Scanning Tunneling Microscopy/Spectroscopy of Vortices in LiFeAs

We investigate vortices in LiFeAs using scanning tunneling microscopy/spectroscopy. Zero-field tunneling spectra show two superconducting gaps without detectable spectral weight near the Fermi energy, evidencing fully-gapped multi-band superconductivity. We image vortices in a wide field range from 0.1 T to 11 T by mapping the tunneling conductance at the Fermi energy. A quasi-hexagonal vortex lattice at low field contains domain boundaries which consist of alternating vortices with unusual coordination numbers of 5 and 7. With increasing field, the domain boundaries become ill-defined, resulting in a uniformly disordered vortex matter. Tunneling spectra taken at the vortex center are characterized by a sharp peak just below the Fermi energy, apparently violating particlehole symmetry. The image of each vortex shows energy-dependent 4-fold anisotropy which may be associated with the anisotropy of the Fermi surface. The vortex radius shrinks with decreasing temperature and becomes smaller than the coherence length estimated from the upper critical field. This is direct evidence of the Kramer-Pesch effect expected in a clean superconductor.Comment: 9 pages, 7 figure

Upper Lumbar Pedicle Screw Insertion Using Three-Dimensional Fluoroscopy Navigation:Assessment of Clinical Accuracy

We used a navigation system to insert 128 pedicle screws into 69 vertebrae (L1 to L3) of 49 consecutive patients. We assessed the pedicle isthmic width and the permission angle for pedicle screw insertion. The permission angle is the angle defined by the greatest medial and lateral trajectories allowable when placing the screw through the center of the pedicle. The rate of narrow-width pedicles (isthmic width less than 5mm) was 5 of 60 pedicles (8%) at L1, 4 of 60 pedicles (7%) at L2, and none (0%) at L3, L4 and L5. The rate of narrow-angle pedicles (a permission angle less than 15 degrees) was 21 of 60 pedicles (35%) at L1, 7 of 60 (12%) at L2, 3 of 60 (5%) at L3, and none (0%) at L4 and L5. Of 128 pedicle screws inserted into 69 vertebrae from L1 to L3, 125 (97.7%) were classified as Grade 1 (no pedicle perforation). In general, the upper lumbar vertebrae have more narrow-width and -angle pedicles. However, we could reduce the rate of pedicle screw misplacement in upper lumbar vertebra using a three-dimensional fluoroscopy and navigation system

Clinical Accuracy of Three-Dimensional Fluoroscopy (IsoC-3D)-Assisted Upper Thoracic Pedicle Screw Insertion

Correct screw placement is especially difficult in the upper thoracic vertebrae. At the cervicothoracic junction (C7-T2), problems can arise because of the narrowness of the pedicle and the difficulty of using a lateral image intensifier there. Other upper thoracic vertebrae (T3-6) pose a problem for screw insertion also because of the narrower pedicle. We inserted 154 pedicle screws into 78 vertebrae (C7 to T6) in 38 patients. Screws were placed using intraoperative data acquisition by an isocentric C-arm fluoroscope (Siremobile Iso-C3D) and computer navigation. Out of 90 pedicle screws inserted into 45 vertebrae between C7 and T2, 87 of the 90 (96.7%) screws were classified as grade 1 (no perforation). Of 64 pedicle screws inserted into 33 vertebrae between T3 and T6, 61 of 64 (95.3%) screws were classified as grade 1. In this study, we reduced pedicle screw misplacement at the level of the C7 and upper thoracic (T1-6) vertebrae using the three-dimensional fluoroscopy navigation system