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Register a new userWhy the critical temperature of high-$T_{rm c}$ cuprate superconductors is so low: The importance of the dynamical vertex structure
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To fathom the mechanism of high-temperature ($T_{rm c}$) superconductivity, the dynamical vertex approximation (D$Gamma$A) is evoked for the two-dimensional repulsive Hubbard model. After showing that our results well reproduce the cuprate phase diagram with a reasonable $T_{rm c}$ and dome structure, we keep track of the scattering processes that primarily affect $T_{rm c}$. We find that local particle-particle diagrams significantly screen the bare interaction at low frequencies, which in turn suppresses antiferromagnetic spin fluctuations and hence the pairing interaction. Thus we identify dynamical vertex corrections as one of the main oppressors of $T_{rm c}$, which may provide a hint toward higher $T_{rm c}$s.
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One of the first finding concerning the superconducting (SC) density $n_{rm sc}$ in cuprates was their small magnitudes that revealed the importance of phase fluctuations. More recently, measurements in a variety of overdoped cuprates indicate that it is also much smaller than expected from BCS theories and falls smoothly to zero as doping is increased. We explain these observations by an electronic phase separation theory with a Ginzburg-Landau potential $V_{rm GL}$ that produces alternating charge domains whose fluctuations lead to localized SC order parameters that are connected by Josephson coupling $E_{rm J}$. The average ${left <E_{rm J}( p,T)right>}$ is proportional to the local superfluid phase stiffness $rho_{rm sc} propto n_{rm sc}$. The fraction of condensed carriers decreases in the overdoped region due to the weakening of $V_{rm GL}$. The results agreed with $rho_{rm sc}(p)$ vs. $T_{rm c}(p)$ and the Drude-like peak measurements.
We report on broad-band infrared ellipsometry measurements of the c-axis conductivity of underdoped RBa_{2}Cu_{3}O_{7-d} (R=Y, Nd, and La) single crystals. Our data provide a detailed account of the spectral weight (SW) redistributions due to the normal state pseudogap (PG) and the superconducting (SC) gap. They show that these phenomena involve different energy scales, exhibit distinct doping dependencies and thus are likely of different origin. In particular, the SW redistribution in the PG state closely resembles the one of a conventional charge- or spin density wave (CDW or SDW) system.
Signatures of strong coupling effects in cuprate high-$T_{c}$ superconductors have been authenticated through a variety of spectroscopic probes. However, the microscopic nature of relevant excitations has not been agreed upon. Here we report on magneto-optical studies of the CuO$_{2}$ plane carrier dynamics in a prototypical high-$T_{c}$ superconductor YBa$%_{2} $Cu$_{3}$O$_{y}$ (YBCO). Infrared data are directly compared with earlier inelastic neutron scattering results by Dai textit{et al}. [Nature (London) textbf{406}, 965 (2000)] revealing a characteristic depression of the magnetic resonance in H $parallel $ textit{c} field less than 7 T. This analysis has allowed us to critically assess the role of magnetic degrees of freedom in producing strong coupling effects for YBCO system.
An understanding of the missing antinodal electronic excitations in the pseudogap state is essential for uncovering the physics of the underdoped cuprate high temperature superconductors. The majority of high temperature experiments performed thus far, however, have been unable to discern whether the antinodal states are rendered unobservable due to their damping, or whether they vanish due to their gapping. Here we distinguish between these two scenarios by using quantum oscillations to examine whether the small Fermi surface pocket, found to occupy only 2% of the Brillouin zone in the underdoped cuprates, exists in isolation against a majority of completely gapped density of states spanning the antinodes, or whether it is thermodynamically coupled to a background of ungapped antinodal states. We find that quantum oscillations associated with the small Fermi surface pocket exhibit a signature sawtooth waveform characteristic of an isolated two-dimensional Fermi surface pocket. This finding reveals that the antinodal states are destroyed by a hard gap that extends over the majority of the Brillouin zone, placing strong constraints on a drastic underlying origin of quasiparticle disappearance over almost the entire Brillouin zone in the pseudogap regime.
We propose and show that the c-axis transport in high-temperature superconductors is controlled by the pseudogap energy and the c-axis resistivity satisfies a universal scaling law in the pseudogap phase. We derived approximately a scaling function for the c-axis resistivity and found that it fits well with the experimental data of Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$, Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+delta}$, and YBa$_2$Cu$_3$O$_{7-delta}$. Our works reveals the physical origin of the semiconductor-like behavior of the c-axis resistivity and suggests that the c-axis hopping is predominantly coherent.
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