57 research outputs found
Control of Impurity Phase Segregation in a PdCrO/CuCrO Heterostructure
PdCrO films are synthesized on CuCrO buffer layers on AlO
substrates. This synthesis is accompanied by impurity phase segregation, which
hampers the synthesis of high quality PdCrO films. The potential causes of
impurity phase segregation were studied by using a combination of experiments
and ab initio calculations. X-ray diffraction and scanning transmission
electron microscopy experiments revealed impurity phases of CuPd
alloy and chromium oxides, CrO and CrO, in PdCrO.
Calculations determined that oxygen deficiency can cause the impurity phase
segregation. Therefore, preventing oxygen release from delafossites could
suppress the impurity phase segregation. The amounts of CrO and
CrO depend differently on temperature and oxygen partial pressure. A
reasonable theory-based explanation for this experimental observation is
provided
Switching Magnetism and Superconductivity with Spin-Polarized Current in Iron-Based Superconductor
We have explored a new mechanism for switching magnetism and
superconductivity in a magnetically frustrated iron-based superconductor using
spin-polarized scanning tunneling microscopy (SPSTM). Our SPSTM study on single
crystal SrVOFeAs shows that a spin-polarized tunneling current can
switch the Fe-layer magnetism into a non-trivial (22) order, not
achievable by thermal excitation with unpolarized current. Our tunneling
spectroscopy study shows that the induced (22) order has
characteristics of plaquette antiferromagnetic order in Fe layer and strongly
suppressed superconductivity. Also, thermal agitation beyond the bulk Fe spin
ordering temperature erases the state. These results suggest a new
possibility of switching local superconductivity by changing the symmetry of
magnetic order with spin-polarized and unpolarized tunneling currents in
iron-based superconductors.Comment: 33 pages, 16 figure
Discovery of Maritrema obstipum (Digenea: Microphallidae) from Migratory Birds in Korea
Adults of Maritrema obstipum (Digenea: Microphallidae) were found in the intestines of 4 species of migratory birds, including the sanderling (Crocethia alba), Kentish plover (Charadrius alexandrines), Mongolian plover (Charadrius mongolus), and red-necked stint (Calidris ruficollis), collected from Yubu Island, Chungcheongnam-do, Korea. The worms of were 451×265 µm in size, and were easily identifiable as Maritrema species by the presence of the cirrus sac, and the ring-like distribution of the vitellaria. More specifically, the ejaculatory duct curved posteromedially, and the 2 parts of vitelline follicles were found to be distinct at the posterior end. The eggs were brown-colored, and 19.8×12.3 µm in size. All these findings implicated M. obstipum as the pertinent species of the worms. Beside these, adult worms of Gynaecotyla squatarolae, Parvatrema duboisi, and Acanthoparyphium sp. were also discovered. This is the first report establishing migratory birds as the natural definitive hosts for M. obstipum
Honeycomb oxide heterostructure: a new platform for Kitaev quantum spin liquid
Kitaev quantum spin liquid, massively quantum entangled states, is so scarce
in nature that searching for new candidate systems remains a great challenge.
Honeycomb heterostructure could be a promising route to realize and utilize
such an exotic quantum phase by providing additional controllability of
Hamiltonian and device compatibility, respectively. Here, we provide epitaxial
honeycomb oxide thin film Na3Co2SbO6, a candidate of Kitaev quantum spin liquid
proposed recently. We found a spin glass and antiferromagnetic ground states
depending on Na stoichiometry, signifying not only the importance of Na vacancy
control but also strong frustration in Na3Co2SbO6. Despite its classical ground
state, the field-dependent magnetic susceptibility shows remarkable scaling
collapse with a single critical exponent, which can be interpreted as evidence
of quantum criticality. Its electronic ground state and derived spin
Hamiltonian from spectroscopies are consistent with the predicted Kitaev model.
Our work provides a unique route to the realization and utilization of Kitaev
quantum spin liquid
Correlation of Fe-Based Superconductivity and Electron-Phonon Coupling in an FeAs/Oxide Heterostructure
Interfacial phonons between iron-based superconductors (FeSCs) and perovskite substrates have received considerable attention due to the possibility of enhancing preexisting superconductivity. Using scanning tunneling spectroscopy, we studied the correlation between superconductivity and e−ph interaction with interfacial phonons in an iron-based superconductor Sr2VO3FeAs (Tc≈33 K) made of alternating FeSC and oxide layers. The quasiparticle interference measurement over regions with systematically different average superconducting gaps due to the e−ph coupling locally modulated by O vacancies in the VO2 layer, and supporting self-consistent momentum-dependent Eliashberg calculations provide a unique real-space evidence of the forward-scattering interfacial phonon contribution to the total superconducting pairing. © 2017 American Physical Society6
Observation of In-Plane Magnetic Field Induced Phase Transitions in FeSe
We investigate thermodynamic properties of FeSe under in-plane magnetic fields using torque magnetometry, specific heat, and magnetocaloric measurements. Below the upper critical field Hc2, we observed the field induced anomalies at H1 ∼ 15 T and H2 ∼ 22 T near H ∥ ab and below a characteristic temperature T* ∼ 2 K. The transition magnetic fields H1 and H2 exhibit negligible dependence on both temperature and field orientation. This contrasts to the strong temperature and angle dependence of Hc2, suggesting that these anomalies are attributed to the field induced phase transitions, originating from the inherent spin-density-wave instability of quasipaticles near the superconducting gap minima or possible Flude-Ferrell-Larkin-Ovchinnikov state in the highly spin-polarized Fermi surfaces. Our observations imply that FeSe, an atypical multiband superconductor with extremely small Fermi energies, represents a unique model system for stabilizing unusual superconducting orders beyond the Pauli limit
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