Physical Review Letters

Appelquist, Thomas ; Dobrescu, Bogdan A; Pontón, Eduardo A; Yee, Ho-Ung A

doi: 10.1103/PhysRevLett.87.181802pmid: N/A

We show that Lorentz and gauge invariance explain the long proton lifetime within the standard model in six dimensions. The baryon-number violating operators have mass dimension 15 or higher. Upon TeV-scale compactification of the two universal extra dimensions on a square T 2 / Z 2 orbifold, a discrete subgroup of the six-dimensional Lorentz group continues to forbid dangerous operators.

Wang, Y; Wells, J; Georgiev, D. G; Boolchand, P. G

doi: 10.1103/PhysRevLett.87.185503pmid: N/A

The count of Lagrangian bonding constraints n c ( y ) in ternary Ge 25 S 7 5 - y I y glasses ( 0 < y < 0.30 ) is established from the molecular structure using Raman scattering and first-principles cluster calculations. The results show that n c ( y ) decreases to 3 as y increases close to y c = 0.162 ( 3 ) , where a sharply defined global minimum in the nonreversing heat flow, Δ H nr ( y ) near T g , is observed in scanning calorimetry. Here we have a rigidity transition induced by I dangling ends, with its sharpness resulting from the absence of self-organization in the random network.

Kawamura, Hikaru ; Li, Mai Suan

doi: 10.1103/PhysRevLett.87.187204pmid: N/A

Spin and chirality orderings of a three-dimensional XY spin glass are studied by extensive Monte Carlo simulations. By calculating an appropriately defined spin-overlap distribution function, we show that the finite-temperature chiral-glass transition does not accompany the standard spin-glass order, giving support to the spin-chirality decoupling picture. Critical behavior of the chiral-glass transition turns out to be different from that of the Ising spin glass. The chiral-glass ordered state exhibits a one-step-like peculiar replica-symmetry breaking.

Dho, Joonghoe ; Kim, W. S; Hur, N. H

doi: 10.1103/PhysRevLett.87.187201pmid: N/A

We have investigated thermal hysteresis of magnetization and resistivity in La 1 - x Sr x MnO 3 ( 0.5 ≤ x ≤ 0.6 ) with an A -type antiferromagnetic structure. For 0.52 ≤ x ≤ 0.56 , the magnetization curve exhibits a counterclockwise (CCW) thermal hysteresis about T N , while the resistivity curve shows a clockwise (CW) thermal hysteresis. On the other hand, samples with 0.58 ≤ x ≤ 0.6 exhibit CCW thermal hystereses in both magnetization and resistivity curves. Remarkably, for x = 0.58 the rotational direction of thermal hysteresis of resistivity changes from CCW to CW by the magnetic field. This anomalous hysteretic behavior is explained by the competing interaction between the three-dimensional (3D) metallic ferromagnetic and two-dimensional (2D) metallic A -type antiferromagnetic phases.

Kotliar, Gabriel ; Savrasov, Sergej Y; Pálsson, Gunnar Y; Biroli, Giulio Y

doi: 10.1103/PhysRevLett.87.186401pmid: N/A

We propose a cellular version of dynamical mean field theory which gives a natural generalization of its original single-site construction and is formulated in different sets of variables. We incorporate a possible nonorthogonality of the tight-binding basis set and prove that the resulting equations lead to manifestly causal self-energies.

Baran, V; Brink, D. M; Colonna, M. M; Di Toro, M. M

doi: 10.1103/PhysRevLett.87.182501pmid: N/A

We estimate the dipole radiation emitted in fusion processes. We show that a classical bremsstrahlung approach can account for both the preequilibrium and the thermal photon emission. We give an absolute evaluation of the preequilibrium component due to the charge asymmetry in the entrance channel, and we study the energy and mass dependence in order to optimize the observation. This dynamical dipole radiation could be a relevant cooling mechanism in the fusion path. We stress the interest in experiments with the new available radioactive beams.

Chen, You-Yu ; Ye, Zhen

doi: 10.1103/PhysRevLett.87.184301pmid: N/A

In this Letter, we present a theoretical analysis of the acoustic transmission through two-dimensional arrays of straight rigid cylinders placed parallel in the air. Both periodic and completely random arrangements of the cylinders are considered. The results for the sound attenuation through the periodic arrays are shown to be in remarkable agreement with the reported experimental data. As the arrangement of the cylinders is randomized, the transmission is significantly reduced for a wider range of frequencies. For the periodic arrays, the acoustic band structures are computed by the plane-wave expansion method and are also shown to agree with previous results.

Wang, Xiao-Gang ; Smith, John R

doi: 10.1103/PhysRevLett.87.186103pmid: N/A

The clean Cu/diamond(111) work of separation is found to be 1.30 J / m 2 . Copper d and diamond p states play a significant role in forming relatively strong Cu/diamond interfacial bonds, while reconstruction of the free diamond(111) surface lowers the work of separation. The single dangling bond diamond termination is the stable interfacial configuration. Hydrogen termination of the diamond lowers the work of separation to 0.21 J / m 2 , consistent with experimental measurements of hydrogen effects on Cu/diamond adhesive strengths. Hydrogen is stable in the Cu/diamond interface.

Ingólfsson, Oddur ; Wodtke, Alec M

doi: 10.1103/PhysRevLett.87.183401pmid: 11690347

We report electron attachment time-of-flight mass spectra of SF 6 clusters over a wide range of cluster sizes, revealing a simple pattern of geometrical shell closings which persists from large clusters ( n ≈ 500 ) to as small as perhaps n = 14 . Quantitative structural properties of these nanocrystallites are derived. These observations, made possible by an extraordinarily gentle ionization method and mass spectral analysis, suggest that bulk crystalline packing may be important for much smaller molecular clusters than previously observed, confirming theoretical predictions.

Lanzani, G; Cerullo, G; Zavelani-Rossi, M; De Silvestri, S

doi: 10.1103/PhysRevLett.87.187402pmid: N/A

The time scale of covalent state relaxation and singlet fission into triplet pairs is determined in a solution of isolated polydiacetylene chains showing a remarkably sharp excitonic transition by applying the transient transmission difference spectroscopy technique with sub-10 fs optical pulses. Photoexcitation into the band of ionic states is followed by a branching within the first 100 fs which populates the band of covalent states. The latter start to dissociate into triplet excitations, completing the process in about 300 fs.