306 research outputs found
Fermi surface and antiferromagnetism in the Kondo lattice: an asymptotically exact solution in d>1 Dimensions
Interest in the heavy fermion metals has motivated us to examine the quantum
phases and their Fermi surfaces within the Kondo lattice model. We demonstrate
that the model is soluble asymptotically exactly in any dimension d>1, when the
Kondo coupling is small compared with the RKKY interaction and in the presence
of antiferromagnetic ordering. We show that the Kondo coupling is exactly
marginal in the renormalization group sense, establishing the stability of an
ordered phase with a small Fermi surface, AFs. Our results have implications
for the global phase diagram of the heavy fermion metals, suggesting a Lifshitz
transition inside the antiferromagnetic region and providing a new perspective
for a Kondo-destroying antiferromagnetic quantum critical point.Comment: 4 pages, 4 figures; (v2) corrected typos and added
reference/acknowledgment; (v3) version as published in Physical Review
Letters (July, 2007
Novel Quantum Criticality in CeRuSi near Absolute Zero Observed by Thermal Expansion and Magnetostriction
We report linear thermal expansion and magnetostriction measurements for
CeRuSi in magnetic fields up to 52.6 mT and at temperatures down to 1
mK. At high temperatures, this compound showed Landau-Fermi-liquid behavior:
The linear thermal expansion coefficient and the magnetostriction coefficient
were proportional to the temperature and magnetic field, respectively. In
contrast, a pronounced non-Fermi-liquid effect was found below 50 mK. The
negative contribution of thermal expansion and magnetostriction suggests the
existence of an additional quantum critical point
Magnetic-field enhanced aniferromagnetism in non-centrosymmetric heavy-fermion superconductor CePtSi
The effect of magnetic field on the static and dynamic spin correlations in
the non-centrosymmetric heavy-fermion superconductor CePtSi was
investigated by neutron scattering. The application of a magnetic field B
increases the antiferromagnetic (AFM) peak intensity. This increase depends
strongly on the field direction: for B[0 0 1] the intensity
increases by a factor of 4.6 at a field of 6.6 T, which corresponds to more
than a doubling of the AFM moment, while the moment increases by only 10 % for
B[1 0 0] at 5 T. This is in strong contrast to the inelastic
response near the antiferromagnetic ordering vector, where no marked field
variations are observed for B[0 0 1] up to 3.8 T. The results
reveal that the AFM state in CePtSi, which coexists with superconductivity,
is distinctly different from other unconventional superconductors.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev.
Enhancing the Superconducting Transition Temperature due to Strong-Coupling Effect under Antiferromagnetic Spin Fluctuations in CeRh1-xIrxIn5 : 115In-NQR Study
We report on systematic evolutions of antiferromagnetic (AFM) spin
fluctuations and unconventional superconductivity (SC) in heavy-fermion (HF)
compounds CeRhIrIn via In
nuclear-quadrupole-resonance (NQR) experiment. The measurements of nuclear
spin-lattice relaxation rate have revealed the marked development of
AFM spin fluctuations as a consequence of approaching an AFM ordered state with
increasing Rh content. Concomitantly the superconducting transition temperature
and the energy gap increase drastically from K and in CeIrIn up to K and in
CeRhIrIn, respectively. The present work suggests that the
AFM spin fluctuations in close proximity to the AFM quantum critical point are
indeed responsible for the onset of strong-coupling unconventional SC with the
line node in the gap function in HF compounds.Comment: 4pages,5figures,to appear in Phys. Rev. Let
Anisotropic magnetic properties of CeAgGe single crystal
In order to investigate the anisotropic magnetic properties of
CeAgGe, we have successfully grown the single crystals, for the first
time, by high temperature solution growth (flux) method. We have performed a
detailed study of the grown single crystals by measuring their electrical
resistivity, magnetic susceptibility, magnetization, specific heat and
magnetoresistance. A clear anisotropy and an antiferromagnetic transition at
= 4.6 K have been observed in the magnetic properties. The magnetic
entropy reaches ln 4 at 20 K indicating that the ground state and the first
excited state are very closely spaced (a quasi-quartet state). From the
specific heat measurements and crystalline electric field (CEF) analysis of the
magnetic susceptibility, we have found the level splitting energies as 5 K and
130 K. The magnetization measurements reveal that the a-axis is the easy axis
of magnetization and the saturation moment is = 1.6 /Ce, corroborating the previous neutron diffraction measurements on a
polycrystalline sample.Comment: Submitted to Phys. Rev.
Thermal transport in the hidden-order state of URuSi
We present a study of thermal conductivity in the normal state of the
heavy-fermion superconductor URuSi. Ordering at 18K leads to a
steep increase in thermal conductivity and (in contrast with all other cases of
magnetic ordering in heavy-fermion compounds) to an enhancement of the Lorenz
number. By linking this observation to several other previously reported
features, we conclude that most of the carriers disappear in the ordered state
and this leads to a drastic increase in both phononic and electronic
mean-free-path.Comment: 5 pages including 4 figure
Magnetic properties of PrCu2 at high pressure
We report a study of the low-temperature high-pressure phase diagram of the intermetallic compound PrCu2, by means of molecular-field calculations and 63,65Cu nuclear-quadrupole-resonance (NQR) measurements under pressure. The pressure-induced magnetically-ordered phase can be accounted for by considering the influence of the crystal electric field on the 4f electron orbitals of the Pr3+ ions and by introducing a pressure-dependent exchange interaction between the corresponding local magnetic moments. Our experimental data suggest that the order in the induced antiferromagnetic phase is incommensurate. The role of magnetic fluctuations both at high and low pressures is also discusse
Evidence for ferromagnetic spin-pairing superconductivity in UGe: A Ge-NQR study under pressure
We report that a novel type of superconducting order parameter has been
realized in the ferromagnetic states in UGe via Ge
nuclear-quadrupole-resonance (NQR) experiments performed under pressure ().
Measurements of the nuclear spin-lattice relaxation rate have
revealed an unconventional nature of superconductivity such that the up-spin
band is gapped with line nodes, but the down-spin band remains gapless at the
Fermi level. This result is consistent with that of a ferromagnetic
spin-pairing model in which Cooper pairs are formed among ferromagnetically
polarized electrons. The present experiment has shed new light on a possible
origin of ferromagnetic superconductivity, which is mediated by ferromagnetic
spin-density fluctuations relevant to the first-order transition inside the
ferromagnetic states.Comment: 5 pages, 5 figure
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