1,833 research outputs found
On non-Fermi liquid quantum critical points in heavy fermion metals
Heavy electron metals on the verge of a quantum phase transition to magnetism
show a number of unusual non-fermi liquid properties which are poorly
understood. This article discusses in a general way various theoretical aspects
of this phase transition with an eye toward understanding the non-fermi liquid
phenomena. We suggest that the non-Fermi liquid quantum critical state may have
a sharp Fermi surface with power law quasiparticles but with a volume not set
by the usual Luttinger rule. We also discuss the possibility that the
electronic structure change associated with the possible Fermi surface
reconstruction may diverge at a different time/length scale from that
associated with magnetic phenomena.Comment: 16 pages, 2 figures. Proceedings of workshop on ``Mottness and
Quantum Criticality", Tobago, West Indies, June 8-19 (2005), to appear in
Annals of Physic
Neel order, quantum spin liquids and quantum criticality in two dimensions
This paper is concerned with the possibility of a direct second order
transition out of a collinear Neel phase to a paramagnetic spin liquid in two
dimensional quantum antiferromagnets. Contrary to conventional wisdom, we show
that such second order quantum transitions can potentially occur to certain
spin liquid states popular in theories of the cuprates. We provide a theory of
this transition and study its universal properties in an expansion.
The existence of such a transition has a number of interesting implications for
spin liquid based approaches to the underdoped cuprates. In particular it
considerably clarifies existing ideas for incorporating antiferromagnetic long
range order into such a spin liquid based approach.Comment: 18 pages, 17 figure
Symmetry Protected Topological phases of Quantum Matter
We describe recent progress in our understanding of the interplay between
interactions, symmetry, and topology in states of quantum matter. We focus on a
minimal generalization of the celebrated topological band insulators to
interacting many particle systems, known as Symmetry Protected Topological
(SPT) phases. In common with the topological band insulators these states have
a bulk gap and no exotic excitations but have non-trivial surface states that
are protected by symmetry. We describe the various possible such phases and
their properties in three dimensional systems with realistic symmetries. We
develop many key ideas of the theory of these states using simple examples. The
emphasis is on physical rather than mathematical properties. We survey insights
obtained from the study of SPT phases for a number of other theoretical
problems.Comment: Invited Review for Annual Reviews of Condensed Matter Physic
Twisted Hubbard Model for Sr2IrO4: Magnetism and Possible High Temperature Superconductivity
Sr2IrO4 has been suggested as a Mott insulator from a single J_eff=1/2 band,
similar to the cuprates. However this picture is complicated by the measured
large magnetic anisotropy and ferromagnetism. Based on a careful mapping to the
J_eff=1/2 (pseudospin-1/2) space, we propose that the low energy electronic
structure of Sr2IrO4 can indeed be described by a SU(2) invariant
pseudospin-1/2 Hubbard model very similar to that of the cuprates, but with a
"twisted" coupling to external magnetic field (a g-tensor with a staggered
antisymmetric component). This perspective naturally explains the magnetic
properties of Sr2IrO4. We also derive several simple facts based on this
mapping and the known results about the Hubbard model and the cuprates, which
may be tested in future experiments on Sr2IrO4. In particular we propose that
(electron-)doping Sr2IrO4 can potentially realize high-temperature
superconductivity.Comment: 5 pages, 1 figure, RevTex4, updated reference
Zero temperature phase transitions in quantum Heisenberg ferromagnets
The purpose of this work is to understand the zero temperature phases, and
the phase transitions, of Heisenberg spin systems which can have an extensive,
spontaneous magnetic moment; this entails a study of quantum transitions with
an order parameter which is also a non-abelian conserved charge. To this end,
we introduce and study a new class of lattice models of quantum rotors. We
compute their mean-field phase diagrams, and present continuum, quantum
field-theoretic descriptions of their low energy properties in different
regimes. We argue that, in spatial dimension , the phase transitions in
itinerant Fermi systems are in the same universality class as the corresponding
transitions in certain rotor models. We discuss implications of our results for
itinerant fermions systems in higher , and for other physical systems.Comment: 45 pages, REVTEX 3.0, 5 EPS figure
Higher angular momentum Kondo liquids
Conventional heavy Fermi liquid phases of Kondo lattices involve the
formation of a "Kondo singlet" between the local moments and the conduction
electrons. This Kondo singlet is usually taken to be in an internal s-wave
angular momentum state. Here we explore the possibility of phases where the
Kondo singlet has internal angular momentum that is d-wave. Such states are
readily accessed in a slave boson mean field formulation, and are energetically
favorable when the Kondo interaction is between a local moment and an electron
at a nearest neighbor site. The properties of the d-wave Kondo liquid are
studied. Effective mass and quasiparticle residue show large angle dependence
on the Fermi surface. Remarkably in certain cases, the quasiparticle residue
goes to zero at isolated points (in two dimensions) on the Fermi surface. The
excitations at these points then include a free fractionalized spinon. We also
point out the possibility of quantum Hall phenomena in two dimensional Kondo
{\em insulators}, if the Kondo singlet has complex internal angular momentum.
We suggest that such d-wave Kondo pairing may provide a useful route to
thinking about correlated Fermi liquids with strong anisotropy along the Fermi
surface.Comment: 12 pages, 7 figure
Topological spin Hall states, charged skyrmions, and superconductivity in two dimensions
We study the properties of two dimensional topological spin hall insulators
which arise through spontaneous breakdown of spin symmetry in systems that are
spin rotation invariant. Such a phase breaks spin rotation but not time
reversal symmetry and has a vector order parameter. Skyrmion configurations in
this vector order parameter are shown to have electric charge that is twice the
electron charge. When the spin Hall order is destroyed by condensation of
skyrmions superconductivity results. This may happen either through doping or
at fixed filling by tuning interactions to close the skyrmion gap. In the
latter case the superconductor- spin Hall insulator quantum phase transition
can be second order even though the two phases break distinct symmetries.Comment: 4 pages, typos corrected, added a footnot
Chiral RKKY interaction in Pr2Ir2O7
Motivated by the potential chiral spin liquid in the metallic spin ice
Pr2Ir2O7, we consider how such a chiral state might be selected from the spin
ice manifold. We propose that chiral fluctuations of the conducting Ir moments
promote ferro-chiral couplings between the local Pr moments, as a chiral
analogue of the magnetic RKKY effect. Pr2Ir2O7 provides an ideal setting to
explore such a chiral RKKY effect, given the inherent chirality of the spin-ice
manifold. We use a slave-rotor calculation on the pyrochlore lattice to
estimate the sign and magnitude of the chiral coupling, and find it can easily
explain the 1.5K transition to a ferro-chiral state.Comment: 9 pages; 7 figure
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