Zero modes for the boundary giant magnons

We study the fermion zero-mode dynamics for open strings ending on the giant graviton branes. For the open string ending on the Z=0$Z=0$ brane, the quantization of the fermion zero-modes of boundary giant magnons reproduces the 256 states of the boundary degrees with the precise realization of the SU(2|2)×SU(2|2)$\mathit{SU}(2|2)\times \mathit{SU}(2|2)$ symmetry algebra. Also for the open string ending on the Y=0$Y=0$ brane, we reproduce the unique vacuum state from the fermion zero-modes.     

Propagating energy modes in the heisenberg chain: Just plain magnons

We show that the oscillations in the energy density observed in classical simulations on ferromagnetic chains are present in the antiferromagnet as well, and are not due to hydrodynamic “second magnon” modes, but arise from a singularity in the non interacting two spin wave density of states.Quantum occupation number effects change qualitatively the nature of the oscillations, producing a perfectly well defined mode at the spin wave frequency as T→0.     

Hydrodynamic modes in dense trapped ultracold gases

We consider the hydrodynamic modes for dense trapped ultracold gases, where the interparticle distance is comparable to the scattering length. We show that the experimental determination of the hydrodynamic mode frequencies allows one to obtain quite directly the equation of state of a dense gas. As an example, we investigate the case of two equal fermionic populations in different hyperfine states with attractive interaction.     

Hydrodynamic modes,soft modes and fluctuation spectra near the threshold of a current instability

We give a full threedimensional treatment of the stability and the fluctuations of the uniform stationary current state in a voltage-controlled current instability. We consider a model which exhibits bulk negative differential conductivity due to Bragg scattering of hot electrons. The model consists of Langevin equations for the mean momentum and the mean energy of the charged carriers, coupled to Maxwell's equations. We investigate the normal modes and the fluctuation spectra of this system, in particular the occurrence of soft modes and of critical fluctuations at the stability limit of the uniform current state. It is shown that the nature of the normal modes is strongly determined by the electromagnetic interactions between the carriers, giving rise to hydrodynamic flux modes and to dielectric relaxation modes. As the threshold field is approached, the dielectric relaxation modes soften and couple strongly to the flux modes. It is shown that as a consequence of this coupling the exponential decay of the correlation functions due to ordinary dielectric relaxation is followed at very long times by a power law decay due to the hydrodynamic modes.Work supported by the Swiss National Science Foundation     

Relaxation of goldstone magnons in a ferrimagnetic semiconductor

The energy spectra and relaxation coefficients of Goldstone modes of spin waves are studied in a ferrimagnetic semiconductor with arbitrary number n of magnetic sublittices at low temperatures.     

Hydrodynamic singularities and clustering in a freely cooling inelastic gas

We employ hydrodynamic equations to follow the clustering instability of a freely cooling dilute gas of inelastically colliding spheres into a well-developed nonlinear regime. We simplify the problem by dealing with a one-dimensional coarse-grained flow. We observe that at a late stage of the instability the shear stress becomes negligibly small, and the gas flows solely by inertia. As a result the flow formally develops a finite-time singularity, as the velocity gradient and the gas density diverge at some location. We argue that flow by inertia represents a generic intermediate asymptotic of unstable free cooling of dilute inelastic gases.     

Interacting topological magnons in a checkerboard ferromagnet

This work is devoted to studying the magnon–magnon interaction effect in a two-dimensional checkerboard ferromagnet with the Dzyaloshinskii–Moriya interaction. Using a first-order Green function method, we analyze the influence of magnon–magnon interaction on the magnon band topology. We find that Chern numbers of two renormalized magnon bands are different above and below the critical temperature, which means that the magnon band gap-closing phenomenon is an indicator for one topological phase ...     

Persistence of magnons in a site-diluted dimerized frustrated antiferromagnet

We present inelastic neutron scattering and thermodynamic measurements characterizing the magnetic excitations in a disordered spin-liquid antiferromagnet with non-magnetic substitution. The parent compound Ba(3)Mn(2)O(8) is a dimerized, quasi-two-dimensional geometrically frustrated quantum disordered antiferromagnet. We substitute this compound with non-magnetic V(5+) for the S=1 Mn(5+) ions, Ba(3)(Mn(1-x)V (x))(2)O(8), and find that the singlet-triplet excitations which dominate the spectrum of the parent compound persist for the full range of substitution examined, up to x=0.3. We also observe additional low-energy magnetic fluctuations which are enhanced at the greatest substitution values.     

Cherenkov emission of magnons by a slow monopole

The energy losses due to Cherenkov emission of magnons during the interaction of a slow heavy monopole with magnetically ordered media are discussed.     

Probing anomalous longitudinal fluctuations of the interacting Bose gas via Bose-Einstein condensation of magnons

The emergence of a finite staggered magnetization in quantum Heisenberg antiferromagnets subject to a uniform magnetic field can be viewed as Bose-Einstein condensation of magnons. Using nonperturbative results for the infrared behavior of the interacting Bose gas, we present exact results for the staggered spin-spin correlation functions of quantum antiferromagnets in a magnetic field at zero temperature. In particular, we show that in dimensions 1相似文献   

One-dimensional gapless magnons in a single anisotropic ferromagnetic nanolayer

Gapless magnons in a plane ferromagnet with normal axis anisotropy are shown to exist besides the usual gapped modes that affect spin dependent transport properties only above a finite temperature. These magnons are one-dimensional objects, in the sense that they are localized inside the domain walls that form in the film. They may play an essential role in the spin dependent scattering processes even down to very low temperatures.     

Low-energy monopole modes of a trapped atomic Fermi gas

We consider the low energy collective monopole modes of a trapped weakly interacting atomic Fermi gas in the collisionless regime. The spectrum is calculated for varying coupling strength and chemical potential. Using an effective Hamiltonian, we derive analytical results that agree well with numerical calculations in various regimes. The onset of superfluidity is shown to lead to effects such as the vanishing of the energy required to create a Cooper molecule at a critical coupling strength and to the emergence of pair vibration excitations. Our analysis suggests ways to experimentally detect the presence of the superfluid phase in trapped atomic Fermi gases.     

Magnetoplasma modes of a spatially periodic two-dimensional electron gas

We examine the magnetoplasma dispersion of a two-dimensional electron gas with a spatially periodic charge density. The system studied is a periodic array of two-dimensional electron gas strips with constant equilibrium density. The integral equation describing the charge fluctuations on the strips, has been derived and solved numerically. The spatial dependence of the form of either propagating or evanescent waves. The latter are associated with the edge modes, recently discovered in electrons on liquid⁴ He. For a periodic array of two-dimensional strips, the modes in different strips, interact and form bands.     

Hydrodynamic response and free surface modes for two immiscible fluids

We consider a system consisting of two immiscible fluids and their interface. The equilibrium interface is assumed to be planar. The velocity fields in the fluids are described by the linearized Navier-Stokes equations with appropriate boundary conditions at the interface. Explicit expressions for the response of the system to arbitrary bulk and/or surface forces are derived. In particular, we consider the transmission and reflection of sound modes and conclude that ultrasonic techniques can be used to measure the coefficient of sliding friction between fluids. In addition, we obtain dispersion relations for the free surface modes.     

Phase-coherent current-driven magnons in magnetic multilayers

We report the detection of electromagnetic waves radiated by current-driven magnons in a Co/Cu magnetic multilayer. The magnons were excited by means of a high current density ≈10⁸ A/cm² injected into the multilayer through a point contact. The point contact itself was used as a high frequency mixer to mix electromagnetic waves radiated by the current-driven magnons with externally generated microwave radiation. Here the external microwaves are used as a direct probe of the high-frequency behavior and partial phase coherence of the current-induced excitations. When the external frequency equaled the frequency of the magnons generated in the multilayer a DC voltage was found to develop across the contact. Investigation of how this voltage varies with exciting current, magnetic field, and microwave frequency provides detailed information on the spectrum of the current-driven magnons. Our observations support the feasibility of a spin-wave maser, or spin-wave amplification by stimulated emission of radiation.     

Excitations from a Bose-Einstein condensate of magnons in coupled spin ladders

The weakly coupled quasi-one-dimensional spin ladder compound (CH3)2CHNH3CuCl3 is studied by neutron scattering in magnetic fields exceeding the critical field of Bose-Einstein condensation of magnons. Commensurate long-range order and the associated Goldstone mode are detected and found to be similar to those in reference to spin-dimer materials. However, for the upper two massive magnon branches, the observed behavior is totally different, culminating in a drastic collapse of excitation bandwidth beyond the transition point.     

Collective modes of a quasi-two-dimensional Bose condensate in large gas parameter regime

We have theoretically studied the collective modes of a quasi-two-dimensional (Q2D) Bose condensate in the large gas parameter regime by using a formalism which treats the interaction energy beyond the mean-field approximation. The results show that incorporation of this higher order term leads to significant modifications in the mode frequencies.