143 research outputs found
Dislocation Majorana Bound States in Iron-based Superconductors
We show that lattice dislocations of topological iron-based superconductors
such as FeTeSe will intrinsically trap non-Abelian Majorana
quasiparticles, in the absence of any external magnetic field. Our theory is
motivated by the recent experimental observations of normal-state topology and
surface magnetism that coexist with superconductivity in FeTeSe,
the combination of which naturally evokes an emergent second-order topological
superconductivity in a two-dimensional subsystem spanned by screw or edge
dislocations. This exemplifies a new embedded higher-order topological phase in
class D, where Majorana zero modes appear around the "corners" of a
low-dimensional embedded subsystem, instead of those of the full crystal. A
nested domain wall theory is developed to understand the origin of these defect
Majorana zero modes. When the surface magnetism is absent, we further find that
pairing symmetry itself is capable of inducing a different type of
class-DIII embedded higher-order topology with defect-bound Majorana Kramers
pairs. We also provide detailed discussions on the real-world material
candidates for our proposals, including FeTeSe, LiFeAs,
-PdBi, and heterostructures of bismuth, etc. Our work establishes
lattice defects as a new venue to achieve high-temperature topological quantum
information processing.Comment: 12 pages, 5 figure
Phase-fluctuation Induced Time-Reversal Symmetry Breaking Normal State
Spontaneous time-reversal symmetry (TRS) breaking plays an important role in
studying strongly correlated unconventional superconductors. When the
superconducting gap functions with different pairing symmetries compete, an
Ising () type symmetry breaking occurs due to the locking of the relative
phase via a second order Josephson coupling. The phase
locking can take place even in the normal state in the phase fluctuation regime
before the onset of superconductivity. If ,
then TRS is broken, otherwise, if , or, , rotational
symmetry is broken leading to a nematic state. In both cases, the order
parameters possess a 4-fermion structure beyond the scope of mean-field theory.
We employ an effective two-component -model assisted by a renormalization
group analysis to address this problem. In addition, a quartetting, or,
charge-``4e", superconductivity can also occur above . Monte-Carlo
simulations are performed and the results are in a good agreement with the
renormalization group analysis. Our results provide useful guidance for
studying novel symmetry breakings in strongly correlated superconductors.Comment: 4+ pages, 3 figures. References are added. Supplementary Material is
updated. Comments are welcom
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