Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOptical Study of the Stripe-Ordered State
223
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The effects of the stripe order on the optical spectra of La-based cuprates are reviewed. The main effect on the high Tc superconducting cuprates is to rapidly reduce the Josephson plasma frequency in the c-axis spectrum as a consequence of weakening of the Josephson coupling between CuO2 layers. This points toward a two dimensional (2D) superconductivity in the stripe phase, although it is difficult to realize a 2D superconductivity in real materials. We also discuss the experimental results suggesting the presence of stripe effect in other cuprates even if they do not show the static stripe phase. Compared to the c-axis spectra, the in-plane spectra are not so dramatically affected by the stripe order, showing a weak gap-like feature and reducing the condensate spectral weight.
rate research
Read More
Temperature dependence of the Hall coefficient, R_H_, has been investigated in charge-spin stripe-ordered La-214 high-T_c_ superconductors. Using the simplest stripe-ordered system of La_2-x_Ba_x_CuO_4_, it has been clarified that both the behavior of R_H_ and its sign exhibit significant dependences on the hole concentration. That is, R_H_ is zero in the ground state of the charge-spin stripe order at x=1/8, while it is negative in the less-stabilized state of the charge stripe for x<1/8. These are interpreted as owing to the delicate balance of the contributions of the hole-like Fermi surface and the possible electron pocket arising from the formation of the charge-spin stripe order.
The origin of the weakly insulatinglike behavior revealed when magnetic fields ($H$) suppress superconductivity in underdoped cuprates has been a longtime mystery. Surprisingly, similar behavior observed recently in La-214 cuprates with striped spin and charge orders is consistent with a metallic, as opposed to insulating, high-field normal state. Here we report a striking finding of the vanishing of the Hall coefficient ($R_mathrm{H}$) in this field-revealed normal state for all $T<(2-6)T_{c}^{0}$, where $T_{c}^{0}$ is the zero-field superconducting transition temperature. In standard models, $R_mathrm{H}$ can only vanish accidentally, and thus $R_mathrm{H}=0$ observed over a wide range of $T$ and $H$ has to imply that charge conjugation (i.e. particle-hole) symmetry is dynamically generated. This is a robust, new fundamental property of the normal state of cuprates with intertwined orders.
In underdoped cuprate superconductors, a rich competition occurs between superconductivity and charge density wave (CDW) order. Whether rotational symmetry breaking (nematicity) occurs intrinsically and generically or as a consequence of other orders is under debate. Here we employ resonant x-ray scattering in stripe-ordered (La,M)_2CuO_4 to probe the relationship between electronic nematicity of the Cu 3d orbitals, structure of the (La,M)_2O_2 layers, and CDW order. We find distinct temperature dependences for the structure of the (La,M)_2O_2 layers and the electronic nematicity of the CuO_2 planes, with only the latter being enhanced by the onset of CDW order. These results identify electronic nematicity as an order parameter that is distinct from a purely structural order parameter in underdoped striped cuprates.
In Ca1-xRExFeAs2 (RE= rare earth), an antiferromagnetic (AFM) phase as well as a structural transition has been reported, even in the electron-overdoped regime. Here we investigated the temperature-dependent in-plane optical spectroscopy of overdoped Ca0.77Nd0.23FeAs2. Upon entering the AFM state, we found an abrupt reduction of low-frequency (500-2 000 cm-1) spectral weight in the optical conductivity. In sharp contrast to the parent compounds of 122 system, where spin-density-wave gaps have been clearly observed in the AFM state, a gap signature is absent in Ca0.77Nd0.23FeAs2. This may be a consequence of the poor nesting condition between hole and electron pockets. However, a spectral weight analysis shows that the reduced spectral weight at low frequency is transferred to the high frequency range (> 4 000 cm-1), pointing to a localization effect. These observations suggest that the AFM order in Ca0.77Nd0.23FeAs2 is most likely to originate from a localized nature rather than Fermi surface nesting.
We have studied the reflectance of the recently discovered superconductor LaO_0.9F0.FeAs in a wide energy range from the far infrared to the visible regime. We report on the observation of infrared active phonons, the plasma edge (PE) and possible interband transitions. On the basis of this data and the reported in-plane penetration depth lambda_L(0) about 254 nm [H. Luetkens et al., Phys. Rev. Lett. v. 101, 0970009 (2008)] a disorder sensitive relatively small value of the total electron electron-boson coupling constant lambda_tot=lambda_e-ph+lambda_e-sp ~ 0.6 +- 0.35 can be estimated adopting an effective single-band picture.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
