Magnetic excitations from the two-dimensional interpenetrating Cu framework in Ba2Cu3O4Cl2

Abstract

We report detailed neutron scattering studies on Ba2Cu3O4Cl2. The compound consists of two interpenetrating sublattices of Cu, labeled as CuA and CuB, each of which forms a square-lattice Heisenberg antiferromagnet. The two sublattices order at different temperatures and effective exchange couplings within the sublattices differ by an order of magnitude. This yields an inelastic neutron spectrum of the CuA sublattice extending up to 300 meV and a much weaker dispersion of CuB going up to around 20 meV. Using a single-band Hubbard model we derive an effective spin Hamiltonian. From this, we find that linear spin-wave theory gives a good description to the magnetic spectrum. In addition, a magnetic field of 10 T is found to produce effects on the CuB dispersion that cannot be explained by conventional spin-wave theory.

Order in Quantum Compass and Orbital egModels

“…The ground state order parameter is almost saturated, m(0) = 0.993, in agreement with the Multiscale Entanglement Renormalization Ansatz (MERA) [4], and the quantum fluctuations are very weak at T = 0 [3]. [29], fully frustrated Villain model [30], eg orbital model [22] and 2D compass model [21]. Unlike the 2D compass model [23], the e g orbital model (3) is not tractable by QMC [26], but the order parameter m(T ) and the susceptibility χ(T ) were found by the VTNR Anzatz.…”

“…The convergence in D is fast [22] and one finds: β 0.126 and γ 1.736 for D ≥ 7; they approach the critical exponents of the 2D Ising model, β = 1 8 and γ = 7 4 . From the convergence of m(T ) and χ(T ) (6) we deduce T c 0.3566 [22].…”

“…The convergence in D is fast [22] and one finds: β 0.126 and γ 1.736 for D ≥ 7; they approach the critical exponents of the 2D Ising model, β = 1 8 and γ = 7 4 . From the convergence of m(T ) and χ(T ) (6) we deduce T c 0.3566 [22]. Note that from the leading ∝ 3 16 σ x i σ x j term in (3) and the Ising model [27] one expects T c 0.4255 but the quantum fluctuations are activated by temperature and reduce the above value of T c by ∼ 16%.…”

“…The method like all tensor network methods doesn't suffer from the sign problem which makes it powerful tool for simulation of weakly entangled models. VTNR was successfully applied to the 2D Hubbard model at T > 0 [20] and to estimate the value of T c for both the 2D compass [21] and the e g orbital model [22]. We discuss the nematic order in the 2D compass model in Sect.…”

Electronic and magnetic excitations in the half-stuffed Cu-O planes of Ba2Cu3O4Cl2 measured by resonant inelastic x-ray scattering

“…Ba 2 Cu 3 O 4 Cl 2 (Ba-2342) provides an opportunity to investigate an intermediate situation between the conventional "empty" corner-sharing CuO 2 square lattice and the fully-stuffed edge-sharing square lattice of T-CuO. Ba-2342 contains Cu-O planes with a Cu 3 O 4 stoichiometry, which can be seen as the superposition of two The Cu A and Cu B sublattices order antiferromagnetically at quite different temperatures, respectively T N,A = 324 K and T N,B = 31 K [15], which already implies a weak coupling and quite different physics on the two sublattice. Below T N,B the ordered moments, ∼ 0.6 µ B on both the Cu A and Cu B sites, are collinear and parallel with the (1,0) direction, as depicted in Fig.…”