Valence modulations in CeRuSn

CeRuSn exhibits an extraordinary room temperature structure at 300~K with coexistence of two types of Ce ions, namely trivalent Ce$^{3+}$ and intermediate valent Ce$^{(4-\delta)+}$, in a metallic environment. The ordered arrangement of these two Ce types on specific crystallographic sites results in a doubling of the unit cell along the $c$-axis with respect to the basic monoclinic CeCoAl-type structure. Below room temperature, structural modulation transitions with very broad hysteresis have been reported from measurements of various bulk properties. X-ray diffraction revealed that at low temperatures the doubling of the CeCoAl type structure is replaced by a different modulated ground state, approximating a near tripling of the basic CeCoAl cell. The transition is accompanied by a significant contraction of the $c$ axis. We present new x-ray absorption near-edge spectroscopy data at the Ce L$_{3}$ absorption edge, measured on a freshly cleaved surface of a CeRuSn single crystal. In contrast to a previous report, the new data exhibit small but significant variations as function of temperature that are consistent with a transition of a fraction of Ce$^{3+}$ ions to the intermediate valence state, analogous to the $\gamma \rightarrow \alpha$ transition in elemental cerium, when cooling through the structural transitions of CeRuSn. Such results in a valence-modulated state

Morphological instability, evolution, and scaling in strained epitaxial films: An amplitude equation analysis of the phase field crystal model

Morphological properties of strained epitaxial films are examined through a mesoscopic approach developed to incorporate both the film crystalline structure and standard continuum theory. Film surface profiles and properties, such as surface energy, liquid-solid miscibility gap and interface thickness, are determined as a function of misfit strains and film elastic modulus. We analyze the stress-driven instability of film surface morphology that leads to the formation of strained islands. We find a universal scaling relationship between the island size and misfit strain which shows a crossover from the well-known continuum elasticity result at the weak strain to a behavior governed by a "perfect" lattice relaxation condition. The strain at which the crossover occurs is shown to be a function of liquid-solid interfacial thickness, and an asymmetry between tensile and compressive strains is observed. The film instability is found to be accompanied by mode coupling of the complex amplitudes of the surface morphological profile, a factor associated with the crystalline nature of the strained film but absent in conventional continuum theory.Comment: 16 pages, 10 figures; to be published in Phys. Rev.

Comment on "Quantum linear Boltzmann equation with finite intercollision time"

Inconsistencies are pointed out in a recent proposal [L. Diosi, Phys. Rev. A 80, 064104 (2009); arXiv:0905.3908v1] for a quantum version of the classical linear Boltzmann equation.Comment: 3 pages; v3: corresponds to published versio

Nuclear condensation and the equation of state of nuclear matter

The isothermal compression of a dilute nucleonic gas invoking cluster degrees of freedom is studied in an equilibrium statistical model; this clusterized system is found to be more stable than the pure nucleonic system. The equation of state (EoS) of this matter shows features qualitatively very similar to the one obtained from pure nucleonic gas. In the isothermal compression process, there is a sudden enhancement of clusterization at a transition density rendering features analogous to the gas-liquid phase transition in normal dilute nucleonic matter. Different observables like the caloric curves, heat capacity, isospin distillation, etc. are studied in both the models. Possible changes in the observables due to recently indicated medium modifications in the symmetry energy are also investigated.Comment: 18 pages and 11 figures. Phys. Rev. C (in press

Noninteracting Fermions in infinite dimensions

Usually, we study the statistical behaviours of noninteracting Fermions in finite (mainly two and three) dimensions. For a fixed number of fermions, the average energy per fermion is calculated in two and in three dimensions and it becomes equal to 50 and 60 per cent of the fermi energy respectively. However, in the higher dimensions this percentage increases as the dimensionality increases and in infinite dimensions it becomes 100 per cent. This is an intersting result, at least pedagogically. Which implies all fermions are moving with Fermi momentum. This result is not yet discussed in standard text books of quantum statistics. In this paper, this fact is discussed and explained. I hope, this article will be helpful for graduate students to study the behaviours of free fermions in generalised dimensionality.Comment: To appear in European Journal of Physics (2010

Geometric creation of quantum vorticity

We consider superfluidity and quantum vorticity in rotating spacetimes. The system is described by a complex scalar satisfying a nonlinear Klein-Gordon equation. Rotation terms are identified and found to lead to the transfer of angular momentum of the spacetime to the scalar field. The scalar field responds by rotating, physically behaving as a superfluid, through the creation of quantized vortices. We demonstrate the vortex nucleation through numerical simulation.Comment: 10 pages, 1 figure, updated to closely resemble published versio