767 research outputs found
Mottness induced phase decoherence suggests Bose-Einstein condensation in overdoped cuprate high-temperature superconductors
Recent observations of diminishing superfluid phase stiffness in overdoped
cuprate high-temperature superconductors challenges the conventional picture of
superconductivity. Here, through analytic estimation and verified via
variational Monte Carlo calculation of an emergent Bose liquid, we point out
that Mottness of the underlying doped holes dictates a strong phase fluctuation
of the superfluid at moderate carrier density. This effect turns the expected
doping-increased phase stiffness into a dome shape, in good agreement with the
recent observation. Specifically, the effective mass divergence due to
"jamming" of the low-energy bosons reproduces the observed nonlinear relation
between phase stiffness and transition temperature. Our results suggest a new
paradigm, in which the high-temperature superconductivity in the cuprates is
dominated by physics of Bose-Einstein condensation, as opposed to
pairing-strength limited Cooper pairing.Comment: 6+3 pages, 4+1 figure
Possible singlet and triplet superconductivity on honeycomb lattice
We study the possible superconducting pairing symmetry mediated by spin and
charge fluctuations on the honeycomb lattice using the extended Hubbard model
and the random-phase-approximation method. From to doping levels,
a spin-singlet -wave is shown to be the leading
superconducting pairing symmetry when only the on-site Coulomb interaction
is considered, with the gap function being a mixture of the nearest-neighbor
and next-nearest-neighbor pairings. When the offset of the energy level between
the two sublattices exceeds a critical value, the most favorable pairing is a
spin-triplet -wave which is mainly composed of the next-nearest-neighbor
pairing. We show that the next-nearest-neighbor Coulomb interaction is also
in favor of the spin-triplet -wave pairing.Comment: 6 pages, 4 figure
Superconducting proximity effect to the block antiferromagnetism in KFeSe
Recent discovery of superconducting (SC) ternary iron selenides has block
antiferromagentic (AFM) long range order. Many experiments show possible
mesoscopic phase separation of the superconductivity and antiferromagnetism,
while the neutron experiment reveals a sizable suppression of magnetic moment
due to the superconductivity indicating a possible phase coexistence. Here we
propose that the observed suppression of the magnetic moment may be explained
due to the proximity effect within a phase separation scenario. We use a
two-orbital model to study the proximity effect on a layer of block AFM state
induced by neighboring SC layers via an interlayer tunneling mechanism. We
argue that the proximity effect in ternary Fe-selenides should be large because
of the large interlayer coupling and weak electron correlation. The result of
our mean field theory is compared with the neutron experiments
semi-quantitatively. The suppression of the magnetic moment due to the SC
proximity effect is found to be more pronounced in the d-wave superconductivity
and may be enhanced by the frustrated structure of the block AFM state.Comment: 6 pages, 6 figure
Where do the hole carriers reside in the new superconducting nickelates?
The families of high-temperature superconductors recently welcome a new
member: hole doped nickelate NdSrNiO with a 15K
transition temperature. To understand its emergent low-energy behaviors and
experimental properties, an immediate key question is whether the
superconducting hole carriers reside in oxygen as in the cuprates, or in nickel
as in most nickelates. We answer this crucial question via a "(LDA+)+ED"
scheme: deriving an effective interacting Hamiltonian of the hole carriers from
density functional LDA+ calculation, and studying its local many-body states
via exact diagonalization. Surprisingly, distinct from the expected Ni
spin-triplet state found in most nickelates, the local ground state of two
holes is actually a Ni-O spin-singlet state with second hole residing greatly
in oxygen. The emerged eV-scale model therefore resembles that of the cuprates,
advocating further systematic experimental comparisons. Tracing the microscopic
origin of this unexpected result to the lack of apical oxygen in this material,
we proposed a route to increase superconducting temperature, and a possible new
quantum phase transition absent in the cuprates.Comment: 6 pages, 2 figure
A double neutron star merger origin for the cosmological relativistic fading source PTF11agg?
The Palomar Transient Factory (PTF) team recently reported the discovery of a
rapidly fading optical transient source, PTF11agg. A long-lived scintillating
radio counterpart was identified, but the search for a high energy counterpart
showed negative results. The PTF team speculated that PTF11agg may represent a
new class of relativistic outbursts. Here we suggest that a neutron star
(NS)-NS merger system with a supra-massive magnetar central engine could be a
possible source to power such a transient, if our line of sight is not on the
jet axis direction of the system. These systems are also top candidates for
gravitational wave sources to be detected in the advanced LIGO/Virgo era. We
find that the PTF11agg data could be explained well with such a model,
suggesting that at least some gravitational wave bursts due to NS-NS mergers
may be associated with such a bright electromagnetic counterpart without a
\gamma-ray trigger.Comment: Accepted for publication in ApJ Letter
Theory for charge and orbital density-wave states in manganite LaSrMnO
We investigate the high temperature phase of layered manganites, and
demonstrate that the charge-orbital phase transition without magnetic order in
LaSrMnO can be understood in terms of the density wave
instability. The orbital ordering is found to be induced by the nesting between
segments of Fermi surface with different orbital characters. The simultaneous
charge and orbital orderings are elaborated with a mean field theory. The
ordered orbitals are shown to be .Comment: published versio
Quantum fluctuation of ferroelectric order in polar metals
Since its discovery a decade ago, "polar metallic phase" has ignited
significant research interest, as it further functionalizes the switchable
electric polarization of materials with additional transport capability,
granting them great potential in next-generation electronic devices. The polar
metallic phase is an unusual metallic phase of matter containing long-range
ferroelectric (FE) order in the electronic and atomic structure. Distinct from
the typical FE insulating phase, this phase spontaneously breaks the inversion
symmetry but without global polarization. Unexpectedly, the FE order is found
to be dramatically suppressed by carriers and destroyed at moderate ~10%
carrier density. Here, we propose a general mechanism based on carrier-induced
quantum fluctuations to explain this puzzling phenomenon. Basically, the
quantum kinetic effect would drive the formation of polaronic quasi-particles
made of the carriers and their surrounding dipoles. The disruption in dipolar
directions can therefore weaken or even destroy the FE order. We demonstrate
such polaron formation and the associated FE suppression via a simple model
using exact diagonalization, perturbation, and quantum Monte Carlo approaches.
This quantum mechanism also provides an intuitive picture for many puzzling
experimental findings, thereby facilitating new designs of multifunctional FE
electronic devices augmented with quantum effects.Comment: 12 pages, 6 figures in tota
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