7 research outputs found
Giant magnetic quantum oscillations in the thermal conductivity of TaAs: Indications of chiral zero sound
Charge transport of topological semimetals has been in the focus of intensive
investigations because of their non-trivial band topology. Heat transport of
these materials, on the other hand, is largely unexplored and remains elusive.
Here we report on an observation of unprecedented, giant magnetic quantum
oscillations of thermal conductivity in the prototypical Weyl semimetal TaAs.
The oscillations are antiphase with the quantum oscillating electronic density
of states of a Weyl pocket, and their amplitudes amount to two orders of
magnitude of the estimation based on the Wiedemann-Franz law. Our analyses show
that all the conventional heat-transport mechanisms through diffusions of
propagating electrons, phonons and electron-hole bipolar excitations, are far
inadequate to account for these phenomena. Taking further experimental facts
that the parallel field configuration favors much higher magneto-thermal
conductivity, we propose that the newly proposed chiral zero sound provides a
reasonable explanation to these exotic phenomena. More work focusing on other
topological semimetals along the same line is badly called for.Comment: 15 pages, 5 figure
Giant Low-Field Cryogenic Magnetocaloric Effect in a Polycrystalline EuB<sub>4</sub>O<sub>7</sub> Compound
To deal with the shortage and high price of helium-3
resources,
adiabatic demagnetization refrigeration technology as an alternative
to helium-3-based refrigeration technology has received much attention.
The magnetism and ultralow-temperature magnetocaloric effect (MCE)
of the EuB4O7 compound have been investigated.
The results of magnetic and quasi-adiabatic demagnetization measurements
suggest the absence of a magnetic order above 0.4 K for EuB4O7. The dipolar interaction between the nearest-neighbor
Eu atoms has a characteristic energy of about 800 mK, which may induce
a large MCE. The maximum magnetic entropy change reaches 22.8, 36.2,
and 47.6 J·kg–1 K–1 at μ0H = 0–10 kOe, 0–20 kOe, and
0–50 kOe, respectively. Measurements by a quasi-adiabatic demagnetization
device show that the lowest temperature achievable (289 mK) for polycrystalline
EuB4O7 is lower than that (362 mK) for the commercial
refrigerant Gd3Ga5O12 (GGG) single
crystals. The hold time is more than 70 min below 700 mK, with an
environment temperature of 2 K, proving that EuB4O7 exhibits superior cooling performance