Anomalous Shubnikov-de Haas effect and observation of the Bloch-Gr\"uneisen temperature in the Dirac semimetal ZrTe5

Appearance of quantum oscillations (QO) in both thermodynamic and transport properties of metals at low temperatures is the most striking experimental consequence of the existence of a Fermi surface (FS). The frequency of these oscillations and the temperature dependence of their amplitude provides essential information about the FS topology and fermionic quasiparticle properties. Here, we report the observation of an anomalous suppression of the QO amplitude seen in resistivity (Shubnikov de-Haas effect) at sub-kelvin temperatures in ZrTe5 samples with a single small FS sheet comprising less than 5% of the first Brillouin zone. By comparing these results with measurements of the magneto-acoustic QO and the recovery of the usual Lifshitz-Kosevich behavior of the Shubnikov de-Haas (SdH) effect in ZrTe$_5$ samples with a multi-sheet FS, we show that the suppression of the SdH effect originates from a decoupling of the electron liquid from the lattice. On crossing the so-called Bloch-Gr\"uneisen temperature, T$_BG$, electron-phonon scattering becomes strongly suppressed and in the absence of Umklapp scattering the electronic liquid regains Galilean invariance. In addition, we show, using a combination of zero-field electrical conductivity and ultrasonic-absorption measurements, that entering this regime leads to an abrupt increase of electronic viscosity

What Has Nonviolence Got To Do With The EU?

Nonviolence has an established tradition in several disciplines, including political theory, international relations and political science. But its potential for the European Union (EU) has not been appraised yet. Thus, we set out to explore nonviolence as an analytical and normative framework for the study of the EU. At the outset, we introduce nonviolence and define our approach to this concept. We then apply our analytical and normative framework to three critical issues concerning the nature of EU power, the democratic deficit and the narrative of integration. We find that nonviolence re‐defines the core dimensions of power and democracy, and imagines the EU in non‐state‐morphic ways, situating praxis at the roots of the integration process and its narrative