The weakness of electron-electron correlations in the itinerant antiferromagnet Cr doped with V has long been considered the reason that neither new collective electronic states or even non Fermi liquid behaviour are observed when antiferromagnetism
in Cr$_{1-x}$V$_{x}$ is suppressed to zero temperature. We present the results of neutron and electron diffraction measurements of several lightly doped single crystals of Cr$_{1-x}$V$_{x}$ in which the archtypal spin density wave instability is progressively suppressed as the V content increases, freeing the nesting-prone Fermi surface for a new striped charge instability that occurs at x$_{c}$=0.037. This novel nesting driven instability relieves the entropy accumulation associated with the suppression of the spin density wave and avoids the formation of a quantum critical point by stabilising a new type of charge order at temperatures in excess of 400 K. Restructuring of the Fermi surface near quantum critical points is a feature found in materials as diverse as heavy fermions, high temperature copper oxide superconductors and now even elemental metals such as Cr.
The lifetime of the $tau$-lepton is measured using the process $e^+e^-rightarrowtau^+tau^-$, where both $tau$-leptons decay to $3pi u_tau$. The result for the mean lifetime, based on $711,mathrm{fb}^{-1}$ of data collected with the Belle detector at
the $Upsilon(4S)$ resonance and $60,mathrm{MeV}$ below, is $tau = (290.17 pm 0.53(mathrm{stat.}) pm 0.33(mathrm{syst.}))cdot10^{-15},mathrm{s}$. The first measurement of the lifetime difference between $tau^+$ and $tau^-$ is performed. The upper limit on the relative lifetime difference between positive and negative $tau$-leptons is $|Deltatau| / tau < 7.0 times 10^{-3}$ at 90% CL.
A parameterization of the $bar pp$ differential elastic scattering cross section in the beam momentum range from 2 to 16 GeV/c is proposed. The parameterization well describes the existing data including the observed diffraction pattern at four-momen
tum transfer $|t|$ up to 1.5-2.0 GeV$^2$. It can be used for detailed calculations of the radiation load on the detectors being designed for the PANDA detector at the future FAIR facility in Darmstadt.
Neutron diffraction measurements on single crystals of Cr1-xVx (x=0, 0.02, 0.037) show that the ordering moment and the Neel temperature are continuously suppressed as x approaches 0.037, a proposed Quantum Critical Point (QCP). The wave vector Q of
the spin density wave (SDW) becomes more incommensurate as x increases in accordance with the two band model. At xc=0.037 we have found temperature dependent, resolution limited elastic scattering at 4 incommensurate wave vectors Q=(1+/-delta_1,2, 0, 0)*2pi/a, which correspond to 2 SDWs with Neel temperatures of 19 K and 300 K. Our neutron diffraction measurements indicate that the electronic structure of Cr is robust, and that tuning Cr to its QCP results not in the suppression of antiferromagnetism, but instead enables new spin ordering due to novel nesting of the Fermi surface of Cr.
We report the synthesis and basic properties of single crystals of a new binary compound, Yb$_{3}$Pt$_{4}$. The Yb ions in this compound are fully trivalent, and heat capacity measurements show that the crystal field scheme involves a doublet ground
state, well separated from the excited states, which are fully occupied above $sim$ 150 K. The heat capacity displays a large, weakly first order anomaly at 2.4 K, where a cusp is observed in the magnetic susceptibility signalling the onset of antiferromagnetic order. The entropy associated with this order is the full Rln2 of the doublet ground state, however the magnetic susceptibility in the ordered phase is dominated by a large and temperature independent component below the Neel temperature. The heat capacity in the ordered state originates with ferromagnetic spin waves, giving evidence for the inherently local moment character of the ordered state. The electrical resistivity is unusually large, and becomes quadratic in temperature exactly at the Neel temperature. The absence of analogous Fermi liquid behavior in the heat capacity and the magnetic susceptibility implies that Yb$_{3}$Pt$_{4}$ is a low electron density system, where the Fermi surface is further gapped by the onset of magnetic order.
