257 research outputs found
Magnetic Excitations of the 2-D Sm Spin Layers in Sm(La,Sr)CuO4
We present specific heat and susceptibility data on Sm(La,Sr)CuO4 in magnetic
fields up to 9 T and temperatures down to 100 mK. We find a broad peak in
specific heat which is insensitive to magnetic field at a temperature of 1.5 K
with a value of 2.65 J/mol K. The magnetic susceptibility at 5 T continues to
increase down to 2 K, the lowest temperature measured. The data suggest that
the Sm spin system may be an ideal realization of the frustrated Heisenberg
antiferromagnet on the square lattice.Comment: 2 pages, 2 figures, submitted to IC
Controllable chirality-induced geometrical Hall effect in a frustrated highly-correlated metal
A current of electrons traversing a landscape of localized spins possessing
non-coplanar magnetic order gains a geometrical (Berry) phase which can lead to
a Hall voltage independent of the spin-orbit coupling within the material--a
geometrical Hall effect. We show that the highly-correlated metal UCu5
possesses an unusually large controllable geometrical Hall effect at T<1.2K due
to its frustration-induced magnetic order. The magnitude of the Hall response
exceeds 20% of the \nu=1 quantum Hall effect per atomic layer, which translates
into an effective magnetic field of several hundred Tesla acting on the
electrons. The existence of such a large geometric Hall response in UCu5 opens
a new field of inquiry into the importance of the role of frustration in
highly-correlated electron materials.Comment: article and supplemental informatio
Momentum Dependence of Resonant Inelastic X-Ray Scattering Spectrum in Insulating Cuprates
The resonant inelastic x-ray scattering spectrum in insulating cuprates is
examined by using the exact diagonalization technique on small clusters in the
two-dimensional Hubbard model with second and third neighbor hopping terms.
When the incident photon energy is tuned near the Cu K absorption edges, we
find that the features of the unoccupied upper Hubbard band can be extracted
from the spectrum through an anisotropic momentum dependence. They provide an
opportunity for the understanding of the different behavior of hole- and
electron-doped superconductors.Comment: 4 pages with 4 figures, to be published in PR
Electronic Structure of New Multiple Band Pt-Pnictide Superconductors APt3P
We report LDA calculated band structure, densities of states and Fermi
surfaces for recently discovered Pt-pnictide superconductors APt3P
(A=Ca,Sr,La), confirming their multiple band nature. Electronic structure is
essentially three dimensional, in contrast to Fe pnictides and chalcogenides.
LDA calculated Sommerfeld coefficient agrees rather well with experimental
data, leaving little space for very strong coupling superconductivity,
suggested by experimental data on specific heat of SrPt3P. Elementary estimates
show, that the values of critical temperature can be explained by rather weak
or moderately strong coupling, while the decrease of superconducting transition
temperature Tc from Sr to La compound can be explained by corresponding
decrease of total density of states at the Fermi level N(E_F). The shape of the
density of states near the Fermi level suggests that in SrPt3P electron doping
(such as replacement Sr by La) decreases N(E_F) and Tc, while hole doping (e.g.
partial replacement of Sr with K, Rb or Cs, if possible) would increase N(E_F)
and possibly Tc.Comment: 5 pages, 5 figure
Spin Liquid State around a Doped Hole in Insulating Cuprates
The numerically exact diagonalization study on small clusters of the t-J
model with the second- and third- neighbor hopping terms shows that a novel
spin liquid state is realized around a doped hole with momentum k=(pi,0) and
energy \sim 2J compared with that with (pi/2,pi/2) in insulating cuprates,
where the spin and charge degrees of freedom are approximately decoupled. Our
finding implies that the excitations in the insulating cuprates are mapped onto
the the d-wave resonating valence bond state.Comment: 4 pages, 4 EPS figures, to be published in J. Phys. Soc. Jpn. Vol.
69, No.1 January, 200
Novel multiple-band superconductor SrPt2As2
We present LDA calculated electronic structure of recently discovered
superconductor SrPt2As2 with Tc=5.2K. Despite its chemical composition and
crystal structure are somehow similar to FeAs-based high-temperature
superconductors, the electronic structure of SrPt2As2 is very much different.
Crystal structure is orthorhombic (or tetragonal if idealized) and has layered
nature with alternating PtAs4 and AsPt4 tetrahedra slabs sandwiched with Sr
ions. The Fermi level is crossed by Pt-5d states with rather strong admixture
of As-4p states. Fermi surface of SrPt2As2 is essentially three dimensional,
with complicated sheets corresponding to multiple bands. We compare SrPt2As2
with 1111 and 122 representatives of FeAs-class of superconductors, as well as
with isovalent (Ba,Sr)Ni2As2 superconductors. Brief discussion of
superconductivity in SrPt2As2 is also presented.Comment: 5 pages, 4 figure
On Measuring Condensate Fraction in Superconductors
An analysis of off-diagonal long-range order in superconductors shows that
the spin-spin correlation function is significantly influenced by the order if
the order parameter is anisotropic on a microscopic scale. Thus, magnetic
neutron scattering can provide a direct measurement of the condensate fraction
of a superconductor. It is also argued that recent measurements in high
temperature superconductors come very close to achieving this goal.Comment: 4 pages, 1 eps figure, RevTex. A new possibility in the underdoped
regime is added. Other corrections are mino
Bilayer Splitting in the Electronic Structure of Heavily Overdoped Bi2Sr2CaCu2O8+d
The electronic structure of heavily overdoped
BiSrCaCuO is investigated by angle-resolved
photoemission spectroscopy. The long-sought bilayer band splitting in this
two-plane system is observed in both normal and superconducting states, which
qualitatively agrees with the bilayer Hubbard model calculations. The maximum
bilayer energy splitting is about 88 meV for the normal state feature, while it
is only about 20 meV for the superconducting peak. This anomalous behavior
cannot be reconciled with the quasiparticle picture.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
c-axis magnetotransport in CeCoIn
We present the results of out-of-plane electrical transport measurements on
the heavy fermion superconductor CeCoIn at temperatures from 40 mK to 400
K and in magnetic field up to 9 T. For 10 K transport measurements show
that the zero-field resistivity changes linearly with temperature
and extrapolates nearly to zero at 0 K, indicative of non-Fermi-liquid (nFL)
behavior associated with a quantum critical point (QCP). The longitudinal
magnetoresistance (LMR) of CeCoIn for fields applied parallel to the
c-axis is negative and scales as between 50 and 100 K, revealing
the presence of a single-impurity Kondo energy scale K.
Beginning at 16 K a small positive LMR feature is evident for fields less than
3 tesla that grows in magnitude with decreasing temperature. For higher fields
the LMR is negative and increases in magnitude with decreasing temperature.
This sizable negative magnetoresistance scales as from 2.6 K to
roughly 8 K, and it arises from an extrapolated residual resistivity that
becomes negative and grows quadratically with field in the nFL temperature
regime. Applying a magnetic field along the c-axis with B B restores
Fermi-liquid behavior in at less than 130 mK. Analysis of the
resistivity coefficient's field-dependence suggests that the QCP in
CeCoIn is located \emph{below} the upper critical field, inside the
superconducting phase. These data indicate that while high- c-axis transport
of CeCoIn exhibits features typical for a heavy fermion system, low-
transport is governed both by spin fluctuations associated with the QCP and
Kondo interactions that are influenced by the underlying complex electronic
structure intrinsic to the anisotropic CeCoIn crystal structure
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