308 research outputs found
Evolution of Paramagnetic Quasiparticle Excitations Emerged in the High-Field Superconducting Phase of CeCoIn5
We present In NMR measurements in a novel thermodynamic phase of CeCoIn5 in
high magnetic field, where exotic superconductivity coexists with the
incommensurate spin-density wave order. We show that the NMR spectra in this
phase provide direct evidence for the emergence of the spatially distributed
normal quasiparticle regions. The quantitative analysis for the field evolution
of the paramagnetic magnetization and newly-emerged low-energy quasiparticle
density of states is consistent with the nodal plane formation, which is
characterized by an order parameter in the Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) state. The NMR spectra also suggest that the spatially uniform
spin-density wave is induced in the FFLO phase.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev. Let
Field-induced quantum critical route to a Fermi liquid in high-temperature superconductors
In high transition temperature (T_c) superconductivity, charge doping is a
natural tuning parameter that takes copper oxides from the antiferromagnet to
the superconducting region. In the metallic state above T_c the standard
Landau's Fermi-liquid theory of metals as typified by the temperature squared
(T^2) dependence of resistivity appears to break down. Whether the origin of
the non-Fermi-liquid behavior is related to physics specific to the cuprates is
a fundamental question still under debate. We uncover a new transformation from
the non-Fermi- to a standard Fermi-liquid state driven not by doping but by
magnetic field in the overdoped high-T_c superconductor Tl_2Ba_2CuO_{6+x}. From
the c-axis resistivity measured up to 45 T, we show that the Fermi-liquid
features appear above a sufficiently high field which decreases linearly with
temperature and lands at a quantum critical point near the superconductivity's
upper critical field -- with the Fermi-liquid coefficient of the T^2 dependence
showing a power-law diverging behavior on the approach to the critical point.
This field-induced quantum criticality bears a striking resemblance to that in
quasi-two dimensional heavy-Fermion superconductors, suggesting a common
underlying spin-related physics in these superconductors with strong electron
correlations.Comment: 6 pages, 4 figure
Effects of Rattling Phonons on the Quasiparticle Excitation and Dynamics in the Superconducting -Pyrochlore KOsO
Microwave penetration depth and surface resistance at 27 GHz are
measured in high quality crystals of KOsO. Firm evidence for
fully-gapped superconductivity is provided from . Below the second
transition at K, the superfluid density shows a step-like
change with a suppression of effective critical temperature .
Concurrently, the extracted quasiparticle scattering time shows a steep
enhancement, indicating a strong coupling between the anomalous rattling motion
of K ions and quasiparticles. The results imply that the rattling phonons help
to enhance superconductivity, and that K sites freeze to an ordered state with
long quasiparticle mean free path below .Comment: 5 pages, 5 figures, to be published in Phys. Rev. Let
Quantum critical point lying beneath the superconducting dome in iron-pnictides
Whether a quantum critical point (QCP) lies beneath the superconducting dome
has been a long-standing issue that remains unresolved in many classes of
unconventional superconductors, notably cuprates, heavy fermion compounds and
most recently iron-pnictides. The existence of a QCP may offer a route to
understand: the origin of their anomalous non-Fermi liquid properties, the
microscopic coexistence between unconventional superconductivity and magnetic
or some exotic order, and ultimately the mechanism of superconductivity itself.
The isovalent substituted iron-pnictide BaFe(AsP) offers a
new platform for the study of quantum criticality, providing a unique
opportunity to study the evolution of the electronic properties in a wide range
of the phase diagram. Recent experiments in BaFe(AsP) have
provided the first clear and unambiguous evidence of a second order quantum
phase transition lying beneath the superconducting dome.Comment: 15 pages, 6 figures, review article submitted to Annual Review of
Condensed Matter Physic
Thermal Conductivity of the Pyrochlore Superconductor KOs2O6: Strong Electron Correlations and Fully Gapped Superconductivity
To elucidate the nature of the superconducting ground state of the
geometrically frustrated pyrochlore KOs2O6 (Tc=9.6K), the thermal conductivity
was measured down to low temperatures (~Tc/100). We found that the
quasiparticle mean free path is strikingly enhanced below a transition at
Tp=7.5K, indicating enormous electron inelastic scattering in the normal state.
In a magnetic field the conduction at T ->0K is nearly constant up to ~0.4Hc2,
in contrast with the rapid growth expected for superconductors with an
anisotropic gap. This unambiguously indicates a fully gapped superconductivity,
in contrast to the previous studies. These results highlight that KOs2O6 is
unique among superconductors with strong electron correlations.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Let
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