935 research outputs found
Evolution of the Hall Coefficient and the Peculiar Electronic Structure of the Cuprate Superconductors
Although the Hall coefficient R_H is an informative transport property of
metals and semiconductors, its meaning in the cuprate superconductors has been
ambiguous because of its unusual characteristics. Here we show that a
systematic study of R_H in La_{2-x}Sr_{x}CuO_{4} single crystals over a wide
doping range establishes a qualitative understanding of its peculiar evolution,
which turns out to reflect a two-component nature of the electronic structure
caused by an unusual development of the Fermi surface recently uncovered by
photoemission experiments.Comment: 4 pages, 5 figures, final version appeared in Phys. Rev. Let
An Infrared study of the Josephson vortex state in high-Tc cuprates
We report the results of the c-axis infrared spectroscopy of La_{2-x} Sr_x
CuO_4 in high magnetic field oriented parallel to the CuO_2 planes. A
significant suppression of the superfluid density with magnetic field rho_s(H)
is observed for both underdoped (x=0.125) and overdoped (x=0.17) samples. We
show that the existing theoretical models of the Josephson vortex state fail to
consistently describe the observed effects and discuss possible reasons for the
discrepancies
Magnetic shape-memory effects in La2-xSrxCuO4 crystals
The magnetic field affects the motion of electrons and the orientation of
spins in solids, but it is believed to have little impact on the crystal
structure. This common perception has been challenged recently by ferromagnetic
shape-memory alloys, where the spin-lattice coupling is so strong that
crystallographic axes even in a fixed sample are forced to rotate, following
the direction of moments. One would, however, least expect any structural
change to be induced in antiferromagnets where spins are antiparallel and give
no net moment. Here we report on such unexpected magnetic shape-memory effects
that take place ironically in one of the best-studied 2D antiferromagnets,
La2-xSrxCuO4 (LSCO). We find that lightly-doped LSCO crystals tend to align
their b axis along the magnetic field, and if the crystal orientation is fixed,
this alignment occurs through the generation and motion of crystallographic
twin boundaries. Both resistivity and magnetic susceptibility exhibit curious
switching and memory effects induced by the crystal-axes rotation; moreover,
clear kinks moving over the crystal surfaces allow one to watch the crystal
rearrangement directly with a microscope or even bare eyes.Comment: 3 pages, 4 figures; shortend version of this paper has been published
in Nature as a Brief Communicatio
Magnetic order in lightly doped La_{2-x}Sr_{x}CuO_{4}
We study long wavelength magnetic excitations in lightly doped
La_{2-x}Sr_{x}CuO_{4} (x < 0.03) detwinned crystals. The lowest energy magnetic
anisotropy induced gap can be understood in terms of the antisymmetric spin
interaction inside the antiferromagnetic (AF) phase. The second magnetic
resonace, analyzed in terms of in-plane spin anisotropy, shows unconventional
behavior within the AF state and led to the discovery of collective spin
excitations pertaining to a field induced magnetically ordered state. This
state persists in a 9 T field to more than 100 K above the N\'{e}el temperature
in x = 0.01.Comment: 5 pages, 5 figure
Diamagnetism and Cooper pairing above in cuprates
In the cuprate superconductors, Nernst and torque magnetization experiments
have provided evidence that the disappearance of the Meissner effect at
is caused by the loss of long-range phase coherence, rather than the vanishing
of the pair condensate. Here we report a series of torque magnetization
measurements on single crystals of (LSCO),
(Bi 2201),
(Bi 2212) and optimal
. Some of the measurements were taken to fields as high
as 45 T. Focusing on the magnetization above , we show that the
diamagnetic term appears at an onset temperature high above
. We construct the phase diagram of both LSCO and Bi 2201 and show that
agrees with the onset temperature of the vortex Nernst signal
. Our results provide thermodynamic evidence against a recent
proposal that the high-temperature Nernst signal in LSCO arises from a
quasiparticle contribution in a charge-ordered state.Comment: 10 pages, 11 figures. Final version with revised text and expanded
discussion and 1 new figure (Fig. 10) and 1 modified fig (Fig. 11). Some new
reference
Magnetic-Field-Induced Localization of Quasiparticles in Underdoped LaSrCuO Single Crystals
Magnetic-field-induced ordering of electrons around vortices is a striking
phenomenon recently found in high- cuprates. To identify its consequence
in the quasiparticle dynamics, the magnetic-field () dependence of the
low-temperature thermal conductivity of LaSrCuO
crystals is studied for a wide doping range. It is found that the behavior of
in the sub-Kelvin region changes drastically across optimum doping,
and the data for underdoped samples are indicative of unusual
magnetic-field-induced localization of quasiparticles; this localization
phenomenon is probably responsible for the unusual "insulating normal state"
under high magnetic fields.Comment: 4 pages, 4 figures, final version published in PR
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