594 research outputs found
Magnetic interactions and spin dynamics in the bond-disordered pyrochlore fluoride NaCaCoF
We report high-frequency/high-field electron spin resonance (ESR) and
high-field magnetization studies on single crystals of the bond-disordered
pyrochlore NaCaCoF. Frequency- and temperature-dependent ESR
investigations above the freezing temperature K reveal the
coexistence of two distinct magnetic phases. A cooperative paramagnetic phase,
evidenced by a gapless excitation mode, is found as well as a spin-glass phase
developing below 20 K which is associated with a gapped low-energy excitation.
Effective -factors close to 2 are obtained for both modes in line with
pulsed high-field magnetization measurements which show an unsaturated
isotropic behavior up to 58 T at 2 K. In order to describe the field-dependent
magnetization in high magnetic fields, we propose an empirical model accounting
for highly anisotropic ionic -tensors expected for this material and taking
into account the strongly competing interactions between the spins which lead
to a frustrated ground state. As a detailed quantitative relation between
effective -factors as determined from ESR and the local -tensors obtained
by neutron scattering [Ross et al., Phys. Rev. B 93, 014433 (2016)] is still
sought after, our work motivates further theoretical investigations of the
low-energy excitations in bond-disordered pyrochlores.Comment: 9 pages, 6 figure
Imaging electronic states on topological semimetals using scanning tunneling microscopy
Following the intense studies on topological insulators, significant efforts
have recently been devoted to the search for gapless topological systems. These
materials not only broaden the topological classification of matter but also
provide a condensed matter realization of various relativistic particles and
phenomena previously discussed mainly in high energy physics. Weyl semimetals
host massless, chiral, low-energy excitations in the bulk electronic band
structure, whereas a symmetry protected pair of Weyl fermions gives rise to
massless Dirac fermions. We employed scanning tunneling microscopy/spectroscopy
to explore the behavior of electronic states both on the surface and in the
bulk of topological semimetal phases. By mapping the quasiparticle interference
and emerging Landau levels at high magnetic field in Dirac semimetals
CdAs and NaBi, we observed extended Dirac-like bulk electronic
bands. Quasiparticle interference imaged on Weyl semimetal TaAs demonstrated
the predicted momentum dependent delocalization of Fermi arc surface states in
the vicinity of the surface-projected Weyl nodes
Classical dilute relativistic plasma in equilibrium. Two-particle distribution function
We consider here a dilute hot plasma which is homogeneous and in equilibrium in the framework of classical relativistic statistical mechanics as formulated recently by the authors. No external fields are present. The two-particle distribution function of the plasma is calculated for any temperature. This distribution will be physically significant, as long as the creation of pairs can be neglected. Several limits which apply at low or high temperatures are discussed. Comparison with previous work from several authors is made
Determination of the Michel Parameters rho, xi, and delta in tau-Lepton Decays with tau --> rho nu Tags
Using the ARGUS detector at the storage ring DORIS II, we have
measured the Michel parameters , , and for
decays in -pair events produced at
center of mass energies in the region of the resonances. Using
as spin analyzing tags, we find , , , , and . In addition, we report
the combined ARGUS results on , , and using this work
und previous measurements.Comment: 10 pages, well formatted postscript can be found at
http://pktw06.phy.tu-dresden.de/iktp/pub/desy97-194.p
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