33 research outputs found
Kramers' degenerate magnetism and superconductivity
Motivated by the recent discovery of odd-parity multipolar antiferromagnetic
order in CeRhAs, we examine the coexistence of such translation
invariant Kramers' degenerate magnetic states and superconductivity. We show
that the presence of such magnetic states generically suppresses
superconductivity, whether it be spin-singlet or spin-triplet, unless the
magnetic state drives a symmetry-required pair density wave (PDW)
superconducting order. We apply our results to CeRhAs, where no pair
density wave order appears; and to the loop current order in the cuprates,
where such pair density wave superconductivity must appear together with
Bogoliubov Fermi surfaces. In the former case, we explain why superconductivity
is not suppressed.Comment: 11 pages, 4 Figure
Extremely Large Magnetoresistance in the Nonmagnetic Metal PdCoO2
Extremely large magnetoresistance is realized in the nonmagnetic layered
metal PdCoO2. In spite of a highly conducting metallic behavior with a simple
quasi-two-dimensional hexagonal Fermi surface, the interlayer resistance
reaches up to 35000% for the field along the [1-10] direction. Furthermore, the
temperature dependence of the resistance becomes nonmetallic for this field
direction, while it remains metallic for fields along the [110] direction. Such
severe and anisotropic destruction of the interlayer coherence by a magnetic
field on a simple Fermi surface is ascribable to orbital motion of carriers on
the Fermi surface driven by the Lorentz force, but seems to have been largely
overlooked until now.Comment: Phys. Rev. Lett. 111, 056601 (2013
Tuning quantum paramagnetism and d-wave superconductivity in single-layer iron chalcogenides by chemical pressure
By substituting S into single-layer FeSe/SrTiO3, chemical pressure is applied
to tune its paramagnetic state that is modeled as an incoherent superposition
of spin-spiral states. The resulting electronic bands resemble an ordered
checkerboard antiferromagnetic structure, consistent with angle-resolved
photoemission spectroscopy measurements. Scanning tunneling spectroscopy
reveals a gap evolving from U-shaped for FeSe to V-shaped for FeS with
decreasing size, attributed to a d-wave superconducting state for which nodes
emerge once the gap size is smaller than the effective spin-orbit coupling
Superconductivity of anomalous pseudospin
Spin-orbit coupling driven by broken inversion symmetry () is known to
lead to unusual magnetic response of superconductors, including extremely large
critical fields for spin-singlet superconductors. This unusual response is also
known to appear in materials that have , provided there is local
-breaking: fermions participating in superconductivity reside on crystal
sites that lack . Here we show that this unusual response exists even when
the crystal sites preserve . Indeed, we argue that the symmetry of Kramers
degenerate fermionic pseudospin is more relevant than the local crystal site
symmetry. We examine and classify non-symmorphic materials with momentum space
spin-textures that exhibit an anomalous pseudospin with different symmetry
properties than usual spin-1/2. We find that this anomalous pseudospin does not
depend on the existence of local breaking crystal sites and it optimizes
the unusual magnetic response traditionally associated with locally
noncentrosymmetric superconductors, dramatically extending the range of
relevant materials. We further show this anomalous pseudospin leads to fully
gapped `nodal' superconductors and provides additional insight into the
breakdown of Blount's theorem for pseudospin triplet superconductors. We apply
our results to UPt, BiS-based superconductors, Fe-based
superconductors, and paramagnetic UCoGe
Band-theoretical prediction of magnetic anisotropy in uranium monochalcogenides
Magnetic anisotropy of uranium monochalcogenides, US, USe and UTe, is studied
by means of fully-relativistic spin-polarized band structure calculations
within the local spin-density approximation. It is found that the size of the
magnetic anisotropy is fairly large (about 10 meV/unit formula), which is
comparable with experiment. This strong anisotropy is discussed in view of a
pseudo-gap formation, of which crucial ingredients are the exchange splitting
of U 5f states and their hybridization with chalcogen p states (f-p
hybridization). An anomalous trend in the anisotropy is found in the series
(US>>USe<UTe) and interpreted in terms of competition between localization of
the U 5f states and the f-p hybridization. It is the spin-orbit interaction on
the chalcogen p states that plays an essential role in enlarging the strength
of the f-p hybridization in UTe, leading to an anomalous systematic trend in
the magnetic anisotropy.Comment: 4 pages, 5 figure