36 research outputs found
Berry curvature unravelled by the Nernst effect in MnGe
The discovery of topological quantum materials represents a striking
innovation in modern condensed matter physics with remarkable fundamental and
technological implications. Their classification has been recently extended to
topological Weyl semimetals, i.e., solid state systems which exhibit the
elusive Weyl fermions as low-energy excitations. Here we show that the Nernst
effect can be exploited as a sensitive probe for determining key parameters of
the Weyl physics, applying it to the non-collinear antiferromagnet MnGe.
This compound exhibits anomalous thermoelectric transport due to enhanced Berry
curvature from Weyl points located extremely close to the Fermi level. We
establish from our data a direct measure of the Berry curvature at the Fermi
level and, using a minimal model of a Weyl semimetal, extract for the first
time the Weyl point energy and their distance in momentum-space
Ga substitution as an effective variation of Mn-Tb coupling in multiferroic TbMnO3
Ga for Mn substitution in multiferroic TbMnO has been performed in
order to study the influence of Mn-magnetic ordering on the Tb-magnetic
sublattice. Complete characterization of TbMnGaO ( = 0,
0.04, 0.1) samples, including magnetization, impedance spectroscopy, and x-ray
resonant scattering and neutron diffraction on powder and single crystals has
been carried out. We found that keeping the same crystal structure for all
compositions, Ga for Mn substitution leads to the linear decrease of and , reflecting the reduction of the exchange
interactions strength and the change of the Mn-O-Mn bond
angles. At the same time, a strong suppression of both the induced and the
separate Tb-magnetic ordering has been observed. This behavior unambiguously
prove that the exchange fields have a strong influence on the
Tb-magnetic ordering in the full temperature range below
and actually stabilize the Tb-magnetic ground state.Comment: 9 pages, 8 figure
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Synthesis and Characterization of Oxide Chloride Sr2VO3Cl, a Layered S = 1 Compound
The mixed-anion compound with composition Sr2VO3Cl has been synthesized for the first time, using the conventional high-temperature solid-state synthesis technique in a closed silica ampule under inert conditions. This compound belongs to the known Sr2TmO3Cl (Tm = Sc, Mn, Fe, Co, Ni) family, but with Tm = V. All homologues within this family can be described with the tetragonal space group P4/nmm (No. 129); from a Rietveld refinement of powder X-ray diffraction data on the Tm = V homologue, the unit cell parameters were determined to a = 3.95974(8) and c = 14.0660(4) Å, and the atomic parameters in the crystal structure could be estimated. The synthesized powder is black, implying that the compound is a semiconductor. The magnetic investigations suggest that Sr2VO3Cl is a paramagnet at high temperatures, exhibiting a μeff = 2.0 μB V-1 and antiferromagnetic (AFM) interactions between the magnetic vanadium spins (θCW = −50 K), in line with the V-O-V advantageous super-exchange paths in the V-O layers. Specific heat capacity studies indicate two small anomalies around 5 and 35 K, which however are not associated with long-range magnetic ordering. 35Cl ss-NMR investigations suggest a slow spin freezing below 4.2 K resulting in a glassy-like spin ground state
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Phonon thermal transport shaped by strong spin-phonon scattering in a Kitaev material Na2Co2TeO6
The report of a half-quantized thermal Hall effect and oscillatory structures in the magnetothermal conductivity in the Kitaev material α-RuCl3 have sparked a strong debate on whether it is generated by Majorana fermion edge currents, spinon Fermi surface, or whether other more conventional mechanisms are at its origin. Here, we report low temperature thermal conductivity (κ) of another candidate Kitaev material, Na2Co2TeO6. The application of a magnetic field (B) along different principal axes of the crystal reveals a strong directional-dependent B impact on κ, while no evidence for mobile quasiparticles except phonons can be concluded at any field. Instead, severely scattered phonon transport prevails across the B−T phase diagram, revealing cascades of phase transitions for all B directions. Our results thus cast doubt on recent proposals for significant itinerant magnetic excitations in Na2Co2TeO6, and emphasize the importance of discriminating true spin liquid transport properties from scattered phonons in candidate materials
Phonon thermal transport shaped by strong spin-phonon scattering in a Kitaev material NaCoTeO
The recent report of a half-quantized thermal Hall effect in the Kitaev
material -RuCl has sparked a strong debate on whether it is
generated by Majorana fermion edge currents or whether other more conventional
mechanisms involving magnons or phonons are at its origin. A more direct
evidence for Majorana fermions which could be expected to arise from a
contribution to the longitudinal heat conductivity at
is elusive due to a very complex magnetic field dependence of
. Here, we report very low temperature (below 1~K) thermal
conductivity () of another candidate Kitaev material,
NaCoTeO. The application of a magnetic field along different
principal axes of the crystal reveals a strong directional-dependent
magnetic-field () impact on . We show that no evidence for
mobile quasiparticles except phonons can be concluded at any field from 0~T to
the field polarized state. In particular, severely scattered phonon transport
is observed across the phase diagram, which is attributed to prominent
magnetic fluctuations. Cascades of phase transitions are uncovered for all directions by probing the strength of magnetic fluctuations via a precise
record of (). Our results thus rule out recent proposals for
itinerant magnetic excitations in NaCoTeO, and emphasise the
importance of discriminating true spin liquid transport properties from
scattered phonons in candidate materials