32 research outputs found
Thermal Conductivity and Specific Heat of the Spin-Ice Compound DyTiO: Experimental Evidence for Monopole Heat Transport
Elementary excitations in the spin-ice compound DyTiO can be
described as magnetic monopoles propagating independently within the pyrochlore
lattice formed by magnetic Dy ions. We studied the magnetic-field dependence of
the thermal conductivity {\kappa}(B) for B || [001] and observe clear evidence
for magnetic heat transport originating from the monopole excitations. The
magnetic contribution {\kappa}_{mag} is strongly field-dependent and correlates
with the magnetization M(B). The diffusion coefficient obtained from the ratio
of {\kappa}_{mag} and the magnetic specific heat is strongly enhanced below 1 K
indicating a high mobility of the monopole excitations in the spin-ice state.Comment: 5 pages, 4 figure
Gibbs' paradox and black-hole entropy
In statistical mechanics Gibbs' paradox is avoided if the particles of a gas
are assumed to be indistinguishable. The resulting entropy then agrees with the
empirically tested thermodynamic entropy up to a term proportional to the
logarithm of the particle number. We discuss here how analogous situations
arise in the statistical foundation of black-hole entropy. Depending on the
underlying approach to quantum gravity, the fundamental objects to be counted
have to be assumed indistinguishable or not in order to arrive at the
Bekenstein--Hawking entropy. We also show that the logarithmic corrections to
this entropy, including their signs, can be understood along the lines of
standard statistical mechanics. We illustrate the general concepts within the
area quantization model of Bekenstein and Mukhanov.Comment: Contribution to Mashhoon festschrift, 13 pages, 4 figure
Structural and dynamical properties of liquid Al-Au alloys
We investigate temperature- and composition dependent structural and dynamical p
roperties of Al-Au melts.
Experiments are performed to obtain accurate density and viscosity data.
The system shows a strong negative excess volume, similar to other Al-based binary alloys.
We develop a molecular-dynamics (MD) model of the melt based on the embedded-atom method (EAM), gauged against the available experimental liquid-state data.
A rescaling of previous EAM potentials for solid-state Au and Al
improves the quantitative agreement with experimental data in the melt.
In the MD simulation, the admixture of Au to Al can be
interpreted as causing a local compression of the less dense Al system,
driven by less soft Au--Au interactions. This local compression provides
a microscopic mechanism explaining the strong negative excess volume
of the melt.
We further discuss the conentration dependence of self- and interdiffusion
and viscosity in the MD model. Al atoms are more mobile than Au, and their
increased mobility is linked to a lower viscosity of the melt