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Added by
Mariano de Souza Prof. Dr.
Publication date
2016
fields
Physics
and research's language is
English
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The Gruneisen ratio ($Gamma$), i.e.,the ratio of the linear thermal expansivity to the specific heat at constant pressure, quantifies the degree of anharmonicity of the potential governing the physical properties of a system. While $Gamma$ has been intensively explored in solid state physics, very little is known about its behavior for gases. This is most likely due to the difficulties posed to carry out both thermal expansion and specific heat measurements in gases with high accuracy as a function of pressure and temperature. Furthermore, to the best of our knowledge a comprehensive discussion about the peculiarities of the Gruneisen ratio is still lacking in the literature. Here we report on a detailed and comprehensive overview of the Gruneisen ratio. Particular emphasis is placed on the analysis of $Gamma$ for gases. The main findings of this work are: emph{i)} for the Van der Waals gas $Gamma$ depends only on the co-volume $b$ due to interaction effects, it is smaller than that for the ideal gas ($Gamma$ = 2/3) and diverges upon approaching the critical volume; emph{ii)} for the Bose-Einstein condensation of an ideal boson gas, assuming the transition as first-order $Gamma$ diverges upon approaching a critical volume, similarly to the Van der Waals gas; emph{iii)} for $^4$He at the superfluid transition $Gamma$ shows a singular behavior. Our results reveal that $Gamma$ can be used as an appropriate experimental tool to explore pressure-induced critical points.
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The magneto-caloric effect (MCE), which is the refrigeration based on the variation of the magnetic entropy, is of great interest in both technological applications and fundamental research. The MCE is quantified by the magnetic Gruneisen parameter $Gamma_{textmd{mag}}$. We report on an analysis of $Gamma_{textmd{mag}}$ for the classical Brillouin-like paramagnet, for a modified Brillouin function taking into account a zero-field splitting originated from the spin-orbit (SO) interaction and for the one-dimensional Ising (1DI) model under longitudinal field. For both Brillouin-like model with SO interaction and the longitudinal 1DI model, for $ T rightarrow$ 0 and vanishing field a sign change of the MCE is observed, suggestive of a quantum phase transition. SO interaction leads to a narrowing of the critical fluctuations upon approaching the critical point. Our findings emphasize the relevance of $Gamma_{textmd{mag}}$ for exploring critical points. Also, we show that the Brillouin model with and without SO interaction can be recovered from the 1DI model in the regime of high-temperatures and vanishing coupling constant $J$.
Using the Bethe ansatz solution, we analytically study expansionary, magnetic and interacting Gruneisen parameters (GPs) for one-dimensional (1D) Lieb-Liniger and Yang-Gaudin models. These different GPs elegantly quantify the dependences of characteristic energy scales of these quantum gases on the volume, the magnetic field and the interaction strength, revealing the caloric effects resulted from the variations of these potentials. The obtained GPs further confirm an identity which is incurred by the symmetry of the thermal potential. We also present universal scaling behavior of these GPs in the vicinities of the quantum critical points driven by different potentials. The divergence of the GPs not only provides an experimental identification of non-Fermi liquid nature at quantum criticality but also elegantly determine low temperature phases of the quantum gases. Moreover, the pairing and depairing features in the 1D attractive Fermi gases can be captured by the magnetic and interacting GPs, facilitating experimental observation of quantum phase transitions. Our results open to further study the interaction- and magnetic-field-driven quantum refrigeration and quantum heat engine in quantum gases of ultracold atoms.
We use the recently-proposed emph{compressible cell} Ising-like model [Phys. Rev. Lett. textbf{120}, 120603 (2018)] to estimate the ratio between thermal expansivity and specific heat (the Gruneisen parameter $Gamma$) in supercooled water. Near the critical pressure and temperature, $Gamma$ increases. The $Gamma$ value diverges near the pressure-induced finite-$T$ critical end-point [Phys. Rev. Lett. textbf{104}, 245701 (2010)] and quantum critical points [Phys. Rev. Lett. textbf{91}, 066404 (2003)], which indicates that two energy scales are governing the system. This enhanced behavior of $Gamma$ is caused by the coexistence of high- and low-density liquids [Science textbf{358}, 1543 (2017)]. Our findings support the proposed liquid-liquid critical point in supercooled water in the No-Mans Land regime, and indicates possible applications of this model to other systems.
At any quantum critical point (QCP) with a critical magnetic field $H_c$, the magnetic Gruneisen parameter $Gamma_{rm H}$, which equals the adiabatic magnetocaloric effect, is predicted to show characteristic signatures such as a divergence, sign change and $T/(H-H_c)^epsilon$ scaling. We categorize thirteen materials, ranging from heavy fermion metals to frustrated magnets, where such experimental signatures have been found. Remarkably, seven stoichiometric materials at ambient pressure show $H_c=0$. However, additional thermodynamic and magnetic experiments suggest that most of them do not show a zero-field QCP. While the existence of a pressure insensitive strange metal state is one possibility, for some of the materials $Gamma_{rm H}$ seems influenced by impurities or a fraction of moments which are not participating in a frozen state. To unambiguously prove zero-field and pressure sensitive quantum criticality, a $Gamma_{rm H}$ divergence is insufficient and also the Gruneisen ratio of thermal expansion to specific heat must diverge.
We report on the confinement of a Bose-Einstein condensate in an annular trap with widely tunable parameters. The trap relies on a combination of magnetic, optical and radio-frequency fields. The loading procedure is discussed. We present annular traps with radii adjusted between 20 and 150 micrometers. We demonstrate the preparation of persistent flows both with a rotating laser stirrer and with a global quadrupole deformation of the ring.Our setup is well adapted for the study of superfluid dynamics.
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