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Register a new userLong-range incommensurate charge fluctuations in (Y,Nd)Ba2Cu3O(6+x)
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There are increasing indications that superconductivity competes with other orders in cuprate superconductors, but obtaining direct evidence with bulk-sensitive probes is challenging. We have used resonant soft x-ray scattering to identify two-dimensional charge fluctuations with an incommensurate periodicity of $bf sim 3.2$ lattice units in the copper-oxide planes of the superconductors (Y,Nd)Ba$_2$Cu$_3$O$_{6+x}$ with hole concentrations $0.09 leq p leq 0.13$ per planar Cu ion. The intensity and correlation length of the fluctuation signal increase strongly upon cooling down to the superconducting transition temperature, $T_c$; further cooling below $T_c$ abruptly reverses the divergence of the charge correlations. In combination with prior observations of a large gap in the spin excitation spectrum, these data indicate an incipient charge-density-wave instability that competes with superconductivity.
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Resonant magnetic modes with odd and even symmetries were studied by inelastic neutron scattering experiments in the bilayer high-$T_c$ superconductor $rm Y_{1-x}Ca_{x}Ba_2Cu_3O_{6+y}$ over a wide doping range. The threshold of the spin excitation continuum in the superconducting state, deduced from the energies and spectral weights of both modes, is compared with the superconducting d-wave gap, measured on the same samples by electronic Raman scattering in the $B_{1g}$ symmetry. Above a critical doping level of $delta simeq 0.19$, both mode energies and the continuum threshold coincide. We find a simple scaling relationship between the characteristic energies and spectral weights of both modes, which indicates that the resonant modes are bound states in the superconducting energy gap, as predicted by the spin-exciton model of the resonant mode.
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.
Spin-triplet superconductors are of extensive current interest because they can host topological state and Majorana ferimons important for quantum computation. The uranium based heavyfermion superconductor UTe$_2$ has been argued as a spin-triplet superconductor similar to UGe$_2$, URhGe, and UCoGe, where the superconducting phase is near (or coexists with) a ferromagnetic (FM) instability and spin-triplet electron pairing is driven by FM spin fluctuations. Here we use neutron scattering to show that although UTe$_2$ exhibits no static magnetic order down to 0.3 K, its magnetism is dominated by incommensurate spin fluctuations near antiferromagnetic (AF) ordering wave vector and extends to at least 2.6 meV. We are able to understand the dominant incommensurate spin fluctuations of UTe$_2$ in terms of its electronic structure calculated using a combined density functional and dynamic mean field theory.
Recent discoveries of charge order and electronic nematic order in the iron-based superconductors and cuprates have pointed towards the possibility of nematic and charge fluctuations playing a role in the enhancement of superconductivity. The Ba1-xSrxNi2As2 system, closely related in structure to the BaFe2As2 system, has recently been shown to exhibit both types of ordering without the presence of any magnetic order. We report single crystal X-ray diffraction, resistance transport measurements, and magnetization of BaSrLate, providing evidence that the previously reported incommensurate charge order with wavevector $(0,0.28,0)_{tet}$ in the tetragonal state of BaNi~vanishes by this concentration of Sr substitution together with nematic order. Our measurements suggest that the nematic and incommensurate charge orders are closely tied in the tetragonal state, and show that the $(0,0.33,0)_{tri}$ charge ordering in the triclinic phase of BaNi2As2 evolves to become $(0,0.5,0)_{tri}$ charge ordering at $x$=0.65 before vanishing at $x$=0.71.
The electronic-structural modulations of Ir$_{1-x}$Pt$_x$Te$_2$ (0 $leqq xleqq$ 0.12) have been examined by resonant elastic x-ray scattering (REXS) and resonant inelastic x-ray scattering (RIXS) techniques at both the Ir and Te edges. Charge-density-wave-like superstructure with wave vectors of $mathbf{Q}$=(1/5 0 $-$1/5), (1/8 0 $-$1/8), and (1/6 0 $-$1/6) are observed on the same sample of IrTe$_2$ at the lowest temperature, the patterns of which are controlled by the cooling speeds. In contrast, superstructures around $mathbf{Q}$=(1/5 0 $-$1/5) are observed for doped samples (0.02 $leqq xleqq$ 0.05). The superstructure reflections persist to higher Pt substitution than previously assumed, demonstrating that a charge density wave (CDW) can coexists with superconductivity. The analysis of the energy-dependent REXS and RIXS lineshape reveals the importance of the Te 5$p$ state rather than the Ir 5$d$ states in the formation of the spatial modulation of these systems. The phase diagram re-examined in this work suggests that the CDW incommensurability may correlate the emergence of superconducting states as-like Cu$_x$TiSe$_2$ and Li$_x$TaS$_2$.
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