1,107 research outputs found
Effects of doping on thermally excited quasiparticles in the high- superconducting state
The physical properties of low energy superconducting quasiparticles in high-
superconductors are examined using magnetic penetration depth and
specific heat experimental data. We find that the low energy density of states
of quasiparticles of LaSrCuO scales with to the
leading order approximation, where is the critical doping concentration
below which . The linear temperature term of the superfluid density is
renormalized by quasiparticle interactions and the renormalization factor times
the Fermi velocity is found to be doping independent.Comment: 3 pages, 3 figures, minor change to the content, fig1 is reploted, to
appear in Phys Rev
Low Temperature Superfluid Response of High-Tc Superconductors
We have reviewed our theoretical and experimental results of the low
temperature superfluid response function of high temperature superconductors
(HTSC). In clean high-Tc materials the in-plane superfluid density rho_s^{ab}
varies linearly with temperature. The slope of this linear T term is found to
scale approximately with 1/Tc which, according to the weak coupling BCS theory
for a d-wave superconductor, implies that the gap amplitude scales
approximately with Tc. A T^5 behavior of the out-of-plane superfluid density
rho_s^c for clean tetragonal HTSC was predicted and observed experimentally in
the single layer Hg-compound HgBa_2CuO_{4+delta}. In other tetragonal high-Tc
compounds with relatively high anisotropy, such as Hg_2Ba_2Ca_2Cu_3O_{8+delta},
rho_s^c varies as T^2 due to disorder effects. In optimally doped
YBa_2Cu_3O_{7-delta}, rho_s^c varies linearly with temperature at low
temperatures, but in underdoped YBa_2Cu_3O_{7-delta}, rho_s^c varies as T^2 at
low temperatures; these results are consistent with our theoretical
calculations.Comment: 26 pages, 8 figure
Systematic behaviour of the in-plane penetration depth in d-wave cuprates
We report the temperature T and oxygen concentration dependences of the
penetration depth of grain-aligned YBa_2Cu_3O_{7-\delta} with \delta= 0.0, 0.3
and 0.43. The values of the in-plane \lambda_{ab}(0) and out-of-plane
\lambda_{c}(0) penetration depths, the low temperature linear term in
\lambda_{ab}(T), and the ratio \lambda_{c}(0) /\lambda_{ab}(T) were found to
increase with increasing . The systematic changes of the linear term in
\lambda_{ab}(T) with T_c found here and in recent work on HgBa_2Ca_{n-1}
Cu_nO_{2n+2+\delta} (n = 1 and 3) are discussed.Comment: 4 pages, 4 figure
Metallic characteristics in superlattices composed of insulators, NdMnO3/SrMnO3/LaMnO3
We report on the electronic properties of superlattices composed of three
different antiferromagnetic insulators, NdMnO3/SrMnO3/LaMnO3 grown on SrTiO3
substrates. Photoemission spectra obtained by tuning the x-ray energy at the Mn
2p -> 3d edge show a Fermi cut-off, indicating metallic behavior mainly
originating from Mn e_g electrons. Furthermore, the density of states near the
Fermi energy and the magnetization obey a similar temperature dependence,
suggesting a correlation between the spin and charge degrees of freedom at the
interfaces of these oxides
Enhanced and continuous electrostatic carrier doping on the SrTiO surface
Paraelectrical tuning of a charge carrier density as high as
10\,cm in the presence of a high electronic carrier mobility on
the delicate surfaces of correlated oxides, is a key to the technological
breakthrough of a field effect transistor (FET) utilising the metal-nonmetal
transition. Here we introduce the Parylene-C/TaO hybrid gate
insulator and fabricate FET devices on single-crystalline SrTiO, which
has been regarded as a bedrock material for oxide electronics. The gate
insulator accumulates up to cm carriers, while the
field-effect mobility is kept at 10\,cm/Vs even at room temperature.
Further to the exceptional performance of our devices, the enhanced
compatibility of high carrier density and high mobility revealed the mechanism
for the long standing puzzle of the distribution of electrostatically doped
carriers on the surface of SrTiO. Namely, the formation and continuous
evolution of field domains and current filaments.Comment: Supplementary Information:
<http://www.nature.com/srep/2013/130424/srep01721/extref/srep01721-s1.pdf
Emergent properties hidden in plane view: Strong electronic correlations at oxide interfaces
Finding new collective electronic states in materials is one of the
fundamental goals of condensed matter physics. Atomic-scale superlattices
formed from transition metal oxides are a particularly appealing hunting ground
for new physics. In bulk form, transition metal oxides exhibit a remarkable
range of magnetic, superconducting, and multiferroic phases that are of great
scientific interest and are potentially capable of providing innovative energy,
security, electronics and medical technology platforms. In superlattices new
states may emerge at the interfaces where dissimilar materials meet.
Here we illustrate the essential features that make transition metal
oxide-based heterostructures an appealing discovery platform for emergent
properties with a few selected examples, showing how charge redistributes,
magnetism and orbital polarization arises and ferroelectric order emerges from
heterostructures comprised of oxide components with nominally contradictory
behavior with the aim providing insight into the creation and control of novel
behavior at oxide interfaces by suitable mechanical, electrical or optical
boundary conditions and excitations.Comment: 16 pages, 5 figure
Theory of the magnetoeletric effect in a lightly doped high-Tc cuprate
In a recent study Viskadourakis et al. discovered that extremely underdoped
La_2CuO_(4+x) is a relaxor ferroelectric and a magnetoelectric material at low
temperatures. It is further observed that the magnetoelectric response is
anisotropic for different directions of electric polarization and applied
magnetic field. By constructing an appropriate Landau theory, we show that a
bi-quadratic magnetoelectric coupling can explain the experimentally observed
polarization dependence on magnetic field. This coupling leads to several novel
low-temperature effects including a feedback enhancement of the magnetization
below the ferroelectric transition, and a predicted magnetocapacitive effect.Comment: 5 pages, 4 figure
Penetration Depth Measurements in MgB_2: Evidence for Unconventional Superconductivity
We have measured the magnetic penetration depth of the recently discovered
binary superconductor MgB_2 using muon spin rotation and low field
-susceptibility. From the damping of the muon precession signal we find the
penetration depth at zero temperature is about 85nm. The low temperature
penetration depth shows a quadratic temperature dependence, indicating the
presence of nodes in the superconducting energy gap.Comment: 4 pages 3 figure
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