The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Yukio Tanaka - One of the best experts on this subject based on the ideXlab platform.
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theory of Tunneling Conductance and surface state transition in superconducting topological insulators
Physical Review B, 2012Co-Authors: Ai Yamakage, Keiji Yada, Masatoshi Sato, Yukio TanakaAbstract:We develop a theory of the Tunneling spectroscopy for superconducting topological insulators (STIs), where the surface Andreev bound states (SABSs) appear as helical Majorana fermions. Based on the symmetry and topological nature of parent topological insulators, we find that the SABSs in the STIs have a structural transition in the energy dispersions. The transition results in a variety of Majorana fermions, by tuning the chemical potential and the effective mass of the energy band. We clarify that Majorana fermions in the vicinity of the transitions give rise to robust zero bias peaks in the Tunneling Conductance between normal metal/STI junctions.
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Theory of Tunneling Conductance for Normal Metal/Insulator/
2008Co-Authors: Triplet Superconductor Junction, Yukio Tanaka, Masashi Yamashiro, Y. Tanuma, Satoshi KashiwayaAbstract:Tunneling Conductance spectra of normal metal/insulator/triplet superconductor junctions are investigated theoretically. As triplet paring states we select several types of symmetries that are promising candidates for the superconducting states in UPt3 and in Sr2RuO4. The calculated Conductance spectra are sensitive to the orientation of the junction which reflects the anisotropy of the pairing states. They show either zero-bias Conductance peaks or gap-like structures depending on the orientation of the junctions. The existence of a residual density of states, peculiar to nonunitary states, is shown to have a significant influence on the properties of the Conductance spectra. Present results serve as a guide for the experimental determination of the symmetry of the pair potentials in UPt3 and Sr2RuO4.
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Temperature dependence of Tunneling Conductance in diffusive normal metal/triplet superconductor junctions
Physica C-superconductivity and Its Applications, 2007Co-Authors: Iduru Shigeta, Takehito Yokoyama, Yasuhiro Asano, Fusao Ichikawa, Yukio TanakaAbstract:The thermal broadening effect on the Tunneling Conductance in diffusive normal metal/triplet superconductor (DN/TS) junctions is studied based on the Usadel equation under the generalized boundary condition. The zero-bias Conductance peak (ZBCP) enhances in the antinodal direction, due to the coexistence of the proximity effect and the midgap Andreev resonant states at the DN/TS junction interface. It is found that the ZBCP is affected by the thermal broadening effect especially for tunnel junctions with the low transparency and the small Thouless energy.
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Thermal Broadening Effect on the Tunneling Conductance in Diffusive Normal Metal / Superconductor Junctions
AIP Conference Proceedings, 2006Co-Authors: Iduru Shigeta, Takehito Yokoyama, Yasuhiro Asano, Yukio TanakaAbstract:Using the circuit theory, we have studied how zero‐bias Conductance dip (ZBCD) and zero‐bias Conductance peak (ZBCP) are smeared by increasing temperature in the diffusive normal metal (DN) / s‐wave or d‐wave superconductor junctions. Tunneling Conductance of the junction is calculated by changing the magnitudes of the resistance in DN, the Thouless energy in DN, the transparency of the insulating barrier, and the angle between the normal to the interface and the crystal axis of d‐wave superconductors. We present a threshold temperature from a possible observation of the ZBCD and ZBCP in line shapes of Tunneling Conductance.
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Theory of Tunneling Conductance in quantum wire/d-wave superconductor junctions
Physica C-superconductivity and Its Applications, 2001Co-Authors: Kimio Tsuchikawa, Nobukatsu Yoshida, Yukio Tanaka, Satoshi Kashiwaya, Jun-ichiro Inoue, Yukihiko TakagakiAbstract:The Tunneling Conductance in quantum wire/insulator/d-wave superconductor junctions is calculated. It is revealed that the low-bias properties of the Tunneling Conductance are influenced significantly by the number of transverse modes in the quantum wire. The zero-bias Conductance peak due to the Andreev bound state vanishes in the single-mode case because of the quantum-mechanical diffraction of the electron wave by the narrow opening [Phys. Rev. B 60 (1999) 9750]. However, with an increase of the number of modes, the amplitude of the Andreev reflection at low voltages is regained.
J. M. Maclaren - One of the best experts on this subject based on the ideXlab platform.
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Electronic structure and spin-dependent Tunneling Conductance under a finite bias
Physical Review B, 2004Co-Authors: Chun Zhang, Xiaoguang Zhang, Predrag S Krstic, Hai-ping Cheng, William H. Butler, J. M. MaclarenAbstract:We present a spin-polarized self-consistent density functional theory (DFT) method for calculation of the electronic structure and transport properties of a system under a finite bias voltage. This method is implemented within the layer Korringa-Kohn-Rostoker approach. We calculate the Tunneling Conductance and the magnetoresistance (MR) of Fe/FeO/MgO/Fe Tunneling junctions as functions of bias voltage. We find that the change in the electronic structure is minimal as a function of bias. The effective capacitance is consistent with the dielectric constant of MgO. The Tunneling Conductance is highly nonlinear. At low biases the TMR ratio is greatly reduced due to the large contribution to the Tunneling current from interface resonance states. This contribution diminishes as the bias voltage increases, leading to an increase of the TMR ratio as a function of bias.
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Spin-dependent Tunneling Conductance of Fe | MgO | Fe sandwiches
Physical Review B, 2001Co-Authors: William H. Butler, Xiaoguang Zhang, Thomas C. Schulthess, J. M. MaclarenAbstract:We present first-principles based calculations of the Tunneling Conductance and magnetoConductance of epitaxial $\mathrm{Fe}(100)|\mathrm{MgO}(100)|\mathrm{Fe}(100)$ sandwiches. Our results indicate that Tunneling is much more interesting and complicated than the simple barrier model used previously. We obtain the following general results: (1) Tunneling Conductance depends strongly on the symmetry of the Bloch states in the electrodes and of the evanescent states in the barrier layer. (2) Bloch states of different symmetry decay at different rates within the barrier. The decay rate is determined by the complex energy bands of the same symmetry in the barrier. (3) There may be quantum interference between the decaying states in the barrier. This leads to an oscillatory dependence of the Tunneling current on ${k}_{\ensuremath{\Vert}}$ and a damped oscillatory dependence on barrier thickness. (4) Interfacial resonance states can allow particular Bloch states to tunnel efficiently through the barrier. For $\mathrm{Fe}(100)|\mathrm{MgO}(100)|\mathrm{Fe}(100)$ our calculations indicate that quite different Tunneling mechanisms dominate the Conductance in the two spin channels. In the majority channel the Conductance is primarily via Bloch electrons with small transverse momentum. One particular state with ${\ensuremath{\Delta}}_{1}$ symmetry is able to effectively couple from the Fe into the MgO. In the minority channel the Conductance is primarily through interface resonance states especially for thinner layers. We predict a large magnetoresistance that increases with barrier thickness.
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spin dependent Tunneling Conductance of fe mgo fe sandwiches
Physical Review B, 2001Co-Authors: W H Butler, Thomas C. Schulthess, X G Zhang, J. M. MaclarenAbstract:We present first-principles based calculations of the Tunneling Conductance and magnetoConductance of epitaxial $\mathrm{Fe}(100)|\mathrm{MgO}(100)|\mathrm{Fe}(100)$ sandwiches. Our results indicate that Tunneling is much more interesting and complicated than the simple barrier model used previously. We obtain the following general results: (1) Tunneling Conductance depends strongly on the symmetry of the Bloch states in the electrodes and of the evanescent states in the barrier layer. (2) Bloch states of different symmetry decay at different rates within the barrier. The decay rate is determined by the complex energy bands of the same symmetry in the barrier. (3) There may be quantum interference between the decaying states in the barrier. This leads to an oscillatory dependence of the Tunneling current on ${k}_{\ensuremath{\Vert}}$ and a damped oscillatory dependence on barrier thickness. (4) Interfacial resonance states can allow particular Bloch states to tunnel efficiently through the barrier. For $\mathrm{Fe}(100)|\mathrm{MgO}(100)|\mathrm{Fe}(100)$ our calculations indicate that quite different Tunneling mechanisms dominate the Conductance in the two spin channels. In the majority channel the Conductance is primarily via Bloch electrons with small transverse momentum. One particular state with ${\ensuremath{\Delta}}_{1}$ symmetry is able to effectively couple from the Fe into the MgO. In the minority channel the Conductance is primarily through interface resonance states especially for thinner layers. We predict a large magnetoresistance that increases with barrier thickness.
Krishnendu Sengupta - One of the best experts on this subject based on the ideXlab platform.
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Unconventional scanning Tunneling Conductance spectra for graphene
Physical Review B, 2010Co-Authors: Kush Saha, I. Paul, Krishnendu SenguptaAbstract:We compute the Tunneling Conductance of graphene as measured by a scanning Tunneling microscope (STM) with a normal/superconducting tip. We demonstrate that for undoped graphene with zero Fermi energy, the first derivative of the Tunneling Conductance with respect to the applied voltage is proportional to the density of states of the STM tip. We also show that the shape of the STM spectra for graphene doped with impurities depends qualitatively on the position of the impurity atom in the graphene matrix and relate this unconventional phenomenon to the pseudospin symmetry of the Dirac quasiparticles in graphene. We suggest experiments to test our theory.
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Theory of Tunneling Conductance of graphene normal metal-insulator-superconductor junctions
Physical Review B, 2007Co-Authors: Subhro Bhattacharjee, M. Maiti, Krishnendu SenguptaAbstract:We calculate the Tunneling Conductance of a graphene normal metal-insulator-superconductor (NIS) junction with a barrier of thickness d and with an arbitrary voltage $V_0$ applied across the barrier region. We demonstrate that the Tunneling Conductance of such a NIS junction is an oscillatory function of both d and $V_0$. We also show that the periodicity and amplitude of such oscillations deviate from their universal values in the thin barrier limit as obtained in an earlier work [S. Bhattacharjee and K. Sengupta, Phys. Rev. Lett. 97, 217001 (2006)] and become a function of the applied voltage $V_0$. Our results reproduce the earlier results on Tunneling Conductance of such junctions in the thin [S. Bhattacharjee and K. Sengupta, Phys. Rev. Lett. 97, 217001 (2006)] and zero [C. W. J. Beenakker, Phys. Rev. Lett. 97, 067007 (2006)] barrier limits as special limiting cases. We discuss the experimental relevance of our results.
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Tunneling Conductance of graphene NIS junctions.
Physical review letters, 2006Co-Authors: Subhro Bhattacharjee, Krishnendu SenguptaAbstract:We show that, in contrast with conventional normal metal-insulator-superconductor (NIS) junctions, the Tunneling Conductance of a NIS junction in graphene is an oscillatory function of the effective barrier strength of the insulating region, in the limit of a thin barrier. The amplitude of these oscillations is maximum for aligned Fermi surfaces of the normal and superconducting regions and vanishes for a large Fermi surface mismatch. The zero-bias Tunneling Conductance, in sharp contrast to its counterpart in conventional NIS junctions, becomes maximum for a finite barrier strength. We also suggest experiments to test these predictions.
Satoshi Kashiwaya - One of the best experts on this subject based on the ideXlab platform.
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Theory of Tunneling Conductance for Normal Metal/Insulator/
2008Co-Authors: Triplet Superconductor Junction, Yukio Tanaka, Masashi Yamashiro, Y. Tanuma, Satoshi KashiwayaAbstract:Tunneling Conductance spectra of normal metal/insulator/triplet superconductor junctions are investigated theoretically. As triplet paring states we select several types of symmetries that are promising candidates for the superconducting states in UPt3 and in Sr2RuO4. The calculated Conductance spectra are sensitive to the orientation of the junction which reflects the anisotropy of the pairing states. They show either zero-bias Conductance peaks or gap-like structures depending on the orientation of the junctions. The existence of a residual density of states, peculiar to nonunitary states, is shown to have a significant influence on the properties of the Conductance spectra. Present results serve as a guide for the experimental determination of the symmetry of the pair potentials in UPt3 and Sr2RuO4.
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Theory of Tunneling Conductance in quantum wire/d-wave superconductor junctions
Physica C-superconductivity and Its Applications, 2001Co-Authors: Kimio Tsuchikawa, Nobukatsu Yoshida, Yukio Tanaka, Satoshi Kashiwaya, Jun-ichiro Inoue, Yukihiko TakagakiAbstract:The Tunneling Conductance in quantum wire/insulator/d-wave superconductor junctions is calculated. It is revealed that the low-bias properties of the Tunneling Conductance are influenced significantly by the number of transverse modes in the quantum wire. The zero-bias Conductance peak due to the Andreev bound state vanishes in the single-mode case because of the quantum-mechanical diffraction of the electron wave by the narrow opening [Phys. Rev. B 60 (1999) 9750]. However, with an increase of the number of modes, the amplitude of the Andreev reflection at low voltages is regained.
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Theory of Tunneling Conductance in quantum-wire/unconventional superconductor junctions
Physica C-superconductivity and Its Applications, 2001Co-Authors: Kimio Tsuchikawa, Nobukatsu Yoshida, Yukio Tanaka, Satoshi Kashiwaya, Jun-ichiro Inoue, Yukihiko TakagakiAbstract:Tunneling Conductance in quantum-wire/insulator/unconventional superconductor (q/I/S) junctions is calculated in the case where the unconventional superconductor has triplet symmetry. Differently from the case in d-wave superconductor junctions, the magnitude of the Tunneling Conductance near zero voltage is enhanced due to the Andreev bound state by the quasiparticle with perpendicular injection. From the Tunneling spectroscopy of q/I/S junctions, we can distinguish p-wave (triplet) superconductor from d-wave (singlet) one.
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Tunneling Conductance and Spatial Dependences of Pair Potentials in Normal Metal-Triplet Superconductor Junctions
Journal of the Physical Society of Japan, 1999Co-Authors: Masashi Yamashiro, Nobukatsu Yoshida, Yukio Tanaka, Satoshi KashiwayaAbstract:Tunneling Conductance spectra in normal metal / insulator / triplet superconductor junctions are theoretically investigated. For the triplet paring states, we select several kinds of the symmetries...
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theory of Tunneling Conductance for normal metal insulator triplet superconductor junction
Journal of the Physical Society of Japan, 1998Co-Authors: Masashi Yamashiro, Yukio Tanaka, Y. Tanuma, Satoshi KashiwayaAbstract:Tunneling Conductance spectra of normal metal/insulator/triplet superconductor junctions are investigated theoretically. As triplet paring states we select several types of symmetries that are promising candidates for the superconducting states in UPt 3 and in Sr 2 RuO 4 . The calculated Conductance spectra are sensitive to the orientation of the junction which reflects the anisotropy of the pairing states. They show either zero-bias Conductance peaks or gap-like structures depending on the orientation of the junctions. The existence of a residual density of states, peculiar to nonunitary states, is shown to have a significant influence on the properties of the Conductance spectra. Present results serve as a guide for the experimental determination of the symmetry of the pair potentials in UPt 3 and Sr 2 RuO 4 .
W Zhang - One of the best experts on this subject based on the ideXlab platform.
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Tunneling Conductance and magnetoresistance of ferromagnet/ferromagnetic insulator (semiconductor)/ferromagnet junctions
Physical Review B, 1998Co-Authors: Yun Li, Bozang Li, W ZhangAbstract:The Tunneling Conductance (TC) and magnetoresistance (TMR) are investigated for magnetic junctions consisting of two ferromagnetic electrodes separated by a ferromagnetic insulator (semiconductor). The investigations are based on the nearly-free-electron approximation. The results show that TC and TMR strongly depend on the magnetization configuration of the junction such that TC and TMR reach their maximums when the magnetic moments of the two electrodes are parallel to each other but antiparallel to that of the barrier, whereas the minimums appear when the magnetic moments of both electrodes and the barrier are parallel. The Tunneling probability (TP) relates to the spin orientation of incident electrons and the magnetization configuration of the junction. The variation of TC and TMR with the relative orientation of magnetization of both electrodes and the barrier can be explained by two effects: the ferromagnet-ferromagnet Tunneling and spin-filtering effect. Our results agree well with experiment.
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Tunneling Conductance and magnetoresistance of ferromagnet ferromagnetic insulator semiconductor ferromagnet junctions
Physical Review B, 1998Co-Authors: W Zhang, Daosheng DaiAbstract:The Tunneling Conductance (TC) and magnetoresistance (TMR) are investigated for magnetic junctions consisting of two ferromagnetic electrodes separated by a ferromagnetic insulator (semiconductor). The investigations are based on the nearly-free-electron approximation. The results show that TC and TMR strongly depend on the magnetization configuration of the junction such that TC and TMR reach their maximums when the magnetic moments of the two electrodes are parallel to each other but antiparallel to that of the barrier, whereas the minimums appear when the magnetic moments of both electrodes and the barrier are parallel. The Tunneling probability (TP) relates to the spin orientation of incident electrons and the magnetization configuration of the junction. The variation of TC and TMR with the relative orientation of magnetization of both electrodes and the barrier can be explained by two effects: the ferromagnet-ferromagnet Tunneling and spin-filtering effect. Our results agree well with experiment.
