1,835 research outputs found
Quantum oscillations and a non-trivial Berry phase in the noncentrosymmetric superconductor BiPd
We report the measurements of de Haas-van Alphen (dHvA) oscillations in the
noncentrosymmetric superconductor BiPd. Several pieces of a complex multi-sheet
Fermi surface are identified, including a small pocket (frequency 40 T) which
is three dimensional and anisotropic. From the temperature dependence of the
amplitude of the oscillations, the cyclotron effective mass is (
0.1) . Further analysis showed a non-trivial -Berry phase is
associated with the 40 T pocket, which strongly supports the presence of
topological states in bulk BiPd and may result in topological superconductivity
due to the proximity coupling to other bands.Comment: 5 pages, 3 figure
Discovery of Griffiths phase in itinerant magnetic semiconductor Fe_{1-x}Co_xS_2
Critical points that can be suppressed to zero temperature are interesting
because quantum fluctuations have been shown to dramatically alter electron gas
properties. Here, the metal formed by Co doping the paramagnetic insulator
FeS, FeCoS, is demonstrated to order ferromagnetically at
where we observe unusual transport, magnetic, and
thermodynamic properties. We show that this magnetic semiconductor undergoes a
percolative magnetic transition with distinct similarities to the Griffiths
phase, including singular behavior at and zero temperature.Comment: 10 pages, 4 figure
ASSET ALLOCATION AND ANNUITY-PURCHASE STRATEGIES TO MINIMIZE THE PROBABILITY OF FINANCIAL RUIN
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75685/1/j.1467-9965.2006.00288.x.pd
Interdisciplinarity and insularity in the diffusion of knowledge: an analysis of disciplinary boundaries between philosophy of science and the sciences
Two fundamentally different perspectives on knowledge diffusion dominate debates about academic disciplines. On the one hand, critics of disciplinary research and education have argued that disciplines are isolated silos, within which specialists pursue inward-looking and increasingly narrow research agendas. On the other hand, critics of the silo argument have demonstrated that researchers constantly import and export ideas across disciplinary boundaries. These perspectives have different implications for how knowledge diffuses, how intellectuals gain and lose status within their disciplines, and how intellectual reputations evolve within and across disciplines. We argue that highly general claims about the nature of disciplinary boundaries are counterproductive, and that research on the nature of specific disciplinary boundaries is more useful. To that end, this paper uses a novel publication and citation network dataset and statistical models of citation networks to test hypotheses about the boundaries between philosophy of science and 11 disciplinary clusters. Specifically, we test hypotheses about whether engaging with and being cited by scientific communities outside philosophy of science has an impact on one’s position within philosophy of science. Our results suggest that philosophers of science produce interdisciplinary scholarship, but they tend not to cite work by other philosophers when it is published in journals outside of their discipline. Furthermore, net of other factors, receiving citations from other disciplines has no meaningful impact—positive or negative—on citations within philosophy of science. We conclude by considering this evidence for simultaneous interdisciplinarity and insularity in terms of scientific trading theory and other work on disciplinary boundaries and communication
Fermi surface, possible unconventional fermions, and unusually robust resistive critical fields in the chiral-structured superconductor AuBe
The noncentrosymmetric superconductor (NCS) AuBe is investigated using a
variety of thermodynamic and resistive probes in magnetic fields of up to 65~T
and temperatures down to 0.3~K. Despite the polycrystalline nature of the
samples, the observation of a complex series of de Haas-van Alphen (dHvA)
oscillations has allowed the calculated bandstructure for AuBe to be validated.
This permits a variety of BCS parameters describing the superconductivity to be
estimated, despite the complexity of the measured Fermi surface. In addition,
AuBe displays a nonstandard field dependence of the phase of dHvA oscillations
associated with a band thought to host unconventional fermions in this chiral
lattice. This result demonstrates the power of the dHvA effect to establish the
properties of a single band despite the presence of other electronic bands with
a larger density of states, even in polycrystalline samples. In common with
several other NCSs, we find that the resistive upper critical field exceeds
that measured by heat capacity and magnetization by a considerable factor. We
suggest that our data exclude mechanisms for such an effect associated with
disorder, implying that topologically protected superconducting surface states
may be involved
Magnetic and thermodynamic properties of cobalt doped iron pyrite: Griffiths Phase in a magnetic semiconductor
Doping of the band insulator FeS with Co on the Fe site introduces a
small density of itinerant carriers and magnetic moments. The lattice constant,
AC and DC magnetic susceptibility, magnetization, and specific heat have been
measured over the range of Co concentration. The variation of
the AC susceptibility with hydrostatic pressure has also been measured in a
small number of our samples. All of these quantities show systematic variation
with including a paramagnetic to disordered ferromagnetic transition at
. A detailed analysis of the changes with temperature and
magnetic field reveal small power law dependencies at low temperatures for
samples near the critical concentration for magnetism, and just above the Curie
temperature at higher . In addition, the magnetic susceptibility and
specific heat are non-analytic around H=0 displaying an extraordinarily sharp
field dependence in this same temperature range. We interpret this behavior as
due to the formation of Griffiths phases that result from the quenched disorder
inherent in a doped semiconductor.Comment: 22 pages including 27 figure
Extreme High-Field Superconductivity in Thin Re Films
We report the high-field superconducting properties of thin, disordered Re
films via magneto-transport and tunneling density of states measurements. Films
with thicknesses in the range of 9 nm to 3 nm had normal state sheet
resistances of 0.2 k to 1 k and corresponding
transition temperatures in the range of 6 K to 3 K. Tunneling spectra were
consistent with those of a moderate coupling BCS superconductor.
Notwithstanding these unremarkable superconducting properties, the films
exhibited an extraordinarily high upper critical field. We estimate their
zero-temperature to be more than twice the Pauli limit. Indeed, in 6
nm samples the estimated reduced critical field 5.6 T/K is
among the highest reported for any elemental superconductor. Although the sheet
resistances of the films were well below the quantum resistance ,
their 's approached the theoretical upper limit of a strongly
disordered superconductor for which .Comment: 12 pages, 10 figure
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