Specific heat of heavy fermion CePd2Si2 in high magnetic fields

We report specific heat measurements on the heavy fermion compound CePd2Si2 in magnetic fields up to 16 T and in the temperature range 1.4-16 K. A sharp peak in the specific heat signals the antiferromagnetic transition at T_N ~ 9.3 K in zero field. The transition is found to shift to lower temperatures when a magnetic field is applied along the crystallographic a-axis, while a field applied parallel to the tetragonal c-axis does not affect the transition. The magnetic contribution to the specific heat below T_N is well described by a sum of a linear electronic term and an antiferromagnetic spin wave contribution. Just below T_N, an additional positive curvature, especially at high fields, arises most probably due to thermal fluctuations. The field dependence of the coefficient of the low temperature linear term, gamma_0, extracted from the fits shows a maximum at about 6 T, at the point where an anomaly was detected in susceptibility measurements. The relative field dependence of both T_N and the magnetic entropy at T_N scales as [1-(B/B_0)^2] for B // a, suggesting the disappearance of antiferromagnetism at B_0 ~ 42 T. The expected suppression of the antiferromagnetic transition temperature to zero makes the existence of a magnetic quantum critical point possible.Comment: to be published in Journal of Physics: Condensed Matte

Photoluminescent diamond nanoparticles for cell labeling: study of the uptake mechanism in mammalian cells

Diamond nanoparticles (nanodiamonds) have been recently proposed as new labels for cellular imaging. For small nanodiamonds (size <40 nm) resonant laser scattering and Raman scattering cross-sections are too small to allow single nanoparticle observation. Nanodiamonds can however be rendered photoluminescent with a perfect photostability at room temperature. Such a remarkable property allows easier single-particle tracking over long time-scales. In this work we use photoluminescent nanodiamonds of size <50 nm for intracellular labeling and investigate the mechanism of their uptake by living cells . By blocking selectively different uptake processes we show that nanodiamonds enter cells mainly by endocytosis and converging data indicate that it is clathrin mediated. We also examine nanodiamonds intracellular localization in endocytic vesicles using immunofluorescence and transmission electron microscopy. We find a high degree of colocalization between vesicles and the biggest nanoparticles or aggregates, while the smallest particles appear free in the cytosol. Our results pave the way for the use of photoluminescent nanodiamonds in targeted intracellular labeling or biomolecule deliver

How do Fermi liquids get heavy and die?

We discuss non-Fermi liquid and quantum critical behavior in heavy fermion materials, focussing on the mechanism by which the electron mass appears to diverge at the quantum critical point. We ask whether the basic mechanism for the transformation involves electron diffraction off a quantum critical spin density wave, or whether a break-down in the composite nature of the heavy electron takes place at the quantum critical point. We show that the Hall constant changes continously in the first scenario, but may ``jump'' discontinuously at a quantum critical point where the composite character of the electron quasiparticles changes.Comment: Revised version with many new references added. To appear as a topical review in Journal of Physics: Condensed Matter Physics. Two column version http://www.physics.rutgers.edu/~coleman/online/questions.ps.g

Analysis of Fourier transform valuation formulas and applications

The aim of this article is to provide a systematic analysis of the conditions such that Fourier transform valuation formulas are valid in a general framework; i.e. when the option has an arbitrary payoff function and depends on the path of the asset price process. An interplay between the conditions on the payoff function and the process arises naturally. We also extend these results to the multi-dimensional case, and discuss the calculation of Greeks by Fourier transform methods. As an application, we price options on the minimum of two assets in L\'evy and stochastic volatility models.Comment: 26 pages, 3 figures, to appear in Appl. Math. Financ

The break up of heavy electrons at a quantum critical point

The point at absolute zero where matter becomes unstable to new forms of order is called a quantum critical point (QCP). The quantum fluctuations between order and disorder that develop at this point induce profound transformations in the finite temperature electronic properties of the material. Magnetic fields are ideal for tuning a material as close as possible to a QCP, where the most intense effects of criticality can be studied. A previous study on theheavy-electron material $YbRh_2Si_2$ found that near a field-induced quantum critical point electrons move ever more slowly and scatter off one-another with ever increasing probability, as indicated by a divergence to infinity of the electron effective mass and cross-section. These studies could not shed light on whether these properties were an artifact of the applied field, or a more general feature of field-free QCPs. Here we report that when Germanium-doped $YbRh_2Si_2$ is tuned away from a chemically induced quantum critical point by magnetic fields there is a universal behavior in the temperature dependence of the specific heat and resistivity: the characteristic kinetic energy of electrons is directly proportional to the strength of the applied field. We infer that all ballistic motion of electrons vanishes at a QCP, forming a new class of conductor in which individual electrons decay into collective current carrying motions of the electron fluid.Comment: Pdf files of article available at http://www.physics.rutgers.edu/~coleman/online/breakup.pdf, pdf file of news and views article available at http://www.physics.rutgers.edu/~coleman/online/nvbreakup.pd

First mock-up of the CBM STS module based on a new assembly concept

A molecular dynamics model has been developed to investigate the effect of the crystallographic orientation on the material deformation behaviors in nano- indentation/scratching of BCC iron. Two cases with different substrate orientations have been simulated. The orientations along x, y and z direction are [001], [100] and [010] for Case I and [111], [-1-12] and [1-10] for Case II, respectively. Case I and Case II exhibit different deformation patterns in the substrate. During indentation, the pile-up can be observed in Case I, but not in Case II. During scratching the pile-up ahead of the movement of the indenter has been enlarged in Case I, while a chip with the disordered atoms is generated in Case II. It has been found that Case I has both higher hardness and larger coefficient of friction. The ratios of the hardness and the coefficient of friction between cases I and II are nearly 2. The reason is attributed to the different crystallographic orientations used in both cases

Specific Heat of URu2_{2}Si2_{2} in Fields to 42 T: Clues to the 'Hidden Order'

The large $\Delta$C observed at 17.5 K in URu$_{2}$Si$_{2}$ is inconsistent with the small, 0.04 $\mu_{B}$ moment measured for the antiferromagnetism observed starting (perhaps coincidentally) at the same temperature. We report measurements of this specific heat transition, thought to be due to some 'hidden order', in magnetic fields between 24 and 42 T, i. e. through the field region where three metamagnetic transtions are known to occur at 35.8, 37.3, and 39.4 T. The response of $\Delta$C in single crystal URu$_{2}$Si$_{2}$ to magnetic field, which includes a change to $\Delta$C being possibly associated with a first order phase transition for high fields, is analyzed to shed further light on the possible explanations of this unknown ordering process. At fields above 35 T, a new high field phase comes into being; the connection between this high field phase revealed by the specific heat and earlier magnetization data is discussed