16 research outputs found
Kohn-Luttinger effect in nested Fermion liquids
We study the Kohn-Luttinger effect in a two-dimensional (2D) nested Fermion
liquid with a repulsive interaction via the renormalization group method and
identify the resulting order parameter symmetry. Using the band structure of
the 2D Hubbard model close to half-filling as a prototype, we construct an
effective low-energy theory. We use multidimensional bosonization to
incorporate the zero-sound channel and find marginal Fermi liquid behavior in
the absence of any instability. We show an analog of the Landau theorem in
nested Fermion liquids, which serves as the criterion of the BCS instability.
Including repulsive or antiferromagnetic exchange interactions in the
low-energy theory, we show that the -wave BCS channel is
renormalized to be the most attractive. Below half-filling, when the nesting is
not perfect, there is competition between the spin-density-wave (SDW) and the
BCS channels; when the SDW coupling is small enough, there occurs a
-wave superconducting instability at sufficiently low
temperatures.Comment: Reference added and typos corrected; 12 pages, RevTex 3.0, 5 figures
in one postscript file (to appear in Phys. Rev. B
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
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
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.
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
The effect of phase fluctuations on the single-particle properties of the underdoped cuprates
We study the effect of order parameter phase fluctuations on the
single-particle properties of fermions in the underdoped cuprate
superconductors using a phenomenological low-energy theory. We identify the
fermion-phase field coupling as the Doppler-shift of the quasiparticle spectrum
induced by the fluctuating superfluid velocity and we calculate the effect of
these fluctuations on the fermion self-energy. We show that the vortex pair
unbinding near the superconducting transition causes a significant broadening
in the fermion spectral function, producing a pseudogap-like feature. We also
discuss the specific heat and show that the phase fluctuation effect is visible
due to the short coherence length.Comment: RevTex 11 pages; 11 epsf figures included. Added and updated
reference