Topological to magnetically ordered quantum phase transition in antiferromagnetic spin ladders with long-range interactions

We study a generalized quantum spin ladder with staggered long range interactions that decay as a power-law with exponent $\alpha$. Using large scale quantum Monte Carlo (QMC) and density matrix renormalization group (DMRG) simulations, we show that this model undergoes a transition from a rung-dimer phase characterized by a non-local string order parameter, to a symmetry broken N\'eel phase. We find evidence that the transition is second order.In the magnetically ordered phase, the spectrum exhibits gapless modes, while excitations in the gapped phase are well described in terms of triplons -- bound states of spinons across the legs. We obtain the momentum resolved spin dynamic structure factor numerically and find a well defined triplon band evolves into a gapless magnon dispersion across the transition. We further discuss the possibility of deconfined criticality in this model.Comment: 16 pages, 7 figure

Recovery of a Luther-Emery phase in the three-band Hubbard model with longer-range hopping

A lightly doped single-band Hubbard model on a two leg ladder exhibits a Luther-Emery phase, while the three-band Hubbard ladder behaves as a Luttinger liquid upon hole doping. In order to understand this discrepancy, we present a systematic density-matrix renormalization group study of the three-band Hubbard model on two-leg cylinders with further-neighbor particle hoppings. The inclusion of the longer-range hopping is motivated by the studies of the single-band Hubbard model in which the further-neighbor hopping terms are suggested to be crucial for the unconventional superconductivity. When the longer-range hopping parameters are small, the ground state is a Luttinger liquid having mutually commensurate superconducting, charge and spin density wave correlations. Increasing the longer-range hopping drives a transition into a Luther-Emery phase with quasi-long ranged superconducting and charge orders but short-ranged spin-spin correlations. By down-folding the three-band Hubbard model into an effective $t$-$t'$-$J$-$J'$ model, we find that in the Luther-Emery phase, both the nearest and second neighbor kinetic energies are enhanced due to an effective increase of copper-oxygen hybridization. Amplifying inter-cell oxygen orbital hopping mirrors the benefits of reducing the charge transfer energy, causing doped holes to favor oxygen orbitals and strengthening superconducting pairing

Adoption and implication of the Biased-Annotator Competence Estimation (BACE) model into COVID-19 vaccine Twitter data: Human annotation for latent message features

Traditional quantitative content analysis approach (human coding method) has weaknesses, such as assuming all human coders are equally accurate once the intercoder reliability for training reaches a threshold score. We applied the Biased-Annotator Competence Estimation (BACE) model (Tyler, 2021), which draws on Bayesian modeling to improve human coding. An important contribution of this model is it takes each coder's potential biases and reliability into consideration and treats the "true" label of each message as a latent parameter, with quantifiable estimation uncertainties. In contrast, in conventional human coding, each message will receive a fixed label without estimates for measurement uncertainties. In this extended abstract, we first summarize the weaknesses of conventional human coding; and then apply the BACE model to COVID-19 vaccine Twitter data and compare BACE with other statistical models; finally, we discuss how the BACE model can be applied to improve human coding of latent message features

Particle-hole asymmetric ferromagnetism and spin textures in the triangular Hubbard-Hofstadter model

In a lattice model subject to a perpendicular magnetic field, when the lattice constant is comparable to the magnetic length, one enters the "Hofstadter regime," where continuum Landau levels become fractal magnetic Bloch bands. Strong mixing between bands alters the nature of the resulting quantum phases compared to the continuum limit; lattice potential, magnetic field, and Coulomb interaction must be treated on equal footing. Using determinant quantum Monte Carlo (DQMC) and density matrix renormalization group (DMRG) techniques, we study this regime numerically in the context of the Hubbard-Hofstadter model on a triangular lattice. In the field-filling phase diagram, we find a broad wedge-shaped region of ferromagnetic ground states for filling factor $\nu \lesssim 1$, bounded by incompressible states at filling factor $\nu = 1$. For magnetic field strengths $\Phi/\Phi_0 \lesssim 0.4$, we observe signatures of SU(2) quantum Hall ferromagnetism in the lowest magnetic Bloch band; however, we find no numerical evidence for conventional quantum Hall skyrmions. At large fields $\Phi/\Phi_0 \gtrsim 0.4$, above the ferromagnetic wedge, we observe a low-spin metallic region with spin correlations peaked at small momenta. We argue that the phenomenology of this region likely results from exchange interaction mixing fractal Hofstadter subbands. The phase diagram derived beyond the continuum limit points to a rich landscape to explore interaction effects in magnetic Bloch bands.Comment: 15 pages, 15 figure

Particle-hole asymmetric ferromagnetism and spin textures in the triangular Hubbard-Hofstadter model

Aggregated numerical data and analysis routines required to reproduce the figures in "Particle-hole asymmetric ferromagnetism and spin textures in the triangular Hubbard-Hofstadter model"Just unzip and run the jupyter notebooks

Bioinspired handheld time-share driven robot with expandable DoFs

Abstract Handheld robots offer accessible solutions with a short learning curve to enhance operator capabilities. However, their controllable degree-of-freedoms are limited due to scarce space for actuators. Inspired by muscle movements stimulated by nerves, we report a handheld time-share driven robot. It comprises several motion modules, all powered by a single motor. Shape memory alloy (SMA) wires, acting as “nerves”, connect to motion modules, enabling the selection of the activated module. The robot contains a 202-gram motor base and a 0.8 cm diameter manipulator comprised of sequentially linked bending modules (BM). The manipulator can be tailored in length and integrated with various instruments in situ, facilitating non-invasive access and high-dexterous operation at remote surgical sites. The applicability was demonstrated in clinical scenarios, where a surgeon held the robot to conduct transluminal experiments on a human stomach model and an ex vivo porcine stomach. The time-share driven mechanism offers a pragmatic approach to build a multi-degree-of-freedom robot for broader applications

<i>In-situ</i> Micro-scale Pb Isotope Identification Characteristics of Metallogenic and Non-metallogenic Pyrites in Sandstone-type Uranium Deposits

BACKGROUND: Sandstone-type uranium deposits contain a large number of pyrites of different shapes and stages. It is difficult to accurately discriminate the pyrite formed before, during or after the metallogenic period solely by observation of pyrite morphology by mineralogy and electron probe microanalysis. Pyrites during the metallogenic period are important information carriers for the genesis and formation process of uranium deposits, and their accurate identification is of great significance. Previous studies both domestically and internationally have used the LA-MC-ICP-MS method to analyze Pb isotopes, but this method has low analytical precision for low-content Pb samples and it is difficult to obtain 204Pb data.OBJECTIVES: To identify metallogenic and non-metallogenic pyrites by in situ micro-scale Pb isotopes.METHODS: Femtosecond laser ablation multi-collector inductively coupled plasma-mass spectrometry (fs-LA-MC-ICP-MS) was used to determine the lead isotope of pyrite in uranium ores.RESULTS: Under the mineralogy microscope, it is clear that the pyrite is related to mineralization and its 206Pb/204Pb ratio is more than ten times or even dozens of times larger than the normal Clark value. 207Pb/204Pb ratio is slightly different, and 208Pb/204Pb ratio is constant. The occurrence of strawberry-shaped pyrites, and non-metallogenic pyrites with uranium minerals growing around them but not interspersed, have normal a 206Pb/204Pb ratio. Pyrites without any contact relationship have no obvious regularity in its Pb isotopes.CONCLUSIONS: In-situ micro-scale Pb isotopic difference of pyrites was combined with appropriate observation of mineralogy morphology and occurrence, resulting in pyrites in the metallogenic period being more accurately identified than previously