551 research outputs found
Coexistence of -loop-current order with checkerboard d-wave CDW/PDW order in a hot-spot model for cuprate superconductors
We investigate the strong influence of the -loop-current order
on both unidirectional and bidirectional d-wave
charge-density-wave/pair-density-wave (CDW/PDW) composite orders along axial
momenta and that emerge in an effective hot spot
model departing from the three-band Emery model relevant to the phenomenology
of the cuprate superconductors. This study is motivated by the compelling
evidence that the -loop-current order described by this model may
explain groundbreaking experiments such as spin-polarized neutron scattering
performed in these materials. Here, we demonstrate, within a saddle-point
approximation, that the -loop-current order clearly coexists with
bidirectional (i.e. checkerboard) d-wave CDW and PDW orders along axial
momenta, but is visibly detrimental to the unidirectional (i.e. stripe) case.
This result has potentially far-reaching implications for the physics of the
cuprates and agrees well with very recent x-ray experiments on YBCO that
indicate that at higher dopings the CDW order has indeed a tendency to be
bidirectional.Comment: Published in Physical Review
The thermopower as a fingerprint of the Kondo breakdown quantum critical point
We propose that the thermoelectric power distinguishes two competing
scenarios for quantum phase transitions in heavy fermions : the
spin-density-wave (SDW) theory and breakdown of the Kondo effect. In the Kondo
breakdown scenario, the Seebeck coefficient turns out to collapse from the
temperature scale , associated with quantum fluctuations of the Fermi
surface reconfiguration. This feature differs radically from the physics of the
SDW theory, where no reconstruction of the Fermi surface occurs, and can be
considered as the hallmark of the Kondo breakdown theory. We test these ideas,
upon experimental results for YbRhSi
Pseudogap, charge order, and pairing density wave at the hot spots in cuprate superconductors
We address the timely issue of the presence of charge ordering at the
hot-spots in the pseudo-gap phase of cuprate superconductors in the context of
an emergent SU(2)-symmetry which relates the charge and pairing sectors.
Performing the Hubbard-Stratonovich decoupling such that the free energy stays
always real and physically meaningful we exhibit three solutions of the
spin-fermion model at the hot spots. A careful examination of their stability
and free energy shows that, at low temperature, the system tends towards a
co-existence of charge density wave (CDW) and the composite order parameter
made of diagonal quadrupolar density wave and pairing fluctuations of Ref.
[Nat. Phys. , 1745 (2013)].The CDW is sensitive to the shape of the
Fermi surface in contrast to the diagonal quadrupolar order, which is immune to
it. SU(2) symmetry within the pseudo-gap phase also applies to the CDW state,
which therefore admits a pairing density pave counterpart breaking time
reversal symmetry.Comment: 15 pages, 15 figures, final version + typo corrected in Eq. (12
collective mode as A Raman resonance in cuprate superconductors
We discuss the possible existence a spin singlet excitation with charge
(-mode) originating the Raman resonance in cuprate
superconductors. This -mode relates the -wave superconducting singlet
pairing channel to a -wave charge channel. We show that the boson
forms a particle-particle bound state below the threshold of the
particle-hole continuum where is the maximum -wave gap. Within a
generalized random phase approximation and Bethe-Salpether approximation study,
we find that this mode has energies similar to the resonance observed by
Inelastic Neutron Scattering (INS) below the superconducting (SC) coherent peak
at in various SC cuprates compounds. We show that it is a very good
candidate for the resonance observed in Raman scattering below the
peak in the symmetry. Since the -mode sits in the channel,
it may be observable via Raman, X -ray or Electron Energy Loss Spectroscopy
probes
Charge orders, magnetism and pairings in the cuprate superconductors
We review the recent developments in the field of cuprate superconductors
with the special focus on the recently observed charge order in the underdoped
compounds. We introduce new theoretical developments following the study of the
antiferromagnetic (AF) quantum critical point (QCP) in two dimensions, in which
preemptive orders in the charge and superconducting (SC) sectors emerged, that
are in turn related by an SU(2) symmetry. We consider the implications of this
proliferation of orders in the underdoped region, and provide a study of the
type of fluctuations which characterize the SU(2) symmetry. We identify an
intermediate energy scale where the SU(2) pairing fluctuations are dominant and
argue that they are unstable towards the formation of a Resonant Peierls
Excitonic (RPE) state at the pseudogap (PG) temperature . We discuss the
implications of this scenario for a few key experiments.Comment: 16 pages, 17 figure
Strong competition between -loop-current order and -wave charge order along the diagonal direction in a two-dimensional hot spot model
We study the fate of the so-called -loop-current order that
breaks both time-reversal and parity symmetries in a two-dimensional hot spot
model with antiferromagnetically mediated interactions, using Fermi surfaces
relevant to the phenomenology of the cuprate superconductors. We start from a
three-band Emery model describing the hopping of holes in the CuO plane
that includes two hopping parameters and , local on-site
Coulomb interactions and and nearest-neighbor
couplings between the fermions in the copper [Cu] and
oxygen [O and O] orbitals. By focusing on the lowest-energy
band, we proceed to decouple the local interaction of the Cu orbital in
the spin channel using a Hubbard-Stratonovich transformation to arrive at the
interacting part of the so-called spin-fermion model. We also decouple the
nearest-neighbor interaction to introduce the order parameter of the
-loop-current order. In this way, we are able to construct a
consistent mean-field theory that describes the strong competition between the
composite order parameter made of a quadrupole-density-wave and -wave
pairing fluctuations proposed in Efetov \emph{et al.} [Nat. Phys. \textbf{9},
442 (2013)] with the -loop-current order parameter that is argued
to be relevant for explaining important aspects of the physics of the pseudogap
phase displayed in the underdoped cuprates.Comment: 16 pages, 5 figures. v2: minor revisions, references added. The
magnetic moment per unit-cell associated with the
-loop-current-phase is calculated and compared with experimental
results. Accepted for publication in Physical Review
Gr\"uneisen ratio at the Kondo breakdown quantum critical point
We show that the scenario of multi-scale Kondo breakdown quantum critical
point (QCP) gives rise to a divergent Gr\"uneisen ratio with an anomalous
exponent 0.7. In particular, we fit the experimental data of
for specific heat, thermal expansion, and
Gr\"uneisen ratio based on our simple analytic expressions. A reasonable
agreement between the experiment and theory is found for the temperature range
between 0.4 K and 10 K. We discuss how the Gr\"uneisen ratio is a key
measurement to discriminate between the Kondo breakdown and spin-density wave
theories
The modulated spin liquid: a new paradigm for URuSi
We argue that near a Kondo breakdown critical point, a spin liquid with
spatial modulations can form. Unlike its uniform counterpart, we find that this
occurs via a second order phase transition. The amount of entropy quenched when
ordering is of the same magnitude as for an antiferromagnet. Moreover, the two
states are competitive, and at low temperatures are separated by a first order
phase transition. The modulated spin liquid we find breaks symmetry, as
recently seen in the hidden order phase of URuSi. Based on this, we
suggest that the modulated spin liquid is a viable candidate for this unique
phase of matter.Comment: 4 pages, 2 figure
Violation of Wiedemann-Franz law at the Kondo breakdown quantum critical point
We study both the electrical and thermal transport near the heavy-fermion
quantum critical point (QCP), identified with the breakdown of the Kondo effect
as an orbital selective Mott transition. We show that the contribution to the
electrical conductivity comes mainly from conduction electrons while the
thermal conductivity is given by both conduction electrons and localized
fermions (spinons), scattered with dynamical exponent . This scattering
mechanism gives rise to a quasi-linear temperature dependence of the electrical
and thermal resistivity. The characteristic feature of the Kondo breakdown
scenario turns out to be emergence of additional entropy carriers, that is,
spinon excitations. As a result, we find that the Wiedemann-Franz ratio should
be larger than the standard value, a fact which enables to differentiate the
Kondo breakdown scenario from the Hertz-Moriya-Millis framework
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