Nonequilibrium phase transition in a driven-dissipative quantum antiferromagnet

A deeper theoretical understanding of driven-dissipative interacting systems and their nonequilibrium phase transitions is essential both to advance our fundamental physics understanding and to harness technological opportunities arising from optically controlled quantum many-body states. This paper provides a numerical study of dynamical phases and the transitions between them in the nonequilibrium steady state of the prototypical two-dimensional Heisenberg antiferromagnet with drive and dissipation. We demonstrate a nonthermal transition that is characterized by a qualitative change in the magnon distribution from subthermal at low drive to a generalized Bose-Einstein form including a nonvanishing condensate fraction at high drive. A finite-size analysis reveals static and dynamical critical scaling at the transition, with a discontinuous slope of the magnon number versus driving field strength and critical slowing down at the transition point. Implications for experiments on quantum materials and polariton condensates are discussed

Witnessing nonequilibrium entanglement dynamics in a strongly correlated fermionic chain

Many-body entanglement in condensed matter systems can be diagnosed from equilibrium response functions through the use of entanglement witnesses and operator-specific quantum bounds. Here, we investigate the applicability of this approach for detecting entangled states in quantum systems driven out of equilibrium. We use a multipartite entanglement witness, the quantum Fisher information, to study the dynamics of a paradigmatic fermion chain undergoing a time-dependent change of the Coulomb interaction. Our results show that the quantum Fisher information is able to witness distinct signatures of multipartite entanglement both near and far from equilibrium that are robust against decoherence. We discuss implications of these findings for probing entanglement in light-driven quantum materials with time-resolved optical and x-ray scattering methods

Floquet-engineered light-cone spreading of correlations in a driven quantum chain

We investigate the light-cone-like spread of electronic correlations in a laser-driven quantum chain. Using the time-dependent density matrix renormalization group, we show that high-frequency driving leads to a Floquet-engineered spread velocity that determines the enhancement of density-density correlations when the ratio of potential and kinetic energies is effectively increased both by either a continuous or a pulsed drive. For large times we numerically show the existence of a Floquet steady state at not too long distances on the lattice with minimal heating. Intriguingly, we find a discontinuity of dynamically scaled correlations at the edge of the light cone, akin to the discontinuity known to exist for quantum quenches in Luttinger liquids. Our work demonstrates the potential of pump-probe experiments for investigating light-induced correlations in low-dimensional materials and puts quantitative speed limits on the manipulation of long-ranged correlations through Floquet engineering

Nonequilibrium brittle fracture propagation: Steady state, oscillations and intermittency

A minimal model is constructed for two-dimensional fracture propagation. The heterogeneous process zone is presumed to suppress stress relaxation rate, leading to non-quasistatic behavior. Using the Yoffe solution, I construct and solve a dynamical equation for the tip stress. I discuss a generic tip velocity response to local stress and find that noise-free propagation is either at steady state or oscillatory, depending only on one material parameter. Noise gives rise to intermittency and quasi-periodicity. The theory explains the velocity oscillations and the complicated behavior seen in polymeric and amorphous brittle materials. I suggest experimental verifications and new connections between velocity measurements and material properties.Comment: To appear in Phys. Rev. Lett., 6 pages, self-contained TeX file, 3 postscript figures upon request from author at [email protected] or [email protected], http://cnls-www.lanl.gov/homepages/rafi/rafindex.htm

On the origin of the Norwegian lemming.

The Pleistocene glacial cycles resulted in significant changes in species distributions, and it has been discussed whether this caused increased rates of population divergence and speciation. One species that is likely to have evolved during the Pleistocene is the Norwegian lemming (Lemmus lemmus). However, the origin of this species, both in terms of when and from what ancestral taxon it evolved, has been difficult to ascertain. Here, we use ancient DNA recovered from lemming remains from a series of Late Pleistocene and Holocene sites to explore the species' evolutionary history. The results revealed considerable genetic differentiation between glacial and contemporary samples. Moreover, the analyses provided strong support for a divergence time prior to the Last Glacial Maximum (LGM), therefore likely ruling out a postglacial colonization of Scandinavia. Consequently, it appears that the Norwegian lemming evolved from a small population that survived the LGM in an ice-free Scandinavian refugium

The METCRAX II Field Experiment: A Study of Downslope Windstorm-Type Flows in Arizona\u2019s Meteor Crater

The second Meteor Crater Experiment (METCRAX II) was conducted in October 2013 at Arizona\u2019s Meteor Crater. The experiment was designed to investigate nighttime downslope windstorm 12type flows that form regularly above the inner southwest sidewall of the 1.2-km diameter crater as a southwesterly mesoscale katabatic flow cascades over the crater rim. The objective of METCRAX II is to determine the causes of these strong, intermittent, and turbulent inflows that bring warm-air intrusions into the southwest part of the crater. This article provides an overview of the scientific goals of the experiment; summarizes the measurements, the crater topography, and the synoptic meteorology of the study period; and presents initial analysis results

No self-similar aggregates with sedimentation

Two-dimensional cluster-cluster aggregation is studied when clusters move both diffusively and sediment with a size dependent velocity. Sedimentation breaks the rotational symmetry and the ensuing clusters are not self-similar fractals: the mean cluster width perpendicular to the field direction grows faster than the height. The mean width exhibits power-law scaling with respect to the cluster size, ~ s^{l_x}, l_x = 0.61 +- 0.01, but the mean height does not. The clusters tend to become elongated in the sedimentation direction and the ratio of the single particle sedimentation velocity to single particle diffusivity controls the degree of orientation. These results are obtained using a simulation method, which becomes the more efficient the larger the moving clusters are.Comment: 10 pages, 10 figure

Highly Pathogenic Avian Influenza Virus Infection of Mallards with Homo- and Heterosubtypic Immunity Induced by Low Pathogenic Avian Influenza Viruses

The potential role of wild birds as carriers of highly pathogenic avian influenza virus (HPAIV) subtype H5N1 is still a matter of debate. Consecutive or simultaneous infections with different subtypes of influenza viruses of low pathogenicity (LPAIV) are very common in wild duck populations. To better understand the epidemiology and pathogenesis of HPAIV H5N1 infections in natural ecosystems, we investigated the influence of prior infection of mallards with homo- (H5N2) and heterosubtypic (H4N6) LPAIV on exposure to HPAIV H5N1. In mallards with homosubtypic immunity induced by LPAIV infection, clinical disease was absent and shedding of HPAIV from respiratory and intestinal tracts was grossly reduced compared to the heterosubtypic and control groups (mean GEC/100 µl at 3 dpi: 3.0×102 vs. 2.3×104 vs. 8.7×104; p<0.05). Heterosubtypic immunity induced by an H4N6 infection mediated a similar but less pronounced effect. We conclude that the epidemiology of HPAIV H5N1 in mallards and probably other aquatic wild bird species is massively influenced by interfering immunity induced by prior homo- and heterosubtypic LPAIV infections

Fur glowing under ultraviolet: in situ analysis of porphyrin accumulation in the skin appendages of mammals

Examples of photoluminescence (PL) are being reported with increasing frequency in a wide range of organisms from diverse ecosystems. However, the chemical basis of this PL remains poorly defined, and our understanding of its potential ecological function is still superficial. Among mammals, recent analyses have identified free-base porphyrins as the compounds responsible for the reddish ultraviolet-induced photoluminescence (UV-PL) observed in the pelage of springhares and hedgehogs. However, the localization of the pigments within the hair largely remains to be determined. Here, we use photoluminescence multispectral imaging emission and excitation spectroscopy to detect, map, and characterize porphyrinic compounds in skin appendages in situ. We also document new cases of mammalian UV-PL caused by free-base porphyrins in distantly related species. Spatial distribution of the UV-PL is strongly suggestive of an endogenous origin of the porphyrinic compounds. We argue that reddish UV-PL is predominantly observed in crepuscular and nocturnal mammals because porphyrins are photodegradable. Consequently, this phenomenon may not have a specific function in intra- or interspecific communication but rather represents a byproduct of potentially widespread physiological processes.publishedVersio