Quantum critical 5f electrons avoid singularities in U(Ru,Rh)(2)Si-2

in Physical Review Letters (2005), 95(2),

We present specific heat measurements of 4% Rh-doped URu2Si2 at magnetic fields around the proposed metamagnetic transition field H(m)similar to 34 T, revealing striking similarities to the isotructural ... [more ▼]

We present specific heat measurements of 4% Rh-doped URu2Si2 at magnetic fields around the proposed metamagnetic transition field H(m)similar to 34 T, revealing striking similarities to the isotructural Ce analog CeRu2Si2 for H > H-m. This suggests that strongly renormalized hybridized-band models apply equally well to both systems. The vanishing bandwidths as H -> H-m are consistent with a quantum-critical point close to H-m. The existence of a phase transition into an ordered phase in the vicinity of H-m for 4% Rh-doped URu2Si2, but not for CeRu2Si2, is consistent with a stronger superexchange in the case of the U 5f system. Irreversible processes at the transition indicate a strong coupling of the 5f orbitals to the lattice, most suggestive of electric quadrupolar order. [less ▲]

Temperature-induced density anomaly in Te-rich liquid Germanium tellurides: p versus sp 3 bonding?

in Physical Review Letters (2005), 95(26), 2678011-26780142678014

The density anomaly of liquid Ge 0.15Te 0.85 measured between 633 and 733 K is investigated with ab initio molecular dynamics calculations at four temperatures and at the corresponding experimental ... [more ▼]

The density anomaly of liquid Ge 0.15Te 0.85 measured between 633 and 733 K is investigated with ab initio molecular dynamics calculations at four temperatures and at the corresponding experimental densities. For box sizes ranging from 56 to 112 atoms, an 8 k-points sampling of the Brillouin zone is necessary to obtain reliable results. Contrary to other Ge chalcogenides, no sp 3 hybridization of the Ge bonding is observed. As a consequence, the negative thermal expansion of the liquid is not related to a tetrahedral bonding as in the case of water or silica. We show that it results from the symmetry recovery of the local environment of Ge atoms that is distorted at low temperature by a Peierls-like mechanism acting in the liquid state in the same way as in the parent solid phases [less ▲]

Functional modes of proteins are among the most robust

in Physical Review Letters (2004), 96

It is shown that a small subset of modes which are likely to be involved in protein functional motions of large amplitude can be determined by retaining the most robust normal modes obtained using ... [more ▼]

It is shown that a small subset of modes which are likely to be involved in protein functional motions of large amplitude can be determined by retaining the most robust normal modes obtained using different protein models. This result should prove helpful in the context of several applications proposed recently, like for solving difficult molecular replacement problems or for fitting atomic structures into low- resolution electron density maps. It may also pave the way for the development of methods allowing us to predict such motions accurately. [less ▲]

First-principles study of the electro-optic effect in ferroelectric oxides

in Physical Review Letters (2004), 93(18),

We first present a method to compute the electro-optic tensor from first principles, explicitly taking into account the electronic, ionic and piezoelectric contributions. We then study the nonlinear optic ... [more ▼]

We first present a method to compute the electro-optic tensor from first principles, explicitly taking into account the electronic, ionic and piezoelectric contributions. We then study the nonlinear optic behavior of three paradigmatic ferroelectric oxides. Our calculations reveal the dominant contribution of the soft mode to the electro-optic coefficients in LiNbO3 and BaTiO3 and its minor role in PbTiO3. We identify the coupling between the electric field and the polar atomic displacements along the B-O chains as the origin of the large electro-optic response in perovskite ABO(3) compounds. [less ▲]

Quantum confinement and fullerenelike surface reconstructions in nanodiamonds

in Physical Review Letters (2003), 90(3), 0374011-03740140374014

We present x-ray absorption and emission experiments and ab initio calculations showing that the size of carbon diamond must be reduced to at least 2 nm, in order to observe an increase of its optical gap ... [more ▼]

We present x-ray absorption and emission experiments and ab initio calculations showing that the size of carbon diamond must be reduced to at least 2 nm, in order to observe an increase of its optical gap, at variance with Si and Ge where quantum confinement effects persist up to 6-7 nm. In addition, our calculations show that the surface of nanodiamond particles larger than sime 1 nm reconstructs in a fullerenelike manner, giving rise to a new family of carbon clusters: bucky diamonds. Signatures of these surface reconstructions are compatible with pre-edge features observed in measured absorption spectra [less ▲]

Comment on "Strong vortex liquid correlation from multiterminal measurements on untwinned YBa2Cu3O7-delta single crystals"

in Physical Review Letters (2002), 88(13),

Time-resolved laser spectroscopy of multiply ionized atoms: Natural radiative lifetimes in CeIV

in Physical Review Letters (2001), 87(27),

Radiative lifetimes have been measured for two excited levels of Ce IV using the time-resolved laser-induced fluorescence technique. Ce3+ ions were produced in a laser-induced plasma. In the measurements ... [more ▼]

Radiative lifetimes have been measured for two excited levels of Ce IV using the time-resolved laser-induced fluorescence technique. Ce3+ ions were produced in a laser-induced plasma. In the measurements, a suitable magnetic field was applied to reduce the recombination between electrons and the ions and thus the background light from the recombination, and special care was exercised to avoid flight-out-of-view effects on the lifetime measurements for the high-velocity ions. The experimental lifetime results, tau = 30(2) ns for the level 49 737 cm(-1) and tau = 30(3) ns for the level 52 226 cm(-1), were compared with relativistic Hartree-Fock calculations (tau = 30.5 and 30.0 ns) indicating a particularly excellent agreement. [less ▲]

Resonance-assisted tunneling in near-integrable systems

in Physical Review Letters (2001), 87(6), 064101

Dynamical tunneling between symmetry related invariant tori is studied in the near-integrable regime. Using the kicked Harper model as an illustration, we show that the exponential decay of the wave ... [more ▼]

Dynamical tunneling between symmetry related invariant tori is studied in the near-integrable regime. Using the kicked Harper model as an illustration, we show that the exponential decay of the wave functions in the classically forbidden region is modified due to coupling processes that are mediated by classical resonances. This mechanism leads to a substantial deviation of the splitting between quasidegenerate eigenvalues from the purely exponential decrease with 1/(h) over bar obtained for the integrable system. A simple semiclassical framework, which takes into account the effect of the resonance substructure on the invariant tori, allows one to quantitatively reproduce the behavior of the eigenvalue splittings. [less ▲]

Evidence of a reentrant Peierls distortion in liquid GeTe

in Physical Review Letters (2000), 85(9), 1950-1953

The local atomic order of semiconducting liquid GeTe is studied using first-principles molecular-dynamics simulations. Our work points out a high degree of alternating chemical order in the liquid and ... [more ▼]

The local atomic order of semiconducting liquid GeTe is studied using first-principles molecular-dynamics simulations. Our work points out a high degree of alternating chemical order in the liquid and demonstrates the presence of a Peierls distortion close above the melting temperature. This distortion, absent in the high temperature crystalline structure of NaCl type, is a remnant of the atomic arrangement in the A7 low temperature crystalline phase. It disappears slowly with temperature, as the liquid evolves from a semiconducting to a metallic state. [less ▲]

Fourfold basal plane anisotropy of the nonlocal magnetization of YNi2B2C

in Physical Review Letters (1999), 83(19), 3920-3923

Studies of single crystal YNi2B2C have revealed a fourfold anisotropy of the equilibrium maenetization in the square crystallographic basal plane. This pi/2 periodicity occurs deep in the superconductive ... [more ▼]

Studies of single crystal YNi2B2C have revealed a fourfold anisotropy of the equilibrium maenetization in the square crystallographic basal plane. This pi/2 periodicity occurs deep in the superconductive mixed state. In this crystal symmetry, an ordinary superconductive mass anisotropy (as in usual London theory) allows only a constant, isotropic response. In contrast, the experimental results are well described by generalized London theory incorporating nonlocal electrodynamics, as needed for this clean, intermediate-kappa superconductor. [less ▲]