41 research outputs found
RKKY Interaction On Surfaces of Topological Insulators With Superconducting Proximity Effect
We consider the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between
magnetic impurities on the surface of a three-dimensional topological insulator
with proximity induced superconductivity. A superconductor placed on the top of
the topological insulator induces a gap in the surface electron states and
gives rise to a long-ranged in-plane antiferromagnetic RKKY interaction. This
interaction is frustrated due to strong spin-orbit coupling, decays as
for , where is the distance between two magnetic impurities and
the superconducting coherence length, and dominates over the
ferromagnetic and Dzyaloshinskii-Moriya type interactions for . We find
the condition for the Yu-Shiba-Rusinov intragap states that are bound to the
magnetic impurities.Comment: 5 pages, 3 figure
Disorder-driven exceptional lines and Fermi ribbons in tilted nodal-line semimetals
We consider the impact of disorder on the spectrum of three-dimensional
nodal-line semimetals. We show that the combination of disorder and a tilted
spectrum naturally leads to a non-Hermitian self-energy contribution that can
split a nodal line into a pair of exceptional lines. These exceptional lines
form the boundary of an open and orientable bulk Fermi ribbon in reciprocal
space on which the energy gap vanishes. We find that the orientation and shape
of such a disorder-induced bulk Fermi ribbon is controlled by the tilt
direction and the disorder properties, which can also be exploited to realize a
twisted bulk Fermi ribbon with nontrivial winding number. Our results put
forward a paradigm for the exploration of non-Hermitian topological phases of
matter.Comment: Main Text (6 pages, 2 figures) + Supplemental Material (7 pages, 1
figure
Superconductivity from incoherent Cooper pairs in strong-coupling regime
We propose a scenario for superconductivity at strong electron-electron
attractive interaction, in the situation when the increase of interaction
strength promotes the nucleation of the local Cooper pairs and forms a state
with a spatially phase incoherent Cooper pair order parameter. We show that
this state can be characterized by a pseudogap and a scattering rate, which are
determined by the self-energy due to electron scattering on phase fluctuations.
At low temperatures, however, long-range correlations between the regions with
different phases become important and establish global phase coherence hence
superconductivity in the system. We develop a mean-field theory to describe a
phase transition between the preformed Cooper pair and superconducting states.
This scenario of superconductivity applies not only to conductors with
parabolic bands but also to the flat-band systems in which flat and dispersive
bands coexist and responsible for the Cooper pair formation as well as their
phase synchronization.Comment: 9 pages, 1 figur
Voltage induced conversion of helical to uniform nuclear spin polarization in a quantum wire
We study the effect of bias voltage on the nuclear spin polarization of a
ballistic wire, which contains electrons and nuclei interacting via hyperfine
interaction. In equilibrium, the localized nuclear spins are helically
polarized due to the electron-mediated Ruderman-Kittel-Kasuya-Yosida (RKKY)
interaction. Focusing here on non-equilibrium, we find that an applied bias
voltage induces a uniform polarization, from both helically polarized and
unpolarized spins available for spin flips. Once a macroscopic uniform
polarization in the nuclei is established, the nuclear spin helix rotates with
frequency proportional to the uniform polarization. The uniform nuclear spin
polarization monotonically increases as a function of both voltage and
temperature, reflecting a thermal activation behavior. Our predictions offer
specific ways to test experimentally the presence of a nuclear spin helix
polarization in semiconducting quantum wires.Comment: 8 pages, 4 figure
Odd-frequency spin-triplet instability in disordered electron liquid
We consider a two-dimensional disordered conductor in the regime when the
superconducting phase is destroyed by the magnetic field. We observe that the
end point of the superconductivity is a quantum critical point separating the
conventional superconducting phase from a state with the odd-frequency
spin-triplet pairing instability. We speculate that this could shed light on a
rather mysterious insulating state observed in strongly disordered
superconducting films in a broad region of the magnetic fields.Comment: 27 pages, 8 figure
Josephson junction through a disordered topological insulator with helical magnetization
We study supercurrent and proximity vortices in a Josephson junction made of disordered surface states of a three-dimensional topological insulator with a proximity induced in-plane helical magnetization. In a regime where the rotation period of helical magnetization is larger than the junction width, we find supercurrent 0 - pi crossovers as a function of junction thickness, magnetization strength, and parameters inherent to the helical modulation and surface states. The supercurrent reversals are associated with proximity induced vortices, nucleated along the junction width, where the number of vortices and their locations can be manipulated by means of the superconducting phase difference and the parameters mentioned above
Antichiral and nematicity-wave superconductivity
Larkin-Ovchinnikov superconducting state has spontaneous modulation of Cooper
pair density, while Fulde-Ferrell state has a spontaneous modulation in the
phase of the order parameter. We report that a quasi-two-dimensional Dirac
metal, under certain conditions has principally different inhomogeneous
superconducting states that by contrast have spontaneous modulation in a
submanifold of a multiple-symmetries-breaking order parameter. The first state
we find can be viewed as a nematic superconductor where the nematicity vector
spontaneously breaks rotational and translational symmetries due to spatial
modulation. The other demonstrated state is a chiral superconductor with
spontaneously broken time-reversal and translational symmetries. It is
characterized by an order parameter, which forms a lattice pattern of
alternating chiralities.Comment: Version published in Physical Review B Rapid Communication
Disorder-driven exceptional lines and Fermi ribbons in tilted nodal-line semimetals
We consider the impact of disorder on the spectrum of three-dimensional nodal-line semimetals. We show that the combination of disorder and a tilted spectrum naturally leads to a non-Hermitian self-energy contribution that can split a nodal line into a pair of exceptional lines. These exceptional lines form the boundary of an open and orientable bulk Fermi ribbon in reciprocal space on which the energy gap vanishes. We find that the orientation and shape of such a disorder-induced bulk Fermi ribbon is controlled by the tilt direction and the disorder properties, which can also be exploited to realize a twisted bulk Fermi ribbon with nontrivial winding number. Our results put forward a paradigm for the exploration of non-Hermitian topological phases of matter
The crystal structure of compositionally homogeneous mixed ceria-zirconia oxides by high resolution X-ray and neutron diffraction methods
Preformed Cooper pairs in flat-band semimetals
Funding Information: The authors are thankful to Vladimir Zyuzin for critical discussions and to Pirinem School of Theoretical Physics for warm hospitality. This research was supported by the Academy of Finland (Project No. 308339) and in parts by the Academy of Finland Centre of Excellence program (Project No. 336810). Publisher Copyright: © 2022 American Physical Society.We study conditions for the emergence of the preformed Cooper pairs in materials hosting flat bands. As a particular example, we consider a semimetal, with a pair of three-band crossing points at which a flat band intersects with a Dirac cone, and focus on the s-wave intervalley pairing channel. The nearly dispersionless nature of the flat band at strong attraction between electrons promotes local Cooper pair formation so that the system may be modeled as an array of superconducting grains. Due to dispersive bands, Andreev scattering between the grains gives rise to the global phase-coherent superconductivity at low temperatures. We develop a mean-field theory to calculate transition temperature between the preformed Cooper pair state and the phase-coherent state for different interaction strengths in the Cooper channel. The transition temperature between semimetal and preformed Cooper pair phases is proportional to the interaction constant, the dependence of the transition temperature to the phase-coherent state on the interaction constant is weaker.Peer reviewe