Dynamical properties of the sine-Gordon quantum spin magnet Cu-PM at zero and finite temperature

The material copper pyrimidine dinitrate (Cu-PM) is a quasi-one-dimensional spin system described by the spin-1/2 XXZ Heisenberg antiferromagnet with Dzyaloshinskii-Moriya interactions. Based on numerical results obtained by the density-matrix renormalization group, exact diagonalization, and accompanying electron spin resonance (ESR) experiments we revisit the spin dynamics of this compound in an applied magnetic field. Our calculations for momentum and frequency-resolved dynamical quantities give direct access to the intensity of the elementary excitations at both zero and finite temperature. This allows us to study the system beyond the low-energy description by the quantum sine-Gordon model. We find a deviation from the Lorentz invariant dispersion for the single-soliton resonance. Furthermore, our calculations only confirm the presence of the strongest boundary bound state previously derived from a boundary sine-Gordon field theory, while composite boundary-bulk excitations have too low intensities to be observable. Upon increasing the temperature, we find a temperature-induced crossover of the soliton and the emergence of new features, such as interbreather transitions. The latter observation is confirmed by our ESR experiments on Cu-PM over a wide range of the applied field.Comment: 17 pages, 16 figures; published version (including final revisions

Milliwatt terahertz harmonic generation from topological insulator metamaterials

Achieving efficient, high-power harmonic generation in the terahertz spectral domain has technological applications, for example in sixth generation (6G) communication networks. Massless Dirac fermions possess extremely large terahertz nonlinear susceptibilities and harmonic conversion efficiencies. However, the observed maximum generated harmonic power is limited, because of saturation effects at increasing incident powers, as shown recently for graphene. Here, we demonstrate room-temperature terahertz harmonic generation in a Bi$_2$Se$_3$ topological insulator and topological-insulator-grating metamaterial structures with surface-selective terahertz field enhancement. We obtain a third-harmonic power approaching the milliwatt range for an incident power of 75 mW - an improvement by two orders of magnitude compared to a benchmarked graphene sample. We establish a framework in which this exceptional performance is the result of thermodynamic harmonic generation by the massless topological surface states, benefiting from ultrafast dissipation of electronic heat via surface-bulk Coulomb interactions. These results are an important step towards on-chip terahertz (opto)electronic applications

Large-scale production of megakaryocytes from human pluripotent stem cells by chemically defined forward programming.

The production of megakaryocytes (MKs)--the precursors of blood platelets--from human pluripotent stem cells (hPSCs) offers exciting clinical opportunities for transfusion medicine. Here we describe an original approach for the large-scale generation of MKs in chemically defined conditions using a forward programming strategy relying on the concurrent exogenous expression of three transcription factors: GATA1, FLI1 and TAL1. The forward programmed MKs proliferate and differentiate in culture for several months with MK purity over 90% reaching up to 2 × 10(5) mature MKs per input hPSC. Functional platelets are generated throughout the culture allowing the prospective collection of several transfusion units from as few as 1 million starting hPSCs. The high cell purity and yield achieved by MK forward programming, combined with efficient cryopreservation and good manufacturing practice (GMP)-compatible culture, make this approach eminently suitable to both in vitro production of platelets for transfusion and basic research in MK and platelet biology.This work was supported by the Leukemia and Lymphoma Society grant, the UK Medical Research Council (Roger Pedersen), the National Institute for Health Research (NIHR; RP-PG-0310-1002; Willem Ouwehand and Cedric Ghevaert) and a core support grant from the Wellcome Trust and MRC to the Wellcome Trust – Medical Research Council Cambridge Stem Cell Institute. Cedric Ghevaert is supported by the British Heart Foundation (FS/09/039); Marloes Tijssen is supported by the European Hematology Association (Research fellowship) and the British Heart Foundation (PG/13/77/30375). Catherine Hobbs was supported by the National Health Service Blood and Transplant. Matthew Trotter was supported by a Medical Research Council Centre grant (MRC Centre for Stem Cell Biology and Regenerative Medicine); since participation in the work described, Matthew Trotter has become an employee of Celgene Research SLU, part of Celgene Corporation. Nicole Soranzo's research and Sanger Institute affiliates are supported by the Wellcome Trust (WT098051 and WT091310), the EU FP7 (Epigenesys 257082 and Blueprint HEAL TH-F5-2011-282510). The Cambridge Biomedical Centre (BRC) hIPSCs core facility is funded by the NIHR.This is the final version of the article. It first appeared from Nature Publishing Group via https://doi.org/10.1038/ncomms1120

Antiferromagnetic resonance in the cubic iridium hexahalides (NH4)2IrCl6 and K2IrCl6

We report on high-field electron spin resonance studies of two iridium hexahalide compounds, (NH$_4$)$_2$IrCl$_6$ and K$_2$IrCl$_6$. In the paramagnetic state, our measurements reveal isotropic $g$-factors $g = 1.79$(1) for the Ir$^{4+}$ ions, in agreement with their cubic symmetries. Most importantly, in the magnetically ordered state, we observe two magnon modes with zero-field gaps of 11.3 and 14.2 K for (NH$_4$)$_2$IrCl$_6$ and K$_2$IrCl$_6$, respectively. Based on that and using linear spin-wave theory, we estimate the nearest-neighbor exchange couplings and anisotropic Kitaev interactions, $J_1/k_B=10.3$ K, $K/k_B=0.7$ K for (NH$_4$)$_2$IrCl$_6$, and $J_1/k_B=13.8$ K, $K/k_B=0.9$ K for K$_2$IrCl$_6$, revealing the nearest-neighbor Heisenberg coupling as the leading interaction term, with only a weak Kitaev anisotropy

Reducing of Sterically Hindered Pyridine Substituted Para-Nitrosophenols

Восстановление пара-нитрозопиридилфенолов гидразингидратом в этаноле позволило получить ранее недоступные перзамещенные пара-аминофенолы с пиридиновыми заместителями. Строение впервые полученных веществ подтверждено методами ИК-, ЯМР 1Н-спектроскопии спектроскопии и масс-спектрометрииReduction of para-nitrosopyridylphenols with hydrazine hydrate in ethanol made it possible to obtain previously unavailable per-substituted para-aminophenols with pyridine substituents. The structure of the compounds obtained for the first time was confirmed by IR, 1H NMR spectroscopy and mass spectrometr