45 research outputs found
Thermopower peak in phase transition region of (1-x)LaCaMnO/xYSZ
The thermoelectric power (TEP) and the electrical resistivity of the
intergranular magnetoresistance (IGMR) composite,
(1-x)LaCaMnO/xYSZ (LCMO/YSZ) with x = 0, 0.75%, 1.25%,
4.5%, 13% 15% and 80% of the yttria-stabalized zirconia (YSZ), have been
measured from 300 K down to 77 K. Pronounced TEP peak appears during the phase
transition for the samples of x 0, while not observed for x = 0. We suggest
that this is due to the magnetic structure variation induced by the lattice
strain which is resulting from the LCMO/YSZ boundary layers. The transition
width in temperature derived from , with being the AC magnetic
susceptibility, supports this interpretation.Comment: 4 pages, 4 eps figures, Latex, J. Appl. Phys 94, 7206 (2003
Crossover between Weak Antilocalization and Weak Localization of Bulk States in Ultrathin Bi2Se3 Films
We report transport studies on the 5 nm thick Bi2Se3 topological insulator
films which are grown via molecular beam epitaxy technique. The angle-resolved
photoemission spectroscopy data show that the Fermi level of the system lies in
the bulk conduction band above the Dirac point, suggesting important
contribution of bulk states to the transport results. In particular, the
crossover from weak antilocalization to weak localization in the bulk states is
observed in the parallel magnetic field measurements up to 50 Tesla. The
measured magneto-resistance exhibits interesting anisotropy with respect to the
orientation of B// and I, signifying intrinsic spin-orbit coupling in the
Bi2Se3 films. Our work directly shows the crossover of quantum interference
effect in the bulk states from weak antilocalization to weak localization. It
presents an important step toward a better understanding of the existing
three-dimensional topological insulators and the potential applications of
nano-scale topological insulator devices
High temperature superconducting FeSe films on SrTiO3 substrates
Interface enhanced superconductivity at two dimensional limit has become one
of most intriguing research directions in condensed matter physics. Here, we
report the superconducting properties of ultra-thin FeSe films with the
thickness of one unit cell (1-UC) grown on conductive and insulating SrTiO3
(STO) substrates. For the 1-UC FeSe on conductive STO substrate (Nb-STO), the
magnetization versus temperature (M-T) measurement shows a diamagnetic signal
at 85 K, suggesting the possibility of superconductivity appears at this high
temperature. For the FeSe films on insulating STO substrate, systematic
transport measurements were carried out and the sheet resistance of FeSe films
exhibits Arrhenius TAFF behavior with a crossover from a single-vortex pinning
region to a collective creep region. More intriguing, sign reversal of Hall
resistance with temperature is observed, demonstrating a crossover from hole
conduction to electron conduction above Tc in 1-UC FeSe films
Selective on/off switching at room temperature of a magnetic bistable {Fe2Co2} complex with single crystal-to-single crystal transformation via intramolecular electron transfer
National Nature Science Foundation of China [21172084, 20802022]; Self-determined research funds of CCNU from the colleges' basic research and operation of MOE [CCNU13F006, CCNU11C01002]A cyano-bridged {Fe2Co2} complex shows reversible single crystal-to-single crystal transformation between diamagnetic and paramagnetic states switched specifically by losing and absorbing methanol at room temperature in the solid state. And the solvent loss form presents temperature- and pressure-induced intramolecular electron transfer behaviour
Landau level splitting in Cd3As2 under high magnetic fields
Three-dimensional topological Dirac semimetals (TDSs) are a new kind of Dirac
materials that exhibit linear energy dispersion in the bulk and can be viewed
as three-dimensional graphene. It has been proposed that TDSs can be driven to
other exotic phases like Weyl semimetals, topological insulators and
topological superconductors by breaking certain symmetries. Here we report the
first transport experiment on Landau level splitting in TDS Cd3As2 single
crystals under high magnetic fields, suggesting the removal of spin degeneracy
by breaking time reversal symmetry. The detected Berry phase develops an
evident angular dependence and possesses a crossover from nontrivial to trivial
state under high magnetic fields, a strong hint for a fierce competition
between the orbit-coupled field strength and the field-generated mass term. Our
results unveil the important role of symmetry breaking in TDSs and further
demonstrate a feasible path to generate a Weyl semimetal phase by breaking time
reversal symmetry.Comment: 31 page