381 research outputs found
Large magnetoresistance in the antiferromagnetic semi-metal NdSb
There has been considerable interest in topological semi-metals that exhibit
extreme magnetoresistance (XMR). These have included materials lacking
inversion symmetry such as TaAs, as well Dirac semi-metals such as Cd3As2.
However, it was reported recently that LaSb and LaBi also exhibit XMR, even
though the rock-salt structure of these materials has inversion symmetry, and
the band-structure calculations do not show a Dirac dispersion in the bulk.
Here, we present magnetoresistance and specific heat measurements on NdSb,
which is isostructural with LaSb. NdSb has an antiferromagnetic groundstate,
and in analogy with the lanthanum monopnictides, is expected to be a
topologically non-trivial semi-metal. We show that NdSb has an XMR of 10^4 %,
even within the AFM state, illustrating that XMR can occur independently of the
absence of time reversal symmetry breaking in zero magnetic field. The
persistence of XMR in a magnetic system offers promise of new functionality
when combining topological matter with electronic correlations. We also find
that in an applied magnetic field below the Neel temperature there is a first
order transition, consistent with evidence from previous neutron scattering
work.Comment: 5 pages, 6 figure
Surface state reconstruction in ion-damaged SmB_6
We have used ion-irradiation to damage the (001) surfaces of SmB_6 single
crystals to varying depths, and have measured the resistivity as a function of
temperature for each depth of damage. We observe a reduction in the residual
resistivity with increasing depth of damage. Our data are consistent with a
model in which the surface state is not destroyed by the ion-irradiation, but
instead the damaged layer is poorly conducting and the initial surface state is
reconstructed below the damage. This behavior is consistent with a surface
state that is topologically protected.Comment: 5 pages, 3 figure
Trends in Kaposi's sarcoma-associated Herpesvirus antibodies prior to the development of HIV-associated Kaposi's sarcoma: a nested case-control study
HIV-associated Kaposi's sarcoma (KS) is a public health challenge in sub-Saharan Africa since both the causative agent, Kaposi's sarcoma associated-herpesvirus (KSHV), and the major risk factor, HIV, are prevalent. In a nested case-control study within a long-standing clinical cohort in rural Uganda, we used stored sera to examine the evolution of antibody titres against the KSHV antigens K8.1 and latency-associated nuclear antigen (LANA) among 30 HIV-infected subjects who subsequently developed HIV-related KS (cases) and among 108 matched HIV/KSHV coinfected controls who did not develop KS. Throughout the 6 years prior to diagnosis, antibody titres to K8.1 and LANA were significantly higher among cases than controls (p < 0.0001), and titres increased prior to diagnosis in the cases. K8.1 titres differed more between KS cases and controls, compared to LANA titres. These differences in titre between cases and controls suggest a role for lytic viral replication in the pathogenesis of HIV-related KS in this setting
Competing magnetic orders in the superconducting state of Nd-doped CeRhIn under pressure
Applied pressure drives the heavy-fermion antiferromagnet CeRhIn
towards a quantum critical point that becomes hidden by a dome of
unconventional superconductivity. Magnetic fields suppress this superconducting
dome, unveiling the quantum phase transition of local character. Here, we show
that magnetic substitution at the Ce site in CeRhIn, either by Nd
or Gd, induces a zero-field magnetic instability inside the superconducting
state. This magnetic state not only should have a different ordering vector
than the high-field local-moment magnetic state, but it also competes with the
latter, suggesting that a spin-density-wave phase is stabilized in zero field
by Nd and Gd impurities - similarly to the case of
CeNdCoIn. Supported by model calculations, we attribute
this spin-density wave instability to a magnetic-impurity driven condensation
of the spin excitons that form inside the unconventional superconducting state
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