59 research outputs found
TaIrTe4 a ternary Type-II Weyl semi-metal
In metallic condensed matter systems two different types of Weyl fermions can
in principle emerge, with either a vanishing (type-I) or with a finite
(type-II) density of states at the Weyl node energy. So far only WTe2 and MoTe2
were predicted to be type-II Weyl semi-metals. Here we identify TaIrTe4 as a
third member of this family of topological semi-metals. TaIrTe4 has the
attractive feature that it hosts only four well-separated Weyl points, the
minimum imposed by symmetry. Moreover, the resulting topological surface states
- Fermi arcs connecting Weyl nodes of opposite chirality - extend to about 1/3
of the surface Brillouin zone. This large momentum-space separation is very
favorable for detecting the Fermi arcs spectroscopically and in transport
experiments
Electron-hole asymmetry in Co- and Mn-doped SrFe2As2
Phase diagram of electron and hole-doped SrFe2As2 single crystals is
investigated using Co and Mn substitution at the Fe-sites. We found that the
spin-density-wave state is suppressed by both dopants, but the superconducting
phase appears only for Co (electron)-doping, not for Mn (hole)-doping. Absence
of the superconductivity by Mn-doping is in sharp contrast to the hole-doped
system with K-substitution at the Sr sites. Distinct structural change, in
particular the increase of the Fe-As distance by Mn-doping is important to have
a magnetic and semiconducting ground state as confirmed by first principles
calculations. The absence of electron-hole symmetry in the Fe-site-doped
SrFe2As2 suggests that the occurrence of high-Tc superconductivity is sensitive
to the structural modification rather than the charge doping.Comment: 7 pages, 6 figure
Nearly isotropic upper critical fields in a SrFeCoAs single crystal
We study temperature dependent upper critical field of a
SrFeCoAs single crystal (\textit{T}=20.2 K) along
\textit{ab}-plane and \textit{c}-axis through resistivity measurements up to 50
T. For the both crystalline directions, becomes nearly isotropic
at zero temperature limit, reaching 48 T. The temperature dependence of
the curves is explained by interplay between orbital and Pauli
limiting behaviors combined with the two band effects.Comment: Proceedings of M2S-IX, Tokyo 200
Parity Transition of Spin-Singlet Superconductivity Using Sublattice Degrees of Freedom
縺(もつ)れ結晶で現れる多重超伝導状態の性質を解明. 京都大学プレスリリース. 2023-04-20.Recently, a superconducting (SC) transition from low-field (LF) to high-field (HF) SC states was reported in CeRh₂As₂, indicating the existence of multiple SC states. It has been theoretically noted that the existence of two Ce sites in the unit cell, the so-called sublattice degrees of freedom owing to the local inversion symmetry breaking at the Ce sites, can lead to the appearance of multiple SC phases even under an interaction inducing spin-singlet superconductivity. CeRh₂As₂ is considered as the first example of multiple SC phases owing to this sublattice degree of freedom. However, microscopic information about the SC states has not yet been reported. In this study, we measured the SC spin susceptibility at two crystallographically inequivalent As sites using nuclear magnetic resonance for various magnetic fields. Our experimental results strongly indicate a spin-singlet state in both SC phases. In addition, the antiferromagnetic phase, which appears within the SC phase, only coexists with the LF SC phase; there is no sign of magnetic ordering in the HF SC phase. The present Letter reveals unique SC properties originating from the locally noncentrosymmetric characteristics
Orbital selective Fermi surface shifts and mechanism of high T superconductivity in correlated AFeAs (A=Li,Na)
Based on the dynamical mean field theory (DMFT) and angle resolved
photoemission spectroscopy (ARPES), we have investigated the mechanism of high
superconductivity in stoichiometric LiFeAs. The calculated spectrum is in
excellent agreement with the observed ARPES measurement. The Fermi surface (FS)
nesting, which is predicted in the conventional density functional theory
method, is suppressed due to the orbital-dependent correlation effect with the
DMFT method. We have shown that such marginal breakdown of the FS nesting is an
essential condition to the spin-fluctuation mediated superconductivity, while
the good FS nesting in NaFeAs induces a spin density wave ground state. Our
results indicate that fully charge self-consistent description of the
correlation effect is crucial in the description of the FS nesting-driven
instabilities.Comment: 5 pages, 4 figures, supporting informatio
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