6 research outputs found
Quantum-critical superconductivity in underdoped cuprates
We argue that the pseudogap phase may be an attribute of the non-BCS pairing
of quantum-critical, diffusive fermions near the antiferromagnetic quantum
critical point. We derive and solve a set of three coupled Eliashberg-type
equations for spin-mediated pairing and show that in some range below the
pairing instability, there is no feedback from superconductivity on fermionic
excitations, and fermions remain diffusive despite of the pairing. We conject
that in this regime, fluctuations of the pairing gap destroy the
superconducting condensate but preserve the leading edge gap in the fermionic
spectral function.Comment: 5 pages, 3 figure
A phenomenological description on an incoherent Fermi liquid near optimal doping in high T_{c} cuprates
Marginal Fermi-liquid physics near optimal doping in high T_{c} cuprates has
been explained within two competing scenarios such as the spin-fluctuation
theory based on an itinerant picture and the slave-particle approach based on a
localized picture. In this study we propose an alternative scenario for the
anomalous transport within the context of the slave-particle approach. Although
the marginal Fermi-liquid phenomenology was interpreted previously within
deconfinement of the compact gauge theory, referred to as the strange metal
phase, we start from confinement, introducing the Polyakov-loop parameter into
an SU(2) gauge theory formulation of the t-J model. The Polyakov-loop parameter
gives rise to incoherent electrons through the confinement of spinons and
holons, which result from huge imaginary parts of self-energy corrections for
spinons and holons. This confinement scenario serves a novel mechanism for the
marginal Fermi-liquid transport in the respect that the scattering source has
nothing to do with symmetry breaking. Furthermore, the incoherent Fermi-liquid
state evolves into the Fermi liquid phase through crossover instead of an
artificial second-order transition as temperature is lowered, where the
crossover phenomenon does not result from the Anderson-Higgs mechanism but
originate from an energy scale in the holon sector. We fit an experimental data
for the electrical resistivity around the optimal doping and find a reasonable
match between our theory and the experiment.Comment: 15 pages. 5 figure. Title has been changed. Final version publishec
in J. Phys.: Condens. Matter 23 (2011) 49570
Singularities in the optical response of cuprates
We argue that the detailed analysis of the optical response in cuprate
superconductors allows one to verify the magnetic scenario of superconductivity
in cuprates, as for strong coupling charge carriers to antiferromagnetic spin
fluctuations, the second derivative of optical conductivity should contain
detectable singularities at , , and
, where is the amplitude of the
superconducting gap, and is the resonance energy of spin
fluctuations measured in neutron scattering. We argue that there is a good
chance that these singularities have already been detected in the experiments
on optimally doped .Comment: 6 pages, 4 figure
Spin orthogonality catastrophe in two-dimensional antiferromagnets and superconductors
We compute the spectral function of a spin S hole injected into a
two-dimensional antiferromagnet or superconductor in the vicinity of a magnetic
quantum critical point. We show that, near van Hove singularities, the problem
maps onto that of a static vacancy carrying excess spin S. The hole creation
operator is characterized by a new boundary anomalous dimension and a vanishing
quasiparticle residue at the critical point. We discuss possible relevance to
photoemission spectra of cuprate superconductors near the anti-nodal points.Comment: (v1) 4 pages, 2 figures; field theory afficionados - see also
cond-mat/0011233; (v2) added figure of Monte Carlo data; (v3) corrected typo
Strongly coupled quantum criticality with a Fermi surface in two dimensions: fractionalization of spin and charge collective modes
We describe two dimensional models with a metallic Fermi surface which
display quantum phase transitions controlled by strongly interacting critical
field theories below their upper critical dimension. The primary examples
involve transitions with a topological order parameter associated with
dislocations in collinear spin density wave ("stripe") correlations: the
gapping of the order parameter fluctuations leads to a fractionalization of
spin and charge collective modes, and this transition has been proposed as a
candidate for the cuprates near optimal doping. The coupling between the order
parameter and long-wavelength volume and shape deformations of the Fermi
surface is analyzed by the renormalization group, and a runaway flow to a
non-perturbative regime is found in most cases. A phenomenological scaling
analysis of simple observable properties of possible second order quantum
critical points is presented, with results quite similar to those near quantum
spin glass transitions and to phenomenological forms proposed by Schroeder et
al. (cond-mat/0011002).Comment: 16 pages, 4 figures; (v2) additional clarifying remark
Neutron resonance in the cuprates and its effect on fermionic excitations
We argue that the exciton scenario for the magnetic resonance in the cuprate superconductors yields a small spectral weight of the resonance, in agreement with experiment. We show that the small weight is related to its concentration in a small region of momentum and energy. Despite this, we find that a large fermionic self-energy can indeed be generated by a resonance with such properties, i.e., the scattering from the resonance substantially affects the electronic properties of the cuprates below Tc