Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSearch for Cooper-pair Fluctuations in Severely Underdoped YBCO Films
76
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The preformed-pairs theory of pseudogap physics in high-$T_C$ superconductors predicts a nonanalytic $T$-dependence for the $ab$-plane superfluid fraction, $rho_S$, at low temperatures in underdoped cuprates. We report high-precision measurements of $rho_S(T)$ on severely underdoped YBa$_2$Cu$_3$O$_{6+x}$ and Y$_{0.8}$Ca$_{0.2}$Ba$_2$Cu$_3$O$_{6+x}$ films. At low $T$, $rho_S$ looks more like $1 - T^2$ than $1 - T^{3/2}$, in disagreement with theory.
rate research
Read More
We apply a recently-developed low-field technique to inductively measure the critical pair momentum $p_c$ in thin, underdoped films of Y$_{1-x}$Ca$_{x}$Ba$_{2}$Cu$_{3}$O$_{7-delta}$ and Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+delta}$ reflecting a wide range of hole doping. We observe that $p_c propto hbar/xi$ scales with $T_c$ and therefore superfluid density $n_s(Trightarrow0)$ in our two-dimensional cuprate films. This relationship was famously predicted by a universal model of the cuprates with a textit{doping-independent} superconducting gap, but has not been observed by high field measurements of the coherence length $xi$ due to field-induced phenomena not included in the theory.
A major obstacle in understanding the mechanism of Cooper pairing in the cuprates is the existence of various intertwined orders associated with spin, charge, and Cooper pairs. Of particular importance is the ubiquitous charge order features that have been observed in a variety of cuprates, especially in the underdoped regime of the phase diagram. To explain the origin of the charge order and its implication to the superconducting phase, many theoretical models have been proposed, such as charge stripes, electronic nematicity, and Fermi surface instability. A highly appealing physical picture is the so-called pair density wave (PDW), a periodic modulation of Cooper paring in space, which may also induce a charge order. To elucidate the existence and nature of the PDW order, here we use scanning tunneling microscopy (STM) to investigate a severely underdoped Bi2Sr2CaCu2O8+{delta}, in which superconductivity just emerges on top of a pronounced checkerboard charge order. By analyzing the spatial distribution of the spectral features characteristic of superconductivity, we observe a periodic modulation of both the superconducting coherence peak and gap depth, demonstrating the existence of a density wave order of Cooper pairing. The PDW order has the same spatial periodicity as the charge order, and the amplitudes of the two orders exhibit clear positive correlation. These results shed important new lights on the origin of and interplay between the charge order and Cooper pairing modulation in the cuprates.
We show that strong electric fields of ~ 30 kV cm^(-1) at terahertz frequencies can significantly weaken the superconducting characteristics of cuprate superconductors. High-power terahertz time-domain spectroscopy (THz-TDS) was used to investigate the in-plane conductivity of YBa2Cu3O7-delta (YBCO) with highly intense single-cycle terahertz pulses. Even though the terahertz photon energy (~ 1.5 meV) was significantly smaller than the energy gap in YBCO (~ 20-30 meV), the optical conductivity was highly sensitive to the field strength of the applied terahertz transients. Possibly, this is due to an ultrafast, field-induced modification of the superconductors effective coupling function, leading to a massive Cooper pair breakup. The effect was evident for several YBCO thin films on MgO and LSAT substrates.
We first review evidence for the Cooper pair insulator (CPI) phase in amorphous nanohoneycomb (NHC) films. We then extend our analysis of superconducting islands induced by film thickness variations in NHC films to examine the evolution of island sizes through the magnetic field-driven SIT. Finally, using the islanding picture, we present a plausible model for the appearance and behavior of the CPI phase in amorphous NHC films.
A microscopic theory for the spin triplet Cooper pairing in non-centrosymmetric superconductors like CePt_3Si and CeTSi_3 (T=Rh, Ir) is presented. The lack of inversion symmetry leads to new anomalous spin fluctuations which stabilize the triplet part in addition to the singlet part originating from the centrosymmetric spin fluctuations. It is shown that both parts have similar nontrivial momentum dependence of A_1 type. Therefore the mixed singlet-triplet gap function has accidental line nodes on both Fermi surface sheets which are stable as function of temperature. This gap function explains the salient features of CePt_3Si and CeTSi_3 superconductors.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
