Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA Frustrated 3-Dimensional Antiferromagnet: Stacked $J_{1}-J_{2}$ Layers
149
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We study a frustrated 3D antiferromagnet of stacked $J_1 - J_2$ layers. The intermediate quantum spin liquid phase, present in the 2D case, narrows with increasing interlayer coupling and vanishes at a triple point. Beyond this there is a direct first-order transition from N{ e}el to columnar order. Possible applications to real materials are discussed.
rate research
Read More
The zero-temperature quantum phase diagram of the spin-$frac{1}{2}$ $J_{1}$--$J_{2}$--$J_{1}^{perp}$ model on an $AA$-stacked bilayer honeycomb lattice is investigated using the coupled cluster method (CCM). The model comprises two monolayers in each of which the spins, residing on honeycomb-lattice sites, interact via both nearest-neighbor (NN) and frustrating next-nearest-neighbor isotropic antiferromagnetic (AFM) Heisenberg exchange iteractions, with respective strengths $J_{1} > 0$ and $J_{2} equiv kappa J_{1}>0$. The two layers are coupled via a comparable Heisenberg exchange interaction between NN interlayer pairs, with a strength $J_{1}^{perp} equiv delta J_{1}$. The complete phase boundaries of two quasiclassical collinear AFM phases, namely the N{e}el and N{e}el-II phases, are calculated in the $kappa delta$ half-plane with $kappa > 0$. Whereas on each monolayer in the N{e}el state all NN pairs of spins are antiparallel, in the N{e}el-II state NN pairs of spins on zigzag chains along one of the three equivalent honeycomb-lattice directions are antiparallel, while NN interchain spins are parallel. We calculate directly in the thermodynamic (infinite-lattice) limit both the magnetic order parameter $M$ and the excitation energy $Delta$ from the $s^{z}_{T}=0$ ground state to the lowest-lying $|s^{z}_{T}|=1$ excited state (where $s^{z}_{T}$ is the total $z$ component of spin for the system as a whole, and where the collinear ordering lies along the $z$ direction) for both quasiclassical states used (separately) as the CCM model state, on top of which the multispin quantum correlations are then calculated to high orders ($n leq 10$) in a systematic series of approximations involving $n$-spin clusters. The sole approximation made is then to extrapolate the sequences of $n$th-order results for $M$ and $Delta$ to the exact limit, $n to infty$.
The zero-temperature phase diagram of the spin-$frac{1}{2}$ $J_{1}$--$J_{2}$--$J_{1}^{perp}$ model on an $AA$-stacked square-lattice bilayer is studied using the coupled cluster method implemented to very high orders. Both nearest-neighbor (NN) and frustrating next-nearest-neighbor Heisenberg exchange interactions, of strengths $J_{1}>0$ and $J_{2} equiv kappa J_{1}>0$, respectively, are included in each layer. The two layers are coupled via a NN interlayer Heisenberg exchange interaction with a strength $J_{1}^{perp} equiv delta J_{1}$. The magnetic order parameter $M$ (viz., the sublattice magnetization) is calculated directly in the thermodynamic (infinite-lattice) limit for the two cases when both layers have antiferromagnetic ordering of either the N{e}el or the striped kind, and with the layers coupled so that NN spins between them are either parallel (when $delta < 0$) or antiparallel (when $delta > 0$) to one another. Calculations are performed at $n$th order in a well-defined sequence of approximations, which exactly preserve both the Goldstone linked cluster theorem and the Hellmann-Feynman theorem, with $n leq 10$. The sole approximation made is to extrapolate such sequences of $n$th-order results for $M$ to the exact limit, $n to infty$. By thus locating the points where $M$ vanishes, we calculate the full phase boundaries of the two collinear AFM phases in the $kappa$--$delta$ half-plane with $kappa > 0$. In particular, we provide the accurate estimate, ($kappa approx 0.547,delta approx -0.45$), for the position of the quantum triple point (QTP) in the region $delta < 0$. We also show that there is no counterpart of such a QTP in the region $delta > 0$, where the two quasiclassical phase boundaries show instead an ``avoided crossing behavior, such that the entire region that contains the nonclassical paramagnetic phases is singly connected.
The low-energy electronic structure of the J_{eff}=1/2 spin-orbit insulator Sr3Ir2O7 has been studied by means of angle-resolved photoemission spectroscopy. A comparison of the results for bilayer Sr3Ir2O7 with available literature data for the related single-layer compound Sr2IrO4 reveals qualitative similarities and similar J_{eff}=1/2 bandwidths for the two materials, but also pronounced differences in the distribution of the spectral weight. In particuar, photoemission from the J_{eff}=1/2 states appears to be suppressed. Yet, it is found that the Sr3Ir2O7 data are in overall better agreement with band-structure calculations than the data for Sr2IrO4.
Heavy transition metal magnets with $J_{rm eff}$ $=$ 1/2 electronic ground states have attracted recent interest due to their penchant for hosting new classes of quantum spin liquids and superconductors. Unfortunately, model systems with ideal $J_{rm eff}$ $=$ 1/2 states are scarce due to the importance of non-cubic local distortions in most candidate materials. In this work, we identify a family of iridium halide systems [i.e. K$_2$IrCl$_6$, K$_2$IrBr$_6$, (NH$_4$)$_2$IrCl$_6$, and Na$_2$IrCl$_6 cdotp $ 6(H$_2$O)] with Ir$^{4+}$ electronic ground states in extremely close proximity to the ideal $J_{rm eff}$ $=$ 1/2 limit, despite a variation in the low-temperature global crystal structures. We also find ordered magnetic ground states for the three anhydrous systems, with single crystal neutron diffraction on K$_2$IrBr$_6$ revealing Type-I antiferromagnetism. This spin configuration is consistent with expectations for significant Kitaev exchange in a face-centered-cubic magnet.
By means of density functional theory plus dynamical mean-field theory (DFT+DMFT) calculations and resonant inelastic x-ray scattering (RIXS) experiments, we investigate the high-pressure phases of the spin-orbit-coupled $J_{rm{eff}}=3/2$ insulator GaTa$_4$Se$_8$. Its metallic phase, derived from the Mott state by applying pressure, is found to carry $J_{rm{eff}}=3/2$ moments. The characteristic excitation peak in the RIXS spectrum maintains its destructive quantum interference of $J_{rm{eff}}$ at the Ta $L_2$-edge up to 10.4 GPa. Our exact diagonalization based DFT+DMFT calculations including spin-orbit coupling also reveal that the $J_{rm{eff}}=3/2$ character can be clearly identified under high pressure. These results establish the intriguing nature of the correlated metallic magnetic phase, which represents the first confirmed example of $J_{rm{eff}}$=3/2 moments residing in a metal. They also indicate that the pressure-induced superconductivity is likely unconventional and influenced by these $J_{rm{eff}}=3/2$ moments. Based on a self-energy analysis, we furthermore propose the possibility of doping-induced superconductivity related to a spin-freezing crossover.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
