The fluctuating population of Sm 4f configurations in topological Kondo insulator SmB6 explored with high-resolution X-ray absorption and emission spectra.

High-resolution partial-fluorescence-yield X-ray absorption and resonant X-ray emission spectra were used to characterize the temperature dependence of Sm 4f configurations and orbital/charge degree of freedom in SmB6. The variation of Sm 4f configurations responds well to the formed Kondo gap, below 140 K, and an in-gap state, below 40 K. The topological in-gap state is correlated with the fluctuating population of Sm 4f configurations that arises via carrier transfer between 3d94f6 and 3d94f5 states; both states are partially delocalized, and the mediating 5d orbital plays the role of a transfer path. Complementary results shown in this work thus manifest the importance of configuration fluctuations and orbital delocalization in the topological surface state of SmB6.

Influence of Fe substitution on the Jahn-Teller distortion and orbital anisotropy in orthorhombic Y(Mn1-xFex)O3 epitaxial films.

Multiferroic YMn1-xFexO3(020) (x = 0.125, 0.25, 0.50) epitaxial thin films with an orthorhombic structure (space group Pbnm) were prepared on a YAlO3(010) substrate by pulsed-laser deposition. Upon Fe substitution, the b-axis was clearly shortened, whereas the a- and c-axes were slightly lengthened based on XRD analysis. To understand the influence of orbital polarization and the Jahn-Teller effect of Mn(3+) on Fe substitution and also the local octahedral-site distortion of Fe(3+) in an environment of Jahn-Teller-active Mn(3+) ions in YMn1-xFexO3 films, we measured the polarization-dependent X-ray absorption spectra at the Mn-L2,3 and Fe-L2,3 edges, and also simulated the experimental spectra using configuration-interaction multiplet calculations. Although Δeg for the Mn(3+) ion decreased from 0.9 eV in pure YMnO3 to 0.6 eV in the half-Fe-substituted sample, a single eg electron was still strongly constrained to the d3y(2)-r(2) orbital for all the Fe concentrations tested. The largest Δeg, 0.5 eV, for the Fe(3+) ion was derived for a sample with 12.5% Fe substitution, and gradually decreased to 0.15 eV for the half-Fe-substituted sample. The local octahedral-site distortion of the Fe(3+) ion inside the YMnO3 lattice was similar to that of the Mn(3+) ion, whereas the Jahn-Teller distortion and GdFeO3-type distortion of the Mn(3+) ion were decreased by the spherical high-spin Fe(3+) ions. The combination of the experimental and theoretical data provides both profound insight into the variation of the Jahn-Teller distortion and orbital anisotropy and instructive information about the magnetic structures in these orthorhombic YMn1-xFexO3 thin films.

Characteristics of fibrillatory activities during spontaneous termination of paroxysmal atrial fibrillation: new insight from high-density right atrium frequency mapping.

BACKGROUND: Sinus node (SN) activity is difficult to assess during atrial fibrillation (AF). The aim of the present study was to investigate SN activity by frequency analysis during AF. METHODS: Thirteen patients with paroxysmal AF and atrial flutter in the right atrium (RA) underwent 3-dimensional noncontact mapping. The fibrillatory activity was recorded from a multielectrode array in the RA. A frequency analysis with 2- and 6-second time-segment lengths was performed. Spectral characteristics (dominant frequency and harmonic index) and isopotential activation maps were used to investigate the spatiotemporal activity of the SN region and the rest of the RA (crista terminalis, septum, and free wall) during the initiation, while ongoing, and before the termination of AF. RESULTS: With duration of 6 seconds, the whole RA had similar trends of frequency distribution. With duration of 2 seconds prior to termination, the SN region exhibited a trend of low-frequency pattern and high-organization distribution, compared with the segments for the 2 to 4 and 4 to 6 seconds before termination. The isopotential activation maps showed the spontaneous earliest activities had wave front propagation patterns similar to those during sinus rhythm (after termination). CONCLUSIONS: The fibrillatory activity of the SN region was organized, and slow activation was detected, by frequency analysis and isopotential mapping, within 2 seconds just prior to AF termination.

Cavotricuspid isthmus: anatomy, electrophysiology, and long-term outcome of radiofrequency ablation.

The cavotricuspid isthmus (CTI) had a complex architecture with an anisotropic conduction property. An incremental pacing from the low right atrial isthmus produced a conduction delay and block, and initiated atrial flutter. Radiofrequency catheter ablation of the CTI was very effective in eliminating the typical atrial flutter. However, atrial fibrillation often occurred after ablation of the isthmus and needs further treatment.

Conduction barriers of atrial flutter: relation to the anatomy.

Atrial flutter (AFL) is a common arrhythmia in clinical practice. Several experimental models such as tricuspid ring model, tricuspid regurgitation model, and atrial crush injury model have provided important information about the role of conduction barriers in the reentrant circuit. Human typical AFL uses the tricuspid annulus as the anterior barrier, and uses the crista terminalis, Eustachian ridge, and sometimes sinus venosa as the posterior boundary. Rate-dependent conduction block was found in the crista terminalis and sinus venosa. Some barriers such as the crista terminalis and Eustachian ridge are not intact. The conduction gap in the barrier can produce another kind of arrhythmia. Understanding the barriers of AFL is necessary for successful radiofrequency ablation.

Electrophysiological mechanisms of atrial flutter.

Atrial flutter (AFL) is a common arrhythmia in clinical practice. Several experimental models such as tricuspid regurgitation model, tricuspid ring model, sterile pericarditis model and atrial crush injury model have provided important information about reentrant circuit and can test the effect of antiarrhythmic drugs. Human atrial flutter has typical and atypical forms. Typical atrial flutter rotates around tricuspid annulus and uses the crista terminalis and sometimes sinus venosa as the boundary. The IVC-tricuspid isthmus is a slow conduction zone and the target of radiofrequency ablation. Atypical atrial flutter may arise from the right or left atrium. Right atrial flutter includes upper loop reentry, free wall reentry and figure of eight reentry. Left atrial flutter includes mitral annular atrial flutter, pulmonary vein-related atrial flutter and left septal atrial flutter. Radiofrequency ablation of the isthmus between the boundaries can eliminate these arrhythmias.