Planar Hall effect in the Weyl semimetal GdPtBi

Observation of Weyl and Dirac Fermions in condensed matter systems is one of the most important discoveries. Among the very few available tools to characterize Weyl semimetals through electrical transport, negative magnetoresistance is most commonly used. Considering shortcomings of this method, new tools to characterize chiral anomaly in Weyl semimetals are desirable. We employ planar Hall effect as an effective technique in half Heusler Weyl semimetal GdPtBi to study chiral anomaly. This compound exhibits a large value of 1.5 mohm cm planar Hall resistivity at 2 K and in 9 T. Our analysis reveals that the observed amplitude is dominated by Berry curvature and chiral anomaly contributions. Through the angle dependent transport studies we establish that GdPtBi with relatively small orbital magnetoresistance is an ideal candidate to observe large planar Hall effect .Comment: Updated text

Topological quantum materials from the viewpoint of chemistry

Topology, a mathematical concept, has recently become a popular and truly transdisciplinary topic encompassing condensed matter physics, solid state chemistry, and materials science. Since there is a direct connection between real space, namely atoms, valence electrons, bonds and orbitals, and reciprocal space, namely bands and Fermi surfaces, via symmetry and topology, classifying topological materials within a single-particle picture is possible. Currently, most materials are classified as trivial insulators, semimetals and metals, or as topological insulators, Dirac and Weyl nodal-line semimetals, and topological metals. The key ingredients for topology are: certain symmetries, the inert pair effect of the outer electrons leading to inversion of the conduction and valence bands, and spin-orbit coupling. This review presents the topological concepts related to solids from the viewpoint of a solid-state chemist, summarizes techniques for growing single crystals, and describes basic physical property measurement techniques to characterize topological materials beyond their structure and provide examples of such materials. Finally, a brief outlook on the impact of topology in other areas of chemistry is provided at the end of the article.Comment: Review Article, 28 Figure

Anisotropic electrical and thermal magnetotransport in the magnetic semimetal GdPtBi

The half-Heusler rare-earth intermetallic GdPtBi has recently gained attention due to peculiar magnetotransport phenomena that have been associated with the possible existence of Weyl fermions, thought to arise from the crossings of spin-split conduction and valence bands. On the other hand, similar magnetotransport phenomena observed in other rare-earth intermetallics have often been attributed to the interaction of itinerant carriers with localized magnetic moments stemming from the $4f$-shell of the rare-earth element. In order to address the origin of the magnetotransport phenomena in GdPtBi, we performed a comprehensive study of the magnetization, electrical and thermal magnetoresistivity on two single-crystalline GdPtBi samples. In addition, we performed an analysis of the Fermi surface via Shubnikov-de Haas oscillations in one of the samples and compared the results to \emph{ab initio} band structure calculations. Our findings indicate that the electrical and thermal magnetotransport in GdPtBi cannot be solely explained by Weyl physics and is strongly influenced by the interaction of both itinerant charge carriers and phonons with localized magnetic Gd-ions and possibly also paramagnetic impurities.Comment: 11 figure

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

Extremely high conductivity observed in the triple point topological metal MoP

Weyl and Dirac fermions have created much attention in condensed matter physics and materials science. Recently, several additional distinct types of fermions have been predicted. Here, we report ultra-high electrical conductivity in MoP at low temperature, which has recently been established as a triple point Fermion material. Here we show that the electrical resistivity is 6 n-ohm cm at 2 K with a large mean free path of 11 microns. de Haas-van Alphen oscillations reveal spin splitting of the Fermi surfaces. In contrast to noble metals with similar conductivity and number of carriers, the magnetoresistance in MoP does not saturate up to 9 T at 2 K. Interestingly, the momentum relaxing time of the electrons is found to be more than 15 times larger than the quantum coherence time. This difference between the scattering scales shows that momentum conserving scattering dominates in MoP at low temperatures.Comment: Updated texts and supplementar

Cation Disorder and Bond Anharmonicity Optimize the Thermoelectric Properties in Kinetically Stabilized Rocksalt AgBiS₂ Nanocrystals

High temperature rocksalt phases of AgBiS₂ and AgBiS_2‑<i>x</i>Se_<i>x</i> (<i>x</i> = 0.05–0.1) have been kinetically stabilized at room temperature in nanocrytals (∼11 nm) by simple solution-based synthesis. Experimental evidence for this derives from variable temperature powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electron diffraction analysis. The band gap of the AgBiS₂ nanocrystals (∼1.0 eV) is blue-shifted by quantum confinement relative to that of the cubic bulk phase of AgBiS₂. Moreover, systematic lower energy shift of the band gap in AgBiS_2‑<i>x</i>Se_<i>x</i> nanocrystals compared to pristine nanocrystalline AgBiS₂ was observed with increasing Se concentration. Existence of fascinating order–disorder type transition in these nanocrystals was evidenced by temperature dependent electrical conductivity, thermopower, and heat capacity measurements. Disordered cation sublattice and nanoscale grain boundaries coupled with strong Bi–S bond anharmonicity allow effective phonon scattering, which leads to minimal lattice thermal conductivity of the nanocrystalline AgBiS₂

Origin of the Order–Disorder Transition and the Associated Anomalous Change of Thermopower in AgBiS₂ Nanocrystals: A Combined Experimental and Theoretical Study

Bulk AgBiS₂ crystallizes in a trigonal crystal structure (space group, <i>P</i>3̅<i>m</i>1) at room temperature, which transforms to a cation disordered rock salt structure (space group, <i>Fm</i>3̅<i>m</i>) at ∼473 K. Surprisingly, at room temperature, a solution-grown nanocrystal of AgBiS₂ crystallizes in a metastable Ag/Bi ordered cubic structure, which transforms to a thermodynamically stable disorded cubic structure at 610 K. Moreover, the order–disorder transition in nanocrystalline AgBiS₂ is associated with an unusual change in thermopower. Here, we shed light on the origin of a order–disorder phase transition and the associated anomalous change of thermopower in AgBiS₂ nanocrystals by using a combined experimental, density functional theory based first-principles calculation and <i>ab initio</i> molecular dynamics simulations. Positron-annilation spectroscopy indicates the presence of higher numbers of Ag vacancies in the nanocrystal compared to that of the bulk cubic counterpart at room temperature. Furthermore, temperature-dependent two-detector coincidence Doppler broadening spectroscopy and Doppler broadening of the annihilation radiation (<i>S</i> parameter) indicate that the Ag vacancy concentration increases abruptly during the order–disorder transition in nanocrystalline AgBiS₂. At high temperature, a Ag atom shuttles between the vacancy and interstitial sites to form a locally disordered cation sublattice in the nanocrystal, which is facilitated by the formation of more Ag vacancies during the phase transition. This process increases the entropy of the system at higher vacancy concentration, which, in turn, results in the unusual rise in thermopower