Thermal compression of atomic hydrogen on helium surface

We describe experiments with spin-polarized atomic hydrogen gas adsorbed on liquid $^{4}$He surface. The surface gas density is increased locally by thermal compression up to $5.5\times10^{12}$ cm$^{-2}$ at 110 mK. This corresponds to the onset of quantum degeneracy with the thermal de-Broglie wavelength being 1.5 times larger than the mean interatomic spacing. The atoms were detected directly with a 129 GHz electron-spin resonance spectrometer probing both the surface and the bulk gas. This, and the simultaneous measurement of the recombination power, allowed us to make accurate studies of the adsorption isotherm and the heat removal from the adsorbed hydrogen gas. From the data, we estimate the thermal contact between 2D hydrogen gas and phonons of the helium film. We analyze the limitations of the thermal compression method and the possibility to reach the superfluid transition in 2D hydrogen gas.Comment: 20 pages, 11 figure

Shift of fibril‐forming ability of the designed α‐helical coiled‐coil peptides into the physiological pH region

Recently, we designed a short α‐helical fibril‐forming peptide (αFFP) that can form α‐helical nanofibrils at acid pH. The non‐physiological conditions of the fibril formation hamper biomedical application of αFFP. It was hypothesized that electrostatic repulsion between glutamic acid residues present at positions (g) of the αFFP coiled‐coil sequence prevent the fibrillogenesis at neutral pH, while their protonation below pH 5.5 triggers axial growth of the fibril. To test this hypothesis, we synthesized αFFPs where all glutamic acid residues were substituted by glutamines or serines. The electron microscopy study confirmed that the modified αFFPs form nanofibrils in a wider range of pH (2.5-11). Circular dichroism spectroscopy, sedimentation, diffusion and differential scanning calorimetry showed that the fibrils are α‐helical and have elongated and highly stable cooperative tertiary structures. This work leads to a better understanding of interactions that control the fibrillogenesis of the αFFPs and opens opportunities for their biomedical applicatio

Coexistence of Superconductivity and Charge Density Waves in Tantalum Disulfide : Experiment and Theory

The coexistence of charge density wave (CDW) and superconductivity in tantalum disulfide (2H-TaS2) at low temperature is boosted by applying hydrostatic pressures to study both vibrational and magnetic transport properties. Around Pc, we observe a superconducting dome with a maximum superconducting transition temperature Tc=9.1 K. First-principles calculations of the electronic structure predict that, under ambient conditions, the undistorted structure is characterized by a phonon instability at finite momentum close to the experimental CDW wave vector. Upon compression, this instability is found to disappear, indicating the suppression of CDW order. The calculations reveal an electronic topological transition (ETT), which occurs before the suppression of the phonon instability, suggesting that the ETT alone is not directly causing the structural change in the system. The temperature dependence of the first vortex penetration field has been experimentally obtained by two independent methods. While a d wave and single-gap BCS prediction cannot describe the lower critical field Hc1 data, the temperature dependence of the Hc1 can be well described by a single-gap anisotropic s-wave order parameter. © 2020 authors. Published by the American Physical Society

Euler-Calogero-Moser system from SU(2) Yang-Mills theory

The relation between SU(2) Yang-Mills mechanics, originated from the 4-dimensional SU(2) Yang-Mills theory under the supposition of spatial homogeneity of the gauge fields, and the Euler-Calogero-Moser model is discussed in the framework of Hamiltonian reduction. Two kinds of reductions of the degrees of freedom are considered: due to the gauge invariance and due to the discrete symmetry. In the former case, it is shown that after elimination of the gauge degrees of freedom from the SU(2) Yang-Mills mechanics the resulting unconstrained system represents the ID_3 Euler-Calogero-Moser model with an external fourth-order potential. Whereas in the latter, the IA_6 Euler-Calogero-Moser model embedded in an external potential is derived whose projection onto the invariant submanifold through the discrete symmetry coincides again with the SU(2) Yang-Mills mechanics. Based on this connection, the equations of motion of the SU(2) Yang-Mills mechanics in the limit of the zero coupling constant are presented in the Lax form.Comment: Revtex, 14 pages, no figures. Abstract changed, strata analysis have been included, typos corrected, references adde

Subcarrier Wave Quantum Key Distribution in Telecommunication Network with Bitrate 800 kbit/s

In the course of work on creating the first quantum communication network in Russia we demonstrated quantum key distribution in metropolitan optical network infrastructure. A single-pass subcarrier wave quantum cryptography scheme was used in the experiments. BB84 protocol with strong reference was chosen for performing key distribution. The registered sifted key rate in an optical cable with 1.5 dB loss was 800 Kbit/s. Signal visibility exceeded 98%, and quantum bit error rate value was 1%. The achieved result is a record for this type of systems

Ionic and electronic structure of sodium clusters up to N=59

We determined the ionic and electronic structure of sodium clusters with even electron numbers and 2 to 59 atoms in axially averaged and three-dimensional density functional calculations. A local, phenomenological pseudopotential that reproduces important bulk and atomic properties and facilitates structure calculations has been developed. Photoabsorption spectra have been calculated for $\mathrm{Na}_2$, $\mathrm{Na}_8$, and $\mathrm{Na}_9^+$ to $\mathrm{Na}_{59}^+$. The consistent inclusion of ionic structure considerably improves agreement with experiment. An icosahedral growth pattern is observed for $\mathrm{Na}_{19}^+$ to $\mathrm{Na}_{59}^+$. This finding is supported by photoabsorption data.Comment: To appear in Phys. Rev. B 62. Version with figures in better quality can be requested from the author

Pion, kaon, proton and anti-proton transverse momentum distributions from p+p and d+Au collisions at sNN=200\sqrt{s_{NN}} = 200 GeV

Identified mid-rapidity particle spectra of $\pi^{\pm}$, $K^{\pm}$, and $p(\bar{p})$ from 200 GeV p+p and d+Au collisions are reported. A time-of-flight detector based on multi-gap resistive plate chamber technology is used for particle identification. The particle-species dependence of the Cronin effect is observed to be significantly smaller than that at lower energies. The ratio of the nuclear modification factor ($R_{dAu}$) between protons $(p+\bar{p})$ and charged hadrons ($h$) in the transverse momentum range $1.2<{p_{T}}<3.0$ GeV/c is measured to be $1.19\pm0.05$(stat)$\pm0.03$(syst) in minimum-bias collisions and shows little centrality dependence. The yield ratio of $(p+\bar{p})/h$ in minimum-bias d+Au collisions is found to be a factor of 2 lower than that in Au+Au collisions, indicating that the Cronin effect alone is not enough to account for the relative baryon enhancement observed in heavy ion collisions at RHIC.Comment: 6 pages, 4 figures, 1 table. We extended the pion spectra from transverse momentum 1.8 GeV/c to 3. GeV/

Azimuthal anisotropy at RHIC: the first and fourth harmonics

We report the first observations of the first harmonic (directed flow, v_1), and the fourth harmonic (v_4), in the azimuthal distribution of particles with respect to the reaction plane in Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). Both measurements were done taking advantage of the large elliptic flow (v_2) generated at RHIC. From the correlation of v_2 with v_1 it is determined that v_2 is positive, or {\it in-plane}. The integrated v_4 is about a factor of 10 smaller than v_2. For the sixth (v_6) and eighth (v_8) harmonics upper limits on the magnitudes are reported.Comment: 6 pages with 3 figures, as accepted for Phys. Rev. Letters The data tables are at http://www.star.bnl.gov/central/publications/pubDetail.php?id=3

Pion-Xi correlations in Au-Au collisions at STAR

We present pion-Xi correlation analysis in Au-Au collisions at sqrt(s_NN)= 200 GeV and sqrt(s_NN) = 62.4 GeV, performed using the STAR detector at RHIC. A Xi*(1530) resonance signal is observed for the first time in Au-Au collisions. Experimental data are compared with theoretical predictions. The strength of the Xi* peak is reproduced in the correlation function assuming that pions and Xis emerge from a system in collective expansion.Comment: To appear in the proceedings of 18th Nuclear Physics Division Conference of the EPS (NPDC18),Prague, 23.8.-29.8. 200

Inclusive pi0 spectra at high transverse momentum in d-Au collisions at RHIC

Preliminary results on inclusive neutral pion production in d-Au collisions at sqrt(s_NN) = 200 GeV in the pseudo-rapidity range 0<eta<1 are presented. The measurement is performed using the STAR Barrel Electromagnetic calorimeter (BEMC). In this paper, the analysis of the first BEMC hadron measurement is described and the results are compared with earlier RHIC findings. The pi0 invariant differential cross sections show good agreement with next-to-leading order (NLO) perturbative QCD calculations.Comment: 4 pages, 5 figures, 18th Nuclear Physics Division Conference of the EPS, Prague, submitted to Nucl. Phys.