We present 75As nuclear magnetic resonance data in the paramagnetic and magnetic states of single crystal CaFe2As2. The electric field gradient and the internal magnetic field at the As sites change discontinuously below the first order structural transition at T0 = 169 K. In the magnetic state, we find a single value of the internal hyperfine field consistent with commensurate antiferromagnetic order of Fe moments pointing in the ab plane. The spin lattice relaxation rate shows Korringa behavior for T<T0/3, reflecting the metallic nature of the ordered state. Surprisingly, 1/T1 exhibits a small peak at 10 K, revealing the presence of slow spin fluctuations that may be associated with domain wall motion.
Zero temperature phase diagram of XXZ spin chain in external magnetic field is investigated at low energies using path integral approach.It has been shown by spin wave analysis and then by nonlinear sigma model transformation that below some critical field the system undergoes quantum Kosterlitz-Thouless phase transition.Above that critical field for low anisotropies the system is saturated while at strong anisotropy the system has Ising antiferromagnetic order.
We study the dynamical spin excitations of the one-dimensional $S=1$ Heisenberg antiferromagnetic chain with single-ion anisotropy by using quantum Monte Carlo simulations and stochastic analytic continuation of imaginary-time correlation function. Using the transverse dynamic spin structure factor, we observe the quantum phase transition with a critical point between the topological Haldane gapped phase and the trivial phase. At the quantum critical point, we find a broad continuum characterized by the Tomonaga-Luttinger liquid similar to a $S=1/2$ Heisenberg antiferromagnetic chain. We furth…
An improved U(1) slave-boson approach is applied to study the optical conductivity of the two dimensional systems of antiferromagnetically correlated electrons over a wide range of hole doping and temperature. Interplay between the spin and charge degrees of freedom is discussed to explain the origin of the peak-dip-hump structure in the in-plane conductivity of high $T_C$ cuprates. The role of spin fluctuations of short range order(spin singlet pair) is investigated. It is shown that the spin fluctuations of the short range order can cause the mid-infrared hump, by exhibiting a linear increas…
We describe some antiferromagnetic systems which exhibit spin gaps. We also discuss the effect of doping one such system, namely, the spin-ladders, with holes. Some model antiferromagnetic systems with spin gap are reviewed for which exact results are available. Exact results for a doped spin-ladder model are also mentioned.
We measured magnetization, specific heat, electron spin resonance, neutron diffraction, and inelastic neutron scattering of CrVMoO$_7$ powder. An antiferromagnetically ordered state appears below $T_{\rm N} = 26.5 \pm 0.8$ K. We consider that the probable spin model for CrVMoO$_7$ is an interacting antiferromagnetic spin-$\frac{3}{2}$ dimer model. We evaluated the intradimer interaction $J$ to be $25 \pm 1$ K and the effective interdimer interaction $J_{\rm eff}$ to be $8.8 \pm 1$ K. CrVMoO$_7$ is a rare spin dimer compound that shows an antiferromagnetically ordered state at atmospheric press…
A spin-singlet ground state with a spin gap has been discovered in antiferromagnetic spin chain substances when the spin value is 1/2, 1 or 2. To find spin gap (singlet-triplet) excitations in spin-3/2 chain substances, we performed inelastic neutron scattering and magnetization measurements on {\it R}CrGeO$_5$ ({\it R} = Y or Sm) powders. As expected, we observed spin gap excitations and the dispersion relation of the lowest magnetic excitations. We proved that the spin system of Cr$^{3+}$ was an antiferromagnetic alternating spin-3/2 chain.
We reinvestigate a doped antiferromagnetic Mott insulator based on the slave-fermion approach of the t-J model, where antiferromagnetic spin fluctuations and doped holes are described by bosonic spinons and fermionic holons, respectively. Earlier studies have shown that an effective field theory for the doped antiferromagnetic Mott insulator is given by a non-relativistic fermion (holon) U(1) gauge theory for charge dynamics and a relativistic boson (spinon) U(1) gauge theory for spin dynamics, thus allowing an anomalous metallic phase where bosonic spinons are gapped away from an antiferromag…
Antiferromagnetism couples electron spin to its orbital motion, thus allowing excitation of electron-spin transitions by an ac electric rather than magnetic field - with absorption, exceeding that of common electron spin resonance at least by four orders of magnitude. In addition to potential applications in spin electronics, this phenomenon may be used as a spectroscopy to study antiferromagnetic materials of interest - from chromium to borocarbides, cuprates, iron pnictides, and organic and heavy fermion conductors.
We investigate how the antiferromagnetic Mott insulator evolves into the d-wave BCS superconductor through hole doping. Allowing spin fluctuations in the strong coupling approach, we find a spin-gapped incoherent metal with preformed pairing as an intermediate phase between the antiferromagnetic Mott insulator and d-wave superconductor. This non-Fermi liquid metal is identified with an infrared stable fixed point in the spin-decomposition gauge theory, analogous to the spin liquid insulator in the slave-boson gauge theory. We consider the single particle spectrum and dynamical spin susceptibil…
The disordered antiferromagnet \pfn (\pfns) is investigated in a wide temperature range by combining Mössbauer spectroscopy and neutron diffraction experiments. It is demonstrated that the magnetic ground state is a {\it microscopic} coexistence of antiferromagnetic and a spin-glass orders. This speromagnet-like phase features frozen-in short-range fluctuations of the Fe$^{3+}$ magnetic moments that are transverse to the long-range ordered antiferromagnetic spin component.
Two-leg spin-1/2 ladder systems consisting of a ferromagnetic leg and an antiferromagnetic leg are considered where the spins on the legs interact through antiferromagnetic rung couplings $J_1$. These ladders can have two geometrical arrangements either zigzag or normal ladder and these systems are frustrated irrespective of their geometry. This frustration gives rise to incommensurate spin density wave, dimer and spin fluid phases in the ground state. The magnetization in the systems decreases linearly with $J^2_1$, and the systems show an incommensurate phase for $0.0<J_1<1.0$. The spin-spin…
The Lieb-Mattis theorem is generalized to an antiferromagnetic spin-ladder model with four-spin cyclic exchange interaction. We prove that for J>2K, the antiferromagnetic ordering of energy levels takes place separately in two sectors, which remain symmetric and antisymmetric under the reflection with respect to the longitudinal axis of the ladder. We prove also that at the self-dual point J=2K, the Lieb-Mattis rule holds in the sectors with fixed number of rung singlets. In both cases, it agrees with the similar rule for Haldane chain with appropriate spin number.
In the paper we describe the modification of spin-wave theory for one-dimensional isotropic antiferromagnet. This theory enables to obtain the energy of magnetic excitations of short wave length and correlation function in agreement with numerical studies.
Spin wave theory is applied to a quantum antiferromagnetic XXZ model on a triangle lattice in the presence of an in-plane magnetic field. The effect of the field is found to enhance the quantum fluctuation and to reduce the sublattice magnetization at the intermediate field strength in the anisotropic case. The possible implication to the field driven quantum phase transition from a spin solid to a spin liquid is discussed.
We measured the temperature dependence of the magnetic susceptibility and specific heat and the magnetic-field dependence of the magnetization of CuInVO$_5$. An antiferromagnetically ordered state appears below $T_{\rm N} = 2.7$ K. We observed a $\frac{1}{2}$ quantum magnetization plateau above 30 T at 1.3 K. We show that the spin system consists of antiferromagnetic spin-$\frac{1}{2}$ tetramers with $J_1 = 240 \pm 20$ and $J_2 = -142 \pm 10$ K for the intratetramer interactions.
In the commented Letter Vogt et al. (Phys.Rev.Lett. 84 (2000) 2969) claim the existence of a spin-state transition in YBaCo2O5. We think that this claim about the change from the low spin to high spin state upon cooling in YBaCo2O5 is errorneous. Keywords: magnetism, 3d ions, low spin.
The magnetization measurements have been performed on the doped spin gap system TlCu_{1-x}Mg_xCl_3 with x <= 0.025. The parent compound TlCuCl_3 is a three-dimensional coupled spin dimer system with the excitation gap Delta/k_B = 7.7 K. The impurity-induced antiferromagnetic ordering was clearly observed. The easy axis lies in the (0,1,0) plane. It was found that the transition temperature increases with increasing Mg^{2+} concentration x, while the spin-flop transition field is almost independent of x. The magnetization curve suggests that the impurity-induced antiferromagnetic ordering coexi…
We have explored the possibility to orient spins in antiferromagnetic thin films with low magnetocrystalline anisotropy via the exchange coupling to adjacent antiferromagnetic films with high magnetocrystalline anisotropy. We have used MnO as a prototype for a system with negligible single-ion anisotropy. We were able to control its spin direction very effectively by growing it as a film on antiferromagnetic CoO films with different predetermined spin orientations. This result may pave the way for tailoring antiferromagnets with low magnetocrystalline anistropy for applications in exchange bia…
The spin dynamic of the metallic A-type antiferromagnetic manganites is studied. An effective nearest-neighbour Heisenberg spin wave dispersion is derived from the double exchange model taking into account the superexchange interaction between the core spins. The result of inelastic neutron scattering experiment on ${Nd}_{0.45}{Sr}_{0.55}{Mn} {O}_{3}$ is qualitatively reproduced. Comparing theory with experimental data two main parameters of the model: nearest-neighbour electron transfer amplitude and superexchange coupling between the core spins are estimated.
Motivated by the discovery of new family 122 iron-based superconductors, we present the theoretical results on the ground state phase diagram, spin wave and dynamic structure factor of the extended $J_{1}-J_{2}$ Heisenberg model. In the reasonable physical parameter region of $K_{2}Fe_{4}Se_{5}$, we fi{}nd the block checkerboard antiferromagnetic order phase is stable. There are two acoustic branches and six optical branches spin wave in the block checkerboard antiferromagnetic phase, which has analytic expression in the high symmetry points. To compare the further neutron scattering experimen…
We report zero and longitudinal magnetic field muon spin relaxation measurements of the spin S=1/2 antiferromagnetic Heisenberg chain material SrCuO2. We find that in a weak applied magnetic field B the spin-lattice relaxation rate follows a power law B^n with n=-0.9(3). This result is temperature independent for 5K < T < 300 K. Within conformal field theory and using the Müller ansatz we conclude ballistic spin transport in SrCuO2.
We present results of a study of the antiferromagnetic spin-1 chain, subject to the simultaneous presence of single-ion anisotropy and external magnetic fields. Using quantum Monte-Carlo based on the stochastic series expansion method we first uncover a rich quantum phase diagram comprising Néel, Haldane, Luttinger liquid, and large anisotropy phases. Second, we scan across this phase diagram over a wide range of parameters, evaluating the transverse dynamic structure factor, which we show to exhibit sharp massive modes, as well as multi particle continua. For vanishing anisotropy and fields, …
Antiferromagnetic Heisenberg integer-spin chains are characterized by a spin-liquid ground state with no long-range order, due to the relevance of quantum fluctuations. Spin anisotropy, however, freezes quantum fluctuations, and the system is magnetized in the presence of a sufficiently large easy-axis anisotropy. We numerically investigate the case S=1, by means of the density-matrix renormalization group, and find that the freezing of the spin liquid into a Néel spin solid, with increasing easy-axis anisotropy, is a continuous quantum phase transition. Numerical evidence indicates that the t…
Using Monte Carlo integration methods, we describe the behavior of the exact four-spinon dynamic structure function $S_{4}$ in the antiferromagnetic spin 1/2 Heisenberg quantum spin chain as a function of the neutron energy $ω$ and momentum transfer $k$. We also determine the four-spinon continuum, the extent of the region in the $(k,ω)$ plane outside which $S_{4}$ is identically zero. In each case, the behavior of $S_{4}$ is shown to be consistent with the four-spinon continuum and compared to the one of the exact two-spinon dynamic structure function $S_{2}$. Overall shape similarity is note…
The efficiency of ultrafast excitation of spins in antiferromagnetic $\mathrm{α-Fe_{2}O_{3}}$ using nearly single-cycle THz pulse is studied as a function of the polarization of the THz pulse and the sample temperature. Above the Morin point the most efficient excitation is achieved when the magnetic field of the THz pulse is perpendicular to the antiferromagnetically coupled spins. Using the experimental results and equations of motion for spins, we show that the mechanism of the spin excitation above and below the Morin point relies on magnetic-dipole interaction of the THz magnetic field wi…
Quasi-one-dimensional quantum antiferromagnets formed by a d-dimensional hypercubic lattice of weakly coupled spin-1/2 antiferromagnetic Heisenberg chains are studied by combining exact results in one-dimension and renormalization group analyses of the interchain correlations. It is shown that d-dimensional magnetic long-range order develops at zero-temperature for infinitesimal antiferromagnetic or ferromagnetic interchain couplings. In the presence of weak bond alternations, the order-disorder transition occurs at a finite interchain coupling. Relevances to the lightly doped quantum antiferr…
We theoretically investigate the spin wave (magnon) excitations in a classical antiferromagnetic spin chain with easy-axis anisotropy. We obtain a Dirac-like equation by linearizing the Landau- Lifshitz-Gilbert equation in this antiferromagnetic system, in contrast to the ferromagnetic system in which a Schrödinger equation is derived. The Hamiltonian operator in the Dirac-like equation is a pseudo-Hermitian. We compute and demonstrate the relativistic Zitterbewegung (trembling motion) in the antiferromagnetic spin chain by measuring the expectation values of the wave packet position.
We present a spin-rotation-invariant Green-function theory for the dynamic spin susceptibility in the spin-1/2 antiferromagnetic Heisenberg model on a stacked honeycomb lattice. Employing a generalized mean-field approximation for arbitrary temperatures, the thermodynamic quantities (two-spin correlation functions, internal energy, magnetic susceptibility, staggered magnetization, N'eel temperature, correlation length) and the spin-excitation spectrum are calculated by solving a coupled system of self-consistency equations for the correlation functions. The temperature dependence of the magnet…
Coherent spin oscillations were non-thermally induced by circularly polarized pulses in fully compensated antiferromagnetic NiO. This effect is attributed to an entirely new mechanism of the action, on the spins, of the effective magnetic field generated by an inverse Faraday effect. The novelty of this mechanism is that spin oscillations are driven by the time derivative of the effective magnetic field acting even on "pure" antiferromagnets with zero net magnetic moment in the ground state. The measured frequencies (1.07 THz and 140 GHz) of the spin oscillations correspond to the out-of-plane…
We give a physical description in terms of percolation theory of the phase transition that occurs when the disorder increases in the random antiferromagnetic spin-1 chain between a gapless phase with topological order and a random singlet phase. We study the statistical properties of the percolation clusters by numerical simulations, and we compute exact exponents characterizing the transition by a real-space renormalization group calculation.
Magnetic correlations in all four phases of pure and doped vanadium sesquioxide V_2O_3 have been examined by magnetic thermal neutron scattering. While the antiferromagnetic insulator can be accounted for by a Heisenberg localized spin model, the long range order in the antiferromagnetic metal is an incommensurate spin-density-wave, resulting from a Fermi surface nesting instability. Spin dynamics in the strongly correlated metal are dominated by spin fluctuations in the Stoner electron-hole continuum. Furthermore, our results in metallic V_2O_3 represent an unprecedentedly complete characteri…
We report the direct measurement of antiferromagnetic spin polarization at the oxygen sites in the multiferroic TbMn2O5, through resonant soft x-ray magnetic scattering. This supports recent theoretical models suggesting that the oxygen spin polarization is key to the magnetoelectric coupling mechanism. The spin polarization is observed through a resonantly enhanced diffraction signal at the oxygen K edge at the commensurate antiferromagnetic wavevector. Using the fdmnes code we have accurately reproduced the experimental data. We have established that the resonance arises through the spin pol…
We study the role of long range dipolar interactions on antiferromagnetic spin chains, from the classical $S\to \infty$ limit to the deep quantum case $S=1/2$, including a transverse magnetic field. To this end, we combine different techniques such as classical energy minima, classical Monte Carlo, linear spin waves, bosonization and DMRG. We find a phase transition from the already reported dipolar ferromagnetic region to an antiferromagnetic region for high enough antiferromagnetic exchange. Thermal and quantum fluctuations destabilize the classical order before reaching magnetic saturation …
The spin-1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain with ferromagnetic next-nearest-neighbour (NNN) interaction is investigated. The ground state is the Haldane phase for weak NNN interaction, and is the ferromagnetic phase for weak antiferromagnetic interaction. We find a series of topologically distinct spin-gap phases with various magnitudes of edge spins for strong NNN interaction. The phase boundaries between these phases are determined on the basis of the DMRG calculation with additional spins that compensate the edge spins. It is found that each of the exact soluti…
We investigate the behavior of antiferromagnetic integer-spin chains in a staggered magnetic field, by means of the density-matrix renormalization group, carefully addressing the role of finite-size effects within the Haldane phase at small fields. In the case of spin S=2, we determine the dependence of the groundstate energy and magnetization on the external field, in the thermodynamic limit, and show how the peculiar finite-size behavior can be connected with the crossover in the groundstate from a spin liquid to a polarized Néel state.
Recent advances in the physics of current-driven antiferromagnetic skyrmions have observed the absence of a Magnus force. We outline the symmetry reasons for this phenomenon, and show that this cancellation will fail in the case of spin polarized currents. Pairing micromagnetic simulations with semiclassical spin wave transport theory, we demonstrate that skyrmions produce a spin-polarized transverse magnon current, and that spin-polarized magnon currents can in turn produce transverse motion of antiferromagnetic skyrmions. We examine qualitative differences in the frequency dependence of the …
We discovered a first-order phase transition between dimerized-antiferromagnetic and uniform-antiferromagnetic phases in impurity-doped spin-Peierls (SP) cuprate Cu{1-x}MgxGeO3. As impurity concentration increases, linear reduction of SP transition temperature (T{SP}) and linear increase of Neel temperature (TN) are observed up to x = 0.023. At this critical concentration (xc) SP transition suddenly disappears and TN jumps discontinuously. The peak of the susceptibility at xc around TN is not so sharp as those at other concentrations, which indicates the phase separation of low and high concen…
We investigate the low-lying excitation of the antiferromagnetic zigzag spin ladder with Möbius boundary condition. Using the Lanczos and Householder diagonalization methods, we calculate the excitation spectrum of the zigzag ladder in the momentum space. We then show that the topological defect generated by the Möbius boundary provides the clear evidence of the single spinon excitation. On the basis of the obtained single-spinon dispersion curve, we analyze the two-spinon scattering states under the usual periodic boundary condition. We further discuss the interaction effect between the spino…
Ultrasound velocity measurements of the orbitally-frustrated GeCo$_2$O$_4$ reveal unusual elastic instabilities due to the phonon-spin coupling within the antiferromagnetic phase. Shear moduli exhibit anomalies arising from the coupling to short-range ferromagnetic excitations. Diplike anomalies in the magnetic-field dependence of elastic moduli reveal magnetic-field-induced orbital order-order transitions. These results strongly suggest the presence of geometrical orbital frustration which causes novel orbital phenomena within the antiferromagnetic phase.
We study the spin transport on a S=1/2 antiferromagnetic chain with external fields which provids a phase angle. The equation of motion becomes the sine-Gordon equation after Jordan-Wigner transformation and bosonization. Soliton solutions of the sine-Gordon equations for a system of finite length are found and the quantum fluctuations are calculated. The spin is transported as the soliton solutions evolves with the adiabatical variation of the phase angle in the phase space. We observe that the spin is transported by ΔS=1, as the phase angle changes by the period of 2π when the quantum fluctu…
The magnetization process of the one-dimensional antiferromagnetic Heisenberg model with the Ising-like anisotropic exchange interaction is studied by the exact diagonalization technique. It results in the evidence of the first-order spin flop transition with a finite magnetization jump in the Néel ordered phase for $S\geq 1$. It implies that the S=1/2 chain is an exceptional case where the metamagnetic transition becomes second-order due to large quantum fluctuations.
The random antiferromagnetic two-leg and zigzag spin-1/2 ladders are investigated using the real space renormalization group scheme and their complete phase diagrams are determined. We demonstrate that the first system belongs to the same universality class of the dimerized random spin-1/2 chain. The zigzag ladder, on the other hand, is in a random singlet phase at weak frustration and disorder. Otherwise, we give additional evidence that it belongs to the universality class of the random antiferromagnetic and ferromagnetic quantum spin chains, although the universal fixed point found in the l…
A spin and phonon excitations spectrum are studied using quantum Monte Carlo method in antiferromagnetic chain with spins $S=1/2$ coupled nonadiabaticity with acoustic phonons . It is found the critical coupling exists to open gap in the triplet excitation spectrum for any phonon velocity. The phase boundaries of delocalized phonons and propagated the bound states of magnon and a phonon are calculated. It is shown that the spherical symmetry of the spin-spin correlation functions is broken . The magnetic and optical properties $CuGeO_3$ are explained without using spin-Peierls transition.
In response to recent chemical attempts to construct higher-spin ladder materials from organic polyradicals, we study the ground-state properties of a wide class of antiferromagnetic spin-1 ladders. Employing various numerical tools, we reveal the rich phase diagram and correct a preceding nonlinear-sigma-model prediction. A variational analysis well interprets the phase competition with particular emphasis on the {\it re-entrant phase boundary} as a function of the rung interaction.
We have measured the thermal conductivity of the one-dimensional (1D) S=1/2 Heisenberg antiferromagnetic spin system of Sr2Cu1-xPdxO3 single crystals including nonmagnetic impurities of Pd2+. It has been found that the mean free path of spinons along the 1D spin chain at low temperatures is very close to the average length of finite spin chains between spin defects estimated from the magnetic susceptibility measurements. This proves that the thermal conduction due to spinons at low temperatures in Sr2CuO3 is ballistic as theoretically expected [Zotos et al.: Phys. Rev. Lett. 55 (1997) 11029].
Easy axis antiferromagnets are robust against external magnetic fields of moderate strength. Spin reorientations in strong fields can provide an insight into more subtle properties of antiferromagnetic materials, which are often hidden by their high ground state symmetry. Here, we investigate theoretically effects of curvature in ring-shaped antiferromagnetic achiral anisotropic spin chains in strong magnetic fields. We identify the geometry-governed helimagnetic phase transition above the spin-flop field between vortex and onion states. The curvature-induced Dzyaloshinskii-Moriya interaction …
The low-energy properties of a system at a critical point may have additional symmetries not present in the microscopic Hamiltonian. This letter presents the theory of a class of multicritical points that provide an interesting example of this in the phase diagrams of random antiferromagnetic spin chains. One case provides an analytic theory of the quantum critical point in the random spin-3/2 chain, studied in recent work by Refael, Kehrein and Fisher (cond-mat/0111295).
We consider the low-temperature behavior of NMR relaxation rates $T_1$ and $T_{2G}$ in the spin-1/2 antiferromagnetic chain. We find that $T_1 \propto const$ and $T_{2G} \propto \sqrt{T}$, with logarithmic corrections. We determine both constants and logarithmic terms by matching perturbative RG with exact results, so that the final expressions for the relaxation rates do not contain any free parameters. Our theoretical results are in excellent agreement with NMR experiments in Sr$_2$CuO$_3$.
Spin transport properties of the one-dimensional Heisenberg antiferromagnetic spin systems for both $S=1/2$ and S=1 are studied by applying twisted boundary magnetic field. The spin current displays significantly different behavior of the spin transport properties between $S=1/2$ and S=1 cases. For the spin-half case, a London equation for the current and the detection of an alternating electric field are proposed for the linear response regime. The correlation functions reveal the spiral nature of spin configuration for both ground state and the spinon excitations. For the spin-one chain othe…
Effects of the site dilution on spin-gapped Heisenberg antiferromagnets with $S=1/2$ and S=1 on a square lattice are investigated by means of the quantum Monte Carlo method. It is found that effective magnetic moments induced around the diluted sites exhibit the antiferromagnetic long-range order in the medium of spin-singlet pairs. Their microscopic structure is examined in detail and important roles of the higher dimensionality than one on the phenomenon are discussed.
Using Bethe-ansatz solutions, we uncover a well-defined continuum in dynamical structure factor $S^{+-}(k,ω)$ of the spin-1/2 antiferromagnetic Heisenberg chain in magnetic fields. It comes from string solutions which continuously connect the mode of the lowest-energy excitations in the zero-field limit and that of bound states of overturned spins from the ferromagnetic state near the saturation field. We confirm the relevance to real materials through comparisons with experimental results.
We present the first results on the low-frequency dynamical and transport properties of random antiferromagnetic spin chains at low temperature ($T$). We obtain the momentum and frequency dependent dynamic structure factor in the Random Singlet (RS) phases of both spin-1/2 and spin-1 chains, as well as in the Random Dimer phase of spin-1/2 chains. We also show that the RS phases are unusual `spin-metals' with divergent low-frequency conductivity at T=0, and follow the spin conductivity through `metal-insulator' transitions tuned by the strength of dimerization or Ising anisotropy in the spin-1…
A theory of low temperature (T) electron spin resonance (ESR) in half-integer spin antiferromagnetic chains is developed using field theory methods and avoiding previous approximations. It is compared to experiments on Cu benzoate. Power laws are predicted for the line-width broadening due to various types of anisotropy. At T -> 0, zero width absorption peaks occur in some cases. The second ESR peak in Cu benzoate, observed at T<.76K, is argued not to indicate Neel order as previously claimed, but to correspond to a sine-Gordon "breather" excitation.
Using the spin wave approximation, we study the decoherence dynamics of a central spin coupled to an antiferromagnetic environment under the application of an external global magnetic field. The external magnetic field affects the decoherence process through its effect on the antiferromagnetic environment. It is shown explicitly that the decoherence factor which displays a Gaussian decay with time depends on the strength of the external magnetic field and the crystal anisotropy field in the antiferromagnetic environment. When the values of the external magnetic field is increased to the critic…
We search for dynamical magnetoelectric phenomena in three-dimensional correlated systems with spin-orbit coupling. We focus on the antiferromagnetic insulator phases where the dynamical axion field is realized by the fluctuation of the antiferromagnetic order parameter. It is shown that the dynamical chiral magnetic effect, an alternating current generation by magnetic fields, emerges due to the time dependences of the order parameter such as antiferromagnetic resonance. It is also shown that the anomalous Hall effect arises due to the spatial variations of the order parameter such as antifer…
We construct spin chains that describe relativistic sigma-models in the continuum limit, using symplectic geometry as a main tool. The target space can be an arbitrary complex flag manifold, and we find universal expressions for the metric and theta-term.
We propose a realization of the electric-field-induced antiferromagnetic resonance. We consider three-dimensional antiferromagnetic insulators with spin-orbit coupling characterized by the existence of a topological term called the $θ$ term. By solving the Landau-Lifshitz-Gilbert equation in the presence of the $θ$ term, we show that, in contrast to conventional methods using ac magnetic fields, the antiferromagnetic resonance state is realized by ac electric fields along with static magnetic fields. This mechanism can be understood as the inverse process of the dynamical chiral magnetic effec…
