Time-dependent spin-wave theory

Rückriegel, Andreas; Kreisel, Andreas; Kopietz, Peter

doi:10.1103/physrevb.85.054422

Cited by 22 publications

(33 citation statements)

References 18 publications

(16 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is, of course, possible to consider the case of the mean spin directed arbitrarily and to write down the Holstein-Primakoff transformation for this case, as has been done by Rückriegel et al [257]. In the general case of a mean spin S j directed arbitrarily, the spin components {S 1 j , S 2 j , S 3 j } are the projections of the spin operator S j on the axes defined by the unit mutually orthogonal vectors e 1 , e 2 , and e 3 , with the latter vector being…”

Section: No Condensation Of Equilibrium Magnonsmentioning

confidence: 99%

Effects of symmetry breaking in finite quantum systems

2013

View full text Add to dashboard Cite

The review considers the peculiarities of symmetry breaking and symmetry transformations and the related physical effects in finite quantum systems. Some types of symmetry in finite systems can be broken only asymptotically. However, with a sufficiently large number of particles, crossover transitions become sharp, so that symmetry breaking happens similarly to that in macroscopic systems. This concerns, in particular, global gauge symmetry breaking, related to Bose-Einstein condensation and superconductivity, or isotropy breaking, related to the generation of quantum vortices, and the stratification in multicomponent mixtures. A special type of symmetry transformation, characteristic only for finite systems, is the change of shape symmetry. These phenomena are illustrated by the examples of several typical mesoscopic systems, such as trapped atoms, quantum dots, atomic nuclei, and metallic grains. The specific features of the review are: (i) the emphasis on the peculiarities of the symmetry breaking in finite mesoscopic systems; (ii) the analysis of common properties of physically different finite quantum systems; (iii) the manifestations of symmetry breaking in the spectra of collective excitations in finite quantum systems. The analysis of these features allows for the better understanding of the intimate relation between the type of symmetry and other physical properties of quantum systems. This also makes it possible to predict new effects by employing the analogies between finite quantum systems of different physical nature.

show abstract

Section: No Condensation Of Equilibrium Magnonsmentioning

confidence: 99%

Effects of symmetry breaking in finite quantum systems

2013

View full text Add to dashboard Cite

show abstract

“…This kind of system has served in the literature as an elementary example for spin superfluidity [18,20,21,23,25,26]. We will now calculate the local precession frequency (28) and the translational spin current (29) for this system to leading order in a 1/S expansion. To facilitate this we expand the spin operators in a local basis defined by the instantaneous direction of the spin polarizationm i (t) = S i (t) /| S i (t) |:…”

Section: A Easy-plane Ferromagnetmentioning

confidence: 99%

“…Especially note that since we self-consistently define the quantization axis as the direction of the local magnetization,m i (t) = S i (t) /| S i (t) |, by definition the HP bosons can never condense [29]. This is completely analogous to the fact that in the superfluid phase of interacting bosons the Bogoliubov quasiparticles, which are the Goldstone modes associated with the spontaneous breaking of the U(1) symmetry in the superfluid state, do not condense provided the condensate wave function is self-consistently defined via the solution of the Gross-Pitaevskii equation.…”

Section: A Easy-plane Ferromagnetmentioning

confidence: 99%

Spin currents, spin torques, and the concept of spin superfluidity

Rückriegel

Kopietz

2017

Phys. Rev. B

Self Cite

View full text Add to dashboard Cite

In magnets with noncollinear spin configuration the expectation value of the conventionally defined spin current operator contains a contribution which renormalizes an external magnetic field and hence affects only the precessional motion of the spin polarization. This term, which has been named angular spin current by Sun and Xie [Phys. Rev. B 72, 245305 (2005)], does not describe the translational motion of magnetic moments. We give a prescription for how to separate these two types of spin transport and show that the translational movement of the spin is always polarized along the direction of the local magnetization. We also show that at vanishing temperature the classical magnetic order parameter in magnetic insulators cannot carry a translational spin current and elucidate how this affects the interpretation of spin supercurrents.

show abstract

“…Whether or not such a state should be called a Bose-Einstein condensate of magnons seems to be a matter of semantics 40,41 . We have argued previously 26,42 that the experimentally observed strong enhancement of the magnon distribution is not accompanied by superfluidity, because a macroscopic occupation of a certain magnon mode is simply equivalent with a change in magnetic order 43 . In Fig.…”

Section: Thermalization Of Magnons In Yigmentioning

confidence: 89%

“…These averages play the role of order parameters; keeping in mind that the magnon operators in YIG describe the quantized fluctuations around the classical ground states, macroscopic values of a C k (t) for one or several wave-vectors describe a macroscopic reorganization of the magnetic state 42 . To describe this phenomenon microscopically, it is necessary to take the magnon-magnon interactions into account.…”

Section: Discussionmentioning

confidence: 99%

Thermalization of magnons in yttrium-iron garnet: Nonequilibrium functional renormalization group approach

2012

Self Cite

View full text Add to dashboard Cite

Using a nonequilibrium functional renormalization group (FRG) approach we calculate the time evolution of the momentum distribution of a magnon gas in contact with a thermal phonon bath. As a cutoff for the FRG procedure we use a hybridization parameter Λ giving rise to an artificial damping of the phonons. Within our truncation of the FRG flow equations the time evolution of the magnon distribution is obtained from a rate equation involving cutoff-dependent nonequilibrium selfenergies, which in turn satisfy FRG flow equations depending on cutoff-dependent transition rates. Our approach goes beyond the Born collision approximation and takes the feedback of the magnons on the phonons into account. We use our method to calculate the thermalization of a quasi twodimensional magnon gas in the magnetic insulator yttrium-iron garnet after a highly excited initial state has been generated by an external microwave field. We obtain good agreement with recent experiments.

show abstract

Time-dependent spin-wave theory

Cited by 22 publications

References 18 publications

Effects of symmetry breaking in finite quantum systems

Effects of symmetry breaking in finite quantum systems

Spin currents, spin torques, and the concept of spin superfluidity

Thermalization of magnons in yttrium-iron garnet: Nonequilibrium functional renormalization group approach

Contact Info

Product

Resources

About