arXiv subjects

Olaf Bossen

Publications and source records attributed to Olaf Bossen.

4 recordsLinked to original sources

arXiv2019

Heat flowing from cold to hot without external intervention by using a 'thermal inductor'

The cooling of boiling water all the way down to freezing, by thermally connecting it to a thermal bath held at ambient temperature without external intervention, would be quite unexpected. We describe the equivalent of a 'thermal inductor', composed of a Peltier element and an electric inductance, which can drive the temperature difference between two bodies to change sign by imposing inertia on the heat flowing between them, and enable continuing heat transfer from the chilling body to its warmer counterpart without the need of an external driving force. We demonstrate its operation in an experiment and show that the process can pass through a series of quasi-equilibrium states while fully complying with the second law of thermodynamics. This 'thermal inductor' extends the analogy between electrical and thermal circuits and could serve, with further progress in thermoelectric materials, to cool hot materials well below ambient temperature without external energy supply or moving parts.

cond-mat.stat-mech↗

arXiv2013

Ac-magnetic susceptibility in the peak-effect region of Nb$_3$Sn

We performed a systematic study of the ac magnetic-susceptibility on a Nb3Sn single crystal which displays a strong peak effect near the upper critical field Hc2. In external magnetic fields above 3 T, the peak effect manifests itself in a single, distinct peak in the real part of the ac susceptibility as a function of temperature T, the size of which continuously increases with increasing magnetic field H. In the imaginary part of the ac susceptibility, on the other hand, a single peak initially grows with increasing H up to a well-defined value, and then splits into two sharp peaks which separate when H is further increased. We explain this surprising behavior by a flux-creep model and taking into account the enhancement of the critical-current density in the peak-effect region near Tc in which Bean's critical-state model seems to apply. Outside this region, the crystal is clearly in a flux-creep regime with finite creep exponent n.

cond-mat.supr-con↗

arXiv2012

Estimates for the thermodynamic signatures of vortex-lattice melting in conventional superconductors

The first-order nature of the vortex-lattice melting transition in copper-based layered high-Tc superconductors is well established. The associated discontinuities in magnetization have been extensively studied, for example, in YBa2Cu3O7 and Bi2Sr2CaCu2O8, while the respective latent heats have been systematically investigated only in YBa2Cu3O7 and related compounds. The apparent absence of such signatures in conventional superconductors such as Nb raises the question whether or not the concept of vortex-lattice melting is applicable at all in such materials. Based on available literature to describe the vortex-state and using the Lindemann criterion, we estimate quantitatively the order of magnitude for the expected latent heats of melting and the associated discontinuities in magnetization, respectively, as functions of a few known material parameters. It turns out that both thermodynamic quantities are not strictly vanishing even in isotropic materials as long as $κ> 1/\sqrt{2}$, but they are small and may often be beyond the available experimental resolution.

cond-mat.supr-con↗

arXiv2011

LC-Circuit Calorimetry

We present a new type of calorimeter in which we couple an unknown heat capacity with the aid of Peltier elements to an electrical circuit. The use of an electrical inductance and an amplifier in the circuit allows us to achieve autonomous oscillations, and the measurement of the corresponding resonance frequency makes it possible to accurately measure the heat capacity with an intrinsic statistical error that decreases as ~t^{-3/2} with measuring time t, as opposed to a corresponding error ~t^{-1/2} in the conventional alternating current (a.c.) method to measure heat capacities. We have built a demonstration experiment to show the feasibility of the new technique, and we have tested it on a gadolinium sample at its transition to the ferromagnetic state.

physics.ins-det↗