Fractional ac Josephson effect in p- and d-wave superconductors

For certain orientations of Josephson junctions between two p_x-wave or two d-wave superconductors, the subgap Andreev bound states produce a 4pi-periodic relation between the Josephson current I and the phase difference phi: I sin(phi/2). Consequently, the ac Josephson current has the fractional frequency eV/h, where V is the dc voltage. In the tunneling limit, the Josephson current is proportional to the first power (not square) of the electron tunneling amplitude. Thus, the Josephson current between unconventional superconductors is carried by single electrons, rather than by Cooper pairs. The fractional ac Josephson effect can be observed experimentally by measuring frequency spectrum of microwave radiation from the junction. We also study junctions between singlet s-wave and triplet p_x-wave, as well as between chiral p_x + ip_y-wave superconductors.Comment: v. 5: minor update of references in proofs; v.4: minor improvements; v.3: major expansion to 13 pages, 6 figures; v.2: significantly expanded to 6 pages; v.1: 4 pages, 2 figures, RevTeX

Fractional ac Josephson effect in unconventional superconductors

For certain orientations of Josephson junctions between two px-wave or two d-wave superconductors, the subgap Andreev bound states produce a 4π-periodic relation between the Josephson current I and the phase difference:φ I sin(φ/2). Consequently, the ac Josephson current has the fractional frequency eV h, where V is the dc voltage. In the tunneling limit, the Josephson current is proportional to the first power (not square) of the electron tunneling amplitude. Thus, the Josephson current between unconventional superconductors is carried by ingle electrons, rather than by Cooper pairs. The fractional ac Josephson effect can be observed experimentally by measuring frequency spectrum of microwave radiation from the junctio

Evidence for partial melt in the crust beneath Mt. Paektu (Changbaishan), Democratic People's Republic of Korea and China

Mt. Paektu (also known as Changbaishan) is an enigmatic volcano on the border between the Democratic People's Republic of Korea (DPRK) and China. Despite being responsible for one of the largest eruptions in history, comparatively little is known about its magmatic evolution, geochronology, or underlying structure. We present receiver function results from an unprecedented seismic deployment in the DPRK. These are the first estimates of the crustal structure on the DPRK side of the volcano and, indeed, for anywhere beneath the DPRK. The crust 60 km from the volcano has a thickness of 35 km and a bulk $V_\text{P}$/$V_\text{S}$ of 1.76, similar to that of the Sino-Korean craton. The $V_\text{P}$/$V_\text{S}$ ratio increases ~20 km from the volcano, rising to >1.87 directly beneath the volcano. This shows that a large region of the crust has been modified by magmatism associated with the volcanism. Such high values of $V_\text{P}$/$V_\text{S}$ suggest that partial melt is present in the crust beneath Mt. Paektu. This region of melt represents a potential source for magmas erupted in the last few thousand years and may be associated with an episode of volcanic unrest observed between 2002 and 2005.This work was supported by the Richard Lounsbery Foundation. The UK seismic instruments and data management facilities were provided under loan number 976 by SEIS-UK at the University of Leicester. The facilities of SEIS-UK are supported by the NERC under Agreement R8/H10/64. J.O.S.H. was supported by an NERC Fellowship NE/I020342/1

How to detect edge electron states in (TMTSF)2X and Sr2RuO4 experimentally

We discuss a number of experiments that could detect the electron edge states in the organic quasi-one-dimensional conductors (TMTSF)2X and the inorganic quasi-two-dimensional perovskites Sr2RuO4. We consider the chiral edges states in the magnetic-field-induced spin-density-wave (FISDW) phase of (TMTSF)2X and in the time-reversal-symmetry-breaking triplet superconducting phase of Sr2RuO4, as well as the nonchiral midgap edge states in the triplet superconducting phase of $(TMTSF)2X. The most realistic experiment appears to be an observation of spontaneous magnetic flux at the edges of Sr2RuO4 by a scanning SQUID microscope.Comment: 6 pages, 5 figures. Submitted to the proceedings of ISCOM-2001 to be published in Synthetic Metals. Uses supplied elsart.cls and synmet.cls. V.2: 1 reference adde

Edge states and determination of pairing symmetry in superconducting Sr2RuO4

We calculate the energy dispersion of the surface Andreev states and their contribution to tunneling conductance for the order parameters with horizontal and vertical lines of nodes proposed for superconducting Sr2RuO4. For vertical lines, we find double peaks in tunneling spectra reflecting the van Hove singularities in the density of surface states originating from the turning points in their energy dispersion. For horizontal lines, we find a single cusp-like peak at zero bias, which agrees very well with the experimental data on tunneling in Sr2RuO4.Comment: 6 pages, 6 figures. V.2: comparison with experiment added and discussion of horizontal nodes expanded. v.3: significant expansion: 1 figure and 2 pages added. v.4: acknowledgements added. Additional viewgraphs with experimental and theoretical curves superimposed are available at http://www2.physics.umd.edu/~yakovenk/talks/Sr2RuO4

Quantum vortex fluctuations in cuprate superconductors

We study the effects of quantum vortex fluctuations in two-dimensional superconductors using a dual theory of vortices, and investigate the relevance to underdoped cuprates where the superconductor-insulator transition (SIT) is possibly driven by quantum vortex proliferation. We find that a broad enough phase fluctuation regime may exist for experimental observation of the quantum vortex fluctuations near SIT in underdoped cuprates. We propose that this scenario can be tested via pair-tunneling experiments which measure the characteristic resonances in the zero-temperature pair-field susceptibility in the vortex-proliferated insulating phase.Comment: RevTex 5 pages, 2 eps figures; expanded; to appear in Phys. Rev.

Midgap edge states and pairing symmetry of quasi-one-dimensional organic superconductors

The singlet s-, d- and triplet p-wave pairing symmetries in quasi-one-dimensional organic superconductors can be experimentally discriminated by probing the Andreev bound states at the sample edges. These states have the energy in the middle of the superconducting gap and manifest themselves as a zero-bias peak in tunneling conductance into the corresponding edge. Their existence is related to the sign change of the pairing potential around the Fermi surface. We present an exact self-consistent solution of the edge problem showing the presence of the midgap states for p_x-wave superconductivity. The spins of the edge state respond paramagnetically to a magnetic field parallel to the vector d that characterizes triplet pairing.Comment: 6 pages, 4 figures. V.2: New section on spin response is added and references are updated. V.3: Final version accepted to PRB. Typos are corrected and important note is added in proof

Edge electron states for quasi-one-dimensional organic conductors in the magnetic-field-induced spin-density-wave phases

We develop a microscopic picture of the electron states localized at the edges perpendicular to the chains in the Bechgaard salts in the quantum Hall regime. In a magnetic-field-induced spin-density-wave state (FISDW) characterized by an integer N, there exist N branches of chiral gapless edge excitations. Localization length is much longer and velocity much lower for these states than for the edge states parallel to the chains. We calculate the contribution of these states to the specific heat and propose a time-of-flight experiment to probe the propagating edge modes directly.Comment: 4 pages, 2 figures. V.2: Minor changes to the final version published in PR