Diffusive-like effects and possible non trivial local topology on the half-Heusler YPdBi compound

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORFINEP - FINANCIADORA DE ESTUDOS E PROJETOSThe non-ambiguous experimental identification of topological states of matter is one of the main interesting problems regarding this new quantum state of matter. In particular, the half-Heusler family RMT (R = rare-earth, T = Pd, Pt or Au and T = Bi, Sb, Pb or Sn) could be a useful platform to explore these states due to their cubic symmetry and the topological properties tunable via their unit cell volume and/or the nuclear charges of the M and T atoms. In this work, we report electron spin resonance (ESR) and complementary macroscopic measurements in the Nd3+-doped putative topologically trivial semimetal YPdBi. Following the Nd3+ ESR lineshape as a function of microwave power, size of the particle and temperature, we have been able to observe an evolution from a Dysonian lineshape to a diffusive-like lineshape. Furthermore, the Nd3+ ESR intensity saturation is concentration dependent, which could be due to a phonon-bottleneck process. Comparing these results with the Nd3+-doped YPtBi, we discuss a possible scenario in which the Nd3+ ions could locally tune the topological properties of the system.8516FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORFINEP - FINANCIADORA DE ESTUDOS E PROJETOS2013/17427-72012/04870-72006/60440-02009/09247-32010/11949-32011/01564-02011/23650-52012/05903-6442230/2014-1304649/2013-9sem informaçãosem informação62. Annual Conference on Magnetism and Magnetic Materials (MMM)2017Pittsburgh, PAIEEE Magnetics SocietyAIP Publishin

Anharmonic rattling vibrations effects in the ESR of Er3+ doped SmB6 Kondo insulator

FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFINANCIADORA DE ESTUDOS E PROJETOS - FINEPCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESWe report X-band Electron Spin Resonance (ESR) experiments on ≈0.2% and ≈0.7 % Er3+ doped SmB6 at low temperature (4 K - 40 K). The crystal field ground state of Er3+ in SmB6 is a Γ8 quartet with a nearby Γ6 excited doublet. The angular dependence of the resonances is not consistent with transitions between pure cubic crystal field states. The data were interpreted in terms of a dynamic Jahn-Teller (JT) effect by a coupling to Γ3 vibrational modes, which we propose to originate from the rattling of the small Er3+ ions in the large SmB6 cage. Our data show an anisotropic pair of E and E' resonances at g ≈4.4 and two nearly isotropic signals at g ≈5.8, one intense and narrow (A vibrational mode) and the other broad and faint, which we attribute to Er3+ ions at lattice sites which are strongly affected by strain, defects and/or extrinsic Al impurities that inhibits the JT effects. Our results are in general consistent with those previously reported by Sturm et al. In addition to the angular dependence of the lines, we discuss the intensities, g-values and the linewidths of the Er3+ transitions as a function of temperature. © 2017 Author(s).We report X-band Electron Spin Resonance (ESR) experiments on ≈0.2% and ≈0.7 % Er3+ doped SmB6 at low temperature (4 K - 40 K). The crystal field ground state of Er3+ in SmB6 is a Γ8 quartet with a nearby Γ6 excited doublet. The angular dependence of the resonances is not consistent with transitions between pure cubic crystal field states. The data were interpreted in terms of a dynamic Jahn-Teller (JT) effect by a coupling to Γ3 vibrational modes, which we propose to originate from the rattling of the small Er3+ ions in the large SmB6 cage. Our data show an anisotropic pair of E and E' resonances at g ≈4.4 and two nearly isotropic signals at g ≈5.8, one intense and narrow (A vibrational mode) and the other broad and faint, which we attribute to Er3+ ions at lattice sites which are strongly affected by strain, defects and/or extrinsic Al impurities that inhibits the JT effects. Our results are in general consistent with those previously reported by Sturm et al. In addition to the angular dependence of the lines, we discuss the intensities, g-values and the linewidths of the Er3+ transitions as a function of temperature.7515FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFINANCIADORA DE ESTUDOS E PROJETOS - FINEPCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFINANCIADORA DE ESTUDOS E PROJETOS - FINEPCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES2011/01564-02011/19924-22012/04870-72012/05903-62013/17427-7Sem informaçãoSem informaçãoSem informação61. Annual Conference on Magnetism and Magnetic Materials31 de Outubro a 4 de Novembro de 2016New Orleans, LAAmerican Institute of Physics PublishingIEEE Magnetics SocietyThis work was supported by the auspices of FAPESP (Grant Nos. 2011/01564-0, 2012/04870-7, 2012/05903-6, 2011/19924-2, 2013/17427-7), CNPq, FINEP and CAPES (Brazil). ZF is supported by the US NSF (Grant No. DMR-0801253) and PS by the US DOE (Grant No. DE-FG02-98ER45707). Work at Los Alamos National Laboratory (LANL) was performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering. PFSR acknowledges a Director's Postdoctoral Fellowship through the LANL LDRD program

Electron spin resonance of GD3+ in three dimensional topological insulator BI2SE3

Bi2Se3 has been claimed to be a three dimensional topological insulator (TI) with topologically protected metallic surface states with exotic properties. We have performed electron spin resonance (ESR) measurements on Gd3+ doped (x approximate to 0.01) Bi2Se3 single crystal grown from stoichiometric melt. For the studied crystals, our preliminary results revealed a partly resolved Gd3+ fine structure spectrum with Dysonian (metallic character) lines. At room temperature, the central line has a g approximate to 1.98, a linewidth Delta H approximate to 95 G and the spectra have a overall splitting of roughly 1300 Oe. As the temperature is decreased, the Gd3+ ESR Delta H of the central line presents a very small Korringa-like behavior b = Delta H/Delta T approximate to 0.013 Oe/K and nearly T-independent g-value. However, for T less than or similar to 40 K, Delta H shows a stronger narrowing effect evolving to Korringa-like behavior (b approximate to 0.15 Oe/K) for T less than or similar to 30 K. Concomitantly with the change in Delta H behavior, the Gd3+ central line g value starts to decrease reaching a value of 1.976 at T less than or similar to 4.2 K. The ESR results are discussed in terms of possible effects of protected topological surface states enlightened by complementary data from macroscopic measurements592International Conference on Strongly Correlated Electron Systems (SCES)2014-07FrançaUniv Grenoble, Grenobl

Orbitally defined field-induced electronic state in a Kondo lattice

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCeRhIn5 is a Kondo-lattice prototype in which a magnetic field B* similar or equal to 31 T induces an abrupt Fermi-surface (FS) reconstruction and pronounced in-plane electrical transport anisotropy all within its antiferromagnetic state. Though the antif1011616CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP140837/2013-2307668/2015-0309483/2018-22012/04870-72012/05903-62017/10581-1We acknowledge enlightening discussions with F. Ronning, P. F. S. Rosa, M. Smidman, L. Jiao, H. Q. Yuan, D. J. Garcia, C. Rettori, and N. Curro. Work at State University of Campinas (Unicamp) was supported by CNPq (Grants No. 140837/2013-2, No. 307668/20

Crystal-field effects in Er3+- and Yb3+-doped hexagonal NaYF4 nanoparticles

COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPSince the up-conversion phenomenon in rare-earths (REs) doped NaYF4 is strongly affected by the crystal electric field (CF), determining the CF parameters, wave functions, and scheme of the energy levels of the RE J multiplets could be crucial to improve and tune the up-conversion efficiency. In this work, the temperature and magnetic field dependent magnetization of NaY1-x[Er(Yb)](x)F-4 hexagonal nanoparticles (NPs) is reported. The data were best fit using the appropriated CF Hamiltonian for the J = 15/2 (J = 7/2) ground state multiplet of Er3+ (Yb3+) ions. The B-2(0), B-4(0), B-6(0), and B-6(6) CF parameters were considered in the Hamiltonian for RE ions located at the hexagonal C-3h point symmetry site of the NaYF4 host lattice. These results allowed us to predict an overall CF splitting of similar to 214 (similar to 356 K) for Er3+ (Yb3+) and the wave functions and their energy levels for the J = 15/2 (J = 7/2) ground state multiplet which are in good agreement with the low temperature electron spin resonance experiments. Besides, our measurements allowed us to calculate all the excited CF J multiplets that yield to a good estimation of the up-conversion light emission linewidth. The nonlinear optical light emission of the studied NaY1-x[Er(Yb)](x)F-4 hexagonal NPs was also compared with the most efficient up-conversion codoped NaY1-x-yErxYbyF4 hexagonal NPs.961617COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPSem informaçãoSem informação2011/19924-22012/04870-72012/05903-62015/23882-4This work was supported and performed under the auspices of the Brazilian agencies CAPES, CNPq, and FAPESP through Grants No. 2011/19924-2, No. 2012/04870-7, No. 2012/05903-6, and No. 2015/23882-4. The SEM data were acquired in the LNNano at the Centro Nacional de Pesquisa em Energia e Materiais (CNPEM) in Campinas-SP, Brazil. D.J.G. acknowledges support from FONCyT (PICT 2012-1069)

Senegal: Presidential elections 2019 - The shining example of democratic transition immersed in muddy power-politics

Whereas Senegal has long been sold as a showcase of democracy in Africa, including peaceful political alternance, things apparently changed fundamentally with the Senegalese presidentials of 2019 that brought new configurations. One of the major issues was political transhumance that has been elevated to the rank of religion in defiance of morality. It threatened political stability and peace. In response, social networks of predominantly young activists, created in 2011 in the aftermath of the Arab Spring focused on grass-roots advocacy with the electorate on good governance and democracy. They proposed a break with a political system that they consider as neo-colonialist. Moreover, Senegal’s justice is frequently accused to be biased, and the servility of the Constitutional Council which is in the first place an electoral court has often been denounced

Diffusive-like effects and possible non trivial local topology on the half-Heusler YPdBi compound

The non-ambiguous experimental identification of topological states of matter is one of the main interesting problems regarding this new quantum state of matter. In particular, the half-Heusler family RMT (R = rare-earth, T = Pd, Pt or Au and T = Bi, Sb, Pb or Sn) could be a useful platform to explore these states due to their cubic symmetry and the topological properties tunable via their unit cell volume and/or the nuclear charges of the M and T atoms. In this work, we report electron spin resonance (ESR) and complementary macroscopic measurements in the Nd3 + -doped putative topologically trivial semimetal YPdBi. Following the Nd3 + ESR lineshape as a function of microwave power, size of the particle and temperature, we have been able to observe an evolution from a Dysonian lineshape to a diffusive-like lineshape. Furthermore, the Nd3 + ESR intensity saturation is concentration dependent, which could be due to a phonon-bottleneck process. Comparing these results with the Nd3 + -doped YPtBi, we discuss a possible scenario in which the Nd3 + ions could locally tune the topological properties of the system

Crystalline electric field study in a putative topologically trivial rare-earth doped YPdBi compound

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORFINEP - FINANCIADORA DE ESTUDOS E PROJETOSTopological states of matter have attracted a lot of attention recently due to their intriguing physical properties and potential applications. In particular, the family of half-Heusler compounds RMT (R = rare earth, M = Pt, Pd or Au, and T. Bi, Sb, Pb or Sn) has been predicted to display tunable topological properties via their cubic unit cell volume and/or the charges of the M and T atoms. In this work, we report electron spin resonance (ESR), along with complementary macroscopic experiments, in the putative topologically trivial rare-earth doped (Gd, Nd and Er) YPdBi. From magnetic susceptibility data analysis constrained by ESR results, we were able to extract the fourth (A(4)) and sixth (A(6)) order crystal field parameters (CFP) for YPdBi and compared them with those already reported to YPtBi, which is known as a topologically non-trivial compound. We observed that the sign of the CFP changes systematically from YPdBi to YPtBi, possibly due to the inversion of the valence and conduction bands at the Fermi level. The enhanced spin-orbit coupling in YPtBi, when compared to YPdBi, induces the band inversion that drives the system to a non-trivial topological state. This band inversion likely has an effect on the effective charges surrounding the magnetic dopants that are probed by the CFP.314617FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORFINEP - FINANCIADORA DE ESTUDOS E PROJETOS2006/60440-02009/09247-32010/11949-32011/01564-02011/23650-52012/04870-72012/05903-62013/17427-72017/10581-12018/11364-7308260/2012-0304649/2013-9442230/2014-1141026/2017-0Sem informaçãoSem informaçã