We study the onset of spin-density wave order in itinerant electron systems via a two-dimensional lattice model amenable to numerically exact, sign-problem-free determinantal quantum Monte Carlo simulations. The finite-temperature phase diagram of the model reveals a dome-shaped d-wave superconducting phase near the magnetic quantum phase transition. Above the critical superconducting temperature, we observe an extended fluctuation regime, which manifests itself in the opening of a gap in the electronic density of states and an enhanced diamagnetic response. While charge density wave fluctuations are moderately enhanced in the proximity of the magnetic quantum phase transition, they remain short-ranged. The striking similarity of our results to the phenomenology of many unconventional superconductors points a way to a microscopic understanding of such strongly coupled systems in a controlled manner. PACS numbers: 74.25.Dw, 74.40.Kb A common feature of many strongly correlated metals, such as the cuprates, the Fe-based superconductors, heavy-fermion compounds, and organic superconductors, is the close proximity of unconventional superconductivity (SC) and spin density wave (SDW) order in their phase diagrams. This suggests that there is a common, universal mechanism at work behind both phenomena [1]. In some of these systems, additional types of competing or coexisting orders appear upon suppressing the SDW order, such as nematic, charge-density wave (CDW), or possibly also pair density wave (PDW) order. Such a complex interplay between multiple types of electronic order, with comparable onset temperature scales, is a recurring theme in strongly correlated systems [2].These findings call for a detailed understanding of the physics of metals on the verge of an SDW transition. It has long been proposed that nearly-critical antiferromagnetic fluctuations can mediate unconventional superconductivity [3,4]. Many studies have focused on the universal properties of an antiferromagnetic quantum critical point (QCP) in a metal [5][6][7][8][9][10][11]. In particular, it has been proposed that superconductivity is anomalously enhanced at the magnetic QCP [12][13][14][15]. The same antiferromagnetic interaction can enhance other subsidiary orders, such as CDW [14,16,17] or PDW [18,19]. Near the QCP, an approximate symmetry relating the SC and density wave order may emerge [14]. The resulting multi-component order parameter would have a substantial fluctuation regime, proposed as the origin of the "pseudogap" observed in the cuprates [16,[20][21][22]. A deep minimum in the penetration depth of the SC at low temperature, seen in the iron-based SC BaFe 2 (As 1−x P x ) 2 [23], has been proposed as a generic manifestation of the underlying antiferromagnetic QCP [24,25].Due to the strong coupling nature of the problem of a nearly antiferromagnetic metal, obtaining analytically controlled solutions has proven difficult. In Ref.[26], a two-dimensional lattice model of a nearly-antiferromagnetic metal amenable to sign-problem-free...

Background:Human head and neck squamous cell carcinoma (HNSCC) fundamentally vary in their susceptibility to different cytotoxic drugs and treatment modalities. There is at present no clinically accepted test system to predict the most effective therapy for an individual patient.Methods:Therefore, we established tumour-derived slice cultures which can be kept in vitro for at least 6 days. Upon treatment with cisplatin, docetaxel and cetuximab, slices were fixed and paraffin sections were cut for histopathological analysis.Results:Apoptotic fragmentation, activation of caspase 3, and cell loss were observed in treated tumour slices. Counts of nuclei per field in untreated compared with treated slices deriving from the same tumour allowed estimation of the anti-neoplastic activity of individual drugs on an individual tumour.Conclusion:HNSCC-derived slice cultures survive well in vitro and may serve not only to improve personalised therapies but also to detect mechanisms of tumour resistance by harvesting surviving tumour cells after treatment.

We report on the coherent coupling of whispering gallery modes (WGM) in a photonic molecule formed from two melamine-formaldehyde spherical microcavities with a thin shell of CdTe nanocrystals. Utilizing a microporous polymer structure to orient the photonic molecule, we have excited the photonic molecule both on and off axis. This controllable geometry has allowed the observation of an off-axis fine structure that consists of very sharp peaks resulting from the removal of the WGM degeneracy with respect to the azimuthal quantum number m. The mode splittings are in very good agreement with theory.

We report on numerically exact determinantal quantum Monte Carlo simulations of the onset of spin-density wave (SDW) order in itinerant electron systems captured by a sign-problem-free two-dimensional lattice model. Extensive measurements of the SDW correlations in the vicinity of the phase transition reveal that the critical dynamics of the bosonic order parameter are well described by a dynamical critical exponent z = 2, consistent with Hertz-Millis theory, but are found to follow a finite-temperature dependence that does not fit the predicted behavior of the same theory. The presence of critical SDW fluctuations is found to have a strong impact on the fermionic quasiparticles, giving rise to a dome-shaped superconducting phase near the quantum critical point. In the superconducting state we find a gap function that has an opposite sign between the two bands of the model and is nearly constant along the Fermi surface of each band. Above the superconducting Tc our numerical simulations reveal a nearly temperature and frequency independent self energy causing a strong suppression of the low-energy quasiparticle spectral weight in the vicinity of the hot spots on the Fermi surface. This indicates a clear breakdown of Fermi liquid theory around these points.

The microscopic modeling of spin-orbit entangled j = 1/2 Mott insulators such as the layered hexagonal Iridates Na2IrO3 and Li2IrO3 has spurred an interest in the physics of Heisenberg-Kitaev models. Here we explore the effect of lattice distortions on the formation of the collective spin-orbital states which include not only conventionally ordered phases but also gapped and gapless spin-orbital liquids. In particular, we demonstrate that in the presence of spatial anisotropies of the exchange couplings conventionally ordered states are formed through an order-by-disorder selection which is not only sensitive to the type of exchange anisotropy but also to the relative strength of the Heisenberg and Kitaev couplings. The spin-orbital liquid phases of the Kitaev limit -a gapless phase in the vicinity of spatially isotropic couplings and a gapped Z2 phase for a dominant spatial anisotropy of the exchange couplings -show vastly different sensitivities to the inclusion of a Heisenberg exchange. While the gapless phase is remarkably stable, the gapped Z2 phase quickly breaks down in what might be a rather unconventional phase transition driven by the simultaneous condensation of its elementary excitations.