61 research outputs found
The Anomalous Hall effect in re-entrant AuFe alloys and the real space Berry phase
The Hall effect has been studied in a series of AuFe samples in the
re-entrant concentration range, as well as in the spin glass range. The data
demonstrate that the degree of canting of the local spins strongly modifies the
anomalous Hall effect, in agreement with theoretical predictions associating
canting, chirality and a real space Berry phase. The canonical parametrization
of the Hall signal for magnetic conductors becomes inappropriate when local
spins are canted.Comment: 4 pages, 1 eps figur
Magnetoelectric effects in an organo-metallic quantum magnet
We observe a bilinear magnetic field-induced electric polarization of 50 in single crystals of NiCl-4SC(NH) (DTN). DTN forms a
tetragonal structure that breaks inversion symmetry, with the highly polar
thiourea molecules all tilted in the same direction along the c-axis.
Application of a magnetic field between 2 and 12 T induces canted
antiferromagnetism of the Ni spins and the resulting magnetization closely
tracks the electric polarization. We speculate that the Ni magnetic forces
acting on the soft organic lattice can create significant distortions and
modify the angles of the thiourea molecules, thereby creating a magnetoelectric
effect. This is an example of how magnetoelectric effects can be constructed in
organo-metallic single crystals by combining magnetic ions with electrically
polar organic elements.Comment: 3 pages, 3 figure
Magnetic Breakdown in the electron-doped cuprate superconductor NdCeCuO: the reconstructed Fermi surface survives in the strongly overdoped regime
We report on semiclassical angle-dependent magnetoresistance oscillations
(AMRO) and the Shubnikov-de Haas effect in the electron-overdoped cuprate
superconductor NdCeCuO. Our data provide convincing evidence
for magnetic breakdown in the system. This shows that a reconstructed
multiply-connected Fermi surface persists, at least at strong magnetic fields,
up to the highest doping level of the superconducting regime. Our results
suggest an intimate relation between translational symmetry breaking and the
superconducting pairing in the electron-doped cuprate superconductors.Comment: 5 pages, 4 figures, submitted to PR
Análise de Transiçao Resistiva e da irreversibilidade magnètica no superconductor YBACUO texturizado
Os supercondutores de alta temperatura crítica, em especial os granulares,
apresentam uma transição resistiva que ocorre em duas etapas: a uma temperatura
acima da temperatura crítica de transição Tc0, chamada de supercondutividade
intragranular e a uma temperatura mais baixa onde ocorre a supercondutividade em
toda a amostra, chamada de supercondutividade intergranular. Em Tc0 ocorre à
ativação das ligações fracas e uma ordem de longo alcance é obtida, neste
momento, a resistência elétrica é nula em toda amostra.
Nos supercondutores de alta temperatura crítica, a linha de irreversibilidade
magnética divide o estado misto do plano H-T em duas regiões: reversível e
irreversível. Na região reversível todo o transporte elétrico sofre dissipação devido
aos efeitos da dinâmica de fluxo magnético no supercondutor. Na região irreversível
todo transporte de corrente elétrica é permitido.
Em supercondutores granulares, as medidas de irreversibilidade magnética e
resistividade nula não dependem das mesmas partes da amostra. Enquanto, a
resistência elétrica depende de um arranjo de grãos que atravessam toda a amostra
a irreversibilidade depende de clusters de grãos bem acoplados. Devido a isso, as
medidas de resistência nula devem estar em pontos abaixo da linha de
irreversibilidade magnética.
O objetivo deste trabalho é analisar as medidas de transporte elétrico e
magnetização e correlacionar às linhas de resistência nula e as linhas de
irreversibilidade magnética, em diferentes orientações de campo-corrente, para uma
amostra com a adição de 30% da fase Y211 (Y2BaCuO5) e comparar os dados
obtidos com uma amostra na qual foram adicionados 17% desta mesma fase.Postprint (published version
The chiral Anomalous Hall effect in re-entrant AuFe alloys
The Hall effect has been studied in a series of AuFe samples in the
re-entrant concentration range, as well as in part of the spin glass range. An
anomalous Hall contribution linked to the tilting of the local spins can be
identified, confirming theoretical predictions of a novel topological Hall term
induced when chirality is present. This effect can be understood in terms of
Aharonov-Bohm-like intrinsic current loops arising from successive scatterings
by canted local spins. The experimental measurements indicate that the chiral
signal persists, meaning scattering within the nanoscopic loops remains
coherent, up to temperatures of the order of 150 K.Comment: 7 pages, 11 eps figures Published version. Minor change
Anisotropic Dirac fermions in a Bi square net of SrMnBi2
We report the highly anisotropic Dirac fermions in a Bi square net of
SrMnBi2, based on a first principle calculation, angle resolved photoemission
spectroscopy, and quantum oscillations for high-quality single crystals. We
found that the Dirac dispersion is generally induced in the (SrBi)+ layer
containing a double-sized Bi square net. In contrast to the commonly observed
isotropic Dirac cone, the Dirac cone in SrMnBi2 is highly anisotropic with a
large momentum-dependent disparity of Fermi velocities of ~ 8. These findings
demonstrate that a Bi square net, a common building block of various layered
pnictides, provide a new platform that hosts highly anisotropic Dirac fermions.Comment: 5 pages, 4 figure
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