51 research outputs found
Magnetic Properties of a Superconductor with no Inversion Symmetry
We study the magnetic properties of a superconductor in a crystal without symmetry, in particular how the lack of this symmetry exhibits itself.
We show that, though the penetration depth itself shows no such effect, for
suitable orientation of magnetic field, there is a magnetic field discontinuity
at the interface which shows this absence of symmetry. The magnetic field
profile of a vortex in the plane is shown to be identical to that of an
ordinary anisotropic superconductor except for a shift in the direction by
(see errata). For a vortex along , there is an
induced magnetization along the radial direction.Comment: J. Low Temp. Physics, 140, 67 (2005); with Errat
Charge superconductivity from pair density wave order in certain high temperature superconductors
A number of spectacular experimental anomalies\cite{li-2007,fujita-2005} have
recently been discovered in certain cuprates, notably {\LBCO} and {\LNSCO},
which exhibit unidirectional spin and charge order (known as ``stripe order'').
We have recently proposed to interpret these observations as evidence for a
novel ``striped superconducting'' state, in which the superconducting order
parameter is modulated in space, such that its average is precisely zero. Here,
we show that thermal melting of the striped superconducting state can lead to a
number of unusual phases, of which the most novel is a charge
superconducting state, with a corresponding fractional flux quantum .
These are never-before observed states of matter, and ones, moreover, that
cannot arise from the conventional Bardeen-Cooper-Schrieffer (BCS) mechanism.
Thus, direct confirmation of their existence, even in a small subset of the
cuprates, could have much broader implications for our understanding of high
temperature superconductivity. We propose experiments to observe fractional
flux quantization, which thereby could confirm the existence of these states.Comment: 5 pages, 2 figures; new version in Nature Physics format with a
discussion of the effective Josephson coupling J2 and minor changes. Mildly
edited abstract. v3: corrected versio
Dislocations and vortices in pair density wave superconductors
With the ground breaking work of the Fulde, Ferell, Larkin, and Ovchinnikov
(FFLO), it was realized that superconducting order can also break translational
invariance; leading to a phase in which the Cooper pairs develop a coherent
periodic spatially oscillating structure. Such pair density wave (PDW)
superconductivity has become relevant in a diverse range of systems, including
cuprates, organic superconductors, heavy fermion superconductors, cold atoms,
and high density quark matter. Here we show that, in addition to charge density
wave (CDW) order, there are PDW ground states that induce spin density wave
(SDW) order when there is no applied magnetic field. Furthermore, we show that
PDW phases support topological defects that combine dislocations in the induced
CDW/SDW order with a fractional vortex in the usual superconducting order.
These defects provide a mechanism for fluctuation driven non-superconducting
CDW/SDW phases and conventional vortices with CDW/SDW order in the core.Comment: 6 pages,1 figure, 1 tabl
Switching of magnetic domains reveals evidence for spatially inhomogeneous superconductivity
The interplay of magnetic and charge fluctuations can lead to quantum phases
with exceptional electronic properties. A case in point is magnetically-driven
superconductivity, where magnetic correlations fundamentally affect the
underlying symmetry and generate new physical properties. The superconducting
wave-function in most known magnetic superconductors does not break
translational symmetry. However, it has been predicted that modulated triplet
p-wave superconductivity occurs in singlet d-wave superconductors with
spin-density wave (SDW) order. Here we report evidence for the presence of a
spatially inhomogeneous p-wave Cooper pair-density wave (PDW) in CeCoIn5. We
show that the SDW domains can be switched completely by a tiny change of the
magnetic field direction, which is naturally explained by the presence of
triplet superconductivity. Further, the Q-phase emerges in a common
magneto-superconducting quantum critical point. The Q-phase of CeCoIn5 thus
represents an example where spatially modulated superconductivity is associated
with SDW order
Spin-flux phase in the Kondo lattice model with classical localized spins
We provide numerical evidence that a spin-flux phase exists as a ground state of the Kondo lattice model with classical local spins on a square lattice. This state manifests itself as a double-e magnetic order in the classical spins with spin density at both (0, pi) and (pi ,0) and further exhibits fermionic spin currents around an elementary plaquette of the square lattice. We examine the spin-wave spectrum of this phase. We further discuss an extension to a face-centered-cubic (fcc) lattice where a spin-flux phase may also exist. On the fee lattice the spin-flux phase manifests itself as a triple-Q magnetically ordered state and may exist in gamma -Mn alloys
Observation of a square flux-line lattice in the unconventional superconductor Sr2RuO4 (vol 396, pg 242, 1998)
The phenomenon of superconductivity continues to be of considerable scientific and practical interest. Underlying this phenomenon is the formation of electron pairs, which in conventional superconductors do not rotate about their centre of mass ('s-wave' pairing; refs 1, 2). This contrasts with the situation in high-temperature superconductors, where the electrons in a pair are believed to have two units of relative angular momentum ('d-wave' pairing; ref. 3 and references therein). Here we report small-angle neutron-scattering measurements of magnetic flux lines in the perovskite superconductor Sr2RuO4 (ref. 4), which is a candidate for another unconventional paired electron state-'p-wave' pairing, which has one unit of angular momentum(5-7). We find that the magnetic flux lines form a square lattice over a wide range of fields and temperatures, which is the result predicted by a recent theory(8,9) of p-wave superconductivity in Sr2RuO4. This theory also indicates that only a fraction of the electrons are strongly paired and that the orientation of the square flux lattice relative to the crystal lattice will determine which parts of the three-sheet Fermi surface of this material are responsible for superconductivity. Our results suggest that superconductivity resides mainly on the 'gamma' sheet(9).</p
- …