3,453 research outputs found
Coexistence of superconductivity and a spin density wave in pnictides: Gap symmetry and nodal lines
We investigate the effect of a spin-density wave (SDW) on
superconductivity in Fe-based superconductors. We show that, contrary to the
common wisdom, no nodes open at the new, reconnected Fermi surfaces when the
hole and electron pockets fold down in the SDW state, despite the fact that the
gap changes sign between the two pockets. Instead, the order
parameter preserves its sign along the newly formed Fermi surfaces. The
familiar experimental signatures of an symmetry are still preserved,
although they appear in a mathematically different way. For a regular case
( the nodes do appear in the SDW state. This distinction suggests a
novel simple way to experimentally separate an state from a regular
in the pnictides. We argue that recently published thermal conductivity
data in the coexisting state are consistent with the but not the
state
Phase sensitive noise in quantum dots under periodic perturbation
We evaluate the ensemble averaged noise in a chaotic quantum dot subject to
DC bias and a periodic perturbation of frequency . The noise displays
cusps at bias that survive the average, even when the
period of the perturbation is far shorter than the dwell time in the dot. These
features are sensitive to the phase of the time-dependent scattering amplitudes
of electrons to pass through the system.Comment: Published version. Improved discussion, with a few small typos
correcte
Compressibility of a 2D electron gas under microwave radiation
Microwave irradiation of a two-dimensional electron gas (2DEG) produces a
non-equilibrium distribution of electrons, and leads to oscillations in the
dissipative part of the conductivity. We show that the same non-equilibrium
electron distribution induces strong oscillations in the 2DEG compressibility
measured by local probes. Local measurements of the compressibility are
expected to provide information about the domain structure of the zero
resistance state of a 2DEG under microwave radiation.Comment: v2: analysis of the wave-vector dependence of the compressibility
added; discussion of the Hall conductivity removed (shifted to
cond-mat/0409590 in a revised form
Spin relaxation in quantum dots due to electron exchange with leads
We calculate spin relaxation rates in lateral quantum dot systems due to
electron exchange between dots and leads. Using rate equations, we develop a
theoretical description of the experimentally observed electric current in the
spin blockade regime of double quantum dots. Single expression fits the entire
current profile and describes the structure of both the conduction peaks and of
the suppressed (`valley') region. Extrinsic rates calculated here have to be
taken into account for accurate extraction of intrinsic relaxation rates due to
the spin-orbit and hyperfine spin scattering mechanisms from spin blockade
measurements.Comment: 4+ pages, 3 figures, submitted to PR
Magnetic penetration depth in the presence of a spin-density wave in multiband superconductors at zero temperature
We present a theoretical description of the London penetration depth of a
multi-band superconductor in the case when both superconducting and
spin-density wave orders coexist. We focus on clean systems and zero
temperature to emphasize the effect of the two competing orders. Our
calculation shows that the supefluid density closely follows the evolution of
the superconducting order parameter as doping is increased, saturating to a BCS
value in the pure superconducting state. Furthermore, we predict a strong
anisotropic in-pane penetration depth induced by the spin-density wave order.Comment: 7 pages, 4 figure
Theory of microwave-induced oscillations in the magnetoconductivity of a 2D electron gas
We develop a theory of magnetooscillations in the photoconductivity of a
two-dimensional electron gas observed in recent experiments. The effect is
governed by a change of the electron distribution function induced by the
microwave radiation. We analyze a nonlinearity with respect to both the dc
field and the microwave power, as well as the temperature dependence determined
by the inelastic relaxation rate.Comment: Extended version of cond-mat/0310668. 12 pages, 4 figures. V2:
published version (minor changes, Fig. 4 corrected, references added
Dynamic Thermal Tomography: New Nde Technique to Reconstruct Inner Solids Structure Using Multiple IR Image Processing
Nondestructive evaluation (NDE) technique appeared as the natural consequence of materials analysis by using a variety of physical fields and particles which being propagated through the specimen are able to produce the image of its inner structure. Disadvantage of traditional “shadow” or “backscattered” images is that the “weak” details are scarcely seen on the background of “stronger” ones. This is why the introduction of the tomographic principles, allowing to “slice” the solid into individual layers, was viewed as a revolution in vision techniques (especially in X-ray imaging). Ultrasonic, ultra-high frequency and nuclear magnetic resonance tomography are under quick development now
Radiation induced oscillations of the Hall resistivity in two-dimensional electron systems
We consider the effect of microwave radiation on the Hall resistivity in
two-dimension electron systems. It is shown that the photon-assisted impurity
scattering of electrons can result in oscillatory dependences of both
dissipative and Hall components of the conductivity and resistivity tensors on
the ratio of radiation frequency to cyclotron frequency. The Hall resistivity
can include a component induced by microwave radiation which is an even
function of the magnetic field. The phase of the dissipative resistivity
oscillations and the polarization dependence of their amplitude are compared
with those of the Hall resistivity oscillations. The developed model can
clarify the results of recent experimental observations of the radiation
induced Hall effect.Comment: 4 pages, 1 figur
Cherenkov Radiation from Pairs and Its Effect on Induced Showers
We calculate the Cherenkov radiation from an pair at small
separations, as occurs shortly after a pair conversion. The radiation is
reduced (compared to that from two independent particles) when the pair
separation is smaller than the wavelength of the emitted light. We estimate the
reduction in light in large electromagnetic showers, and discuss the
implications for detectors that observe Cherenkov radiation from showers in the
Earth's atmosphere, as well as in oceans and Antarctic ice.Comment: Final version, with minor changes, to appear in PRD. 5 pages with 4
figure
- …