7 research outputs found
Synthesis and Properties of LaSrNiO and LaSrNiO
Superconductivity has been realized in films of LaSrNiO. Here
we report synthesis and characterization of polycrystalline samples of
LaSrNiO and LaSrNiO ().
Magnetization and resistivity measurements reveal that LaSrNiO
are paramagnetic metals and LaSrNiO exhibit insulating
behavior. Superconductivity is not detected in bulk samples of
LaSrNiO. The absence of superconductivity in bulk
LaSrNiO may be due to the generation of hydroxide during
reduction or a small amount of nickel impurities. The effect of interface in
films of LaSrNiO may also play a role for superconductivity.Comment: 9 pages, 4 figure
Electronic correlations and energy gap in the bilayer nickelate LaNiO
The discovery of superconductivity with a critical temperature of 80~K in
LaNiO under pressure has received enormous attention.
LaNiO is not superconducting under ambient pressure but
exhibits a density-wave-like transition at ~K.
Understanding the electronic correlations, charge dynamics and dominant
orbitals are important steps towards the mechanism of superconductivity and
other instabilities. Here, our optical study shows that LaNiO
features strong electronic correlations which significantly reduce the
electron's kinetic energy and place it in the proximity of the Mott phase. The
low-frequency optical conductivity reveals two Drude components arising from
multiple bands dominated by the Ni- and Ni-
orbitals at the Fermi level. Above , the scattering rates for both
Drude components vary linearly with temperature, indicating non-Fermi-liquid
behavior which may be associated with spin-fluctuation scattering. Below
, a gap opens in the Ni- orbital, suggesting the
importance of the Ni- orbital in the density-wave-like
instability. Our experimental results provide key insights into the mechanism
of the density-wave-like order and superconductivity in
LaNiO.Comment: 26 pages, 4 figures, Comments are welcome and appreciate
Single crystal growth and superconductivity in RbNiSe
We report the synthesis and characterization of RbNiSe, an analog of
the iron chalcogenide superconductor RbFeSe, via transport, angle
resolved photoemission spectroscopy, and density functional theory
calculations. A superconducting transition at = 1.20 K is identified.
In normal state, RbNiSe shows paramagnetic and Fermi liquid behaviors.
A large Sommerfeld coefficient yields a heavy effective electron mass of
. In the superconducting state, zero-field electronic
specific-heat data can be described by a two-gap BCS model, indicating
that RbNiSe is a multi-gap superconductor. Our density functional
theory calculations and angle resolved photoemission spectroscopy measurements
demonstrate that RbNiSe exhibits relatively weak correlations and
multi-band characteristics, consistent with the multi-gap superconductivity.Comment: 7 pages, 4 figure
Orbital-Dependent Electron Correlation in Double-Layer Nickelate La3Ni2O7
The latest discovery of high temperature superconductivity near 80K in
La3Ni2O7 under high pressure has attracted much attention. Many proposals are
put forth to understand the origin of superconductivity. The determination of
electronic structures is a prerequisite to establish theories to understand
superconductivity in nickelates but is still lacking. Here we report our direct
measurement of the electronic structures of La3Ni2O7 by high-resolution
angle-resolved photoemmission spectroscopy. The Fermi surface and band
structures of La3Ni2O7 are observed and compared with the band structure
calculations. A flat band is formed from the Ni-3dz2 orbitals around the zone
corner which is 50meV below the Fermi level. Strong electron correlations are
revealed which are orbital- and momentum-dependent. Our observations will
provide key information to understand the origin of high temperature
superconductivity in La3Ni2O7.Comment: 18 pages, 4 figure
Superconductivity near 80 Kelvin in single crystals of La3Ni2O7 under pressure
High-transition-temperature (high-T_c) superconductivity in cuprates has been
discovered for more than three decades, but the underlying mechanism remains a
mystery. Cuprates are the only unconventional superconducting family that host
bulk superconductivity with T_cs above the liquid nitrogen boiling temperature
at 77 Kelvin. Here we report an observation of superconductivity in single
crystals of La3Ni2O7 with a maximum T_c of 80 Kelvin at pressures between
14.0-43.5 gigapascals using high-pressure resistance and mutual inductive
magnetic susceptibility measurements. The superconducting phase under high
pressure exhibits an orthorhombic structure of Fmmm space group with the
3d_(x^2-y^2 ) and 3d_(z^2 ) orbitals of Ni cations strongly interacting with
oxygen 2p orbitals. Our density functional theory calculations suggest the
superconductivity emerges coincidently with the metallization of the
{\sigma}-bonding bands under the Fermi level, consisting of the 3d_(z^2 )
orbitals with the apical oxygens connecting Ni-O bilayers. Thus, our
discoveries not only reveal important clues for the high-T_c superconductivity
in this Ruddlesden-Popper double-layered perovskite nickelates but also provide
a new family of compounds to investigate the high-T_c superconductivity
mechanism.Comment: 15 pages with extended dat
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Single-crystal growth and superconductivity in RbNi2Se2
We report the synthesis and characterization of RbNi2Se2, an analog of the iron chalcogenide superconductor RbxFe2Se2, via transport, angle-resolved photoemission spectroscopy, and density functional theory calculations. A superconducting transition at Tc=1.20 K is identified. In the normal state, RbNi2Se2 shows paramagnetic and Fermi-liquid behaviors. A large Sommerfeld coefficient yields an effective electron mass of mββ6me. In the superconducting state, zero-field electronic specific-heat data Ces can be described by a two-gap BCS model, indicating that RbNi2Se2 is a possible multigap superconductor. Our density functional theory calculations and angle-resolved photoemission spectroscopy measurements demonstrate that RbNi2Se2 exhibits relatively weak correlations and multiband characteristics, consistent with the multigap superconductivity
Exchange field enhanced upper critical field of the superconductivity in compressed antiferromagnetic EuTe2
We report high pressure studies on the C-type antiferromagnetic semiconductor
EuTe2 up to 36.0 GPa. A structural transition from the I4/mcm to C2/m space
group is identified at ~16 GPa. Superconductivity is discovered above ~5 GPa in
both the I4/mcm and C2/m space groups. In the low-pressure phase (< 16 GPa),
the antiferromagnetic transition temperature is enhanced with increasing
pressure due to the enhanced magnetic exchange interactions. Magnetoresistance
measurements indicate an interplay between the local moments of Eu2+ and the
conduction electrons of Te 5p orbits. The upper critical field of the
superconductivity is well above the Pauli limit. Across the structural
transition to the high-pressure phase (> 16 GPa), EuTe2 becomes nonmagnetic and
the superconducting transition temperature evolves smoothly with the upper
critical field below the Pauli limit. Therefore, the high upper critical field
of EuTe2 in the low-pressure phase is due to the exchange field compensation
effect of the Eu magnetic order and the superconductivity in both structures
may arise in the framework of the BCS theory.Comment: 11 pages,5 figures with 8 pages supplementar