Short-distance breakdown of the Higgs mechanism and the robustness of the BCS theory for charged superconductors

Through the Higgs mechanism, the long-range Coulomb interaction eliminates the low-energy Goldstone phase mode in superconductors and transfers spectral weight all the way up to the plasma frequency. Here we show that the Higgs mechanism breaks down for length scales shorter than the superconducting coherence length while it stays intact, even at high energies, in the long-wavelength limit. This effect is a consequence of the composite nature of the Higgs field of superconductivity and the broken Lorentz invariance in a solid. Most importantly, the breakdown of the Higgs mechanism inside the superconducting coherence volume is crucial to ensure the stability of the BCS mean-field theory in the weak-coupling limit. We also show that changes in the gap equation due to plasmon-induced fluctuations can lead to significant corrections to the mean-field theory and reveal that changes in the density-fluctuation spectrum of a superconductor are not limited to the vicinity of the gap.Comment: 10 pages, 4 figure

Inducing an optical Feshbach resonance via stimulated Raman coupling

We demonstrate a novel method of inducing an optical Feshbach resonance based on a coherent free-bound stimulated Raman transition. In our experiment atoms in a Rb87 Bose-Einstein condensate are exposed to two phase-locked Raman laser beams which couple pairs of colliding atoms to a molecular ground state. By controlling the power and relative detuning of the two laser beams, we can change the atomic scattering length considerably. The dependence of scattering length on these parameters is studied experimentally and modelled theoretically.Comment: 8 pages, 8 figures, submitted to PR

A Closer Look on the Polyhydroxybutyrate- (PHB-) Negative Phenotype of Ralstonia eutropha PHB-4

The undefined poly(3-hydroxybutyrate)- (PHB-) negative mutant R. eutropha PHB-4 was generated in 1970 by 1-nitroso-3-nitro-1-methylguanidine (NMG) treatment. Although being scientific relevant, its genotype remained unknown since its isolation except a recent first investigation. In this study, the mutation causing the PHA-negative phenotype of R. eutropha PHB-4 was confirmed independently: sequence analysis of the phaCAB operon identified a G320A mutation in phaC yielding a stop codon, leading to a massively truncated PhaC protein of 106 amino acids (AS) in R. eutropha PHB-4 instead of 589 AS in the wild type. No other mutations were observed within the phaCAB operon. As further mutations probably occurred in the genome of mutant PHB-4 potentially causing secondary effects on the cells' metabolism, the main focus of the study was to perform a 2D PAGE-based proteome analysis in order to identify differences in the proteomes of the wild type and mutant PHB-4. A total of 20 differentially expressed proteins were identified which provide valuable insights in the metabolomic changes of mutant PHB-4. Besides excretion of pyruvate, mutant PHB-4 encounters the accumulation of intermediates such as pyruvate and acetyl-CoA by enhanced expression of the observed protein species: (i) ThiJ supports biosynthesis of cofactor TPP and thereby reinforces the 2-oxoacid dehydrogenase complexes as PDHC, ADHC and OGDHC in order to convert pyruvate at a higher rate and the (ii) 3-isopropylmalate dehydrogenase LeuB3 apparently directs pyruvate to synthesis of several amino acids. Different (iii) acylCoA-transferases enable transfer reactions between organic acid intermediates, and (iv) citrate lyase CitE4 regenerates oxaloacetate from citrate for conversion with acetyl-CoA in the TCC in an anaplerotic reaction. Substantial amounts of reduction equivalents generated in the TCC are countered by (v) synthesis of more ubiquinones due to enhanced synthesis of MenG2 and MenG3, thereby improving the respiratory chain which accepts electrons from NADH and succinate

Vestigial nematic order and superconductivity in the doped topological insulator CuₓBi₂Se₃

If the topological insulator Bi2Se3 is doped with electrons, superconductivity with Tc = 3–4 K emerges for a low density of carriers (n = 1020 cm−3) and with a small ratio of the superconducting coherence length and Fermi wave length: ξ/λ F  = 2…4. These values make fluctuations of the superconducting order parameter increasingly important, to the extend that the Tc-value is surprisingly large. Strong spin–orbit interaction led to the proposal of an odd-parity pairing state. This begs the question of the nature of the transition in an unconventional superconductor with strong pairing fluctuations. We show that for a multi-component order parameter, these fluctuations give rise to a nematic phase at Tnem > Tc. Below Tc several experiments demonstrated a rotational symmetry breaking where the Cooper pair wave function is locked to the lattice. Our theory shows that this rotational symmetry breaking, as vestige of the superconducting state, already occurs above Tc. The nematic phase is characterized by vanishing off-diagonal long range order, yet with anisotropic superconducting fluctuations. It can be identified through direction-dependent para-conductivity, lattice softening, and an enhanced Raman response in the Eg symmetry channel. In addition, nematic order partially avoids the usual fluctuation suppression of Tc

Prospectively defined murine mesenchymal stem cells inhibit Klebsiella pneumoniae-induced acute lung injury and improve pneumonia survival

Background: Numerous studies have described the immunosuppressive capacity of mesenchymal stem cells (MSC) but these studies use mixtures of heterogeneous progenitor cells for in vitro expansion. Recently, multipotent MSC have been prospectively identified in murine bone marrow (BM) on the basis of PDFGRa+ SCA1+ CD45- TER119- (PaS) expression but the immunomodulatory capacity of these MSC is unknown. Methods: We isolated PaS MSC by high-purity FACS sorting of murine BM and after in vitro expansion we analyzed the in vivo immunomodulatory activity during acute pneumonia. PaS MSC (1?×?106) were applied intratracheally 4 h after acute respiratory Klebsiella pneumoniae induced infection. Results: PaS MSC treatment resulted in significantly reduced alveolitis and protein leakage in comparison to mock-treated controls. PaS MSC-treated mice exhibited significantly reduced alveolar TNF-a and IL-12p70 expression, while IL-10 expression was unaffected. Dissection of respiratory dendritic cell (DC) subsets by multiparameter flow cytometry revealed significantly reduced lung DC infiltration and significantly reduced CD86 costimulatory expression on lung CD103+ DC in PaS MSC-treated mice. In the post-acute phase of pneumonia, PaS MSC-treated animals exhibited significantly reduced respiratory IL-17+ CD4+ T cells and IFN-gamma+ CD4+ T cells. Moreover, PaS MSC treatment significantly improved overall pneumonia survival and did not increase bacterial load. Conclusion: In this study we demonstrated for the first time the feasibility and in vivo immunomodulatory capacity of prospectively defined MSC in pneumonia

Phonon-induced rotation of the electronic nematic director in superconducting Bi2_{2}Se3_{3}

The doped topological insulator $A_{x}\mathrm{Bi_{2}Se_{3}}$, with $A=\{\mathrm{Cu},\mathrm{Sr},\mathrm{Nb}\}$, becomes a nematic superconductor below $T_{c}\sim3-4\,\mathrm{K}$. The associated electronic nematic director is described by an angle $\alpha$ and is experimentally manifested in the elliptical shape of the in-plane critical magnetic field $H_{c2}$. Because of the threefold rotational symmetry of the lattice, $\alpha$ is expected to align with one of three high-symmetry directions corresponding to the in-plane nearest-neighbor bonds, consistent with a $Z_{3}$-Potts nematic transition. Here, we show that the nematic coupling to the acoustic phonons, which makes the nematic correlation length tend to diverge along certain directions only, can fundamentally alter this phenomenology in trigonal lattices. Compared to hexagonal lattices, the former possesses a sixth independent elastic constant $c_{14}$ due to the fact that the in-plane shear strain doublet $(\epsilon_{xx}-\epsilon_{yy},-2\epsilon_{xy})$ and the out-of-plane shear strain doublet $(2\epsilon_{yz},-2\epsilon_{xz})$ transform as the same irreducible representation. We find that, when $c_{14}$ overcomes a threshold value, which is expected to be the case in doped $\mathrm{Bi_{2}Se_{3}}$, the nematic director $\alpha$ unlocks from the high-symmetry directions due to the competition between the quadratic phonon-mediated interaction and the cubic nematic anharmonicity. This implies the breaking of the residual in-plane twofold rotational symmetry ($C_{2x}$), resulting in a triclinic phase. We discuss the implications of these findings to the structure of nematic domains and to the shape of the in-plane $H_{c2}$ in $A_{x}\mathrm{Bi_{2}Se_{3}}$, and to presence of nodes inside the superconducting state.Comment: 24 pages, 10 figure