80 research outputs found
Collective magnetic excitations of symmetric magnetic states in iron-based superconductors
We study the collective magnetic excitations of the recently discovered
symmetric spin-density wave states of iron-based superconductors with
particular emphasis on their orbital character based on an itinerant
multiorbital approach. This is important since the symmetric
spin-density wave states exist only at moderate interaction strengths where
damping effects from a coupling to the continuum of particle-hole excitations
strongly modifies the shape of the excitation spectra compared to predictions
based on a local moment picture. We uncover a distinct orbital polarization
inherent to magnetic excitations in symmetric states, which provide a
route to identify the different commensurate magnetic states appearing in the
continuously updated phase diagram of the iron-pnictide family.Comment: 5+7 pages, 3+2 figure
Persistent current-carrying state of charge quasuparticles in -ribbon featuring single Dirac cone
The formation of persistent charge currents in mesoscopic systems remains an
interesting and actual topic of condensed matter research. Here, we analyze the
formation of spontaneous arising persistent currents of charged fermions in
2-dimensional electron-hole ribbons on the top and bottom of a 3-dimensional
topological insulator. In such a device the two-dimensional Dirac fermions with
opposite chiralities are spatially separated that allows these currents to flow
in the opposite directions without compensating each other. The nature of this
phenomenon is based on the interference of the quasiparticle quantum waves
which are scattered with asymmetric scattering phases at the lateral n-p chiral
junction and then reflected back by the external boundaries of the ribbon. As a
result quasiparticles in the ribbon are shown to be in unified electron-hole
quantum states carrying the persistent current.Comment: 7 pages, 3 figure
Spin-orbit coupling, minimal model and potential Cooper-pairing from repulsion in BiS-superconductors
We develop the realistic minimal electronic model for recently discovered
BiS superconductors including the spin-orbit coupling based on a
first-principles band structure calculations. Due to strong spin-orbit
coupling, characteristic for the Bi-based systems, the tight-binding low-energy
model necessarily includes , , and orbitals. We analyze a
potential Cooper-pairing instability from purely repulsive interaction for the
moderate electronic correlations using the so-called leading angular harmonics
approximation (LAHA). For small and intermediate doping concentrations we find
the dominant instabilities to be -wave, and -wave
symmetries, respectively. At the same time, in the absence of the sizable spin
fluctuations the intra and interband Coulomb repulsion are of the same
strength, which yields the strongly anisotropic behaviour of the
superconducting gaps on the Fermi surface in agreement with recent ARPES
findings. In addition, we find that the Fermi surface topology for BiS
layered systems at large electron doping can resembles the doped iron-based
pnictide superconductors with electron and hole Fermi surfaces with sufficient
nesting between them. This could provide further boost to increase in
these systems.Comment: 10 pages, 3 figure
Antiferromagnetism in Iron-Based Superconductors: Selection of Magnetic Order and Quasiparticle Interference
The recent discovery of superconductivity in the iron-based layered pnictides
with T_c ranging between 26 and 56K generated enormous interest in the physics
of these materials. Here, we review some of the peculiarities of the
antiferromagnetic order in the iron pnictides, including the selection of the
stripe magnetic order and the formation of the Ising-nematic state in the
unfolded BZ within an itinerant description. In addition we analyze the
properties of the quasiparticle interference spectrum in the parent
antiferromagnetic phase.Comment: Invited talk at SCES 2013, to published in JPSJ Special Topic
Quasiparticle approach to the transport in infinite-layer nickelates
The normal-state transport properties of superconducting infinite-layer
nickelates are investigated within an interacting three-orbital model. It
includes effective Ni-, Ni- bands as well as the
self-doping band degree of freedom. Thermopower, Hall coefficient and optical
conductivity are modelled within a quasiparticle approximation to the
electronic states. Qualitative agreement in comparison to experimentally
available Hall data is achieved, with notably a temperature-dependent sign
change of the Hall coefficient for larger hole doping . The Seebeck
coefficient changes from negative to positive in a non-trivial way with ,
but generally shows only modest temperature dependence. The optical
conductivity shows a pronounced Drude response and a prominent peak structure
at higher frequencies due to interband transitions. While the quasiparticle
picture is surely approximative to low-valence nickelates, it provides
enlightening insights into the multiorbital nature of these challenging
systems.Comment: 7 pages, 3 figure
Long-range Ising spins models emerging from frustrated Josephson junctions arrays with topological constraints
Geometrical frustration in correlated systems can give rise to a plethora of
novel ordered states and intriguing phases. Here, we analyze theoretically
vertex-sharing frustrated Kagome lattice of Josephson junctions and identify
various classical and quantum phases. The frustration is provided by
periodically arranged - and - Josephson junctions. In the frustrated
regime the macroscopic phases are composed of different patterns of
vortex/antivortex penetrating each basic element of the Kagome lattice, i.e., a
superconducting triangle interrupted by three Josephson junctions. We obtain
that numerous topological constraints, related to the flux quantization in any
hexagon loop, lead to highly anisotropic and long-range interaction between
well separated vortices (antivortices). Taking into account this interaction
and a possibility of macroscopic "tunneling" between vortex and antivortex in
single superconducting triangles we derive an effective Ising-type spin
Hamiltonian with strongly anisotropic long-range interaction. In the
classically frustrated regime we calculate numerically the
temperature-dependent spatially averaged spins polarization, ,
characterizing the crossover between the ordered and disordered
vortex/antivortex states. In the coherent quantum regime we analyze the lifting
of the degeneracy of the ground state and the appearance of the highly
entangled states.Comment: 10 pages, 9 figures and 2 Appendice
Eliashberg theory of superconductivity and inelastic rare-earth impurity scattering in filled skutterudite LaPrOsSb
We study the influence of inelastic rare-earth impurity scattering on
electron-phonon mediated superconductivity and mass renormalization in
(LaPr)OsSb compounds. Solving the strong coupling
Eliashberg equations we find that the dominant quadrupolar component of the
inelastic scattering on Pr impurities yields an enhancement of the
superconducting transition temperature T in LaOsSb and
increases monotonically as a function of Pr concentration. The calculated
results are in good agreement with the experimentally observed T
dependence. Our analysis suggests that phonons and quadrupolar excitations
cause the attractive electron interaction which results in the formation of
Cooper pairs and singlet superconductivity in PrOsSb.Comment: 5 pages,4 figures, revised title suggested by editor, original fig.4
and fig.5 combined together, discussion added before conclusio
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