5,795 research outputs found

### Evolution from Non-Fermi to Fermi Liquid Transport Properties by Isovalent Doping in BaFe2(As1-xPx)2 Superconductors

The normal-state charge transport is studied systematically in high-quality
single crystals of BaFe$_2$(As$_{1-x}$P$_x$)$_2$ ($0 \leq x \leq 0.71$). By
substituting isovalent P for As, the spin-density-wave (SDW) state is
suppressed and the dome-shaped superconducting phase ($T_c \lesssim 31$ K)
appears. Near the SDW end point ($x\approx0.3$), we observe striking linear
temperature ($T$) dependence of resistivity in a wide $T$-range, and remarkable
low-$T$ enhancement of Hall coefficient magnitude from the carrier number
estimates. We also find that the magnetoresistance apparently violates the
Kohler's rule and is well scaled by the Hall angle $\Theta_H$ as
$\Delta\rho_{xx}/\rho_{xx} \propto \tan^2\Theta_H$. These non-Fermi liquid
transport anomalies cannot be attributed to the simple multiband effects. These
results capture universal features of correlated electron systems in the
presence of strong antiferromagnetic fluctuations.Comment: 4 pages, 4 figure

### Cu-spin dynamics in the overdoped regime of La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ probed by muon spin relaxation

Muon-spin-relaxation measurements have been performed for the partially
Zn-substituted La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ with y=0-0.10 in the overdoped
regime up to x=0.30. In the 3 % Zn-substituted samples up to x=0.27,
exponential-like depolarization of muon spins has been observed at low
temperatures, indicating Zn-induced slowing-down of the Cu-spin fluctuations.
The depolarization rate decreases with increasing x and almost no fast
depolarization of muon spins has been observed for x=0.30 where
superconductivity disappears. The present results suggest that the dynamical
stripe correlations exist in the whole superconducting regime of
La_2-x_Sr_x_CuO_4_ and that there is no quantum critical point at x~0.19.Comment: 6 pages, 5 figure

### Microscopic Model for Photoinduced Magnetism in the Molecular Complex $[Mo(IV)(CN)_2(CN-CuL)_6]^{8+}$ Perchlorate

A theoretical model for understanding photomagnetism in the heptanuclear
complex $[Mo(IV)(CN)_2(CN-CuL)_6]^{8+}$ perchlorate is developed. It is a
many-body model involving the active orbitals on the transition metal ions. The
model is exactly solved using a valence bond approach. The ground state
solution of the model is highly degenerate and is spanned by five S=0 states,
nine S=1 states, five S=2 states and one S=3 state. The orbital occupancies in
all these states correspond to six $Cu(II)$ ions and one diamagnetic $Mo(IV)$
ion. The optically excited charge-transfer (CT) state in each spin sector occur
at nearly the same excitation energy of 2.993 eV for the physically reasonable
parameter values. The degeneracy of the CT states is largest in the S=3 sector
and so is the transition dipole moment from the ground state to these excited
states. Thus laser irradiation with light of this energy results in most
intense absorption in the S=3 sector. The life-time of the S=3 excited states
is also expected to be the largest as the number of states below that energy is
very sparse in this spin sector when compared to other spin sectors. These twin
features of our model explain the observed photomagnetism in the
$[Mo(IV)(CN)_2(CN-CuL)_6]^{8+}$ complex.Comment: 8 pages, 6 figures and 1 tabl

### Weak coupling d-wave BCS superconductivity and unpaired electrons in overdoped La_{2-x}Sr_{x}CuO_{4} single crystals

The low-temperature specific heat (SH) of overdoped La_{2-x}Sr_{x}CuO_{4}
single crystals (0.178=<x=<0.290) has been measured. For the superconducting
samples (0.178=<x=<0.238), the derived gap values (without any adjusting
parameters) approach closely onto the theoretical prediction
\Delta_{0}=2.14k_{B}T_{c} for the weak-coupling d-wave BCS superconductivity.
In addition, the residual term \gamma(0) of SH at H=0 increases with x
dramatically when beyond x~0.22, and finally evolves into the value of a
complete normal metallic state at higher doping levels, indicating growing
amount of unpaired electrons. We argue that this large \gamma(0) cannot be
simply attributed to the pair breaking induced by the impurity scattering,
instead the phase separation is possible.Comment: 6 pages, 6 figures; Contents added; Accepted for publication in Phys.
Rev.

### Development of Cu-spin correlation in Bi_1.74_Pb_0.38_Sr_1.88_Cu_1-y_Zn_y_O_6+d_ high-temperature superconductors observed by muon spin relaxation

A systematic muon-spin-relaxation study in Bi-2201 high-Tc cuprates has
revealed for the first time that the Cu-spin correlation (CSC) is developed at
low temperatures below 2 K in a wide range of hole concentration where
superconductivity appears. The CSC tends to become weak gradually with
increasing hole-concentration. Moreover, CSC has been enhanced through the 3%
substitution of Zn for Cu. These results are quite similar to those observed in
La-214 high-Tc cuprates. Accordingly, it has been suggested that the intimate
relation between the so-called spin-charge stripe correlations and
superconductivity is a universal feature in hole-doped high-Tc cuprates.
Furthermore, apparent development of CSC, which is suppressed through the Zn
substitution oppositely, has been observed in non-superconducting heavily
overdoped samples, being argued in the context of a recently proposed
ferromagnetic state in heavily overdoped cuprates.Comment: 6 pages, 5 figure

### Flavor Mixing in the Gauge-Higgs Unification

Gauge-Higgs unification is the fascinating scenario solving the hierarchy
problem without supersymmetry. In this scenario, the Standard Model (SM) Higgs
doublet is identified with extra component of the gauge field in higher
dimensions and its mass becomes finite and stable under quantum corrections due
to the higher dimensional gauge symmetry. On the other hand, Yukawa coupling is
provided by the gauge coupling, which seems to mean that the flavor mixing and
CP violation do not arise at it stands. In this talk, we discuss that the
flavor mixing is originated from simultaneously non-diagonalizable bulk and
brane mass matrices. Then, this mechanism is applied to various flavor changing
neutral current (FCNC) processes via Kaluza-Klein (KK) gauge boson exchange at
tree level and constraints for compactification scale are obtained.Comment: 5 pages, prepared for the proceedings of the International Workshop
on Grand Unified Theories (GUT2012) held at Yukawa Institute for Theoretical
Physics, March 15-17 2012, Kyoto, Japa

### Ordering Process and Its Hole Concentration Dependence of the Stripe Order in La{2-x}Sr{x}NiO{4}

Ordering process of stripe order in La{2-x}Sr{x}NiO{4} with x being around
1/3 was investigated by neutron diffraction experiments. When the stripe order
is formed at high temperature, incommensurability \epsilon of the stripe order
has a tendency to show the value close to 1/3 for the samples with x at both
sides of 1/3. With decreasing temperature, however, \epsilon becomes close to
the value determined by the linear relation of \epsilon = n_h, where n_h is a
hole concentration. This variation of the \epsilon strongly affects the
character of the stripe order through the change of the carrier densities in
stripes and antiferromagnetic domains.Comment: 5 pages, 3 figures, REVTeX, to be published in Phys. Rev.

### Distinct Fe-induced magnetic states in the underdoped and overdoped regimes of La2-xSrxCu1-yFeyO4 revealed by muon spin relaxation

Zero-field and longitudinal-field muon-spin-relaxation measurements have been
performed in partially Fe-substituted La2-xSrxCu1-yFeyO4 in a wide range of
hole concentration, to investigate the magnetic state induced by the Fe
substitution recently suggested from the neutron-scattering measurements [Phys.
Rev. Lett. 107, 127002 (2011)]. It has been found that the magnetic transition
temperature is notably enhanced through the 1% Fe substitution in a wide range
of hole concentration where superconductivity appears in Fe-free La2-xSrxCuO4.
In the underdoped regime, the Fe-induced magnetic order can be understood in
terms of the concept of stripe pinning by Fe as in the case of the Zn-induced
one in La2-xSrxCu1-yZnyO4. In the overdoped regime, on the other hand, the
Fe-induced magnetic order is short-ranged, which is distinct from the stripes.
It is plausible that a spin-glass state of Fe spins derived from the
Ruderman-Kittel-Kasuya-Yosida interaction is realized in the overdoped regime,
suggesting a change of the ground state from the strongly correlated state to
the Fermi-liquid state with hole doping in La-214 high-Tc cuprates.Comment: 10 pages, 6 figures, accepted for publication in Phys. Rev.

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