424 research outputs found
A predictive standard model for heavy electron systems
We propose a predictive standard model for heavy electron systems based on a
detailed phenomenological two-fluid description of existing experimental data.
It leads to a new phase diagram that replaces the Doniach picture, describes
the emergent anomalous scaling behavior of the heavy electron (Kondo) liquid
measured below the lattice coherence temperature, T*, seen by many different
experimental probes, that marks the onset of collective hybridization, and
enables one to obtain important information on quantum criticality and the
superconducting/antiferromagnetic states at low temperatures. Because T* is
~J^2\rho/2, the nearest neighbor RKKY interaction, a knowledge of the
single-ion Kondo coupling, J, to the background conduction electron density of
states, \rho, makes it possible to predict Kondo liquid behavior, and to
estimate its maximum superconducting transition temperature in both existing
and newly discovered heavy electron families.Comment: 4 pages, 2 figures, submitted to J. Phys.: Conf. Ser. for SCES 201
Hybridization-driven gap in U3Bi4Ni3: a 209Bi NMR/NQR study
We report 209Bi NMR and NQR measurements on a single crystal of the Kondo
insulator U3Bi4Ni3. The 209Bi nuclear spin-lattice relaxation rate ()
shows activated behavior and is well-fit by a spin gap of 220 K. The 209Bi
Knight shift (K) exhibits a strong temperature dependence arising from 5f
electrons, in which K is negative at high temperatures and increases as the
temperature is lowered. Below 50 K, K shows a broad maximum and decreases
slightly upon further cooling. Our data provide insight into the evolution of
the hyperfine fields in a fully gapped Kondo insulator based on 5f electron
hybridization.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
Emergent states in heavy electron materials
We obtain the conditions necessary for the emergence of various low
temperature ordered states (local moment antiferromagnetism, unconventional
superconductivity, quantum criticality, and Landau Fermi liquid behavior) in
Kondo lattice materials by extending the two-fluid phenomenological theory of
heavy electron behavior to incorporate the concept of hybridization
effectiveness. We use this expanded framework to present a new phase digram and
consistent physical explanation and quantitative description of measured
emergent behaviors such as the pressure variation of the onset of local moment
antiferromagnetic ordering at T_N, the magnitude of the ordered moment, the
growth of superconductivity within that ordered state, the location of a
quantum critical point, and of a delocalization line in the
pressure/temperature phase diagram at which local moments have disappeared and
the heavy electron Fermi surface has grown to its maximum size. We apply our
model to CeRhIn_5 and a number of other heavy electron materials and find good
agreement with experiment.Comment: 20 pages, 8 figures, 1 tabl
Uncovering the Hidden Order in URu2Si2 by Impurity Doping
We report the use of impurities to probe the hidden order parameter of the
strongly correlated metal URu_2Si_2 below the transition temperature T_0 ~ 17.5
K. The nature of this order parameter has eluded researchers for more than two
decades, but is accompanied by the development of a partial gap in the single
particle density of states that can be detected through measurements of the
electronic specific heat and nuclear spin-lattice relaxation rate. We find that
impurities in the hidden order phase give rise to local patches of
antiferromagnetism. An analysis of the coupling between the antiferromagnetism
and the hidden order reveals that the former is not a competing order parameter
but rather a parasitic effect of the latter.Comment: 4 pages, 4 figure
Crystalline Electric Field Excitations in the Heavy Fermion Superconductor CeCoIn_5
The crystalline electric field (CEF) energy level scheme of the heavy fermion
superconductor CeCoIn_5 has been determined by means of inelastic neutron
scattering (INS). Peaks observed in the INS spectra at 8 meV and 27 meV with
incident neutron energies between E_i=30-60 meV and at a temperature T = 10 K
correspond to transitions from the ground state to the two excited states,
respectively. The wavevector and temperature dependence of these peaks are
consistent with CEF excitations. Fits of the data to a CEF model yield the CEF
parameters B^0_2=-0.80 meV, B^0_4=0.059 meV, and |B^4_4|= 0.137 meV
corresponding to an energy level scheme: Gamma_7^(1) (0)[=0.487|+/-5/2> -
0.873|-/+3/2>], Gamma_7^(2) (8.6 meV, 100 K), and Gamma_6 (24.4 meV, 283 K).Comment: uses latex packages revtex4,amsmath,graphicx,natbib, 9th Annual
MMM-Intermag Conference, (Accepted for publication in J. Appl. Phys.) 7
pages, 2 figure
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