzii hybrids. The Ace-1 mutation was only detected in An. gambiae and An. gambiae-coluzzii hybrids at low frequencies varying between 0.006 and 0.02, while the Gste2 mutation was found in all the species with a frequency ranging between 0.02 and 0.25. The Ace-1 and Gste2 genes were highly diversified with twenty-two and thirty-one different haplotypes, respectively. The neutrality tests on each gene indicated a negative Tajima's D, suggesting the abundance of rare alleles. The presence and spread of the Ace-1 and Gste2 resistance mutations represent a serious threat to of the effectiveness and the sustainability of IRS-based interventions using carbamates or organophosphates to manage the widespread pyrethroids resistance in Senegal. These data are of the highest importance to support the NMCP for evidence-based vector control interventions selection and targeting
The one dimensional Kondo lattice model at partial band filling
The Kondo lattice model introduced in 1977 describes a lattice of localized
magnetic moments interacting with a sea of conduction electrons. It is one of
the most important canonical models in the study of a class of rare earth
compounds, called heavy fermion systems, and as such has been studied
intensively by a wide variety of techniques for more than a quarter of a
century. This review focuses on the one dimensional case at partial band
filling, in which the number of conduction electrons is less than the number of
localized moments. The theoretical understanding, based on the bosonized
solution, of the conventional Kondo lattice model is presented in great detail.
This review divides naturally into two parts, the first relating to the
description of the formalism, and the second to its application. After an
all-inclusive description of the bosonization technique, the bosonized form of
the Kondo lattice hamiltonian is constructed in detail. Next the
double-exchange ordering, Kondo singlet formation, the RKKY interaction and
spin polaron formation are described comprehensively. An in-depth analysis of
the phase diagram follows, with special emphasis on the destruction of the
ferromagnetic phase by spin-flip disorder scattering, and of recent numerical
results. The results are shown to hold for both antiferromagnetic and
ferromagnetic Kondo lattice. The general exposition is pedagogic in tone.Comment: Review, 258 pages, 19 figure
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