1,316 research outputs found
Damped Topological Magnons in the Kagom\'{e}-Lattice Ferromagnets
We demonstrate that interactions can substantially undermine the
free-particle description of magnons in ferromagnets on geometrically
frustrated lattices. The anharmonic coupling, facilitated by the
Dzyaloshinskii-Moriya interaction, and a highly-degenerate two-magnon continuum
yield a strong, non-perturbative damping of the high-energy magnon modes. We
provide a detailed account of the effect for the ferromagnet on the
kagom\'e lattice and propose further experiments.Comment: 4.5 p + 4 figs main, 8 p + 16 figs supplemental, typos correcte
Phonon assisted tunneling in Josephson junctions
The expression for additional subgap current in the presence of
electron-phonon interaction is derived. We show that the phonon assisted
tunneling leads to appearance of peaks on current-voltage characteristics at
the Josephson frequencies corresponding to the Raman-active phonons. The
relation of the obtained results to experimental observations are discussed.Comment: 8 pages, submitted to PR
Ab initio calculations of the physical properties of transition metal carbides and nitrides and possible routes to high-Tc
Ab initio linear-response calculations are reported of the phonon spectra and
the electron-phonon interaction for several transition metal carbides and
nitrides in a NaCl-type structure. For NbC, the kinetic, optical, and
superconducting properties are calculated in detail at various pressures and
the normal-pressure results are found to well agree with the experiment.
Factors accounting for the relatively low critical temperatures Tc in
transition metal compounds with light elements are considered and the possible
ways of increasing Tc are discussed.Comment: 19 pages, 7 figure
Topography of Spin Liquids on a Triangular Lattice
Spin systems with frustrated anisotropic interactions are of significant
interest due to possible exotic ground states. We have explored their phase
diagram on a nearest-neighbor triangular lattice using the density-matrix
renormalization group and mapped out the topography of the region that can
harbor a spin liquid. We find that this spin-liquid phase is continuously
connected to a previously discovered spin-liquid phase of the isotropic
model. The two limits show nearly identical spin correlations,
making the case that their respective spin liquids are isomorphic to each
other.Comment: Accepted to PRL; 5 p., 11+ p. supplemental; main text is longer than
the accepted versio
Disorder-Induced Mimicry of a Spin Liquid in YbMgGaO
We suggest that a randomization of the pseudo-dipolar interaction in the
spin-orbit-generated low-energy Hamiltonian of YbMgGaO due to an
inhomogeneous charge environment from a natural mixing of Mg and
Ga can give rise to orientational spin disorder and mimic a
spin-liquid-like state. In the absence of such quenched disorder, and
density matrix renormalization group calculations both show robust ordered
states for the physically relevant phases of the model. Our scenario is
consistent with the available experimental data and further experiments are
proposed to support it.Comment: 5+ main text, 7+ supplemental, text asymptotically close to PR
Rethinking -RuCl
We argue that several empirical constraints strongly restrict parameters of
the effective microscopic spin model describing -RuCl. In
particular, such constraints dictate a substantial \emph{positive} off-diagonal
anisotropic coupling, , not anticipated previously. The
renormalization by quantum fluctuations allows to reconcile larger values of
the advocated bare parameters with their earlier assessments and provides a
consistent description of the field evolution of spin excitations in the
paramagnetic phase. We assert that large anisotropic terms inevitably result in
strong anharmonic coupling of magnons, necessarily leading to broad features in
their spectra due to decays, in accord with the observations in
-RuCl. Using duality transformations, we explain the origin of the
pseudo-Goldstone mode that is ubiquitous to the studied parameter space and is
present in -RuCl. Our analysis offers a description of
-RuCl as an easy-plane ferromagnet with antiferromagnetic
further-neighbor and strong off-diagonal couplings, which is in a fluctuating
zigzag ground state proximate to an incommensurate phase that is continuously
connected to a ferromagnetic one.Comment: As accepted to Phys. Rev. of Rethinking (PRR). Typos in Appendix
fixed, award-winning acknowledgement
Critical temperature and giant isotope effect in presence of paramagnons
We reconsider the long-standing problem of the effect of spin fluctuations on
the critical temperature and isotope effect in a phonon-mediated
superconductor. Although the general physics of the interplay between phonons
and paramagnons had been rather well understood, the existing approximate
formulas fail to describe the correct behavior of for general phonon
and paramagnon spectra. Using a controllable approximation, we derive an
analytical formula for which agrees well with exact numerical solutions
of the Eliashberg equations for a broad range of parameters. Based on both
numerical and analytical results, we predict a strong enhancement of the
isotope effect when the frequencies of spin fluctuation and phonons are of the
same order. This effect may have important consequences for near-magnetic
superconductors such as MgCNiComment: 5 pages, 2 figure
Nanoengineered Curie Temperature in Laterally-Patterned Ferromagnetic Semiconductor Heterostructures
We demonstrate the manipulation of the Curie temperature of buried layers of
the ferromagnetic semiconductor (Ga,Mn)As using nanolithography to enhance the
effect of annealing. Patterning the GaAs-capped ferromagnetic layers into
nanowires exposes free surfaces at the sidewalls of the patterned (Ga,Mn)As
layers and thus allows the removal of Mn interstitials using annealing. This
leads to an enhanced Curie temperature and reduced resistivity compared to
unpatterned samples. For a fixed annealing time, the enhancement of the Curie
temperature is larger for narrower nanowires.Comment: Submitted to Applied Physics Letters (minor corrections
Signatures of Quantum Chaos and fermionization in the incoherent transport of bosonic carriers in the Bose-Hubbard chain
We analyse the stationary current of Bose particles across the Bose-Hubbard
chain connected to a battery, focusing on the effect of inter-particle
interactions. It is shown that the current magnitude drastically decreases as
the strength of inter-particle interactions exceeds the critical value which
marks the transition to quantum chaos in the Bose-Hubbard Hamiltonian. We found
that this transition is well reflected in the non-equilibrium many-body density
matrix of the system. Namely, the level-spacing distribution for eigenvalues of
the density matrix changes from Poisson to Wigner-Dyson distributions. With the
further increase of the interaction strength, the Wigner-Dyson spectrum
statistics changes back to the Poisson statistics which now marks
fermionization of the bosonic particles. With respect to the stationary
current, this leads to the counter-intuitive dependence of the current
magnitude on the particle number.Comment: 5 pages, 5 figure
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