Polarized and unpolarized neutron scattering was used to measure the wave vector-and frequencydependent magnetic fluctuations in the normal state (from the superconducting transition temperature, Tc = 35, up to 350 K) of single crystals of La1.86Sr0.14CuO4. The peaks which dominate the fluctuations have amplitudes that decrease as T −2 and widths that increase in proportion to the thermal energy, kBT (where kB is Boltzmann's constant), and energy transfer added in quadrature. The nearly singular fluctuations are consistent with a nearby quantum critical point.The normal state of the metallic cuprates is as unusual as their superconductivity. For example, the electrical resistivity of samples with optimal superconducting properties is linear in temperature (T) from above 1000 K to T c [1]. Correspondingly, infrared reflectivity reveals charge fluctuations with a characteristic energy scale that is proportional only to T [1,2]. Furthermore, the effective number of charge carriers, as measured with the classic Hall effect, is strangely T-dependent. Even so, the Hall angle, a measure of the deflection of carriers in the material by an external magnetic field, follows a T −2 law [3]. Thus, the metallic charge carriers in the doped cuprates exhibit peculiar but actually quite simple properties [4] in the normal state. Also, these properties do not vary much between the different high-T c families.Electrons carry spin as well as charge, so it is reasonable to ask whether the normal state magnetic properties, derived from the spins, are as simple and universal as those derived from the charges. Experiments to probe the spins include classical magnetic susceptometry, where the magnetization in response to a homogeneous external magnetic field is measured, and resonance experiments, where nuclear dipole and quadrupolar relaxation is used to monitor the electron spins. The spin-sensitive measurements yield more complex and less universal results than those sensitive to charge, and indeed do not seem obviously related to the frequency-dependent conductivity, σ(ω, T ), probed in electrical, microwave and optical experiments. In particular, there is little evidence for magnetic behavior which is as nearly singular, in the sense of diverging (for T → 0) amplitudes, time constants, or length scales, as the behavior of σ(ω, T ).We report nearly singular behavior of the magnetic fluctuations in the simplest of high-T c materials, namely, the compound La 2−x Sr x CuO 4 whose fundamental building blocks are single CuO 2 layers, as determined by inelastic magnetic neutron scattering. A beam of mono-energetic neutrons is first prepared and then scattered from the sample, and the outgoing neutrons are labeled according to their energies and directions to establish an angle and energy-dependent scattering probability, or cross-section, d2 σ/dωdΩ. Because the neutron spin and the electron spins in the sample interact through magnetic dipole coupling, the cross-section is directly proportional to the magnetic structure function, S(Q, ω),...

We report a study of the magnetization density in the mixed state of the unconventional superconductor Sr2RuO4. On entering the superconducting state we find no change in the magnitude or distribution of the induced moment for a magnetic field of 1 Tesla applied within the RuO2 planes. Our results are consistent with a spin-triplet Cooper pairing with spins lying in the basal plane. This is in contrast with similar experiments performed on conventional and high-Tc superconductors.Sr 2 RuO 4 has attracted attention since it was discovered [1] to be a superconductor. The superconductivity of this compound is interesting because it is isostructural with the high-T c material La 2−x Sr x CuO 4 and because the superconducting state appears unconventional (i.e. not of the s-wave singlet type). The low-temperature normal-state of Sr 2 RuO 4 is a quasi-2D Fermi liquid with enhanced quasiparticles [2]. Soon after the discovery of superconductivity in Sr 2 RuO 4 , it was suggested [3,4] [10]. While there is general agreement that the superconducting state of Sr 2 RuO 4 is unconventional, the nature of the wavefunction is still controversial [3,4,[11][12][13][14]. A knowledge of the spin susceptibility in the superconducting state provides constraints on the pairing wavefunction of a superconductor. Such information can be obtained indirectly by nuclear-resonance techniques through the measurement of the polarization of the s electrons on a given site. Alternatively, neutron scattering can directly measure the magnetization density induced by an applied magnetic field. This technique was first used by Shull and Wedgewood [15] to study V 3 Si and more recently it has been applied to heavy-fermion [16] and high-T c [17] superconductors. In this letter we report a study of the induced magnetization of Sr 2 RuO 4 through the superconducting transition. On entering the superconducting state we find no change in the magnitude or distribution of the induced moment. Our results are in contrast to similar observations on conventional and high-T c superconductors and are consistent with triplet spin-pairing in Sr 2 RuO 4 .The single crystal of Sr 2 RuO 4 used in this study (C117) was prepared by a floating-zone method [18] in an infrared image furnace. A piece of approximate dimensions 1.5 mm× 2mm × 5 mm was cut using a diamond saw. A.c. susceptibility measurements indicated a sharp superconducting transition with T c =1.47 K and B c2 (T = 100mK)=1.43 T for B [110]. To perform our neutron scattering experiments, the sample was glued to a copper stage using Stycast 2850FT. The copper support was connected to a dilution refrigerator via two 1mm 2 diameter copper wires. In the present experiment we applied the magnetic field along the [110] direction. The large anisotropy in B c2 means that the mutual alignment of the magnetic field and [110] is crucial. Accurate alignment was achieved by mounting the sample and copper stage on a micro-goniometer inside a 2.5 T magnet. In order to verify that the crystal was correctly aligned and at l...