Development of the pulse NMR method utilizing the short-lived β-emitter 12 B

Measurements of the spin-spin relaxation time T ₂ of the short-lived $\upbeta $ -emitter $^{12}B (I^{\uppi }$ = 1^?+?, T _1/2 = 20 ms) in Si have been performed. By applying the spin echo method to $\upbeta $ -NMR measurements, the intrinsic T ₂ for ¹²B in Si was successfully determined with the effect of the static magnetic field inhomogeneity removed. The temperature dependence of T ₂ for ¹²B in Si shows that T ₂ becomes longer with increasing temperature, which seems to reflect the effect of motional narrowing.     

Matter radii and wave function admixtures in 2n halo nuclei

We analyze longitudinal pion spectra from $\ensuremath \sqrt{s_{NN}}=2$ GeV to $\ensuremath \sqrt{s_{NN}}=20$ GeV within Landau??s hydrodynamical model and the UrQMD hybrid approach. From the measured data on the widths of the pion rapidity spectra, we extract the sound velocity c _s ² in the dense stage of the reactions. It is found that the sound velocity has a local minimum (indicating the softest point in the equation of state, EoS) at $\ensuremath \sqrt{s_{NN}}=4\mbox{--}9$ GeV, an energy range accessible at the Facility for Antiproton and Ion Research (FAIR) as well as the RHIC-Beam Energy Scan (RHIC-BES). This softening of the EoS is compatible with the formation of a QGP at the onset of deconfinement. The extracted sound velocities are then used to calculate an excitation function for the mean transverse mass of pions from the hybrid model. We find that, above $\ensuremath \sqrt{s_{NN}} \approx 10$ GeV, even the lowest c _s ² gives a considerably larger $\ensuremath \langle m_T\rangle$ of pions compared to data.     

Electronic structure and properties of high-T c superconducting cuprates in the normal and superconducting phases within the LDA + GTB approach

Theoretical investigations of the properties of high-T _c superconducting cuprates within the LDA + GTB method taking into account the magnetic and phonon pairing mechanisms have been reviewed. These properties are the concentration-dependent electronic structure, quantum phase transitions with a change in the topology of the Fermi surface, and the superconducting phase of the $d_{x^2 - y^2 }$ symmetry.     

NQR study of spin-freezing in superconducting La2−x Sr x CuO4: the example ofx = 0.06

Nuclear quadrupole resonance (NQR)¹³⁹La and⁶³Cu spin-lattice relaxation rateT ₁ ^t-1 measurements in a La_1.94Sr_0.06CuO₄ single crystal are described. Slowing-down of Cu²⁺ spin fluctuations is evidenced through a dramatic increase of¹³⁹ T ₁ ^?1 on cooling. While the onset of diamagnetism occurs atT _c = 8 K,¹³⁹ T ₁ ^?1 has a peak atT _g ? 5 K, when the characteristic frequency of magnetic fluctuations reaches the NQR frequencyv _Q ? 9 MHz. In agreement with a number of previous studies, these results show that the so-called “cluster spin-glass” phase persists in the superconducting regime. Issues concerning the coexistence of the two phases are discussed.     

Pulsed ESR on the organic ion radical salt: 3,3′-diethyl-4,4′-dimethyl-2,2′-thiazolocyanine-[TCNQ]2

We present firstT _1e ^?1 andT _2e ^?1 measurements on the organic ion radical salt 3,3′-diethyl-4,4′-dimethyl-2,2′-thiazolocyanine-(TCNQ)₂ as function of temperature and of orientation. The electronic spin diffusion constant could be determined directly by the electron spin echo field gradient technique:D (300 K)=0.03±0.02 cm²/sec. Pulsed ESR experiments have — in comparison to conventional cw-ESR — the advantage to monitor viaT _1e ^?1 andT _2e ^?1 the spectral density of dynamical processes at different frequencies. This is shown in a general manner on 3,3′-diethyl-4,4′-dimethyl-2,2′-thiazolocyanine-(TCNQ)₂. Between 300 and 60 K,T _1e ^?1 andT _2e ^?1 are close in amplitude and have a similar temperature dependence. At 60 K their degeneracy is lifted, yielding a quantitative value for the effective spin exchange between localized spinsτ _ex ^?1 sec^?1 and via the absolute value of the relaxation an average distance of the localized centers of about 12 Å. The dynamical data as evaluated above cannot be correlated with the conductivity, clearly indicating that the conduction electrons are a minority, not being monitored by the ESR-experiments.     

Dynamics of a dissipative two level system. II

The problem of quantum coherence in a symmetric double well potential with a dimensionless damping coefficient α for classical motion is studied within a spin 1/2-boson model. The experimentally measured probabilityp(t) of refinding a definite initial state after timet is approximately expressed by the transverse spin relaxation function ?(t), which is determined from a three-pole approximation, that incorporates both the correct long and short time behaviour. For a bare tunnelsplitting δ small compared to the heat bath cutoffω _c we find, that the oscillating component of ?(t) is negligible compared to the relaxational one unless α is of orderΔ/ω _c . Thusp(t)?(1+exp(?νt))/2 with a mean tunneling rateν proportional to \(\tilde \Delta = \Delta (\Delta /\omega _c )^{\frac{\alpha }{{2 - \alpha }}} \) for α < 2 andT ? \(\tilde \Delta \) and proportional toΔ ²/ω _c ·(T/ω _c ) ^α?1 otherwise. The results apply directly to recent measurements of the dynamics of flux states in a SQUID.     

Giant thermal hysteresis of sound velocity and internal friction in a La0.8Sr0.2MnO3 single crystal

Temperature dependences of the velocity of longitudinal sound V ₁ and the internal friction Q ^?1 are studied for a La_0.8Sr_0.2MnO₃ single crystal in the temperature range 5–350 K. The latter includes the temperature of the structural phase transition T _s ≈95 K (from the Pnma orthorhombic low-temperature phase to the $R\bar 3c$ rhombohedral high-temperature one) and the Curie point T _c =308 K. Near the temperatures T _s and T _c , the curves V ₁(T) and Q ^?1(T) exhibit pronounced singularities. Outside the vicinities of T _s and T _c , the velocity of sound monotonically decreases with increasing temperature. A thermal hysteresis of giant width is observed in the aforementioned dependences. The hysteresis is attributed to the following mechanism: when the crystal under study is heated starting at temperatures T<T _s , some regions occupied by the Pnma low-temperature phase are retained in the $R\bar 3c$ matrix up to the temperature T=350 K.     

Comments on |V ub /V cb | and |V ub | from non-leptonic B decays within the perturbative QCD approach

The Color String Percolation Model (CSPM) is used to determine the equation of state (EOS) of the Quark–Gluon Plasma (QGP) produced in central Au–Au collisions at $\sqrt{s_{\mathit{NN}}} = 200$  A GeV using STAR data at RHIC. When the initial density of interacting colored strings exceeds the 2D percolation threshold a cluster is formed, which defines the onset of color deconfinement. These interactions also produce fluctuations in the string tension which transforms the Schwinger particle (gluon) production mechanism into a maximum entropy thermal distribution analogous to QCD Hawking–Unruh radiation. The single string tension is determined by identifying the known value of the universal hadron limiting temperature T _c =167.7±2.6 MeV with the CSPM temperature at the critical percolation threshold parameter ξ _c =1.2. At midrapidity the initial Bjorken energy density and the initial temperature determine the number of degrees of freedom consistent with the formation of a ～2+1 flavor QGP. An analytic expression for the equation of state, the sound velocity $C_{s}^{2}(\xi)$ is obtained in CSPM. The CSPM $C_{s}^{2}(\xi)$ and the bulk thermodynamic values energy density ε/T ⁴ and entropy density s/T ³ are in excellent agreement in the phase transition region with recent lattice QCD simulations (LQCD) by the HotQCD Collaboration.     

Multiple quantum coherences: New NMR tools to study materials and living systems

Intermolecular multiple-quantum coherences have been proven in recent years to provide a novel contrast mechanism to study heterogeneity in liquid systems. This subject represents a source of remarkable interest in the fields of physics of matter and biomedicine. Recent results achieved on intermolecular double-quantum signal transverse relaxation decay in confined liquid systems (such as in vivo bone marrow in trabecular bone, and doped water in glass capillary pipes) are reported and discussed in this paper. Correlated two-dimensional spectroscopy revamped by asymmetricz-gradient echo detection-like sequences were implemented in order to perform intermolecular doublequantum transverse relaxationT _2DQ andT _2DQ ^* measurements. Our experimental results indicated that the relationshipT _2,n ^* =T ₂ ^* /n betweenn-quantum transverse relaxation time and the conventional singlequantumT ₂ ^* only applies for homogeneous systems and fails in the case of highly heterogeneous systems like porous systems.     

New spectral representation and evaluation of f π and the quark condensate \left\langle {\bar qq} \right\rangle in the terms of string tension

New spectral representations for f _π and chiral condensate are derived in QCD and used for calculations in the large-N _c limit. Both quantities are expressed in this limit through string tension σ and gluon correlation length T _g without fitting parameters. As a result, one obtains $\left\langle {\bar qq} \right\rangle = - N_c \sigma ^2 T_g a_1 $ , $f_\pi = \sqrt {N_c } \sigma T_g a_2 $ , with a ₁=0.0823, a ₂=0.30. Taking σ=0.18 GeV² and T _g=1 GeV^?1, as known from analytic and lattice calculations, this yields $\left\langle {\bar qq} \right\rangle $ (μ=2 GeV)=?(0.225 GeV)³, f _π=0.094 GeV, which is close to the standard values.     

Z c (4025) as the hadronic molecule with hidden charm

We have studied the loosely bound $D^{*}\bar{D}^{*}$ system. Our results indicate that the recently observed charged charmonium-like structure Z _c (4025) can be an ideal $D^{*}\bar{D}^{*}$ molecular state. We have also investigated its pionic, dipionic, and radiative decays. We stress that both the scalar isovector molecular partner Z _c0 and three isoscalar partners ${\tilde{Z}}_{c0,c1,c2}$ should also exist if Z _c (4025) is a $D^{*}\bar{D}^{*}$ molecular state in the framework of the one-pion-exchange model. Z _c0 can be searched for in the channel e ⁺ e ^?→Y→Z _c0(4025)(ππ)_P-wave where Y can be Y(4260) or any other excited 1^?? charmonium or charmonium-like states such as Y(4360), Y(4660), etc. The isoscalar $D^{*}\bar{D}^{*}$ molecular states ${\tilde{Z}}_{c0,c2}$ with 0⁺(0⁺⁺) and 0⁺(2⁺⁺) can be searched for in the three pion decay channel $e^{+}e^{-}\to Y \to {\tilde{Z}}_{c0,c2} (3\pi)^{I=0}_{\text{P-wave}}$ . The isoscalar molecular state ${\tilde{Z}}_{c1}$ with 0^?(1^+?) can be searched for in the channel ${\tilde{Z}}_{c1}\eta$ . Experimental discovery of these partner states will firmly establish the molecular picture.     

On the free energy of the hopfield model

The general theory of inhomogeneous mean-field systems of Raggio and Werner provides a variational expression for the (almost sure) limiting free energy density of the Hopfield model $$H_{N,p}^{\{ \xi \} } (S) = - \frac{1}{{2N}}\sum\limits_{i,j = 1}^N {\sum\limits_{\mu = 1}^N {\xi _i^\mu \xi _j^\mu S_i S_j } } $$ for Ising spinsS _i andp random patterns ξ^μ=(ξ ₁ ^μ ,ξ ₂ ^μ ,...,ξ _N ^μ ) under the assumption that $$\mathop {\lim }\limits_{N \to \gamma } N^{ - 1} \sum\limits_{i = 1}^N {\delta _{\xi _i } = \lambda ,} \xi _i = (\xi _i^1 ,\xi _i^2 ,...,\xi _i^p )$$ exists (almost surely) in the space of probability measures overp copies of {?1, 1}. Including an “external field” term ?ξ _μ ^p h^μμξ _i=1 ^N ξ _i ^μ S_i, we give a number of general properties of the free-energy density and compute it for (a)p=2 in general and (b)p arbitrary when λ is uniform and at most the two componentsh ^μ1 andh ^μ2 are nonzero, obtaining the (almost sure) formula $$f(\beta ,h) = \tfrac{1}{2}f^{ew} (\beta ,h^{\mu _1 } + h^{\mu _2 } ) + \tfrac{1}{2}f^{ew} (\beta ,h^{\mu _1 } - h^{\mu _2 } )$$ for the free energy, wheref ^cw denotes the limiting free energy density of the Curie-Weiss model with unit interaction constant. In both cases, we obtain explicit formulas for the limiting (almost sure) values of the so-called overlap parameters $$m_N^\mu (\beta ,h) = N^{ - 1} \sum\limits_{i = 1}^N {\xi _i^\mu \left\langle {S_i } \right\rangle } $$ in terms of the Curie-Weiss magnetizations. For the general i.i.d. case with Prob {ξ _i ^μ =±1}=(1/2)±?, we obtain the lower bound 1+4?²(p?1) for the temperatureT _c separating the trivial free regime where the overlap vector is zero from the nontrivial regime where it is nonzero. This lower bound is exact forp=2, or ε=0, or ε=±1/2. Forp=2 we identify an intermediate temperature region between T_*=1?4?² and T_c=1+4?² where the overlap vector is homogeneous (i.e., all its components are equal) and nonzero.T _* marks the transition to the nonhomogeneous regime where the components of the overlap vector are distinct. We conjecture that the homogeneous nonzero regime exists forp≥3 and that T_*=max{1?4?²(p?1),0}.     

First search for double- \beta decay of platinum by ultra-low background HP Ge \gamma spectrometry

A search for double- $ \beta$ processes in ¹⁹⁰Pt and ¹⁹⁸Pt was realized with the help of ultra-low background HP Ge 468cm^3 $ \gamma$ spectrometer in the underground Gran Sasso National Laboratories of the INFN (Italy). After 1815 h of data taking with 42.5g platinum sample, T _1/2 limits on 2 $ \beta$ processes in ¹⁹⁰Pt ( $ \varepsilon$ $ \beta^{+}_{}$ and 2 $ \varepsilon$ have been established on the level of 10¹⁴-10¹⁶y, 3 to 4 orders of magnitude higher than those known previously. In particular, a possible resonant double-electron capture in ¹⁹⁰Pt was restricted on the level of 2.9×10¹⁶ y at 90% C.L. In addition, T _1/2 limit on 2 $ \beta^{-}_{}$ decay of ¹⁹⁸Pt (2 $ \nu$ +0 $ \nu$ ) to the 2⁺ ₁ excited level of ¹⁹⁸Hg has been set at the first time: T _1/2 > 3.5×10¹⁸ y. The radiopurity level of the used platinum sample is reported.     

K S 0 , Λ and ≡ production at intermediate to high pT from Au+Au collisions at \sqrt {s_{NN} } = 39, 11.5 and 7.7 GeV

We report on the p _T dependence of nuclear modification factors (R _CP) for K _S ⁰ , ??, ?? and the $\bar NK_S^0 $ ratios at mid-rapidity from Au+Au collisions at $\sqrt {s_{NN} } $ = 39, 11.5 and 7.7 GeV. At $\sqrt {s_{NN} } $ = 39 GeV, the R _CP data show a baryon/meson separation at intermediate p _T and a suppression for K _S ⁰ for p _T up to 4.5 GeV/c; the $\bar \Lambda K_S^0 $ shows baryon enhancement in the most central collisions. However, at $\sqrt {s_{NN} } $ = 11.5 and 7.7 GeV, R _CP shows less baryon/meson separation and $\bar NK_S^0 $ shows almost no baryon enhancement. These observations indicate that the matter created in Au+Au collisions at $\sqrt {s_{NN} } $ = 11.5 or 7.7 GeV might be distinct from that created at $\sqrt {s_{NN} } $ = 39 GeV.     

Peculiarities of performance of the spin valve for the superconducting current

The spin valve effect for the superconducting current based on the superconductor/ferromagnet proximity effect has been studied for a CoO _x /Fe1/Cu/Fe2/Cu/Pb multilayer. The magnitude of the effect ΔT _c = T _c ^AP ? T _c ^P , where T _c ^P and T _c ^AP are the superconducting transition temperatures for the parallel (P) and antiparallel (AP) orientation of magnetizations, respectively, has been measured for different thicknesses of the Fe1 layer d _Fe1. The obtained dependence of the effect on d _Fe1 reveals that ΔT _c can be increased in comparison with the case of a half-infinite Fe1 layer considered by the previous theory. A maximum of the spin valve effect occurs at d _Fe1 ～ d _Fe2. At the optimal value of d _Fe1 almost full switching from the normal to the superconducting state when changing the mutual orientation of magnetizations of the iron layers Fe1 and Fe2 from P to AP is demonstrated.     

Propagation of sound and spectrally resolved rayleigh scattering in weakly ionized plasmas

The scattering mechanisms possible in weakly ionized plasmas are reviewed. The different cases can be discerned by means of the magnitude of three characteristic parameters: 2π/ωτ _c being the ratio of scattering time and mean free collision time, y=1/kλ _c being the scattering parameter defined as the ratio of scattering length and mean free collision path, and χω/c _{s, T} ² being the ratio between the product of thermometric conductivity and scattering frequency to the square of the adiabatic or isothermal sound velocity. For \({{2\pi } \mathord{\left/ {\vphantom {{2\pi } {\omega \tau _c<< 1}}} \right. \kern-0em} {\omega \tau _c<< 1}}\) quantum mechanical formulae have to be used, whereas in the opposite case classical treatments are applicable. The classical methods are Boltzmann equation formalisms ify?1, and fluid dynamics ify?1. In the fluid dynamical case there appear two waves for low frequencies, \({{\chi \omega } \mathord{\left/ {\vphantom {{\chi \omega } {c_{s, T}^2 }}} \right. \kern-0em} {c_{s, T}^2 }}<< 1\) , an adiabatic one which can propagate with weak damping and an isobaric one which cannot propagate, both wave types yielding together three scattered lines. In the opposite case of high frequencies, \({{\chi \omega } \mathord{\left/ {\vphantom {{\chi \omega } {c_{s, T}^2 }}} \right. \kern-0em} {c_{s, T}^2 }} > > 1\) , the scattering behavior is different from ordinary hydrodynamics. Here also do exist two types of waves, isochoric and isothermal, but none of them can propagate. Since the intensity of the scattered isochoric wave can be neglected, there is only one scattered line. Local temperatures and particle densities can be determined from the scattered spectrum. On the other hand, transport coefficients like shear and bulk viscosity as well as thermometric conductivity can be derived from sound absorption or Rayleigh scattering experiments if an independent temperature measurement is performed at the same time. The general formalism is applied to a weakly ionized hydrogen arc plasma.     

Nuclear spin relaxation of Xe in liquid Te

By the method of time differential perturbed angular distribution following a nuclear reaction, the relaxation rateT _r ^?1 of the 8 msI ^π=10⁺ isomer of¹³²Xe has been measured in liquid Te. Between 670 °K (supercooled liquid) and 1,000 °K the rate decreases from about 720/s by about a factor of two. From existing experimental material it is concluded thatT _r ^?1 is mainly due to quadrupolar interaction (T _r ^?1 ≈T _Q ^?1 ). Its magnitude is discussed considering the metallic and the noble gas limit as models for the Xe-Te-interactions. The temperature dependenceT _Q(T) apparently does not correlate with the diffusion constant of Te in contrast to a simplified theoretical treatment. — The nuclearg value of the isomer has been determined to be g=(?)0.195(5) thus confirming the configuration (vh_11/2)².     

Das kritische Magnetfeld Hc∥ von dünnen supraleitenden Filmen

Thin superconducting films in a surface parallel magnetic field are considered, assuming that the order parameter is constant in space. Without any further restrictions on the film thickness,a, an equation for the critical field is derived. In the clean limit, this equation is valid only in the vicinity of T_c, but in the dirty limit it is valid for all temperatures. Our results, for specular reflection, are identical with those obtained byThompson andBaratoff. But for not too thin films we find essential differences between the results for specular and for diffus reflection. For very thin films (a?v/2πT _c), considered in detail byde Gennes andTinkham and byShapoval, our results are in agreement with those obtained byShapoval. In the opposit limit (a?v/2π T _c), the most essential corrections to the Ginzburg-Landau result obtained byLüders are rederived.     

Anisotropy of microwave conductivity in the superconducting and normal states of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript>−<Emphasis Type="Italic">x</Emphasis>: 3D-2D crossover

The imaginary parts of microwave conductivity σ″(T<T_c) and resistivity ρ (_T)=1/σ(T>T_c) along (σ _ab ^″ and ρ_ab) and across and (σ _c ^″ and ρ_c the cuprate ab planes of a YBa₂Cu₃O_7?x crystal with the oxygen doping level x varying from 0.07 to 0.47 were measured in the temperature range 5≤ T≤200 K. In the superconducting state, the σ _ab ^″ (T)/σ _ab ^″ (0) and σ _c ^″ (T/σ _c ^″ (0) curves coincide for an optimally doped (x=0.07) crystal, but, with an increase in x, the slopes of the σ _c ^″ (T)/σ _c ^″ (0) curves decrease noticeably at T<T_c/3, on the background of small changes happening to the σ _ab ^″ (T/σ _ab ^″ (0) curves. The two-dimensional (2D) transport along the ab planes in the normal state of YBa₂Cu₃O_7?x is always metallic, but there is a crossover (at x=0.07) from the Drude to hopping (at x>0.07) conductivity along the c axis. This is confirmed both by the estimates of the lowest metallic and the highest tunneling conductivities along the c axis and by quantitative comparison of the measured ρ_c(T) curves with the curves calculated in the polaron model of quasiparticle transport along the c axis.     

Decay studies of K isomers in 254No

A detailed $ \gamma$ spectroscopic decay study of two K isomers in ²⁵⁴No was performed. In addition to the previously reported $ \gamma$ lines two new transitions of E = 778 , 856keV could be attributed to the decay pattern of ^254m1No ( T _1/2 = 275±7 ms). The population of an excited band built up on this isomer ( $\ensuremath K^{\pi} =8^{-}$ by the decay of ^254m2No ( T _1/2 = 198±13 μs) could be proven by measuring delayed $ \gamma$ - $ \gamma$ coincidences between transitions stemming from the decay of both isomeric states. The energies of the band members could be established up to $\ensuremath I^{\pi} = 15^{-}$ . A spontaneous fission branch of (2.0±1.2)×10^-4 was measured for ^254m1No , an upper limit of $ \le$ 1.2×10^-4 was estimated for ^254m2No . These values demonstrate the high stability of multi-quasiparticle configurations against spontaneous fission. Evidence for an $ \alpha$ decay branch of ^254m1No in the order of 1×10^-4 was found.