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Register a new userObservation of cyclotron resonance and measurement of the hole mass in optimally-doped La$_{2-x}$Sr$_{x}$CuO$_4$
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Using time-domain terahertz spectroscopy in pulsed magnetic fields up to 31 T, we measure the terahertz optical conductivity in an optimally-doped thin film of the high temperature superconducting cuprate La$_{1.84}$Sr$_{0.16}$CuO$_4$. We observe systematic changes in the circularly-polarized complex optical conductivity that are consistent with cyclotron absorption of p-type charge carriers characterized by a cyclotron mass of $4.9pm 0.8$ $m_{rm e}$, and a scattering rate that increases with magnetic field. These results open the door to studies aimed at characterizing the degree to which electron-electron interactions influence carrier masses in cuprate superconductors.
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We present a study of the thermoelectric (Seebeck and Nernst) response in heavily overdoped, non-superconducting La$_{1.67}$Sr$_{0.33}$CuO$_4$. In spite of the electron-like curvature of the Fermi surface, the Seebeck coefficient is positive at low temperatures. Such a feature, previously observed in copper, silver, gold and lithium, is caused by a non-trivial energy dependence of the scattering time. We argue that this feature implies a strong asymmetry between the lifetime of occupied and unoccupied states along the zone diagonals and such an electron-hole asymmetry impedes formation of Cooper pairs along the nodal direction in the superconducting ground state emerging at lower doping levels.
The superconducting properties of high-tc materials are functions of carriers concentration, which is controlled by the concentration of defects including heterovalent cations, interstitial oxygen ions, and oxygen vacancies. Here we combine low-temperature thermal treatment of La$_{2-x}$Sr$_{x}$CuO$_{4}$ epitaxial thin films and confocal Raman spectroscopy to control and investigate oxygen vacancies. We demonstrate that the apical site is the most favorable position to accommodate oxygen vacancies under low-temperature annealing conditions. Additionally we show that in high-quality films of overdoped La$_{2-x}$Sr$_{x}$CuO$_{4}$, oxygen vacancies strongly deform the oxygen environment around the copper ions. This observation is consistent with previous defect-chemical studies, and calls for further investigation of the defect induced properties in the overdoped regime of the hole-doped lanthanum cuprates.
We investigate the hole and lattice dynamics in a prototypical high temperature superconducting system La{2-x}Sr{x}CuO{4} using infrared spectroscopy. By exploring the anisotropy in the electronic response of CuO2 planes we show that our results support the notion of stripes. Nevertheless, charge ordering effects are not apparent in the phonon spectra. All crystals show only the expected infrared active modes for orthorhombic phases without evidence for additional peaks that may be indicative of static charge ordering. Strong electron-phonon interaction manifests itself through the Fano lineshape of several phonon modes. This analysis reveals anisotropic electron-phonon coupling across the phase diagram, including superconducting crystals. Due to the ubiquity of the CuO2 plane, these results may have implications for other high Tc superconductors.
Charge order in underdoped and optimally doped high-$T_mathrm{c}$ superconductors Bi$_{2}$Sr$_{2-x}$La$_x$CuO$_{6+delta}$ (Bi2201) is investigated by Cu $L_3$ edge resonant inelastic x-ray scattering (RIXS). We have directly observed charge density modulation in the optimally doped Bi2201 at momentum transfer $Q_{|} simeq 0.23$ rlu, with smaller intensity and correlation length with respect to the underdoped sample. This demonstrates that short-range charge order in Bi2201 persists up to optimal doping, as in other hole-doped cuprates. We explored the nodal (diagonal) direction and found no charge order peak, confirming that charge order modulates only along the Cu-O bond directions. We measured the out-of-plane dependence of charge order, finding a flat response and no maxima at half integer emph{L} values. This suggests there is no out-of-plane phase correlation in single layer Bi2201, at variance from YBa$_2$Cu$_3$O$_{6+x}$ and La$_{2-x}$(Ba,Sr)$_x$CuO$_4$. Combining our results with data from the literature we assess that charge order in Bi2201 exists in a large doping range across the phase diagram, i.e. $0.07 lesssim p lesssim 0.16$, demonstrating thereby that it is intimately entangled with the antiferromagnetic background, the pseudogap and superconductivity.
The discovery of charge- and spin-density-wave (CDW/SDW) orders in superconducting cuprates has altered our perspective on the nature of high-temperature superconductivity (SC). However, it has proven difficult to fully elucidate the relationship between the density wave orders and SC. Here using resonant soft X-ray scattering we study the archetypal cuprate, La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) over a broad doping range. We reveal the existence of two types of CDW orders in LSCO, namely CDW stripe order and CDW short-range order (SRO). While the CDW-SRO is suppressed by SC, it is partially transformed into the CDW stripe order with developing SDW stripe order near the superconducting $T_{rm c}$. These findings indicate that the stripe orders and SC are inhomogeneously distributed in the superconducting CuO$_2$ planes of LSCO. This further suggests a new perspective on the putative pair-density-wave order that coexists with SC, SDW, and CDW orders.
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