Universality class of quantum criticality in the two-dimensional Hubbard model at intermediate temperatures (t2/U≪T≪tt^2/U\ll T\ll t)

We show that the dilute Fermi gas quantum critical universality class quantitatively describes the Mott/metal crossover of the two-dimensional Hubbard model for temperatures somewhat less than (roughly half) the tunneling but much greater than (roughly twice) the superexchange energy. We calculate the observables expected to be universal near the transition --- density and compressibility --- with numerically exact determinantal quantum Monte Carlo. We find they are universal functions of the chemical potential. Despite arising from the strongly correlated regime of the Hubbard model, these functions are given by the weakly interacting, dilute Fermi gas model. These observables and their derivatives are the only expected universal static observables of this universality class, which we also confirm by verifying there is no scaling collapse of the kinetic energy, fraction of doubly occupied sites, and nearest neighbor spin correlations. Our work resolves the universality class of the intermediate temperature Mott/metal crossover, which had alternatively been proposed to be described by more exotic theories. However, in the presence of a Zeeman magnetic field, we find that interplay of spin with itinerant charge can lead to physics beyond the dilute Fermi gas universality class.Comment: Main text: 4 pages, 2 figures (6 panels). Supplementary info.: 2 pages, 3 figures (7 panels

Kitaev honeycomb and other exotic spin models with polar molecules

We show that ultracold polar molecules pinned in an optical lattice can be used to access a variety of exotic spin models, including the Kitaev honeycomb model. Treating each molecule as a rigid rotor, we use DC electric and microwave fields to define superpositions of rotational levels as effective spin degrees of freedom, while dipole–dipole interactions give rise to interactions between the spins. In particular, we show that, with sufficient microwave control, the interaction between two spins can be written as a sum of five independently controllable Hamiltonian terms proportional to the five rank-2 spherical harmonics Y_2, q (θ, φ), where (θ, φ) are the spherical coordinates of the vector connecting the two molecules. To demonstrate the potential of this approach beyond the simplest examples studied in [S.R. Manmana et al., Phys. Rev. B. 87, 081106 (2013)], we focus on the realisation of the Kitaev honeycomb model, which can support exotic non-Abelian anyonic excitations. We also discuss the possibility of generating spin Hamiltonians with arbitrary spin S, including those exhibiting SU(N=2S+1) symmetry

Topological phases in ultracold polar-molecule quantum magnets

We show how to use polar molecules in an optical lattice to engineer quantum spin models with arbitrary spin S≥1/2 and with interactions featuring a direction-dependent spin anisotropy. This is achieved by encoding the effective spin degrees of freedom in microwave-dressed rotational states of the molecules and by coupling the spins through dipolar interactions. We demonstrate how one of the experimentally most accessible anisotropies stabilizes symmetry protected topological phases in spin ladders. Using the numerically exact density matrix renormalization group method, we find that these interacting phases—previously studied only in the nearest-neighbor case—survive in the presence of long-range dipolar interactions. We also show how to use our approach to realize the bilinear-biquadratic spin-1 and the Kitaev honeycomb models. Experimental detection schemes and imperfections are discussed

Spectroscopy of dipolar fermions in 2D pancakes and 3D lattices

Motivated by ongoing measurements at JILA, we calculate the recoil-free spectra of dipolar interacting fermions, for example ultracold heteronuclear molecules, in a one-dimensional lattice of two-dimensional pancakes, spectroscopically probing transitions between different internal (e.g., rotational) states. We additionally incorporate p-wave interactions and losses, which are important for reactive molecules such as KRb. Moreover, we consider other sources of spectral broadening: interaction-induced quasiparticle lifetimes and the different polarizabilities of the different rotational states used for the spectroscopy. Although our main focus is molecules, some of the calculations are also useful for optical lattice atomic clocks. For example, understanding the p-wave shifts between identical fermions and small dipolar interactions coming from the excited clock state are necessary to reach future precision goals. Finally, we consider the spectra in a deep 3D lattice and show how they give a great deal of information about static correlation functions, including \textit{all} the moments of the density correlations between nearby sites. The range of correlations measurable depends on spectroscopic resolution and the dipole moment.Comment: 14 pages, 6 figure

A Novel Dielectric Anomaly in Cuprates and Nickelates: Signature of an Electronic Glassy State

The low-frequency dielectric response of hole-doped insulators La_{2}Cu_{1-x}Li_{x}O_{4} and La_{2-x}Sr_{x}NiO_{4} shows a large dielectric constant \epsilon ^{'} at high temperature and a step-like drop by a factor of 100 at a material-dependent low temperature T_{f}. T_{f} increases with frequency and the dielectric response shows universal scaling in a Cole-Cole plot, suggesting that a charge glass state is realized both in the cuprates and in the nickelates.Comment: 5 pages, 4 figure

The evolution of community peer support values: reflections from three UK mental health project teams: The McPin peer support evaluation writing collaborative

OBJECTIVE: To explore emergent values for community-based peer support in three projects and use of peer research methodology. BACKGROUND: Peer support refers to the support people with shared lived experiences provide to each other. Its roots are in the civil rights movement, providing alternatives to clinical treatments. This method of support is delivered in different settings, with varying degrees of structure. In this paper, it includes shared experience of mental health issues. METHODS: We reviewed interview data from two evaluations and one development project - mental health (n = 69), women-only (n = 40), and maternal mental health (n = 24), respectively. Each project used peer research methods. Peer support values from each project were compared, along with reflections from mostly peer researchers who worked on them (n = 11). RESULTS: Six peer support values emerged and were found to be identifiable and applicable in different contexts. Decisions on facilitation and leadership varied across projects and generated some concerns over professionalisation, including non-peer leadership. Frameworks were viewed as broadly useful, but peer support is heterogenous, and peer researchers were concerned about over-rigid application of guidance. DISCUSSION: We propose caution applying frameworks for peer support. Values must remain flexible and peer-led, evolving in new contexts such as COVID-19. Evaluators have a responsibility to consider any potentially negative consequences of their work and mitigate them. This means ensuring research outputs are useful to the peer support community, and knowledge production is based upon methodologies, such as peer research, that complement and are consistent with the values of peer support itself

The evolution of community peer support values: reflections from three UK mental health project teams: The McPin peer support evaluation writing collaborative

Objective: To explore emergent values for community-based peer support in three projects and use of peer research methodology. Background: Peer support refers to the support people with shared lived experiences provide to each other. Its roots are in the civil rights movement, providing alternatives to clinical treatments. This method of support is delivered in different settings, with varying degrees of structure. In this paper, it includes shared experience of mental health issues. Methods: We reviewed interview data from two evaluations and one development project - mental health (n = 69), women-only (n = 40), and maternal mental health (n = 24), respectively. Each project used peer research methods. Peer support values from each project were compared, along with reflections from mostly peer researchers who worked on them (n = 11). Results: Six peer support values emerged and were found to be identifiable and applicable in different contexts. Decisions on facilitation and leadership varied across projects and generated some concerns over professionalisation, including non-peer leadership. Frameworks were viewed as broadly useful, but peer support is heterogenous, and peer researchers were concerned about over-rigid application of guidance. Discussion: We propose caution applying frameworks for peer support. Values must remain flexible and peer-led, evolving in new contexts such as COVID-19. Evaluators have a responsibility to consider any potentially negative consequences of their work and mitigate them. This means ensuring research outputs are useful to the peer support community, and knowledge production is based upon methodologies, such as peer research, that complement and are consistent with the values of peer support itself

Exosome-Producing Follicle Associated Epithelium Is Not Involved in Uptake of PrPd from the Gut of Sheep (Ovis aries): An Ultrastructural Study

In natural or experimental oral scrapie infection of sheep, disease associated prion protein (PrPd) often first accumulates in Peyer's patch (PP) follicles. The route by which infectivity reaches the follicles is unknown, however, intestinal epithelial cells may participate in intestinal antigenic presentation by delivering exosomes as vehicles of luminal antigens. In a previous study using an intestinal loop model, following inoculation of scrapie brain homogenate, inoculum associated PrPd was detected by light microscopy shortly (15 minutes to 3.5 hours) after inoculation in the villous lacteals and sub-mucosal lymphatics. No PrPd was located within the follicle-associated epithelium (FAE), sub-FAE domes or the PP follicles. To evaluate this gut loop model and the transportation routes in more detail, we used electron microscopy (EM) to study intestinal tissues exposed to scrapie or control homogenates for 15 minutes to 10 days. In addition, immuno-EM was used to investigate whether exosomes produced in the FAE may possess small amounts of PrPd that were not detectable by light microscopy. This study showed that the integrity of the intestinal epithelium was sustained in the intestinal loop model. Despite prominent transcytotic activity and exosome release from the FAE of the ileal PP in sheep, these structures were not associated with transportation of PrPd across the mucosa. The study did not determine how infectivity reaches the follicles of PPs. The possibility that the infectious agent is transported across the FAE remains a possibility if it occurs in a form that is undetectable by the methods used in this study. Infectivity may also be transported via lymph to the blood and further to all other lymphoid tissues including the PP follicles, but the early presence of PrPd in the PP follicles during scrapie infection argues against such a mechanism

Common Features at the Start of the Neurodegeneration Cascade

A single-molecule study reveals that neurotoxic proteins share common structural features that may trigger neurodegeneration, thus identifying new targets for therapy and diagnosis