Robust Zero Energy Bound States Localized at Magnetic Impurities in Iron-based Superconductors

We investigate the effect of spin-orbit coupling on the in-gap bound states localized at magnetic impurities in multi-band superconductors with unconventional (sign-changed) and conventional (sign-unchanged) $s$-wave pairing symmetry, which may be relevant to iron-based superconductors. Without spin-orbit coupling, for spin-singlet superconductors it is known that such bound states cross zero energy at a critical value of the impurity scattering strength and acquire a finite spin-polarization. Moreover, the degenerate, spin-polarized, zero energy bound states are unstable to applied Zeeman fields as well as deviation of the impurity scattering strength away from criticality. Using a T-matrix formalism as well as analytical arguments, we show that, in the presence of spin-orbit coupling, the zero-energy bound states localized at magnetic impurities in unconventional, sign-changed, $s$-wave superconductors acquire surprising robustness to applied Zeeman fields and variation in the impurity scattering strength, an effect which is absent in the conventional, sign-unchanged, $s$-wave superconductors. Given that the iron-based multi-band superconductors may possess a substantial spin-orbit coupling as seen in recent experiments, our results may provide one possible explanation to the recent observation of surprisingly robust zero bias scanning tunneling microscope peaks localized at magnetic impurities in iron-based superconductors provided the order parameter symmetry is sign changing $s_{+-}$-wave.Comment: 8 pages, 5 figure

Online Forum Thread Retrieval using Pseudo Cluster Selection and Voting Techniques

Online forums facilitate knowledge seeking and sharing on the Web. However, the shared knowledge is not fully utilized due to information overload. Thread retrieval is one method to overcome information overload. In this paper, we propose a model that combines two existing approaches: the Pseudo Cluster Selection and the Voting Techniques. In both, a retrieval system first scores a list of messages and then ranks threads by aggregating their scored messages. They differ on what and how to aggregate. The pseudo cluster selection focuses on input, while voting techniques focus on the aggregation method. Our combined models focus on the input and the aggregation methods. The result shows that some combined models are statistically superior to baseline methods.Comment: The original publication is available at http://www.springerlink.com/. arXiv admin note: substantial text overlap with arXiv:1212.533

Thermal activation energy of 3D vortex matter in NaFe1-xCoxAs (x=0.01, 0.03 and 0.07) single crystals

We report on the thermally activated flux flow dependency on the doping dependent mixed state in NaFe1-xCoxAs (x=0.01, 0.03, and 0.07) crystals using the magnetoresistivity in the case of B//c-axis and B//ab-plane. It was found clearly that irrespective of the doping ratio, magnetoresistivity showed a distinct tail just above the Tc, offset associated with the thermally activated flux flow (TAFF) in our crystals. Furthermore, in TAFF region the temperature dependence of the activation energy follows the relation U(T, B)=U_0 (B) (1-T/T_c )^q with q=1.5 in all studied crystals. The magnetic field dependence of the activation energy follows a power law of U_0 (B)~B^(-{\alpha}) where the exponent {\alpha} is changed from a low value to a high value at a crossover field of B=~2T, indicating the transition from collective to plastic pinning in the crystals. Finally, it is suggested that the 3D vortex phase is the dominant phase in the low-temperature region as compared to the TAFF region in our series samples

Effect of Imperceptible Vibratory Noise Applied to Wrist Skin On Fingertip Touch Evoked Potentials – An EEG Study

Random vibration applied to skin can change the sense of touch. Specifically, low amplitude white-noise vibration can improve fingertip touch perception. In fact, fingertip touch sensation can improve even when imperceptible random vibration is applied to other remote upper extremity areas such as wrist, dorsum of the hand, or forearm. As such, vibration can be used to manipulate sensory feedback and improve dexterity, particularly during neurological rehabilitation. Nonetheless, the neurological bases for remote vibration enhanced sensory feedback are yet poorly understood. This study examined how imperceptible random vibration applied to the wrist changes cortical activity for fingertip sensation. We measured somatosensory evoked potentials to assess peak-to-peak response to light touch of the index fingertip with applied wrist vibration versus without. We observed increased peak-to-peak somatosensory evoked potentials with wrist vibration, especially with increased amplitude of the later component for the somatosensory, motor, and premotor cortex with wrist vibration. These findings corroborate an enhanced cortical-level sensory response motivated by vibration. It is possible that the cortical modulation observed here is the result of the establishment of transient networks for improved perception

Spin-Wave Propagation in the Presence of Interfacial Dzyaloshinskii-Moriya Interaction

In ferromagnetic thin films, broken inversion symmetry and spin-orbit coupling give rise to interfacial Dzyaloshinskii-Moriya interactions. Analytic expressions for spin-wave properties show that the interfacial Dzyaloshinskii-Moriya interaction leads to non-reciprocal spin-wave propagation, i.e. different properties for spin waves propagating in opposite directions. In favorable situations, it can increase the spin-wave attenuation length. Comparing measured spin wave properties in ferromagnet$|$normal metal bilayers and other artificial layered structures with these calculations can provide a useful characterization of the interfacial Dzyaloshinskii-Moriya interactions.Comment: 7 pages, 4 figure