Magnetism of gadolinium nanoparticles near <Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript>

Influence of temperature and magnetic field H on magnetism of spherical Gd nanoparticles of different sizes (89, 63, 47, 28, and 18 nm) was studied in the temperature range 250 K < T < 325 K. The particles were obtained by metal vapor condensation in the flow of helium. The particles with d = 18 nm did not show a magnetic transition; their structure is a combination of two cubic phases (FCC1 and FCC2). Large particles remained in the HCP phase and had an admixture of the FCC1 phase, the amount of which decreased as the particle sizes increased; magnetic transition took place at T _c = 293 K. The admixture of O₂ did not alter the structure but decreased the magnetization σ and magnetic permeability μ. An orientation transition in polycrystalline gadolinium initiated by the magnetic field H was proved in an experiment. The orientation transition in Gd particles smaller than 63 nm, the magnetic structure of which is close to the single-domain structure, occurred near T _c without the influence of H.     

Anion height dependence of <Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> and the density of states in iron-based superconductors

Systematic ab initio LDA calculations were performed for all the typical representatives of recently discovered class of iron-based high-temperature superconductors: REOFe(As,P) (RE = La, Ce, Nd, Sm, Tb), Ba₂Fe₂As, (Sr,Ca)FFeAs, Sr₄Sc₂O₆Fe₂P₂, LiFeAs and Fe(Se,Te). Non-monotonic behavior of total density of states at the Fermi level is observed as a function of anion height relative to Fe layer with maximum at about Δz _a ～ 1.37 Å, attributed to changing Fe-As (P, Se, Te) hybridization. This leads to a similar dependence of superconducting transition temperature T _c as observed in the experiments. The fit of this dependence to elementary BCS theory produces semiquantitative agreement with experimental data for T _c for the whole class of iron-based superconductors. The similar fit to Allen-Dynes formula underestimates T _c in the vicinity of the maximum, signifying the possible importance of non-phonon pairing in this region. These results unambiguously demonstrate that the main effect of T _c variation between different types of iron-based superconductors is due to the corresponding variation of the density of states at the Fermi level.     

Investigations of the interlayer coupling in high-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> cuprates

Low-field magnetizationM(H) measurements can be used to probe the nature of the screening currents and the interlayer coupling in high-T _c cuprates. Here we compare theM(H) behaviour of single crystals of Bi₂Sr₂CaCu₂O₈ and fully oxygenated and oxygen reduced YBa₂Cu₃O_7??. In YBa₂Cu₃O₇, theM(H) behaviour is consistent with anisotropic 3D superconductivity whilst in Bi₂Sr₂CaCu₂O₈, the surface screening currents are strongly affected by the presence of vortices, implying that the CuO₂ planes are coupled via a weak Josephson interaction. In oxygen-deficient YBa₂Cu₃O_6.7 (T _c =63K), theM(H) behaviour at low temperatures is similar to that found for Bi₂Sr₂CaCu₂O₈, implying that the removal of oxygen from the chains has resulted in a dimensional crossover of the superconducting state in YBa₂Cu₃O_7??. As the temperature approachesT _c , the 3D behaviour is eventually restored as thec-axis coherence length ξ _c becomes comparable with the interlayer spacingd.     

Summary on high <Emphasis Type="Italic">p</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript> probes

Results on high-p _T probes shown at the Hard Probes 2008 Conference are summarized, with an appreciation of the improvements in precision of the measurements and experimental techniques since the beginning of RHIC operation. Particular attention is given to the latest measurements of the nuclear modification factor of identified particles, photon-hadron correlation measurements, and full jet reconstruction.     

Pseudogap behavior of nuclear spin relaxation in high-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> superconductors in terms of phase separation

We analyze anew experiments on the NMR in cuprates and find an important information on their phase separation and its strip character hidden in the dependence of 1/⁶³T₁ on the degree of doping. In a broad class of materials, 1/⁶³T₁ is the sum of two terms: the temperature-independent one attributed to “ incommensurate” strips that occur at external doping and a “universal” temperature-dependent term ascribed to moving metallic and antiferromagnetic subphases. We argue that the frustrated first-order phase transition in a broad temperature interval bears a dynamical character.     

Possible universal cause of high-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> superconductivity in different metals

Using the theory of high-temperature superconductivity based on the idea of the fermion-condensation quantum phase transition (FCQPT), we show that neither the d-wave pairing symmetry, the pseudogap phenomenon, nor the presence of the Cu-O₂ planes is of decisive importance for the existence of high-T _c superconductivity. We analyze recent experimental data on this type of superconductivity in different materials and show that these facts can be understood within the theory of superconductivity based on the FCQPT. The latter can be considered as a universal cause of high-T _c superconductivity. The main features of a room-temperature superconductor are discussed.     

Irradiation-induced suppression of the critical temperature in high-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> superconductors: Pair breaking versus phase fluctuations

Experiments on the irradiation-induced suppression of the critical temperature in high-T _c superconductors are analyzed within the mean-field Abrikosov-Gor’kov-like approach. It is shown that the experimental data for YBa₂Cu₃O_7-δ single crystals can be quantitatively explained by the pair-breaking effects under the assumption of the combined effect of potential and spin-flip scattering on the critical temperature and with an accounting for a nonpure d-wave superconducting order parameter.     

Magnetic and superconducting properties of FeAs-based high-<Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> superconductors with Gd

We report on successful synthesis under high pressure of a series of polycrystalline GdFeAsO_{1 − x} F _x high-T _c superconductors with different oxygen deficiency x = 0.12−0.16 and also with no fluorine. We have found that the high-pressure synthesis technique is crucial for obtaining the single-phase superconducting materials: by sythesizing the same compounds with no pressure in ampoules, we obtained non-superconducting materials with an admixture of incidental phases. Critical temperature for all the materials was in the range 40 to 53 K. The temperature derivative of the critical field dH _c2/dT is remarkably high, indicating potentially high value of the second critical field H _c2 ∼ 130 T.     

Recent high-<Emphasis Type="Italic">p</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript> results from STAR

We present selected recent results of multi-hadron correlation measurements in azimuth and pseudorapidity at intermediate and high p _T in Au+Au collisions at , from the STAR experiment at RHIC. At intermediate p _T , measurements are presented that attempt to determine the origin of the associated near-side (small Δφ) yield at large pseudo-rapidity difference Δη that is found to be present in heavy ion collisions. In addition, results are reported on new multi-hadron correlation measures at high-p _T that use di-hadron triggers and multi-hadron cluster triggers with the goal to constrain the underlying jet kinematics better than in the existing measurements of inclusive spectra and di-hadron correlations.     

1/<Emphasis Type="Italic">N</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> countings in baryons

The 1/N _c -power countings for baryon decays and configuration mixings are determined by means of a nonrelativistic quark picture. Such countings are expected to be robust under changes in the quark masses and, therefore, valid as these become light. It is shown that excited baryons have natural widths of \(\mathcal{O}(N_c^0 )\). These dominant widths are due to the decays that proceed directly to the ground-state baryons, with cascade decays being suppressed to \(\mathcal{O}(1/N_c )\). Configuration mixings, defined as mixings between states belonging to different O(3) × SU(2N _f ) multiplets, are shown to be subleading in an expansion in \(1/\sqrt {N_c }\) when they involve the ground-state baryons, while the mixings between excited states can be \(\mathcal{O}(N_c^0 )\).     

<Emphasis Type="Italic">z</Emphasis>-Scaling and high-<Emphasis Type="Italic">p</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript> particle production in hadron-hadron and hadron-nucleus collisions at high energies

The general features of particle production in hadron-hadron and hadron-nucleus collisions at high energy and transverse momentum using the concept of z-scaling are reviewed. z-Presentation of experimental data on the inclusive cross sections obtained at ISR, SPS, and Tevatron is presented and its properties are discussed. It is argued that the properties reflect the fundamental symmetries such as self-similarity, locality, and fractality. z-Scaling is used to predict particle yields in hadron-hadron and hadron-nucleus collisions at RHIC and LHC energies. The violation of z-scaling is considered as a signature of new physics phenomena.     

Topological electronic transition in cuprate high-<Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> superconductors occurring before the superconducting transition

It is shown for the first time that the superconducting transition in optimally doped Y- and Bi-based high-T _c superconductors is preceded by the Lifshitz topological transition in their electron systems. A intense hole-electron conversion occurring in the system of charge carriers at T = T _c + (~10 K) is a clear cut signature of such transition.     

Decay Behaviors of the <Emphasis Type="Italic">P</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Hadronic Molecules

In this proceeding, we present our recent work on decay behaviors of the P_c hadronic molecules, which can help to disentangle the nature of the two P_c pentaquark-like structures. The results turn out that the relative ratio of the decays of P _c ⁺ (4380) to \({\bar D *}{\Lambda _c}\) and J/ψp is very different for P_c being a \({\bar D *}{\Sigma _c}\) or \(\bar D\Sigma _c *\) bound state with \({J^P} = \frac{{{3 - }}}{2}\) And from the total decay width, we find that P_c(4380) being a \(\bar D\Sigma _c *\) molecule state with \({J^P} = \frac{{{3 - }}}{2}\) and P_c(4450) being a \({\bar D *}{\Sigma _c}\) molecule state with \({J^P} = \frac{{{5 + }}}{2}\) is more favorable to the experimental data.     

Entropy for <Emphasis Type="Italic">SU</Emphasis>(3)<Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> quark states

We discuss the quantum state structure using the standard model for three colored quarks in the fundamental representations of SU(3)_c making up the singlet ground state of the hadrons. This allows us to calculate a finite von Neumann entropy from the quantum reduced density matrix, which we explicitly evaluate for the quarks in a model for the meson and baryon states.Received: 9 December 2003, Revised: 23 January 2004, Published online: 8 April 2004D.E. Miller: om0@psu.eduPermanent address: Department of Physics, Pennsylvania State University, Hazleton Campus, Hazleton, Pennsylvania, 18201 USA     

Top-quark <Emphasis Type="Italic">p</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript>-spectra at CMS and flavor independence of <Emphasis Type="Italic">z</Emphasis>-scaling

We present new results of analysis of top-quark differential cross sections obtained by the CMS Collaboration in pp collisions in the framework of the z-scaling approach. The spectra are measured over a wide range of collision energy \(\sqrt s = 7,8,13TeV\) and transverse momentum p _T = 30?500 GeV/c of top-quark using leptonic and jet decay modes. Flavor independence of the scaling function ψ(z) is verified in the new kinematic range. The results of analysis of the top-quark spectra obtained at the LHC are compared with similar spectra measured in \(\overline p p\) collisions at the Tevatron energy \(\sqrt s = 1.96TeV\). A tendency to saturation of ψ(z) for the process at low z and a power-law behavior of ψ(z) at high z is observed. The measurements of high-p _T is observed. The measurements of highspectra of the top-quark production at highest LHC energy is of interest for verification of self-similarity of particle production, understanding flavor origin and search for new physics symmetries with top-quark probe.     

Quasiparticles in the superconducting state of high-<Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> metals

We consider the behavior of quasiparticles in the superconducting state of high-T_c metals within the framework of the theory of the superconducting state based on the fermion condensation quantum phase transition. We show that the behavior coincides with the behavior of Bogoliubov quasiparticles, whereas the maximum value of the superconducting gap and other exotic properties are determined by the presence of the fermion condensate. If at low temperatures the normal state is recovered by the application of a magnetic field suppressing the superconductivity, the induced state can be viewed as a Landau-Fermi liquid. These observations are in good agreement with recent experimental facts.     

Elliptic flow and the high <Emphasis Type="Italic">p</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript> ridge in Au+Au collisions

In this paper we look for correlations between intermediate p _T particle pairs and the v ₂ of the remaining low p _T particles. We find that the shape of the flow vector distribution, which is calculated from all low p _T tracks, depends in a non-trivial way on the angular separation between the high p _T particle pairs in the event. Our analysis is based on 200 GeV Au+Au collisions measured with the STAR detector.     

Hadroproduction of heavy quarkonia at high energies within the <Emphasis Type="Italic">k</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript>-factorization approach

On the basis of the k _T -factorization approach, heavy-quarkonium \((c\bar c,b\bar b)\) hadroproduction at high energies is considered within nonrelativistic QCD in the leading order in α _s and v. The p _T spectra of various S-and P-wave quarkonium states at the Tevatron collider energies (run I and run II) are fitted, and sets of octet nonperturbative matrix elements are obtained for three different versions of the noncollinear gluon distribution in the proton.     

Pomeron loops in the perturbative QCD with large <Emphasis Type="Italic">N</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript>

The lowest order pomeron loop is calculated for the leading conformal weight with full dependence of the triple-pomeron vertex on intermediate conformal weights. The loop is found to be convergent. Its contribution to the pomeron Green function begins to dominate already at rapidities 10–15. The pomeron pole renormalization is found to be quite small due to a rapid fall of the triple-pomeron vertex with rising conformal weights.