758 research outputs found
Magnetic phase diagram of the iron pnictides in the presence of spin-orbit coupling: Frustration between and magnetic phases
We investigate the impact of spin anisotropic interactions, promoted by
spin-orbit coupling, on the magnetic phase diagram of the iron-based
superconductors. Three distinct magnetic phases with Bragg peaks at
and are possible in these systems: one (i.e. orthorhombic)
symmetric stripe magnetic phase and two (i.e. tetragonal) symmetric
magnetic phases. While the spin anisotropic interactions allow the magnetic
moments to point in any direction in the phase, they restrict the
possible moment orientations in the phases. As a result, an interesting
scenario arises in which the spin anisotropic interactions favor a phase,
but the other spin isotropic interactions favor a phase. We study this
frustration via both mean-field and renormalization-group approaches. We find
that, to lift this frustration, a rich magnetic landscape emerges well below
the magnetic transition temperature, with novel , , and mixed
- phases. Near the putative magnetic quantum critical point, spin
anisotropies promote a stable Gaussian fixed point in the renormalization-group
flow, which is absent in the spin isotropic case, and is associated with a
near-degeneracy between and phases. We argue that this frustration
is the reason why most phases in the iron pnictides only appear inside
the phase, and discuss additional manifestations of this frustration in
the phase diagrams of these materials.Comment: 21 pages, 19 figures, published versio
Emergent magnetic degeneracy in iron pnictides due to the interplay between spin-orbit coupling and quantum fluctuations
Recent experiments in iron pnictide superconductors reveal that, as the
putative magnetic quantum critical point is approached, different types of
magnetic order coexist over a narrow region of the phase diagram. Although
these magnetic configurations share the same wave-vectors, they break distinct
symmetries of the lattice. Importantly, the highest superconducting transition
temperature takes place close to this proliferation of near-degenerate magnetic
states. In this paper, we employ a renormalization group calculation to show
that such a behavior naturally arises due to the effects of spin-orbit coupling
on the quantum magnetic fluctuations. Formally, the enhanced magnetic
degeneracy near the quantum critical point is manifested as a stable Gaussian
fixed point with a large basin of attraction. Implications of our findings to
the superconductivity of the iron pnictides are also discussed.Comment: 6 pages, 2 figures, published versio
Enhanced nematic fluctuations near an antiferromagnetic Mott insulator and possible application to high- cuprates
Motivated by the widespread experimental observations of nematicity in
strongly underdoped cuprate superconductors, we investigate the possibility of
enhanced nematic fluctuations in the vicinity of a Mott insulator that displays
N\'eel-type antiferromagnetic order. By performing a strong-coupling expansion
of an effective model that contains both Cu- and O- orbitals on the
square lattice, we demonstrate that quadrupolar fluctuations in the
-orbitals inevitably generate a biquadratic coupling between the spins of
the -orbitals. The key point revealed by our classical Monte Carlo
simulations and large- calculations is that the biquadratic term favors
local stripe-like magnetic fluctuations, which result in an enhanced nematic
susceptibility that onsets at a temperature scale determined by the effective
Heisenberg exchange . We discuss the impact of this type of nematic order on
the magnetic spectrum and outline possible implications on our understanding of
nematicity in the cuprates.Comment: 11 pages, 4 figures; includes Supplemental Material (14 pages, 4
figures
Dimensional crossover and cold-atom realization of topological Mott insulators
We propose a cold-atom setup which allows for a dimensional crossover from a
two-dimensional quantum spin Hall insulating phase to a three-dimensional
strong topological insulator by tuning the hopping between the layers. We
further show that additional Hubbard onsite interactions can give rise to spin
liquid-like phases: weak and strong topological Mott insulators. They represent
the celebrated paradigm of a quantum state of matter which merely exists
because of the interplay of the non-trivial topology of the band structure and
strong interactions. While the theoretical understanding of this phase has
remained elusive, our proposal shall help to shed some light on this exotic
state of matter by paving the way for a controlled experimental investigation
in optical lattices.Comment: 4+ pages, 3 figures; includes Supplemental Material (3 pages, 1
figure
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