다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Experimentalists have observed the predicted half-integer quantum Hall effect using the topological insulator BiSbTeSe2, which exhibits topological surface states at room temperature, with each surface contributing a half quantum of Hall conductance.

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Observation of topological surface state quantum Hall effect in an intrinsic three-dimensional topological insulator

We report the characterization of Bi${}_{2}$Te${}_{2}$Se crystals obtained by the modified Bridgman and Bridgman-Stockbarger crystal-growth techniques. X-ray-diffraction study confirms an ordered Se-Te distribution in the inner and outer chalcogen layers, respectively, with a small amount of mixing. The crystals displaying high resistivity ($g1\\phantom{\\rule{0.28em}{0ex}}\\ensuremath{\\Omega}\\phantom{\\rule{0.16em}{0ex}}\\mathrm{cm}$) and low carrier concentration ($\\ensuremath{\\sim}\\phantom{\\rule{-0.16em}{0ex}}5\\ifmmode\\times\\else\\texttimes\\fi{}{10}^{16}$/cm${}^{3}$) at 4 K were found in the central region of the long Bridgman-Stockbarger crystal, which we attribute to very small differences in defect density along the length of the crystal rod. Analysis of the temperature-dependent resistivities and Hall coefficients reveals the possible underlying origins of the donors and acceptors in this phase.

Low carrier concentration crystals of the topological insulator Bi$_2$Te$_2$Se

In addition to a bulk energy gap, topological insulators accommodate a conducting, linearly dispersed Dirac surface state. This state is predicted to become massive if time reversal symmetry is broken, and to become insulating if the Fermi energy is positioned inside both the surface and bulk gaps. We introduced magnetic dopants into the three-dimensional topological insulator dibismuth triselenide (Bi2Se3) to break the time reversal symmetry and further position the Fermi energy inside the gaps by simultaneous magnetic and charge doping. The resulting insulating massive Dirac fermion state, which we observed by angle-resolved photoemission, paves the way for studying a range of topological phenomena relevant to both condensed matter and particle physics.

http://absimage.aps.org/image/MAR11/MWS_MAR11-2010-000638.pdf

Massive Dirac Fermion on the Surface of a Magnetically Doped Topological Insulator

We report on measurements of the ac Josephson effect in three-dimensional topological insulator (TI) Josephson junctions with Fermi energy tuning using a back gate. We successfully tune the Fermi energy into the bulk gap of the TI. We observe that the Josephson energy as a function of the gate voltage has a dip feature, indicating the presence of specular Andreev reflections. We study the ac Josephson effect with detection of both Shapiro steps and Josephson emission. The obtained results show no signature of Majorana modes. With the support of simulations, we conclude that the observation of the fractional ac Josephson effect may be complicated by both a large parallel capacitance and a small ratio of current carried in $4\ensuremath{\pi}$ period modes compared to conventional $2\ensuremath{\pi}$ modes.

https://link.aps.org/accepted/10.1103/PhysRevB.101.115410

Experimental study of ac Josephson effect in gate-tunable (Bi 1 -x Sb x ) 2 Te 3 thin-film Josephson junctions

We studied magnetized topological insulator/superconductor junctions with the expectation of unconventional superconductive states holding Majorana fermions induced by superconductive proximity effects on the surface states of magnetized topological insulators (TIs), attached by conventional superconductors. We introduced Fe-doped BiSbTe2Se as an ideal magnetic TI and used the developed junction fabrication process to access the proximity-induced surface superconducting states. The bulk single crystals of the Fe-doped TI showed excellent bulk-insulating properties and ferromagnetism simultaneously at a low temperature. Meanwhile, the fabricated junctions also showed an insulating behavior above 100 K, as well as metallic conduction at a low temperature, which reflects bulk carrier freezing. In addition, we observed a proximity-induced gap structure in the conductance spectra. These results indicate that the junctions using the established materials and process are preferable to observe unconventional superconducting states which are induced via the surface channels of the magnetized TI. We believe that the developed process can be applied for the fabrication of complicated junctions and suites for braiding operations.

Proximity-Induced Superconducting States of Magnetically Doped 3D Topological Insulators with High Bulk Insulation

Topological insulators with broken time-reversal symmetry and the Fermi level within the magnetic gap at the Dirac cone provides exotic topological magneto-electronic phenomena. Here, we introduce an improved magnetically doped topological insulator, Fe-doped BiSbTe2Se (Fe-BSTS) bulk single crystal, with an ideal Fermi level. Scanning tunneling microscopy and spectroscopy (STM/STS) measurements revealed that the surface state possesses a Dirac cone with the Dirac point just below the Fermi level by 12 meV. The normalized dI/dV spectra suggest a gap opening with Δmag ∼55 meV, resulting in the Fermi level within the opened gap. Ionic-liquid gated-transport measurements also support the Dirac point just below the Fermi level and the presence of the magnetic gap. The chemical potential of the surface state can be fully tuned by ionic-liquid gating, and thus the Fe-doped BSTS provides an ideal platform to investigate exotic quantum topological phenomena.

Magnetic Gap of Fe-Doped BiSbTe2Se Bulk Single Crystals Detected by Tunneling Spectroscopy and Gate-Controlled Transports.

The transport properties of a topological Josephson junction fabricated from a magnetically doped topological insulator (TI) were investigated. The conductance spectra of the Nb/Fe-Bi$_2$Te$_2$Se/Nb junction below 1 K showed an unusual trident-shaped zero-bias conductance peak with a tiny peak width of $\sim$ 6 $\mu$V. The central peak of the trident peak presents the dc-Josephson current, and the side peaks may reflect an induced unconventional Cooper pairing. Additionally, the critical currents followed inverse to temperature, which may also reflect the presence of an unconventional proximity effect. Furthermore, microwave irradiation derived a drastic change in the conductance spectra from the peak structure into oscillatory ones, a hallmark of the ac-Josephson supercurrent. The current-phase relation of the ac-Josephson effect under high power radiofrequency-irradiation was found to be 4$\pi$-periodic. The results suggest that the junction based on magnetically doped 3D TIs may realize an unconventional Cooper pairing, thus enabling access to the basic physics of Majorana bound states and unconventional superconductivity.

Unusual Superconducting Proximity Effect in Magnetically Doped Topological Josephson Junctions

The transport properties of a topological Josephson junction fabricated from a magnetically doped topological insulator (TI) were investigated. The conductance spectra of the Nb/Fe-Bi2Te2Se/Nb junc...

Rikizo Yano

Papers

Proximity-Induced Superconducting States of Magnetically Doped 3D Topological Insulators with High Bulk Insulation

Magnetic Gap of Fe-Doped BiSbTe2Se Bulk Single Crystals Detected by Tunneling Spectroscopy and Gate-Controlled Transports.

Unusual Superconducting Proximity Effect in Magnetically Doped Topological Josephson Junctions

Unusual Superconducting Proximity Effect in Magnetically Doped Topological Josephson Junctions