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The quasi-two-dimensional metal Sr2RuO4is one of the best characterized unconventional superconductors, yet the nature of its superconducting order parameter is still under debate1–3. This information is crucial to determine the pairing mechanism of Cooper pairs. Here we use ultrasound velocity to probe the superconducting state of Sr2RuO4. This thermodynamic probe is sensitive to the symmetry of the material, and therefore, it can help in identifying the symmetry of the superconducting order parameter4,5. Indeed, we observe a sharp jump in the shear elastic constant c66as the temperature is increased across the superconducting transition. This directly implies that the superconducting order parameter is of a two-component nature. On the basis of symmetry arguments and given the other known properties of Sr2RuO4(refs. 6–8), we discuss which states are compatible with this requirement and propose that the two-component order parameter {dxz; dyz} is the most likely candidate.

Dirac fermions with highly dispersive linear bands1–3are usually considered weakly correlated due to the relatively large bandwidths (W) compared to Coulomb interactions (U). With the discovery of nodal-line semimetals, the notion of the Dirac point has been extended to lines and loops in momentum space. The anisotropy associated with nodal-line structure gives rise to greatly reduced kinetic energy along the line. However, experimental evidence for the anticipated enhanced correlations in nodal-line semimetals is sparse. Here, we report on prominent correlation effects in a nodal-line semimetal compound, ZrSiSe, through a combination of optical spectroscopy and density functional theory calculations. We observed two fundamental spectroscopic hallmarks of electronic correlations: strong reduction (1/3) of the free-carrier Drude weight and also the Fermi velocity compared to predictions of density functional band theory. The renormalization of Fermi velocity can be further controlled with an external magnetic field. ZrSiSe therefore offers the rare opportunity to investigate correlation-driven physics in a Dirac system.

One or a few layers of van der Waals (vdW) materials are promising for applications in nanoscale electronics. Established properties include high mobility in graphene, a large direct gap in monolayer MoS2, the quantum spin Hall effect in monolayer WTe2and so on. These exciting properties arise from electron quantum confinement in the two-dimensional limit. Here, we use angle-resolved photoemission spectroscopy to reveal directional massless Dirac fermions due to one-dimensional confinement of carriers in the layered vdW material NbSi0.45Te2. The one-dimensional directional massless Dirac fermions are protected by non-symmorphic symmetry, and emerge from a stripe-like structural modulation with long-range translational symmetry only along the stripe direction as we show using scanning tunnelling microscopy. Our work not only provides a playground for investigating further the properties of directional massless Dirac fermions, but also introduces a unique component with one-dimensional long-range order for engineering nano-electronic devices based on heterostructures of vdW materials.

Weyl (WSMs) evolve from Dirac semimetals in the presence of broken time-reversal symmetry (TRS) or space-inversion symmetry. The WSM phases in TaAs-class materials and photonic crystals are due to the loss of space-inversion symmetry. For TRS-breaking WSMs, despite numerous theoretical and experimental efforts, few examples have been reported. In this Article, we report a new type of magnetic semimetal Sr1−yMn1−zSb2(y, z < 0.1) with nearly massless relativistic fermion behaviour (m∗=  0.04 − 0.05m0, where m0is the free-electron mass). This material exhibits a ferromagnetic order for 304 K  <  T  <  565 K, but a canted antiferromagnetic order with a ferromagnetic component for T  <  304 K. The combination of relativistic fermion behaviour and ferromagnetism in Sr1−yMn1−zSb2offers a rare opportunity to investigate the interplay between relativistic fermions and spontaneous TRS breaking.

Ceramic cuprates of La1.85Sr0.15Cu1-yMgyO4with 0.00≤y≤0.30 are synthesized. The resistivity dependence of temperature is obtained up to room temperature. The metal-insulator transition at the range of higher doping level (y> 0.10) is observed. There is no impurity phase detected in the entire Mg-doped region. The structure of these Mg-doped samples is characterized by X-ray diffraction studies. The atomic structural parameters are obtained by Rietveld refinements for the Mg-doped samples with y≤0.30. No phase transition is detected within the accuracy of our experiments. The Mg doping reduce the local Jahn-Teller distortion of the CuO6octahedra. Some meaningful bond distances are determined according to the refined results. According to the variations of the lattice parameters with y, the whole doping range could be divided into two regions: low doping level (LDL) and high doping level (HDL). The bond length between the two apical oxygen atoms in the CuO6octahedra for the Mg-doped samples increases with increasing content of Mg in the LDL, and high doping level (HDL). The bond length between the two apical oxygen atoms in the CuO6octahedra for the Mg-doped samples increases with increasing content of Mg in the LDL, and decreases in the HDL.

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We describe direct pulsed image recording onto a bistable optically addressed spatial light modulator in particle image velocimetry (PIV). By coupling this technique with the parallel optical spatial autocorrelator for PIV data processing, one can obtain a fluid flow map within seconds without the necessity for off-line processing. The feasibility of recording a double-pulsed particle image is explored and demonstrated experimentally.

In order to exploit the full potential offered by optical correlation processing in the analysis of transparencies obtained by particle image velocimetry one needs to advance the transparency and to track the position of correlation peaks at great speed. In the following, this procedure is discussed with reference to an optical analysis system based on a high-speed ferroelectric optically addressed spatial light modulator. We present a system that uses scanning optics both to scan through the input transparency and to locate the correlation peaks in the resulting optical output distributions as a practical solution to the problem. The feasibility of this approach is demonstrated at a processing speed of ~ 500 autocorrelations/s when a one-dimensional acousto-optic output scanning device is used.

Polycrystalline samples of Bi1.8Pb0.2Sr2Cu1−xFexOy have been investigated by means of electron diffraction (ED), Raman scattering and resistivity measurements. It has been found that Fe doping influences markedly the lattice parameters and decreases the monoclinic modulation wavelength. The change of the frequency of the OSr phonon mode around 625 cm−1 can satisfactorily be interpreted by the “charge transfer” effect. The change of transport properties is also discussed.

The transport properties of the samples Bi1.8Pb0.2Sr2Can−1CunO2n+4+δ(n=1, 2) was studied by means of thermoelectric power and resistivity. We found that the spin gap exists in the normal states of both underdoped and overdoped samples of Bi1.8Pb0.2Sr2CuO6+δand Bi1.8Pb0.2Sr2CaCu2O8+δwith decreasing oxygen content in both systems.

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