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Register a new userLong-range charge density wave proximity effect at cuprate-manganate interfaces
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The interplay between charge density waves (CDWs) and high-temperature superconductivity is currently under intense investigation. Experimental research on this issue is difficult because CDW formation in bulk copper-oxides is strongly influenced by random disorder, and a long-range-ordered CDW state in high magnetic fields is difficult to access with spectroscopic and diffraction probes. Here we use resonant x-ray scattering in zero magnetic field to show that interfaces with the metallic ferromagnet La$_{2/3}$Ca$_{1/3}$MnO$_3$ greatly enhance CDW formation in the optimally doped high-temperature superconductor YBa$_2$Cu$_3$O$_{6+delta}$ ($bf delta sim 1$), and that this effect persists over several tens of nm. The wavevector of the incommensurate CDW serves as an internal calibration standard of the charge carrier concentration, which allows us to rule out any significant influence of oxygen non-stoichiometry, and to attribute the observed phenomenon to a genuine electronic proximity effect. Long-range proximity effects induced by heterointerfaces thus offer a powerful method to stabilize the charge density wave state in the cuprates, and more generally, to manipulate the interplay between different collective phenomena in metal oxides.
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One of the main challenges in understanding high TC superconductivity is to disentangle the rich variety of states of matter that may coexist, cooperate, or compete with d-wave superconductivity. At center stage is the pseudogap phase, which occupies a large portion of the cuprate phase diagram surrounding the superconducting dome [1]. Using scanning tunneling microscopy, we find that a static, non-dispersive, checkerboard-like electronic modulation exists in a broad regime of the cuprate phase diagram and exhibits strong doping dependence. The continuous increase of checkerboard periodicity with hole density strongly suggests that the checkerboard originates from charge density wave formation in the anti-nodal region of the cuprate Fermi surface. These results reveal a coherent picture for static electronic orderings in the cuprates and shed important new light on the nature of the pseudogap phase.
Using a mix of numerical and analytic methods, we show that recent NMR $^{17}$O measurements provide detailed information about the structure of the charge-density wave (CDW) phase in underdoped YBa$_2$Cu$_3$O$_{6+x}$. We perform Bogoliubov-de Gennes (BdG) calculations of both the local density of states and the orbitally resolved charge density, which are closely related to the magnetic and electric quadrupole contributions to the NMR spectrum, using a microscopic model that was shown previously to agree closely with x-ray experiments. The BdG results reproduce qualitative features of the experimental spectrum extremely well. These results are interpreted in terms of a generic hotspot model that allows one to trace the origins of the NMR lineshapes. We find that four quantities---the orbital character of the Fermi surface at the hotspots, the Fermi surface curvature at the hotspots, the CDW correlation length, and the magnitude of the subdominant CDW component---are key in determining the lineshapes.
To understand the origin of unconventional charge-density-wave (CDW) states in cuprate superconductors, we establish the self-consistent CDW equation, and analyze the CDW instabilities based on the realistic Hubbard model, without assuming any $q$-dependence and the form factor. Many higher-order many-body processes, which are called the vertex corrections, are systematically generated by solving the CDW equation. When the spin fluctuations are strong, the uniform $q=0$ nematic CDW with $d$-form factor shows the leading instability. The axial nematic CDW instability at $q = Q_a = (delta,0)$ ($delta approx pi/2$) is the second strongest, and its strength increases under the static uniform CDW order. The present theory predicts that uniform CDW transition emerges at a high temperature, and it stabilize the axial $q = Q_a$ CDW at $T = T_{CDW}$. It is confirmed that the higher-order Aslamazov-Larkin processes cause the CDW orders at both $q = 0$ and $Q_a$.
Charge density wave (CDW) correlations have recently been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured by x-ray scattering at zero and low fields. Here we combine a pulsed magnet with an x-ray free electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields up to 28 Tesla. While the zero-field CDW order, which develops below T ~ 150 K, is essentially two-dimensional, at lower temperature and beyond 15 Tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW onsets around the zero-field superconducting transition temperature, yet the incommensurate in-plane ordering vector is field-independent. This implies that the two forms of CDW and high-temperature superconductivity are intimately linked.
We report transport measurements under very high current densities $j$, up to $sim10^8$~A/cm$^2$, of quasi-one-dimensional charge-density wave (CDW) conductors NbSe$_3$ and TaS$_3$. Joule heating has been minimized by using a point-contact configuration or by measuring samples with extremely small cross-sections. Above $j_c approx 10^7$~A/cm$^2$ we find evidence for suppression of the Peierls gap and development of the metallic state. The critical CDW velocity corresponding with $j_0$ is comparable with the sound velocity, and with $Delta/ hbar k_F$ ($k_F$ is the Fermi wave vector), which corresponds to the depairing current. Possible scenarios of the Peierls state destruction are discussed.
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