2,390 research outputs found
Fermi Surface and Magnetism in the Kondo lattice: A Continuum Field Theory Approach
We consider the Fermi surface inside the antiferromagnetic ordered region of
a Kondo lattice system in an arbitrary dimension higher than one. We establish
the existence of , an antiferromagnetic phase whose Fermi surface
is ``small,'' in the sense that the local moments do not participate in the
Fermi-surface formation. This is in contrast to the ``large'' Fermi surface
that is typically assumed for heavy fermion metals. We extend our earlier work
to the case that the Fermi surface of the conduction electrons intersects the
antiferromagnetic Brillouin zone boundary. Our results provide a new
perspective on local quantum criticality. In addition, our results imply that,
for the phase, it is important to keep track of the dynamical
screening processes; we suggest that this effect is not captured in a recent
variational Monte-Carlo study of the Kondo lattice.Comment: 2 pages, 1 embedded eps figure, proceedings of SCES'0
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
Metallic Ferromagnetism in the Kondo Lattice
Metallic magnetism is both ancient and modern, occurring in such familiar
settings as the lodestone in compass needles and the hard drive in computers.
Surprisingly, a rigorous theoretical basis for metallic ferromagnetism is still
largely missing. The Stoner approach perturbatively treates Coulomb
interactions when the latter need to be large, while the Nagaoka approach
incorporates thermodynamically negligible electrons into a half-filled band.
Here, we show that the ferromagnetic order of the Kondo lattice is amenable to
an asymptotically exact analysis over a range of interaction parameters. In
this ferromagnetic phase, the conduction electrons and local moments are
strongly coupled but the Fermi surface does not enclose the latter (i.e. it is
small). Moreover, non-Fermi liquid behavior appears over a range of frequencies
and temperatures. Our results provide the basis to understand some
long-standing puzzles in the ferromagnetic heavy fermion metals, and raises the
prospect for a new class of ferromagnetic quantum phase transitions.Comment: 21 pages, 9 figures, including Supporting Informatio
The suppression of hidden order and onset of ferromagnetism in URu2Si2 via Re substitution
Substitution of Re for Ru in the heavy fermion compound URu2Si2 suppresses
the hidden order transition and gives rise to ferromagnetism at higher
concentrations. The hidden order transition of URu(2-x)Re(x)Si2, tracked via
specific heat and electrical resistivity measurements, decreases in temperature
and broadens, and is no longer observed for x>0.1. A critical scaling analysis
of the bulk magnetization indicates that the ferromagnetic ordering temperature
and ordered moment are suppressed continuously towards zero at a critical
concentration of x = 0.15, accompanied by the additional suppression of the
critical exponents gamma and (delta-1) towards zero. This unusual trend appears
to reflect the underlying interplay between Kondo and ferromagnetic
interactions, and perhaps the proximity of the hidden order phase.Comment: 8 pgs, 5 figs, ICM 2009; please refer to Phys. Rev. Lett. 103, 076404
(2009), arXiv:0908.1809 for details on magnetic scaling and phase diagram
(reference added to this version
5,8-Dibromo-2,11-dithiaÂ[3,3](2,6)pyridinoÂparacycloÂphane
The title compound, C15H13Br2NS2 [systematic name: 12,15-dibromo-2,7-dithia-1(1,4)-benzena-5(2,6)-pyridinaoctaÂphane], contains a dibromo-substituted benzene ring and a pyridine ring that are linked by a pair of bridging —CH2SCH2— groups. There is a weak π–π interÂaction between the rings, the distance between the ring centroids being 3.572 (4) Å. The rings are not parallel, but form a dihedral angle of 18.29 (4)°
Global Phase Diagram of the Kondo Lattice: From Heavy Fermion Metals to Kondo Insulators
We discuss the general theoretical arguments advanced earlier for the T=0
global phase diagram of antiferromagnetic Kondo lattice systems, distinguishing
between the established and the conjectured. In addition to the well-known
phase of a paramagnetic metal with a "large" Fermi surface (P_L), there is also
an antiferromagnetic phase with a "small" Fermi surface (AF_S). We provide the
details of the derivation of a quantum non-linear sigma-model (QNLsM)
representation of the Kondo lattice Hamiltonian, which leads to an effective
field theory containing both low-energy fermions in the vicinity of a Fermi
surface and low-energy bosons near zero momentum. An asymptotically exact
analysis of this effective field theory is made possible through the
development of a renormalization group procedure for mixed fermion-boson
systems. Considerations on how to connect the AF_S and P_L phases lead to a
global phase diagram, which not only puts into perspective the theory of local
quantum criticality for antiferromagnetic heavy fermion metals, but also
provides the basis to understand the surprising recent experiments in
chemically-doped as well as pressurized YbRh2Si2. We point out that the AF_S
phase still occurs for the case of an equal number of spin-1/2 local moments
and conduction electrons. This observation raises the prospect for a global
phase diagram of heavy fermion systems in the Kondo-insulator regime. Finally,
we discuss the connection between the Kondo breakdown physics discussed here
for the Kondo lattice systems and the non-Fermi liquid behavior recently
studied from a holographic perspective.Comment: (v3) leftover typos corrected. (v2) Published version. 32 pages, 4
figures. Section 7, on the connection between the Kondo lattice systems and
the holographic models of non-Fermi liquid, is expanded. (v1) special issue
of JLTP on quantum criticalit
Quantum Criticality and Global Phase Diagram of Magnetic Heavy Fermions
Quantum criticality describes the collective fluctuations of matter
undergoing a second-order phase transition at zero temperature. It is being
discussed in a number of strongly correlated electron systems. A prototype case
occurs in the heavy fermion metals, in which antiferromagnetic quantum critical
points have been explicitly observed. Here, I address two types of
antiferromagnetic quantum critical points. In addition to the standard
description based on the fluctuations of the antiferromagnetic order, a local
quantum critical point is also considered. It contains inherently quantum modes
that are associated with a critical breakdown of the Kondo effect. Across such
a quantum critical point, there is a sudden collapse of a large Fermi surface
to a small one. I also consider the proximate antiferromagnetic and
paramagnetic phases, and these considerations lead to a global phase diagram.
Finally, I discuss the pertinent experiments on the antiferromagnetic heavy
fermions, briefly address the case of ferromagnetic heavy fermions, and outline
some directions for future studies.Comment: (v2) reference added, and typos corrected; (v1) 10 pages, 2 figures,
based on a plenary talk given at the International Conference on Quantum
Criticality and Novel Phases (QCNP09, Dresden
The major and minor wall teichoic acids prevent the sidewall localization of vegetative DL-endopeptidase LytF in Bacillus subtilis
This is the pre-peer reviewed version of the following article: MOLECULAR MICROBIOLOGY 70(2): 297-310, 2008, which has been published in final form http://www3.interscience.wiley.com/journal/121385465/abstract.ArticleMOLECULAR MICROBIOLOGY. 70(2): 297-310 (2008)journal articl
Long range order and two-fluid behavior in heavy electron materials
The heavy electron Kondo liquid is an emergent state of condensed matter that
displays universal behavior independent of material details. Properties of the
heavy electron liquid are best probed by NMR Knight shift measurements, which
provide a direct measure of the behavior of the heavy electron liquid that
emerges below the Kondo lattice coherence temperature as the lattice of local
moments hybridizes with the background conduction electrons. Because the
transfer of spectral weight between the localized and itinerant electronic
degrees of freedom is gradual, the Kondo liquid typically coexists with the
local moment component until the material orders at low temperatures. The
two-fluid formula captures this behavior in a broad range of materials in the
paramagnetic state. In order to investigate two-fluid behavior and the onset
and physical origin of different long range ordered ground states in heavy
electron materials, we have extended Knight shift measurements to
URuSi, CeIrIn and CeRhIn. In CeRhIn we find that the
antiferromagnetic order is preceded by a relocalization of the Kondo liquid,
providing independent evidence for a local moment origin of antiferromagnetism.
In URuSi the hidden order is shown to emerge directly from the Kondo
liquid and so is not associated with local moment physics. Our results imply
that the nature of the ground state is strongly coupled with the hybridization
in the Kondo lattice in agreement with phase diagram proposed by Yang and
Pines.Comment: 9 pages, 13 figure
Limits on the Superconducting Order Parameter in NdFeAsOF from Scanning SQUID Microscopy
Identifying the symmetry of the superconducting order parameter in the
recently-discovered ferro-oxypnictide family of superconductors,
RFeAsOF, where is a rare earth, is a high priority. Many of
the proposed order parameters have internal phase shifts, like the d-wave
order found in the cuprates, which would result in direction-dependent phase
shifts in tunnelling. In dense polycrystalline samples, these phase shifts in
turn would result in spontaneous orbital currents and magnetization in the
superconducting state. We perform scanning SQUID microscopy on a dense
polycrystalline sample of \NdFeAsOF with K and find
no such spontaneous currents, ruling out many of the proposed order parameters.Comment: 10 pages, 5 figures; to appear in JPS
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