Electrical and Thermal Transport at the Planckian Bound of Dissipation in the Hydrodynamic Electron Fluid of WP2

Materials with strongly-correlated electrons exhibit interesting phenomena such as metal-insulator transitions and high-temperature superconductivity. In stark contrast to ordinary metals, electron transport in these materials is thought to resemble the flow of viscous fluids. Despite their differences, it is predicted that transport in both, conventional and correlated materials, is fundamentally limited by the uncertainty principle applied to energy dissipation. Here we discover hydrodynamic electron flow in the Weyl-semimetal tungsten phosphide (WP2). Using thermal and magneto-electric transport experiments, we observe the transition from a conventional metallic state, at higher temperatures, to a hydrodynamic electron fluid below 20 K. The hydrodynamic regime is characterized by a viscosity-induced dependence of the electrical resistivity on the square of the channel width, and by the observation of a strong violation of the Wiedemann-Franz law. From magneto-hydrodynamic experiments and complementary Hall measurements, the relaxation times for momentum and thermal energy dissipating processes are extracted. Following the uncertainty principle, both are limited by the Planckian bound of dissipation, independent of the underlying transport regime

Signatures of a magnetic-field-induced Lifshitz transition in the ultra-quantum limit of the topological semimetal ZrTe5

The quantum limit (QL) of an electron liquid, realised at strong magnetic fields, has long been proposed to host a wealth of strongly correlated states of matter. Electronic states in the QL are, for example, quasi-one dimensional (1D), which implies perfectly nested Fermi surfaces prone to instabilities. Whereas the QL typically requires unreachably strong magnetic fields, the topological semimetal ZrTe5 has been shown to reach the QL at fields of only a few Tesla. Here, we characterize the QL of ZrTe5 at fields up to 64 T by a combination of electrical-transport and ultrasound measurements. We find that the Zeeman effect in ZrTe5 enables an efficient tuning of the 1D Landau band structure with magnetic field. This results in a Lifshitz transition to a 1D Weyl regime in which perfect charge neutrality can be achieved. Since no instability-driven phase transitions destabilise the 1D electron liquid for the investigated field strengths and temperatures, our analysis establishes ZrTe5 as a thoroughly understood platform for potentially inducing more exotic interaction-driven phases at lower temperatures

Non-Abelian anomalous (super)fluids in thermal equilibrium from differential geometry

We apply differential geometry methods to the computation of the anomalyinduced hydrodynamic equilibrium partition function. Implementing the imaginary-time prescription on the Chern-Simons effective action on a stationary background, we obtain general closed expressions for both the invariant and anomalous part of the partition function. This is applied to the Wess-Zumino-Witten action for Goldstone modes, giving the equilibrium partition function of superfluids. In all cases, we also study the anomalyinduced gauge currents and energy-momentum tensor, providing explicit expressions for them.This work has been supported by Plan Nacional de Altas Energías Spanish MINECO grants FPA2015-64041-C2-1-P, FPA2015-64041-C2-2-P, and by Basque Government grant IT979-16. The research of E.M. is also supported by Spanish MINEICO and European FEDER funds grant FIS2017-85053-C2-1-P, Junta de Andalucía grant FQM-225, as well as by Universidad del País Vasco UPV/EHU through a Visiting Professor appointment and by Spanish MINEICO Ramón y Cajal Progra

A semblance of the first Spanish women pioneers in the scientific-technical area

[EN] Although the Spanish Consejo Superior de Investigaciones Científicas focuses its research on eight major scientific-technical areas, which cover most of human knowledge, from the most basic or fundamental aspects of science to the most complex technological developments; from human and social sciences to food science and technology through Biology, Biomedicine, Physics, Chemistry, Materials, natural resources or agricultural sciences, the disciplines that have traditionally been considered to constitute this area are Mathematics, Physics, Chemistry, Biology, Architecture and Engineering. This communication shows a brief semblance of Spanish women who can be considered pioneers, because they are the first graduates or the first Ph.D. doctors, in each of these disciplines. The objective is that society in general, for which almost certainly these women are practically unknown, can take them as a reference and an example of what women are capable of doing in any field of life, even though they have to overcome many difficulties of all kinds, of gender, fundamentally, to achieve their purposes and also to succeed in fields that originally seem to be destined only for males.[ES] Aunque el Consejo Superior de Investigaciones Científicas centra su investigación en torno a ocho grandes áreas científico-técnicas, que cubren la mayor parte del conocimiento humano, desde los aspectos más básicos o fundamentales de la ciencia hasta los desarrollos tecnológicos más complejos; desde las ciencias humanas y sociales a la ciencia y tecnología de alimentos pasando por la Biología, la Biomedicina, la Física, la Química, los materiales, los recursos naturales o las ciencias agrarias, tradicionalmente se ha considerado que las disciplinas que conforman este área de conocimiento son Matemáticas, Física, Química, Biología, Arquitectura e Ingeniería. En este artículo se muestra una breve semblanza de las mujeres españolas que pueden considerarse pioneras, por ser las primeras licenciadas o las primeras doctoras, en cada una de esas disciplinas. El objetivo es que la sociedad en general, para la que casi con toda seguridad estas mujeres son prácticamente desconocidas, pueda tomarlas como referente y ejemplo de lo que las mujeres son capaces de hacer en cualquier estamento de la vida, aun teniendo que superar numerosas dificultades de todo tipo, de género, fundamentalmente, para lograr sus propósitos y también conseguir triunfar en campos que originariamente parecen estar destinados solo a los varones.Núñez Valdés, J. (2019). Una semblanza de las primeras mujeres españolas pioneras en el área científico-técnica. Ciencia, Técnica y Mainstreaming Social. (3):34-44. https://doi.org/10.4995/citecma.2019.11142SWORD34443Algora Alba, Carlos (1996). El Instituto-Escuela de Sevilla (1932-36), Diputación de Sevilla, sección Ciencias Sociales, número 7.Araque, Natividad (2008): "Jenara Vicenta Arnal Yarza: una científica y catedrática pionera en España" en Faísca: Revista de altas capacidades, 14, 16, 27-49.Araque, Natividad, Villa, Núria (2011): "La labor de las primeras directoras de los Institutos de Enseñanza Media de Madrid: Beatriz Galindo y Emperatriz María de Austria" en Participación Educativa, número extraordinario, 225-239Carbonell, Carmen y Núñez, Juan (2010): "100 a-os de derechos: la primera mujer española doctora en Física". En II Congreso Universitario Nacional Investigación y Género. Universidad de Sevilla, 781 - 792.Durán, María José, Escudero, Ana María, Núñez, Juan y Regodón, Elena (2011): "La arquitectura, un lugar para las mujeres". En III Congreso Universitario Nacional Investigación y Género. Universidad de Sevilla, 1392 - 1407.Flecha García, Consuelo (1996): Las primeras universitarias en España, 1872-1910. Narcea Ediciones, 1996. 264 páginas.Gómez, L., Núñez, Juan, Ramos, A. (2016): "Un paseo por la vida de las primeras mujeres biólogas en España". En III International Conference Gender and Communication y I Congreso de Micromachismo en la Comunicación, Facultad de Comunicación. Universidad de Sevilla. 7 y 8 de abril, 2016.González-Martín, Francisco Javier (2013): "Pilar Careaga y Basabe (1908-1993): Feminismo católico y militancia política en el franquismo" en Aportes, 81, a-o XXVIII, 159-189.Magallón-Portolés, Carmen (1997): "Mujeres en las ciencias físico-químicas en España: el Instituto Nacional de Ciencias y el Instituto Nacional de Física y Química (1910-1936)" en Llull, 20, 39, 529. AAAMagallón Portolés, Carmen (1998): Pioneras españolas en la ciencia. Las mujeres del Instituto Nacional de Física y Química. Consejo Superior de Investigaciones Científicas.Magallón-Portolés, Carmen (1991): "La incorporación de las mujeres a las carreras científicas en la España Contemporánea: la Facultad de Ciencias de Zaragoza (1882-1936)" en Llull, 14, 27, 531-549.Magallón-Portolés, Carmen (2001): "La residencia de estudiantes para señoritas y el laboratorio Foster (Mujeres de ciencia en España a principios del siglo XX)", en Endoxa: Series Filosóficas, n." 14, 157-181.Maraver, Rocío, Núñez, Juan. (2009): "Carmen Martínez Sancho y el Instituto Murillo de Sevilla: una relación de entrega y generosidad". En I Congreso Universitario Andaluz Investigación y Género. Universidad de Sevilla, 17 y 18 de junio de 2009, 883-893.Núñez, Juan., Rodríguez-Antón, B., Rodríguez-Remesal, E. (2014a): "Primeras mujeres doctoras en Química en España". En V Congreso Universitario Nacional Investigación y Género. Universidad de Sevilla, 21 y 22 de junio de 2012, 1287-1298.Núñez, Juan., Alonso, Alejandro y Arroyo, María (2014b). "Primeras mujeres licenciadas en Farmacia en España" V Congreso Universitario Nacional Investigación y Género. Universidad de Sevilla, 03 y 04 de Julio de 2014, página 5.Sánchez-Ron, José Manuel (2014): Conversación de Margarita Salas y José Manuel Sánchez Ron. Mercurio. Fundación José Manuel Lara. La ciencia en la Academia.Torreira, M., Núñez, Juan. (2018): "Pilar Careaga, mujer adelantada a su época". En IV International Conference on Gender and Communication, Sevilla, 7 y 9 de marzo de 2018, página 8

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

Experimental signatures of the mixed axial-gravitational anomaly in the Weyl semimetal NbP

Weyl semimetals are materials where electrons behave effectively as a kind of massless relativistic particles known asWeyl fermions. These particles occur in two flavours, or chiralities, and are subject to quantum anomalies, the breaking of a conservation law by quantum fluctuations. For instance, the number of Weyl fermions of each chirality is not independently conserved in parallel electric and magnetic field, a phenomenon known as the chiral anomaly. In addition, an underlying curved spacetime provides a distinct contribution to a chiral imbalance, an effect known as the mixed axial-gravitational anomaly, which remains experimentally elusive. However, the presence of a mixed gauge-gravitational anomaly has recently been tied to thermoelectrical transport in a magnetic field, even in flat spacetime, opening the door to experimentally probe such type of anomalies in Weyl semimetals. Using a temperature gradient, we experimentally observe a positive longitudinal magnetothermoelectric conductance (PMTC) in the Weyl semimetal NbP for collinear temperature gradients and magnetic fields (DT || B) that vanishes in the ultra quantum limit. This observation is consistent with the presence of a mixed axial-gravitational anomaly. Our work provides clear experimental evidence for the existence of a mixed axial-gravitational anomaly of Weyl fermions, an outstanding theoretical concept that has so far eluded experimental detection