2,624 research outputs found
Field-tuned quantum critical point of antiferromagnetic metals
A magnetic field applied to a three-dimensional antiferromagnetic metal can
destroy the long-range order and thereby induce a quantum critical point. Such
field-induced quantum critical behavior is the focus of many recent
experiments. We investigate theoretically the quantum critical behavior of
clean antiferromagnetic metals subject to a static, spatially uniform external
magnetic field. The external field does not only suppress (or induce in some
systems) antiferromagnetism but also influences the dynamics of the order
parameter by inducing spin precession. This leads to an exactly marginal
correction to spin-fluctuation theory. We investigate how the interplay of
precession and damping determines the specific heat, magnetization,
magnetocaloric effect, susceptibility and scattering rates. We point out that
the precession can change the sign of the leading \sqrt{T} correction to the
specific heat coefficient c(T)/T and can induce a characteristic maximum in
c(T)/T for certain parameters. We argue that the susceptibility \chi =\partial
M/\partial B is the thermodynamic quantity which shows the most significant
change upon approaching the quantum critical point and which gives experimental
access to the (dangerously irrelevant) spin-spin interactions.Comment: 12 pages, 8 figure
Measurement of calcium isotopes (ÎŽ44Ca) using a multicollector TIMS technique
We propose a newâmulticollector techniqueâ for the thermal ionization mass spectrometer (TIMS) measurement of calcium (Ca) isotope ratios improving average internal statistical uncertainty of the 44Ca/40Ca measurements by a factor of 2â4 and average sample throughput relative to the commonly used âpeak jumping methodâ by a factor of 3. Isobaric interferences with potassium (40K+) and titanium (48Ti+) or positively charged molecules like 24Mg19F+, 25Mg19F+, 24Mg16O+ and 27Al16O+ can either be corrected or are negligible. Similar, peak shape defects introduced by the large dispersion of the whole Ca isotope mass range from 40â48 atomic mass units (amu) do not influence Ca-isotope ratios. We use a 43Ca/48Ca double spike with an iterative double spike correction algorithm for precise isotope measurement
Magnetic-Field Induced Quantum Critical Point in YbRhSi
We report low-temperature calorimetric, magnetic and resistivity measurements
on the antiferromagnetic (AF) heavy-fermion metal YbRhSi ( 70
mK) as a function of magnetic field . While for fields exceeding the
critical value at which the low temperature resistivity
shows an dependence, a divergence of upon
reducing to suggests singular scattering at the whole Fermi
surface and a divergence of the heavy quasiparticle mass. The observations are
interpreted in terms of a new type of quantum critical point separating a
weakly AF ordered from a weakly polarized heavy Landau-Fermi liquid state.Comment: accepted for publication in Phys. Rev. Let
The population of white dwarf binaries with hot subdwarf companions
Hot subdwarfs (sdBs) are core helium-burning stars, which lost almost their
entire hydrogen envelope in the red-giant phase. Since a high fraction of those
stars are in close binary systems, common envelope ejection is an important
formation channel. We identified a total population of 51 close sdB+WD binaries
based on time-resolved spectroscopy and multi-band photometry, derive the WD
mass distribution and constrain the future evolution of these systems. Most WDs
in those binaries have masses significantly below the average mass of single
WDs and a high fraction of them might therefore have helium cores. We found 12
systems that will merge in less than a Hubble time and evolve to become either
massive C/O WDs, AM\,CVn systems, RCrB stars or even explode as supernovae type
Ia.Comment: 5 pages, 2 figures, to appear in the proceedings of the 19th European
White Dwarf Workshop, ASP Conf. Se
Avoided Antiferromagnetic Order and Quantum Critical Point in CeCoIn
We measured specific heat and resistivity of heavy fermion CeCoIn5 between
the superconducting critical field and 9 T, with field in the
[001] direction, and at temperatures down to 50mK. At 5T the data show Non
Fermi Liquid behavior down to the lowest temperatures. At field above 8T the
data exhibit crossover from the Fermi liquid to a Non Fermi Liquid behavior. We
analyzed the scaling properties of the specific heat, and compared both
resistivity and the specific heat with the predictions of a spin-fluctuation
theory. Our analysis leads us to suggest that the NFL behavior is due to
incipient antiferromagnetism (AF) in CeCoIn5, with the quantum critical point
in the vicinity of the . Below the AF phase which competes
with the paramagnetic ground state is superseded by the superconducting
transition.Comment: 5 pages, 3 figure
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