Fermi Surface Reconstruction without Breakdown of Kondo Screening at Quantum Critical Point

Motivated by recent Hall-effect experiment in YbRh$_2$Si$_2$, we study ground state properties of a Kondo lattice model in a two-dimensional square lattice using variational Monte Carlo method. We show that there are two types of phase transition, antiferromagnetic transition and topological one (Fermi surface reconstruction). In a wide region of parameters, these two transitions occur simultaneously without the breakdown of Kondo screening, accompanied by a discontinuous change of the Hall coefficient. This result is consistent with the experiment and gives a novel theoretical picture for the quantum critical point in heavy fermion systems.Comment: 4 pages, 3 figures, submitted to Physical Review Letter

Variation of Internal Friction with Magnetization in Nickel

The internal friction Q^ of nickel annealed at 1000℃ for 10hr was measured in a magnetic field by the electrostatic driving method. The results obtained are as follows : (1) With decreasing magnetic field H from a magnetically saturated state, Q^ increases from about H=30 Oe and shows a maximum at H=15 Oe. (2) The magnetic hysteresis loss Q^_h was separated from the whole Q^ through measurement of the dynamic stress with an interference comparameter. (3) When Q^_h is expressed as a function of magentization I/I_s, Q^_h shows a maximum at I/I_s=0.6 ; it becomes smaller with increasing driving frequency f and vanishes at f=5.8 kHz

Specific Heats of Fe-Ni (fcc) Alloys at High Temperature

Specific heats at constant pressure, C_p, of Fe-Ni (fcc) alloys have been measured a temperatures 300～1000 K. For alloys containing more than 50%Ni, the C_p-T curve shows a sharp λ-type peak at ferromagnetic Curie temperature. For the alloys less in concentration of nickel, however, only a dull peak is observed. The C_p-T curve is analyzed using the values of thermal expansion coefficient and of compressibility measured on the same conditions, separating the magnetic contribution from total specific heats

Surface tension measurement of glass melts by the maximum bubble pressure method

The maximum bubble pressure method was used to obtain accurate surface tension measurements. The dependence of apparent surface tension value on bubble growth time was measured for times from several to longer than a thousand seconds. The static surface tension value was obtained by extrapolating bubble growth time to infinity. The dynamic surface tension, which is familiar in colloids, could not be directly obtained because of the high viscosity of glass melt. The effects of capillary tip material and shape were also examined. This method is applicable to melts with viscosity less than 10^3.5 dPa s. The reproducibility in the measurement was within a few percent