Showing papers on "Spin wave published in 2007"
TL;DR: The observation of spin transport, as well as Larmor spin precession, over micrometre-scale distances in single graphene layers is reported, indicating that spin coherence extends underneath all of the contacts.
Abstract: Electronic transport in single or a few layers of graphene is the subject of intense interest at present. The specific band structure of graphene, with its unique valley structure and Dirac neutrality point separating hole states from electron states, has led to the observation of new electronic transport phenomena such as anomalously quantized Hall effects, absence of weak localization and the existence of a minimum conductivity. In addition to dissipative transport, supercurrent transport has also been observed. Graphene might also be a promising material for spintronics and related applications, such as the realization of spin qubits, owing to the low intrinsic spin orbit interaction, as well as the low hyperfine interaction of the electron spins with the carbon nuclei. Here we report the observation of spin transport, as well as Larmor spin precession, over micrometre-scale distances in single graphene layers. The 'non-local' spin valve geometry was used in these experiments, employing four-terminal contact geometries with ferromagnetic cobalt electrodes making contact with the graphene sheet through a thin oxide layer. We observe clear bipolar (changing from positive to negative sign) spin signals that reflect the magnetization direction of all four electrodes, indicating that spin coherence extends underneath all of the contacts. No significant changes in the spin signals occur between 4.2 K, 77 K and room temperature. We extract a spin relaxation length between 1.5 and 2 mum at room temperature, only weakly dependent on charge density. The spin polarization of the ferromagnetic contacts is calculated from the measurements to be around ten per cent.
2,110 citations
TL;DR: Spin Hall conductivities obtained from both the direct and inverse spin Hall effects are experimentally confirmed to be the same, demonstrating the Onsager reciprocal relations between spin and charge currents.
Abstract: Reversible spin Hall effect comprising the direct and inverse spin Hall effects was electrically detected at room temperature. A platinum wire with a strong spin-orbit interaction is used not only as a spin current absorber but also as a spin-current source in the specially designed lateral structure. The obtained spin Hall conductivities are $2.4\ifmmode\times\else\texttimes\fi{}{10}^{4}\text{ }\text{ }(\ensuremath{\Omega}\mathrm{m}{)}^{\ensuremath{-}1}$ at room temperature, ${10}^{4}$ times larger than the previously reported values of semiconductor systems. Spin Hall conductivities obtained from both the direct and inverse spin Hall effects are experimentally confirmed to be the same, demonstrating the Onsager reciprocal relations between spin and charge currents.
932 citations
Book•
01 Jan 2007TL;DR: In this article, the authors propose a solution to selected problems in random media, from particles to fields, from spin wave to statistical fields, and from fields to lattice systems.
Abstract: 1. Collective behaviour, from particles to fields 2. Statistical fields 3. Fluctuations 4. The scaling hypothesis 5. Perturbative renormalization group 6. Lattice systems 7. Series expansions 8. Beyond spin waves 9. Dissipative dynamics 10. Directed paths in random media Solutions to selected problems Index.
376 citations
22 Jan 2007
TL;DR: In this article, a new SU(2) spin rotation symmetry was discovered for spin-orbit coupled systems, which is robust against spin-independent disorder and interactions, and is generated by operators whose wavevector depends on the coupling strength.
Abstract: Spin-orbit coupled systems generally break the spin rotation symmetry. However, for a model with equal Rashba and Dresselhauss coupling constant (the ReD model), and for the [110] Dresselhauss model, a new type of SU(2) spin rotation symmetry is discovered. This symmetry is robust against spin-independent disorder and interactions, and is generated by operators whose wavevector depends on the coupling strength. It renders the spin lifetime infinite at this wavevector, giving rise to a Persistent Spin Helix (PSH). We obtain the spin fluctuation dynamics at, and away, from the symmetry point, and suggest experiments to observe the PSH.
257 citations
TL;DR: The temperature variation of the spin Hall conductivity is analyzed to identify the dominant scattering mechanism and implies that the spin accumulation originates from bulk scattering inside the Pt wire and the spin diffusion length limits the SHE.
Abstract: We have studied the evolution of the spin Hall effect (SHE) in the regime where the material size responsible for the spin accumulation is either smaller or larger than the spin diffusion length. Lateral spin valve structures with Pt insertions were successfully used to measure the spin absorption efficiency as well as the spin accumulation in Pt induced through the spin Hall effect. Under a constant applied current the results show a decrease of the spin accumulation signal is more pronounced as the Pt thickness exceeds the spin diffusion length. This implies that the spin accumulation originates from bulk scattering inside the Pt wire and the spin diffusion length limits the SHE. We have also analyzed the temperature variation of the spin Hall conductivity to identify the dominant scattering mechanism.
208 citations
TL;DR: A theory of collective mode dynamics in the helical magnets coupled to electric polarization via spin-orbit interaction is developed, and role of these low-lying modes in the neutron scattering and antiferromagnetic resonance is revealed.
Abstract: We develop a theory of collective mode dynamics in the helical magnets coupled to electric polarization via spin-orbit interaction. The low-lying modes associated with the ferroelectricity are not the transverse optical phonons, but are the spin waves hybridized with the electric polarization. This hybridization leads to the Drude-like dielectric function $\ensuremath{\epsilon}(\ensuremath{\omega})$ in the limit of zero magnetic anisotropy. There are two additional low-lying modes: phason of the spiral and rotation of helical plane along the polarization axis. Role of these low-lying modes in the neutron scattering and antiferromagnetic resonance is revealed, and a novel experiment to detect the dynamical magnetoelectric coupling is discussed.
195 citations
TL;DR: In this article, the authors used inelastic neutron scattering to demonstrate that collective spin excitations in optimally doped La2−xSrxCuO4 are more structured than previously thought.
Abstract: The excitations responsible for producing high-temperature superconductivity in the copper oxides have yet to be identified. Two promising candidates are collective spin excitations and phonons1. A recent argument against spin excitations is based on their inability to explain structures observed in electronic spectroscopies such as photoemission2,3,4,5 and optical conductivity6,7. Here, we use inelastic neutron scattering to demonstrate that collective spin excitations in optimally doped La2−xSrxCuO4 are more structured than previously thought. The excitations have a two-component structure with a low-frequency component strongest around 18 meV and a broader component peaking near 40–70 meV. The second component carries most of the spectral weight and its energy matches structures observed in photoemission2,3,4,5 in the range 50–90 meV. Our results demonstrate that collective spin excitations can explain features of electronic spectroscopies and are therefore likely to be strongly coupled to the electron quasiparticles.
165 citations
TL;DR: In this article, the authors summarized experimental results for the magnetic thermal conductivity κmag of several compounds which are good representations of different low-dimensional quantum spin models, i.e. arrangements of S=1/2 spins in the form of two-dimensional (2D) square lattices and one-dimensional structures such as chains and two-leg ladders.
Abstract: Transport properties provide important information about the mobility, elastic and inelastic of scattering of excitations in solids. Heat transport is well understood for phonons and electrons, but little is known about heat transport by magnetic excitations. Very recently, large and unusual magnetic heat conductivities were discovered in low-dimensional quantum magnets. This article summarizes experimental results for the magnetic thermal conductivity κmag of several compounds which are good representations of different low-dimensional quantum spin models, i.e. arrangements of S=1/2 spins in the form of two-dimensional (2D) square lattices and one-dimensional (1D) structures such as chains and two-leg ladders. Remarkable properties of κmag have been discovered: It often dwarfs the usual phonon thermal conductivity and allows the identification and analysis of different scattering mechanisms of the relevant magnetic excitations.
144 citations
TL;DR: In this article, the authors conducted micromagnetic numerical studies on the strong radiation of spin waves (SWs) produced by the magnetic-field-induced reversal of a magnetic vortex core, as well as their wave behaviors in magnetic nanowires.
Abstract: We conducted micromagnetic numerical studies on the strong radiation of spin waves (SWs) produced by the magnetic-field-induced reversal of a magnetic vortex core, as well as their wave behaviors in magnetic nanowires. It was found that the radial SWs can be emitted intensively from a vortex core in a circular dot by virtue of localized large torques employed at the core, and then can be injected into a long nanowire via their contact. These SWs exhibit wave characteristics such as propagation, reflection, transmission, interference, and dispersion. These results offer a preview of the generation, delivery, and manipulation of SWs in magnetic elements, which are applicable to information-signal processing in potential SW devices.
144 citations
TL;DR: The origin and the general properties of the phenomenological equations describing coupling between charge and spin currents are discussed and the effect provides means to study spin accumulation by electrical measurements.
Abstract: Because of spin-orbit interaction, an electrical current is accompanied by a spin current resulting in spin accumulation near the sample edges. Due again to spin-orbit interaction this causes a small decrease of the sample resistance. An applied magnetic field will destroy the edge spin polarization leading to a positive magnetoresistance. This effect provides means to study spin accumulation by electrical measurements. The origin and the general properties of the phenomenological equations describing coupling between charge and spin currents are also discussed.
123 citations
TL;DR: In this paper, the dispersion relation for collective modes in patterned arrays through the numerical solution of an eigenvalue problem for an integral operator has been investigated and quantitatively explained by a theoretical model.
Abstract: Magnetization dynamics of dipolarly coupled nanowire arrays has been studied by Brillouin light scattering. Measurements performed in uniformly magnetized wires as a function of the transferred wave vector demonstrated the existence of several discrete collective modes, propagating through the structure with a periodic dispersion curve encompassing several Brillouin zones relative to the artificial spatial periodicity. This experimental evidence has been quantitatively explained by a theoretical model which permits the calculation of the dispersion relation for collective modes in patterned arrays through the numerical solution of an eigenvalue problem for an integral operator.
TL;DR: In this article, the authors have bombarded graphite samples with protons at low temperatures and low fluences to attenuate the large thermal annealing produced during irradiation.
Abstract: We have bombarded graphite samples with protons at low temperatures and low fluences to attenuate the large thermal annealing produced during irradiation. The overall optimization of sample handling allowed us to find Curie temperatures ${T}_{c}\ensuremath{\gtrsim}350\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ at the fluences used. The magnetization versus temperature shows unequivocally a linear dependence, which can be interpreted as due to excitations of spin waves in a two-dimensional Heisenberg model with a weak uniaxial anisotropy.
TL;DR: The magnetic excitations in multiferroic TbMnO3 have been studied by inelastic neutron scattering in the spiral and sinusoidally ordered phases and three low-lying magnons whose character has been fully determined using neutron-polarization analysis are found.
Abstract: The magnetic excitations in multiferroic TbMnO3 have been studied by inelastic neutron scattering in the spiral and sinusoidally ordered phases. At the incommensurate magnetic zone center of the spiral phase, we find three low-lying magnons whose character has been fully determined using neutron-polarization analysis. The excitation at the lowest energy is the sliding mode of the spiral, and two modes at 1.1 and 2.5 meV correspond to rotations of the spiral rotation plane. These latter modes are expected to couple to the electric polarization. The 2.5 meV mode is in perfect agreement with recent infrared-spectroscopy data giving strong support to its interpretation as a hybridized phonon-magnon excitation.
TL;DR: By using a combination of different analytic methods, the large time asymptotic behavior of the spin-spin dynamical correlation function for strong interparticle repulsion is derived.
Abstract: We investigate the propagation of spin excitations in a one-dimensional ferromagnetic Bose gas. While the spectrum of longitudinal spin waves in this system is soundlike, the dispersion of transverse spin excitations is quadratic, making a direct application of the Luttinger liquid theory impossible. By using a combination of different analytic methods we derive the large time asymptotic behavior of the spin-spin dynamical correlation function for strong interparticle repulsion. The result has an unusual structure associated with a crossover from the regime of trapped spin wave to an open regime and does not have analogues in known low-energy universality classes of quantum 1D systems.
TL;DR: In this article, spectral measurements of spin-wave excitations driven by direct spin-polarized current in a free layer of nanoscale was presented, and it was shown that large-amplitude coherent spinwave modes are excited over a wide range of bias current.
Abstract: We present spectral measurements of spin-wave excitations driven by direct spin-polarized current in a free layer of nanoscale ${\mathrm{Ir}}_{20}{\mathrm{Mn}}_{80}∕{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}∕\mathrm{Cu}∕{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ spin valves The measurements reveal that large-amplitude coherent spin-wave modes are excited over a wide range of bias current The frequency of these excitations exhibits a series of jumps as a function of current due to transitions between different localized nonlinear spin-wave modes of the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ nanomagnet We find that micromagnetic simulations employing the Landau-Lifshitz-Gilbert equation of motion augmented by the Slonczewski spin-torque term (LLGS) accurately describe the frequency of the current-driven excitations including the mode transition behavior However, LLGS simulations give qualitatively incorrect predictions for the amplitude of excited spin waves as a function of current
TL;DR: In this article, the Fermi surface instabilities of the Pomeranchuk type in the spin triplet channel with high orbital partial wave (F{sub l}{sup a} (l > 0) were studied and the ordered phases were classified into two classes, dubbed the {alpha} and {beta}-phases by analogy to the superfluid {sup 3}He-A and B-Phases.
Abstract: We study the Fermi surface instabilities of the Pomeranchuk type in the spin triplet channel with high orbital partial waves (F{sub l}{sup a} (l > 0)). The ordered phases are classified into two classes, dubbed the {alpha} and {beta}-phases by analogy to the superfluid {sup 3}He-A and B-phases. The Fermi surfaces in the {alpha}-phases exhibit spontaneous anisotropic distortions, while those in the {beta}-phases remain circular or spherical with topologically non-trivial spin configurations in momentum space. In the {alpha}-phase, the Goldstone modes in the density channel exhibit anisotropic overdamping. The Goldstone modes in the spin channel have nearly isotropic underdamped dispersion relation at small propagating wavevectors. Due to the coupling to the Goldstone modes, the spin wave spectrum develops resonance peaks in both the {alpha} and {beta}-phases, which can be detected in inelastic neutron scattering experiments. In the p-wave channel {beta}-phase, a chiral ground state inhomogeneity is spontaneously generated due to a Lifshitz-like instability in the originally nonchiral systems. Possible experiments to detect these phases are discussed.
TL;DR: In this paper, the authors employed pump-probe investigations on the femto and picosecond timescale to study the ultrafast dynamics of electrons, spin-waves, and phonons after intense optical excitation.
Abstract: The dynamics of collective excitations of electrons, phonons, and spins are of fundamental interest to develop a microscopic understanding of interactions among elementary excitations and of the respective relaxation mechanisms. The present work employs pump–probe investigations on the femto- and picosecond timescale to study the ultrafast dynamics of electrons, spin-waves, and phonons after intense optical excitation. The Gd(0001) surface, which serves as a model system for a ferromagnetic metal, is investigated by complementary time-resolved techniques, photoelectron spectroscopy and linear/nonlinear optical spectroscopy. The energy relaxation of hot electrons is analysed by transient changes of the electron distribution function and of the complex self-energy of the occupied component of the 5dz2 surface state. In combination with a simplified description by the two-temperature model this analysis characterizes the optically excited state quantitatively. We analyse the mechanism that leads to a drop in spin polarization upon optical excitation, which is observed in nonlinear magneto-optics. Since the exchange splitting, analysed by photoemission, is not affected under these non-equilibrium conditions, we propose spin-flip scattering of hot electrons to be responsible. The Gd(0001) surface presents a previously unknown coupled phonon–magnon mode, which can be excited by femtosecond laser pulses. Time-resolved detection of the optical second harmonic yield separates spin dynamics from electron and lattice contributions. A coherent phonon–magnon mode at 3 THz, which is driven by electronic excitations of surface and bulk states, is observed. Time-resolved photoemission provides information on the interaction mechanism. We find that the binding energy of the surface state oscillates at the same frequency. In combination with calculations of the surface state binding energy upon lattice contraction this suggests a phonon–magnon coupling due to spin-flip scattering, in contrast to the conventional type mediated by spin–orbit interaction.
TL;DR: In this paper, the results from Brillouin light scattering experiments on guided spin waves propagating along metallic magnetic stripes are presented and analyzed, and it is shown that each standing spin-wave resonance across the stripe width is associated with a particular guided mode.
Abstract: Results from Brillouin light scattering experiments on guided spin waves propagating along metallic magnetic stripes are presented and analyzed. The spin waves propagate along the stripe axis and form mode families due to geometrical confinement in the stripe geometry. In consequence, the allowed wave vectors are quantized in the transverse directions by stripe width and height. We show that each standing spin-wave resonance across the stripe width is associated with a particular guided mode. In the case of stripes magnetized along their length, the group velocity of the guided modes is negative and all modes have a volume character. When the stripes are magnetized along their width, the modes are characterized by a positive group velocity, and the spectrum consists of a series of volume and localized modes.
TL;DR: This study provides evidence for a strong coupling between magnons and phonons, evidenced by the opening of a gap below T(N) in the dispersion of the transverse acoustic phonon mode polarized along the ferroelectric axis.
Abstract: Inelastic neutron scattering measurements have been performed on $Y{\mathrm{MnO}}_{3}$, aiming to study the interplay between spin and lattice degrees of freedom in this hexagonal multiferroic material. Our study provides evidence for a strong coupling between magnons and phonons, evidenced by the opening of a gap below ${T}_{N}$ in the dispersion of the transverse acoustic phonon mode polarized along the ferroelectric axis. The resulting upper phonon branch is found to lock on one of the spin-wave modes. These findings are discussed in terms of a possible hybridization between the two types of elementary excitations.
TL;DR: A new reliable method combining template synthesis and nanolithography-based contacting technique to elaborate current perpendicular-to-plane giant magnetoresistance spin valve nanowires, which are very promising for the exploration of electrical spin transfer phenomena.
Abstract: We have developed a new reliable method combining template synthesis and nanolithography-based contacting technique to elaborate current perpendicular-to-plane giant magnetoresistance spin valve nanowires, which are very promising for the exploration of electrical spin transfer phenomena. The method allows the electrical connection of one single nanowire in a large assembly of wires embedded in anodic porous alumina supported on Si substrate with diameters and periodicities to be controllable to a large extent. Both magnetic excitations and switching phenomena driven by a spin-polarized current were clearly demonstrated in our electrodeposited NiFe/Cu/ NiFe trilayer nanowires. This novel approach promises to be of strong interest for subsequent fabrication of phase-locked arrays of spin transfer nano-oscillators with increased output power for microwave applications.
TL;DR: This work has demonstrated an ultrafast nonthermal excitation of spin waves with a phase that depends on the angular momentum of the photons.
Abstract: Ultrashort laser pulses have been used to study the effect of circularly polarized light on spins in the ferrimagnetic metal GdFeCo. By turning the sample into a multidomain state and thereby suppressing the observation of the heating effect of light, we have been able to demonstrate an ultrafast nonthermal excitation of spin waves with a phase that depends on the angular momentum of the photons. These results demonstrate the possibility of ultrafast coherent control of the magnetization in this metallic system.
TL;DR: In this paper, a spin-polarized current is injected from a Ni81Fe19 thin film to a two-dimensional electron gas (2DEG) made of InAs based epitaxial multilayers.
Abstract: The authors demonstrate fully electrical detection of spin injection in InAs quantum wells. A spin-polarized current is injected from a Ni81Fe19 thin film to a two-dimensional electron gas (2DEG) made of InAs based epitaxial multilayers. Injected spins accumulate and diffuse out in the 2DEG, and the spins are electrically detected by a neighboring Ni81Fe19 electrode. The observed spin diffusion length is 1.8μm at 20K. The injected spin polarization across the Ni81Fe19∕InAs interface is 1.9% at 20K and remains at 1.4% even at room temperature. Their experimental results will contribute significantly to the realization of a practical spin field effect transistor.
TL;DR: In this paper, a theory for the determination of the collective spin-wave modes of regular arrays of magnetic particles, taking into account the dipolar interaction among particles, was developed, and the frequencies and profiles of the spin modes of arrays of permalloy cylindrical particles with different interparticle separation were calculated with a numerical implementation of this model, using a three-dimensional representation of the magnetic particles in their actual nonuniform fundamental state.
Abstract: We have developed a theory for the determination of the collective spin-wave modes of regular arrays of magnetic particles, taking into account the dipolar interaction among particles. The frequencies and profiles of the spin modes of arrays of permalloy cylindrical particles with different interparticle separation have been calculated with a numerical implementation of this model, using a three-dimensional representation of the magnetic particles in their actual nonuniform fundamental state. The results show a very good agreement with recently published experimental data, and allow us to discuss the dispersion curves and some relevant properties of the Brillouin light-scattering intensity from spin modes in periodic arrays.
TL;DR: In this paper, the authors investigated scattering of exchange spin waves by a model nonuniformity of the effective magnetic field and demonstrated limitations imposed upon the size and the speed of operation of such a device by a requirement that it be controlled by an external uniform magnetic field.
Abstract: We have investigated scattering of exchange spin waves by a model nonuniformity of the effective magnetic field. In particular, certain profiles of the nonuniformity are characterized by a total transmission of the spin wave intensity while inducing large shifts to the phase of transmitted spin waves. These properties are discussed in the context of potential application within a spin wave logic device—a spin wave interferometer containing such a nonuniformity in one of its branches. We demonstrate limitations imposed upon the size and the speed of operation of such a device by a requirement that it be controlled by an external uniform magnetic field.
TL;DR: In this article, the magnetic and structural properties of ErFeO3, TmFeO 3, and YbFeO-3 single crystals were studied over a wide temperature range.
Abstract: Magnetic and structural characteristics of ErFeO3, TmFeO3, and YbFeO3 single crystals were studied over a wide temperature range. Magnetic measurements found that the spin-rotation transitions in all crystals are well described by the earlier proposed theory with no fitting parameters. Additionally, they have shown the absence of the magnetic compensation point in TmFeO3 and a noticeable growth of the c-axis magnetization at low temperatures in TmFeO3 and ErFeO3. The x-ray measurements found no symmetry-lowering lattice distortions during the reorientation. Overall, the measurements cover a wide range of material parameters and demonstrate the generality of the modified mean field theory of the Γ4→Γ24→Γ2 orientation phase transitions in orthoferrites.
TL;DR: In this paper, the spin transport in insulating antiferromagnets described by the isotropic Heisenberg model in two and three dimensions is analyzed in the Ising regime.
Abstract: We analyze spin transport in insulating antiferromagnets described by the $XXZ$ Heisenberg model in two and three dimensions. Spin currents can be generated by a magnetic-field gradient or, in systems with spin-orbit coupling, perpendicular to a time-dependent electric field. The Kubo formula for the longitudinal spin conductivity is derived analogously to the Kubo formula for the optical conductivity of electronic systems. The spin conductivity is calculated within interacting spin-wave theory. In the Ising regime, the $XXZ$ magnet is a spin insulator. For the isotropic Heisenberg model, the dimensionality of the system plays a crucial role: In $d=3$ the regular part of the spin conductivity vanishes linearly in the zero frequency limit, whereas in $d=2$ it approaches a finite zero frequency value.
TL;DR: In this article, the spin diffusion processes in lateral structures are investigated using non-local spin injection techniques, and efficient spin injection and detection are accomplished by optimizing the probe configuration and junction structures on the basis of spin resistance.
Abstract: Laterally configured ferromagnetic/nonmagnetic multi-terminal spintronic devices enable the performance of detailed study of spin accumulation in nonmagnets. The spin diffusion processes in lateral structures are investigated using nonlocal spin injection techniques. Efficient spin injection and detection are accomplished by optimizing the probe configuration and junction structures on the basis of the concept of spin resistance. The magnetization switching of a nanoscale ferromagnet is finally realized using efficient spin current absorption behaviour induced by nonlocal spin injection.
TL;DR: In this paper, a detailed experimental and theoretical analysis of the spin dynamics of two-dimensional electron gases (2DEGs) in a series of $n$-doped quantum wells was presented.
Abstract: We present a detailed experimental and theoretical analysis of the spin dynamics of two-dimensional electron gases (2DEGs) in a series of $n$-doped $\mathrm{Ga}\mathrm{As}∕{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ quantum wells. Picosecond-resolution polarized pump-probe reflection techniques were applied in order to study in detail the temperature, concentration, and quantum-well-width dependencies of the spin relaxation rate of a small photoexcited electron population. A rapid enhancement of the spin lifetime with temperature up to a maximum near the Fermi temperature of the 2DEG was demonstrated experimentally. These observations are consistent with the D'yakonov-Perel' spin-relaxation mechanism controlled by electron-electron collisions. The experimental results and theoretical predictions for the spin relaxation times are in good quantitative agreement.
TL;DR: High-resolution scanning tunnelling microscopy measurements of the electron-doped high-Tc superconductor Pr0.88LaCe0.12CuO4 reveal a bosonic excitation (mode) that is consistent with both spin-excitations in PLCCO measured by inelastic neutron scattering and a low-energy acoustic phonon mode, but differs substantially from the oxygen vibrational mode identified in BSCCO.
Abstract: Perhaps the most debated current issue in the field of high-temperature superconductivity is the microscopic origin of the superconducting 'glue' that binds electrons into superconducting pairs. The leading contenders are lattice vibrations (phonons) and spin excitations, with the additional possibility of pairing without mediators. Niestemski et al. report spatially resolved, reproducible spectroscopy of the electron-doped superconductor known as PLCCO that reveal a collective mode in the material's electronic excitations at 10.5 ± 2.5 meV. This is consistent with an electronic origin of the mode — and possibly the superconducting 'glue' — consistent with the involvement of spin-excitations rather than phonons. A bosonic excitation (mode) at energies 10.5 ± 2.5 meV in the electron doped superconductor Pr0.88LaCe0.12CuO4 (PLCCO) is reported. The analysis of this indicates an electronic origin of the mode consistent with spin excitations rather than phonons. Despite recent advances in understanding high-transition-temperature (high-Tc) superconductors, there is no consensus on the origin of the superconducting ‘glue’: that is, the mediator that binds electrons into superconducting pairs. The main contenders are lattice vibrations1,2 (phonons) and spin-excitations3,4, with the additional possibility of pairing without mediators5. In conventional superconductors, phonon-mediated pairing was unequivocally established by data from tunnelling experiments6. Proponents of phonons as the high-Tc glue were therefore encouraged by the recent scanning tunnelling microscopy experiments on hole-doped Bi2Sr2CaCu2O8-δ (BSCCO) that reveal an oxygen lattice vibrational mode whose energy is anticorrelated with the superconducting gap energy scale7. Here we report high-resolution scanning tunnelling microscopy measurements of the electron-doped high-Tc superconductor Pr0.88LaCe0.12CuO4 (PLCCO) (Tc = 24 K) that reveal a bosonic excitation (mode) at energies of 10.5 ± 2.5 meV. This energy is consistent with both spin-excitations in PLCCO measured by inelastic neutron scattering (resonance mode)8 and a low-energy acoustic phonon mode9, but differs substantially from the oxygen vibrational mode identified in BSCCO. Our analysis of the variation of the local mode energy and intensity with the local gap energy scale indicates an electronic origin of the mode consistent with spin-excitations rather than phonons.
TL;DR: In this article, the theoretical prediction of Q balls in relativistic quantum fields is realized experimentally in superfluid 3He-B. This Q ball is another representative of a state with phase coherent precession of nuclear spins, similar to the well-known homogeneously precessing domain, which we interpret as Bose-Einstein condensation of spin waves.
Abstract: The theoretical prediction of Q balls in relativistic quantum fields is realized here experimentally in superfluid 3He-B. The condensed-matter analogs of relativistic Q balls are responsible for an extremely long-lived signal of magnetic induction observed in NMR at the lowest temperatures. This Q ball is another representative of a state with phase coherent precession of nuclear spins in 3He-B, similar to the well-known homogeneously precessing domain, which we interpret as Bose-Einstein condensation of spin waves--magnons. At large charge Q, the effect of self-localization is observed. In the language of relativistic quantum fields it is caused by interaction between the charged and neutral fields, where the neutral field provides the potential for the charged one. In the process of self-localization the charged field modifies locally the neutral field so that the potential well is formed in which the charge Q is condensed.