7,740 research outputs found
Experimental tests of the chiral anomaly magnetoresistance in the Dirac-Weyl semimetals NaBi and GdPtBi
In the Dirac/Weyl semimetal, the chiral anomaly appears as an "axial" current
arising from charge-pumping between the lowest (chiral) Landau levels of the
Weyl nodes, when an electric field is applied parallel to a magnetic field . Evidence for the chiral anomaly was obtained from the longitudinal
magnetoresistance (LMR) in NaBi and GdPtBi. However, current jetting
effects (focussing of the current density ) have raised general concerns
about LMR experiments. Here we implement a litmus test that allows the
intrinsic LMR in NaBi and GdPtBi to be sharply distinguished from pure
current jetting effects (in pure Bi). Current jetting enhances along the
mid-ridge (spine) of the sample while decreasing it at the edge. We measure the
distortion by comparing the local voltage drop at the spine (expressed as the
resistance ) with that at the edge (). In Bi,
sharply increases with but decreases (jetting effects are
dominant). However, in NaBi and GdPtBi, both and
decrease (jetting effects are subdominant). A numerical simulation allows the
jetting distortions to be removed entirely. We find that the intrinsic
longitudinal resistivity in NaBi decreases by a factor of
10.9 between = 0 and 10 T. A second litmus test is obtained from the
parametric plot of the planar angular magnetoresistance. These results
strenghthen considerably the evidence for the intrinsic nature of the
chiral-anomaly induced LMR. We briefly discuss how the squeeze test may be
extended to test ZrTe.Comment: 17 pages, 8 figures, new co-authors added, new Fig. 6a added. In
press, PR
Tunable Unidirectional Sound Propagation through a Sonic-Crystal-Based Acoustic Diode
Nonreciprocal wave propagation typically requires strong nonlinear materials to break time reversal symmetry. Here, we utilized a
sonic-crystal-based acoustic diode that had broken spatial inversion
symmetry and experimentally realized sound unidirectional transmission
in this acoustic diode. These novel phenomena are attributed to
different mode transitions as well as their associated different energy
conversion efficiencies among different diffraction orders at two sides
of the diode. This nonreciprocal sound transmission could be
systematically controlled by simply mechanically rotating the square
rods of the sonic crystal. Different from nonreciprocity due to the
nonlinear acoustic effect and broken time reversal symmetry, this new
model leads to a one-way effect with higher efficiency, broader
bandwidth, and much less power consumption, showing promising
applications in various sound devices
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