The temperature-dependent redistribution of the spectral weight of the CuO
2
plane–derived conduction band of the YBa
2
Cu
3
O
6.9
high-temperature superconductor (superconducting transition ...temperature = 92.7 kelvin) was studied with wide-band (0.01– to 5.6–electron volt) spectroscopic ellipsometry. A superconductivity-induced transfer of the spectral weight involving a high-energy scale in excess of 1 electron volt was observed. Correspondingly, the charge carrier spectral weight was shown to decrease in the superconducting state. The ellipsometric data also provide detailed information about the evolution of the optical self-energy in the normal and superconducting states.
The temperature-dependent redistribution of the spectral weight of the CuO2 plane-derived conduction band of the YBa2Cu3O(6.9) high-temperature superconductor (superconducting transition temperature ...= 92.7 kelvin) was studied with wide-band (0.01- to 5.6-electron volt) spectroscopic ellipsometry. A superconductivity-induced transfer of the spectral weight involving a high-energy scale in excess of 1 electron volt was observed. Correspondingly, the charge carrier spectral weight was shown to decrease in the superconducting state. The ellipsometric data also provide detailed information about the evolution of the optical self-energy in the normal and superconducting states.
Raman scattering experiments have been performed on
Na
x
CoO
2
as a function of temperature at the composition
x
=
0.5
where a structural instability and a metal–insulator transition have been ...observed. Three additional phonon modes are observed compared to samples with larger
x
. An in situ annealing study (
T
max
=
550
K
) with the initial presence of water vapor at ambient conditions reveals an irreversible structural instability of this composition.
Neutron and X-ray scattering experiments have provided mounting evidence for spin and charge ordering phenomena in underdoped cuprates. These range from early work on stripe correlations in Nd-LSCO ...to the latest discovery of charge-density-waves in YBa2Cu3O(6+x). Both phenomena are characterized by a pronounced dependence on doping, temperature and an externally applied magnetic field. Here, we show that these electron-lattice instabilities exhibit also a previously unrecognized bulk-surface dichotomy. Surface-sensitive electronic and structural probes uncover a temperature-dependent evolution of the CuO2 plane band dispersion and apparent Fermi pockets in underdoped Bi2 Sr(2-x) La(x) CuO(6+δ) (Bi2201), which is directly associated with an hitherto-undetected strong temperature dependence of the incommensurate superstructure periodicity below 130 K. In stark contrast, the structural modulation revealed by bulk-sensitive probes is temperature-independent. These findings point to a surface-enhanced incipient charge-density-wave instability, driven by Fermi surface nesting. This discovery is of critical importance in the interpretation of single-particle spectroscopy data, and establishes the surface of cuprates and other complex oxides as a rich playground for the study of electronically soft phases.
The Cu substitution by Zn and Ni impurities and its influence on the mass renormalization effects in angle resolved photoelectron spectra (ARPES) of Bi
2Sr
2CaCu
2O
8+
δ
is addressed. We show that ...the nonmagnetic Zn atoms have much stronger effect both in nodal and antinodal parts of the Brillouin zone than magnetic Ni. The observed changes are consistent with the behaviour of the spin resonance mode as seen by inelastic neutron scattering in YBCO-123. This strongly suggests that the “peak-dip-hump” and the “kink” in ARPES on the one side and neutron resonance on the other are closely related features.
We report the successful growth of high-quality Sr
3Fe
2O
7−
x
single crystals with volumes of up to 0.3
cm
3 by using the floating zone method. Compositional homogeneity of the crystals was verified ...by powder X-ray diffraction, optical and electron microscope measurements. The X-ray rocking curves of the Sr
3Fe
2O
7−
x
single crystal gave a full-width at half-maximum (FWHM) of Bragg reflections of 0.02–0.03°. The influence of the growth rate on the crystal size and quality was demonstrated. The effect of oxygen annealing was studied by magnetic susceptibility and Raman light scattering experiments. The Fe(+3)/Fe(+4) ratio was determined both from the magnetization and thermo-gravimetric data.
Phys. Rev. B 100, 081101(R), 2019 We used Raman light scattering to study the current-stabilized nonequilibrium
semimetallic and metallic phases in Ca$_2$RuO$_4$. By determining the local
temperature ...through careful analysis of the Stokes and anti-Stokes intensities,
we find that Joule heating can be completely avoided by supplying sufficient
cooling power in a helium-flow cryostat, and that the current induces the
semimetallic state without inducing any significant heating. We further
investigate the current-induced semimetallic state as a function of temperature
and current. We confirm the absence of long-range antiferromagnetic order and
identify a substantial Fano broadening of several phonons, which suggests
coupling to charge and orbital fluctuations. Our results demonstrate that the
semimetallic state is a genuine effect of the applied electrical current and
that the current-induced phases have characteristics distinct from the
equilibrium ones.
Phys. Rev. X 10, 011053 (2020) Optical excitation in the cuprates has been shown to induce transient
superconducting correlations above the thermodynamic transition temperature,
$T_C$, as evidenced ...by the terahertz frequency optical properties in the
non-equilibrium state. In YBa$_2$Cu$_3$O$_{6+x}$ this phenomenon has so far
been associated with the nonlinear excitation of certain lattice modes and the
creation of new crystal structures. In other compounds, like
La$_{2-x}$Ba$_x$CuO$_4$, similar effects were reported also for excitation at
near infrared frequencies, and were interpreted as a signature of the melting
of competing orders. However, to date it has not been possible to
systematically tune the pump frequency widely in any one compound, to
comprehensively compare the frequency dependent photo-susceptibility for this
phenomenon. Here, we make use of a newly developed optical parametric
amplifier, which generates widely tunable high intensity femtosecond pulses, to
excite YBa$_2$Cu$_3$O$_{6.5}$ throughout the entire optical spectrum (3 - 750
THz). In the far-infrared region (3 - 25 THz), signatures of non-equilibrium
superconductivity are induced only for excitation of the 16.4 THz and 19.2 THz
vibrational modes that drive $c$-axis apical oxygen atomic positions. For
higher driving frequencies (25 - 750 THz), a second resonance is observed
around the charge transfer band edge at ~350 THz. These observations highlight
the importance of coupling to the electronic structure of the CuO$_2$ planes,
either mediated by a phonon or by charge transfer.
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