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Superconducting properties change in confined geometries. Here we study the effects of strong confinement in nanosized Pb islands on Si(111) 7×7. Small hexagonal islands with diameters less than 50 nm and a uniform height of seven atomic layers are formed by depositing Pb at low temperature and annealing at 300 K. We measure the tunneling spectra of individual Pb nanoislands using a low-temperature scanning tunneling microscope operated at 0.6 K and follow the narrowing of the superconducting gap as a function of magnetic field. We find the critical magnetic field, at which the superconducting gap vanishes, reaches several Tesla, which represents a greater than 50-fold enhancement compared to the bulk value. By independently measuring the size of the superconducting gap, and the critical magnetic field that quenches superconductivity for a range of nanoislands, we can correlate these two fundamental parameters and estimate the maximal achievable critical field for 7 ML Pb nanoislands to be 7 T. [ABSTRACT FROM AUTHOR]

Energy-dependent apparent step heights of two-dimensional ultrathin Pb islands grown on the Si(111)6 × 6-Au surface have been investigated by a combination of scanning tunneling microscopy, first-principles densityfunctional theory, and the particle-in-a-box model calculations. The apparent step height shows the thicknessand energy-dependent oscillatory behaviors, which are directly related to the spilling of electron states into the vacuum exhibiting a quantum size effect. This has been unambiguously proven by extensive first-principles scanning tunneling microscopy and spectroscopy simulations. An electronic contribution to the apparent step height is directly determined. At certain energies it reaches values as high as a half of the atomic contribution. The applicability of the particle-in-a-box model to the spilling of electron states is also discussed. [ABSTRACT FROM AUTHOR]

Using the ultrarelativistic quantum molecular dynamics (UrQMD) model, we investigate azimuthal correlations in p-Pb collisions at √sNN = 5.02 TeV. Comparison with the experimental data shows that UrQMD cannot reproduce the multiplicity dependence of two- and four-particle cumulants, especially the transition from positive to negative values of c2{4} in high-multiplicity events, which has been taken as experimental evidence of collectivity in p-Pb collisions. Meanwhile, UrQMD cannot describe the differential elliptic flow v2(pT) of all charged hadrons at various multiplicity classes. These discrepancies show that the simulated hadronic p-Pb systems cannot generate enough collective flow as observed in experiment, the associated hadron emissions are largely influenced by nonflow effects. However, the characteristic v2(pT) mass ordering of pions, kaons, and protons is observed in UrQMD, which is the consequence of hadronic interactions and not necessarily associated with strong fluid-like expansions. [ABSTRACT FROM AUTHOR]

We supplement the Heavy Ion Jet Interaction Generator (HIJING) code with a collective cascade recipe and updated Martin-Stirling-Thorne-Watt (MSTW2009) parton distribution functions (PDFs) to describe nonsingle diffractive (NSD) p + p and Pb collisions at CERN Large Hadron Collider energies. The collective cascade, developed in the space of an impact parameter, is used to induce nuclear modification of nucleon, that are involved in primary interactions, inside the dense nuclear medium. It is found that the improved HIJING (ImHIJING) code (that with MSTW2009 PDFs) reproduces rather well the pseudorapidity density, the multiplicity, and the transverse momentum distributions of charged particles within the pseudorapidity interval |nc.m.system| < 2.4 in NSD p + p collisions at √sNN = 0.9, 2.36, and 7 TeV. The ImHIJING with collective cascade calculations is also shown to be a good fit to the pseudorapidity density (in the laboratory system) and transverse momentum (pT) dependence of the nuclear modification of charged particles in NSD p + Pb collisions at √sNN = 5.02 TeV. The effects of the collective cascade are clearly seen in the target (3 < n1ab < 4) and central (within |nc.m.system| < 0.3 at 1 < pT < 8 GeV/c) interaction regions when studying the pseudorapidity density and transverse momentum dependence of the nuclear modification factor of the charged particles, respectively. [ABSTRACT FROM AUTHOR]

We report the results of the femtoscopic analysis of pairs of identical pions measured in p-Pb collisions at ↶sNN = 5.02 TeV. Femtoscopic radii are determined as a function of event multiplicity and pair momentum in three spatial dimensions. As in the pp collision system, the analysis is complicated by the presence of sizable background correlation structures in addition to the femtoscopic signal. The radii increase with event multiplicity and decrease with pair transverse momentum. When taken at comparable multiplicity, the radii measured in p-Pb collisions, at high multiplicity and low pair transverse momentum, are 10%-20% higher than those observed in pp collisions but below those observed in A-A collisions. The results are compared to hydrodynamic predictions at large event multiplicity as well as discussed in the context of calculations based on gluon saturation. [ABSTRACT FROM AUTHOR]

For a shape-soft nucleus, the deformation change with increasing angular momentum of rotation can be significant. Total-Routhian-surface (TRS) calculations include the shape changes, but angular momentum is not conserved (neither is it a good quantum number, nor is it kept unchanged in the whole TRS mesh). In the projected shell model (PSM), the angular momentum appears as a good quantum number, but calculations have usually been performed with fixed deformation. In the present work, by performing angular-momentum projection on the mean-field potential-energy surface (PES), we can obtain an angular-momentum-conserved PES which gives deformation for a rotational state at a given spin. In order to investigate the shape-changing effect, we have chosen neutron-deficient Hg and Pb isotopes in which shape coexistence occurs. We interpret the irregular rotational behavior of the oblate bands at low spin as arising from deformation changes which are induced by collective rotation. At higher spin, the oblate rotational spectrum can also be influenced by the crossing between the K = 0 ground-state band and a low-AT two-quasineutron band. Calculated g factors for the states of oblate bands are given for future experimental testing, and the intrinsic structures of high-A" oblate states are investigated. [ABSTRACT FROM AUTHOR]

The article focuses on a research which represents numerical prediction of the neutron density distribution of isotope of (lead 208Pb) using various nonrelativistic and relativistic mean-field models for the nuclear structure. Topics discussed include analysis of charge density distribution of 208 Pb with the Lead Radius Experiment PREX, analysis of parity-violating asymmetry parameter of the lead isotope and implication of neutron skin of 208 Pb in astrophysics.

Nanoclusters containing metallic lead and lead oxide have been produced by self-assembly out of a primary mixture of lead atoms and oxygen in a reactive sputtering-based cluster source. Comparison of the valence and core-level responses in the photoelectron spectra shows that clusters have a core-shell structure with a lead-oxide core coated by an outer shell of metallic lead. This core-shell order is opposite to that typical for most microscopic and macroscopic materials. We explain this by the peculiarities of the cluster production kinetics and by the system's energy minimization striving due to what lead oxide is placed in the core of the mixed cluster. [ABSTRACT FROM AUTHOR]

The controversies about the structure of the true ground state of pseudorhombohedral compositions of Pb(ZrxTi1-x)O3 (PZT) are addressed using a 6% Sr2+ substituted sample with x = 0.550. Sound velocity measurements reveal a phase transition at Tc ~ 279 K. The temperature dependence of full width at half maximum of (hOO)pc peaks and the unit cell volume also show anomalies around 279 K even though there is no indication of any change of space group in the synchrotron x-ray powder diffraction (SXRD) patterns. The neutron powder diffraction patterns reveal appearance of superlattice peaks below Tc ~ 279 K, confirming the existence of an antiferrodistortive phase transition. The Rietveld analysis of the room-temperature and low-temperature SXRD data below Tc shows that the structure corresponds to single monoclinic phase in the Cm space group while the analysis of neutron powder diffraction data reveals that the structure of the ground-state phase below Tc corresponds to the Cc space group. Our analysis shows that the structural models for the ground-state phase based on the R3c space group with or without the coexistence of the room-temperature monoclinic phase in the Cm space group can be rejected. [ABSTRACT FROM AUTHOR]

The ALICE experiment has measured the inclusive J/&psgr; ip production in Pb-Pb collisions at √SNN = 2.76 TeV down to zero transverse momentum in the rapidity range 2.5 < y <4. A suppression of the inclusive J/&psgr; tp yield in Pb-Pb is observed with respect to the one measured in pp collisions scaled by the number of binary nucleon-nucleon collisions. The nuclear modification factor, integrated over the 0%-80% most central collisions, is 0.545 ± 0.032(stat) ± 0.083(syst) and does not exhibit a significant dependence on the collision centrality. These features appear significantly different from measurements at lower collision energies. Models including J/&psgr; ip production from charm quarks in a deconfined partonic phase can describe our data. [ABSTRACT FROM AUTHOR]

The study of thermal operations allows one to investigate the ultimate possibilities of quantum states and of nanoscale thermal machines. Whilst fairly general, these results typically do not apply to continuous variable systems and do not take into account that, in many practically relevant settings, system-environment interactions are effectively bilinear. Here we tackle these issues by focusing on Gaussian quantum states and channels. We provide a complete characterization of the most general Gaussian thermal operation acting on an arbitrary number of bosonic modes, which turn out to be all embeddable in a Markovian dynamics, and derive necessary and sufficient conditions for state transformations under such operations in the single-mode case, encompassing states with nonzero coherence in the energy eigenbasis (i.e., squeezed states). Our analysis leads to a no-go result for the technologically relevant task of algorithmic cooling: We show that it is impossible to reduce the entropy of a system coupled to a Gaussian environment below its own or the environmental temperature, by means of a sequence of Gaussian thermal operations interspersed by arbitrary (even non-Gaussian) unitaries. These findings establish fundamental constraints on the usefulness of Gaussian resources for quantum thermodynamic processes. [ABSTRACT FROM AUTHOR]

When traversing the QCD medium, high-p⊥ partons lose energy, which is typically measured by suppression, and predicted by various energy-loss models. A crucial test of different energy-loss mechanisms is their functional dependence on the length of traversed medium (i.e., path-length dependence). The upcoming experimental measurements will, for the first time, generate data that may allow to clearly assess this dependence, in particular, by comparing results from Pb + Pb collisions with future measurements in smaller systems. However, to perform such a test, it is crucial to choose an optimal observable. To address this, we here use both analytical and numerical analyses to propose a novel--simple, yet accurate and robust--observable for assessing the path-length dependence of the energy loss. Our numerical results show that, by using this observable, different (underlying) energy-loss mechanisms may be directly differentiated from the experimental data, which is, in turn, crucial for understanding the properties of the created QCD medium. [ABSTRACT FROM AUTHOR]

We investigate the emergence of temperature T in the system-plus-reservoir paradigm starting from the fundamental microcanonical scenario at total fixed energy E where, contrary to the canonical approach, T = T (E) is not a control parameter but a derived auxiliary concept. As shown by Schwinger for the regime of weak coupling γ between subsystems, T (E) emerges from the saddle-point analysis leading to the ensemble equivalence up to corrections O (1/√ N) in the number of particles N that defines the thermodynamic limit. By extending these ideas for finite γ, while keeping N → ∞, we provide a consistent generalization of temperature T (E, γ) in strongly coupled systems, and we illustrate its main features for the specific model of quantum Brownian motion where it leads to consistent microcanonical thermodynamics. Interestingly, while this T (E, γ) is a monotonically increasing function of the total energy E, its dependence with γ is a purely quantum effect notably visible near the ground-state energy and for large energies differs for Markovian and non-Markovian regimes. [ABSTRACT FROM AUTHOR]