10 research outputs found
준금속의 위상학적 초전도성
No full text학위논문(박사) - 한국과학기술원 : 물리학과, 2020.8,[vii, 67 p. :]In this dissertation, we investigate topological superconducting states in semimetals. Unlike many of previous literatures which focused on Dirac/Weyl semimetals, we investigated physical properties of spin-orbit coupled multi-band systems where the electrons with higher-pseudospin can be realized near the Fermi level. We found new kind of topological superconducting phases which have gapless Bogoliubov quasiparticles and furthermore have topological invariants for each nodal line or Bogoliubov Fermi surface. Adopting the Ginzburg–Landau theory, we also investigate the stability of each phase within one-loop calculations.한국과학기술원 :물리학과
Pair Density Waves and Supercurrent Diode Effect in Altermagnets
No full textMetallic altermagnets are unusual collinear magnets that feature zero net
magnetization with momentum-dependent spin splitting. Here, we show that this
spin splitting can induce pair density wave states even in the absence of
external magnetic fields. Focusing on BCS-type attractive interactions, we find
the stabilization of symmetrically distinct pair density wave states depending
on the chemical potential. These states include Fulde-Ferrell and
Fulde-Ferrell* states, both of which break inversion symmetry. We investigate
the supercurrent properties and discover non-reciprocal supercurrents for both
the Fulde-Ferrell and Fulde-Ferrell* states with distinct spatial dependencies.
We propose that the supercurrent diode effect can serve as an experimental tool
for distinguishing between different pair density waves in metallic
altermagnets and discuss the relation to material candidates.Comment: 9 pages, 5 figure
Triplet-Superconductivity in Triple-Band Crossings
No full textMulti-band superconductivity in topological semimetals are the paradigms of
unconventional superconductors. Their exotic gap structures and topological
properties have fascinated searching for material realizations and
applications. In this paper, we focus on triple point fermions, a new type of
band crossings, and we claim that their superconductivity uniquely stabilizes
spin-triplet pairing. Unlike conventional superconductors and other multi band
superconductors, such triplet superconductivity is the novel phenomena of
triple point fermions where the spin-singlet pairing is strictly forbidden in
the on-site interaction due to the Fermi statistics. We find that two distinct
triplet superconductors, characterized by the presence and absence of
time-reversal symmetry, are allowed which in principle can be controlled by
tuning the chemical potential. For the triplet superconductor with
time-reversal symmetry, we show that topologically protected nodal lines are
realized. In contrast, for time-reversal broken case, the complication of
topologically protected Bogoliubov Fermi surfaces emerges. Our theoretical
study provides a new guidance for searching triplet superconductivities and
their exotic implications.Comment: 7 pages, 3 figure
Topological triplet-superconductivity in spin-1 semimetal
No full textSpin-triplet superconductors are expected to host topological excitations, which makes them potentially useful materials for future quantum technologies. Here, the authors theoretically report a triple point semimetal that, through triple point fermions, stabilizes an s-wave spin-triplet pairing distinct from conventional BCS and other multi-band superconductors. Superconductivity in topological semimetals gives a new paradigm of unconventional superconductors. Their exotic gap structures and topological properties have fascinated searching for material realizations and applications. In this work, we focus on a triple point semimetal where quasiparticle excitations, triple point fermions, carry the effective integer spin-1 in two distinct valleys. Our work demonstrates that the triple point fermion stabilizes inter-valley s-wave spin-triplet pairing. This is due to Fermi statistics, which strictly forbids the formation of inter-valley s-wave spin-singlet pairings. This feature is clearly distinct from the BCS and other multi-band superconductors. We find that two distinct inter-valley s-wave spin-triplet superconductors are allowed which in principle can be controlled by tuning the chemical potential: time-reversal symmetric (s(z)) state with topologically protected nodal lines and time-reversal broken (s(x) + is(y)) state with topologically protected Bogoliubov Fermi surfaces. Our study provides guidance in searching for spin-triplet superconductivity.11Nsciescopu
Nonlinear spectroscopy of bound states in perturbed Ising spin chains
No full textWe study the nonlinear response of non-integrable 1D spin models using
infinite matrix-product state techniques. As a benchmark and demonstration of
the method, we first calculate the 2D coherent spectroscopy for the exactly
soluble ferromagnetic transverse field Ising model, where excitations are
freely moving domain-walls. We then investigate the distinct signatures of
confined bound states by introducing a longitudinal field and observe the
emergence of strong non-rephasing like signals. To interpret the observed
phenomena, we use a two-kink approximation to perturbatively compute the 2D
spectra. We find good agreement in comparison with the exact results of the
infinite matrix-product state method in the strongly confined regime. We
discuss the relevance of our results for quasi1D Ising spin chain materials
such as .Comment: 9 pages, 5 figure
Shedding Light on Microscopic Details: 2D Spectroscopy of 1D Quantum Ising Magnets
No full textThe identification of microscopic models describing the low-energy properties
of correlated materials has been a central goal of spectroscopic measurements.
We demonstrate how 2D non-linear spectroscopy can be used to distinguish
effective spin models whose linear responses show similar behavior. Motivated
by recent experiments on the quasi-1D Ising magnet CoNbO, we focus on
two proposed models, the ferromagnetic twisted Kitaev chain with bond dependent
interactions and the transverse field Ising model. The dynamical spin structure
factor probed in linear response displays similar broad spectra for both models
from their fermionic domain wall excitations. In sharp contrast, the 2D
non-linear spectra of the two models show clear qualitative differences: those
of the twisted Kitaev model contain off-diagonal peaks originating from the
bond dependent interactions and transitions between different fermion bands
absent in the transverse field Ising model. We discuss the different signatures
of spin fractionalization in integrable and non-integrable regimes of the
models and their connection to experiments.Comment: 10 pages, 6 figure
Multipolar superconductivity in Luttinger semimetals
No full textTopological superconductivity in multiband systems has received much attention due to a variety of possible exotic superconducting order parameters as well as nontrivial bulk and surface states. While the impact of coexisting magnetic order on superconductivity, such as ferromagnetic superconductors, has been studied for many years, the implication of coexisting multipolar order has not been explored much despite the possibility of multipolar hidden order in a number of f-electron materials. In this work, we investigate topological properties of multipolar superconductors that may arise when quadrupolar local moments are coupled to conduction electrons in the multiband Luttinger semimetal. We show that the multipolar ordering of local moments leads to various multipolar superconductors with distinct topological properties. We apply these results to the quadrupolar Kondo semimetal system, PrBi, by deriving the microscopic multipolar Kondo model and examining the possible superconducting order parameters
Topological d plus s wave superconductors in a multiorbital quadratic band touching system
No full textRealization of topological superconductors is one of the most important goals in studies of topological phases in quantum materials. In this work we theoretically propose a way to attain topological superconductors with nontrivial Fermi surfaces of Bogoliubov quasiparticles. Considering the interacting Luttinger model with j = 3/2 electrons, we investigate the dominant superconducting channels for a multiorbital quadratic band touching system with finite chemical potential, which breaks the particle-hole symmetry in the normal state. Notably, while the system generally favors d-wave pairing, the absence of the particle-hole symmetry necessarily induces s-wave pairing and such emergence of s-wave pairing leads to new types of topological d s wave superconductors and selects particular d-wave pairing channels. Based on the Landau theory with SO(3) symmetry, we demonstrate that two kinds of topological superconductors are energetically favored; uniaxial nematic phase with secondary s-wave pairing (d(3z2-r2 )+ s) and time-reversal-symmetry broken phase with secondary s-wave pairing (d(3z2-r2) + d(xy) +id(x2-y2) + s). These superconductors contain either nodal lines or Fermi pockets of gapless Bogoliubov quasiparticles and moreover exhibit topological invariants, leading to nontrivial surface states such as drumhead like surface states or Fermi arcs. We discuss applications of our theory to relevant families of materials, especially half-Heusler compound YPtBi, and suggest possible future experiments.11Nsciescopu
