9 research outputs found
Charge Transport and Quantum Phase Transitions in Singlet Superconductor - Ferromagnet - Singlet Superconductor Junctions
We study the Josephson current, I_J, in a junction consisting of two s-wave
superconductors that are separated by a ferromagnetic barrier possessing a
magnetic and non-magnetic scattering potential, g and Z, respectively. We
discuss the general dependence of I_J on g, Z, and the phase difference \phi
between the two superconductors. Moreover, we compute the critical current, I_c
for given g and Z, and show that it possesses two lines of non-analyticity in
the (g, Z)-plane. We identify those regions in the (g, Z)-plane where the
Josephson current changes sign with increasing temperature without a change in
the relative phase between the two superconductors, i.e., without a transition
between a 0 and \pi state of the junction. Finally, we show that by changing
the relative phase \phi, it is possible to tune the junction through a
first-order quantum phase transition in which the spin polarization of the two
superconductors' combined ground state changes from =0 to =1/2.Comment: final version, published in Phys. Rev.
Spin susceptibility in bilayered cuprates: resonant magnetic excitations
We study the momentum and frequency dependence of the dynamical spin
susceptibility in the superconducting state of bilayer cuprate superconductors.
We show that there exists a resonance mode in the odd as well as the even
channel of the spin susceptibility, with the even mode being located at higher
energies than the odd mode. We demonstrate that this energy splitting between
the two modes arises not only from a difference in the interaction, but also
from a difference in the free-fermion susceptibilities of the even and odd
channels. Moreover, we show that the even resonance mode disperses downwards at
deviations from . In addition, we demonstrate that there
exists a second branch of the even resonance, similar to the recently observed
second branch (the -mode) of the odd resonance. Finally, we identify the
origin of the qualitatively different doping dependence of the even and odd
resonance. Our results suggest further experimental test that may finally
resolve the long-standing question regarding the origin of the resonance peak.Comment: 8 pages, 5 figure
Integration of selectively grown topological insulator nanoribbons in superconducting quantum circuits
We report on the precise integration of nm-scale topological insulator
Josephson junctions into mm-scale superconducting quantum circuits via
selective area epitaxy and local stencil lithography. By studying dielectric
losses of superconducting microwave resonators fabricated on top of our
selective area growth mask, we verify the compatibility of this in situ
technique with microwave applications. We probe the microwave response of
on-chip microwave cavities coupled to topological insulator-shunted
superconducting qubit devices and observe a power dependence that indicates
nonlinear qubit behaviour. Our method enables integration of complex networks
of topological insulator nanostructures into superconducting circuits, paving
the way for both novel voltage-controlled Josephson and topological qubits.Comment: 11 pages, 6 figure
Superconductivity
Conceived as the definitive reference in a classic and important field of modern physics, this extensive and comprehensive handbook systematically reviews the basic physics, theory and recent advances in the field of superconductivity. Leading researchers, including Nobel laureates, describe the state-of-the-art in conventional and unconventional superconductors at a particularly opportune time, as new experimental techniques and field-theoretical methods have emerged. In addition to full-coverage of novel materials and underlying mechanisms, the handbook reflects continued intense research into electron-phone based superconductivity. Considerable attention is devoted to high-Tc superconductivity, novel superconductivity, including triplet pairing in the ruthenates, novel superconductors, such as heavy-Fermion metals and organic materials, and also granular superconductors. What’s more, several contributions address superconductors with impurities and nanostructured superconductors. Important new results on current problems are presented in a manner designed to stimulate further research. Numerous illustrations, diagrams and tables make this book especially useful as a reference work for researchers, students and teachers. Treating the entire superconductivity field, this unparalleled reference resource carefully blends theoretical studies with experimental results to provide the scientist and engineers an indispensable foundation for further research
Novel superfluids
This book reports on the latest developments in the field of Superfluidity. The phenomenon has had a tremendous impact on the fundamental sciences as well as a host of technologies. It began with the discovery of superconductivity in mercury in 1911, which was ultimately described theoretically by the theory of Bardeen Cooper and Schriever (BCS) in 1957. The analogous phenomena, superfluidity, was discovered in helium in 1938 and tentatively explained shortly thereafter as arising from a Bose-Einstein Condensation (BEC) by London. But the importance of superfluidity, and the range of systems in which it occurs, has grown enormously. In addition to metals and the helium liquids the phenomena has now been observed for photons in cavities, excitons in semiconductors, magnons in certain materials, and cold gasses trapped in high vacuum. It very likely exist for neutrons in a neutron star and, possibly, in a conjectured quark state at their center. Even the Universe itself can be regarded as being in a kind of superfluid state. All these topics are discussed by experts in the respective subfields
Novel Josephson Effect in Triplet-Superconductor–Ferromagnet–Triplet-Superconductor Junctions
We predict a novel type of Josephson effect to occur in triplet-superconductor–ferromagnet–tripletsuperconductor
Josephson junctions. We show that the Josephson current, IJ, exhibits a rich dependence on the relative orientation between the ferromagnetic moment and the d vectors of the superconductors. This dependence can be used to build several types of Josephson current switches. Moreover, we predict
an unconventional sign change of IJ with increasing temperature
Novel Josephson Effect in Triplet-Superconductor–Ferromagnet–Triplet-Superconductor Junctions
Integration of Topological Insulator Josephson Junctions in Superconducting Qubit Circuits
The integration of semiconductor Josephson junctions (JJs) in superconducting quantum circuits provides a versatile platform for hybrid qubits and offers a powerful way to probe exotic quasiparticle excitations. Recent proposals for using circuit quantum electrodynamics (cQED) to detect topological superconductivity motivate the integration of novel topological materials in such circuits. Here, we report on the realization of superconducting transmon qubits implemented with (Bi0.06Sb0.94)2Te3topological insulator (TI) JJs using ultrahigh vacuum fabrication techniques. Microwave losses on our substrates, which host monolithically integrated hardmasks used for the selective area growth of TI nanostructures, imply microsecond limits to relaxation times and, thus, their compatibility with strong-coupling cQED. We use the cavity-qubit interaction to show that the Josephson energy of TI-based transmons scales with their JJ dimensions and demonstrate qubit control as well as temporal quantum coherence. Our results pave the way for advanced investigations of topological materials in both novel Josephson and topological qubits