Theoretical study of the electronic states of hollandite vanadateK2V8O16

Abstract

We consider electronic properties of hollandite vanadate K2V8O16, a one-dimensional zigzag-chain system of t2g orbitals in a mixed valent state. We first calculate the Madelung energy and obtain the relative stability of several charge-ordering patterns to determine the most stable one that is consistent with the observed superlattice structure. We then develop the strong-coupling perturbation theory to derive the effective spin-orbit Hamiltonian, starting from the triply-degenerate t2g orbitals in the VO6 octahedral structure. We apply an exact-diagonalization technique on small clusters of this Hamiltonian and obtain the orbital-ordering pattern and spin structures in the ground state. We thereby discuss the electronic and magnetic properties of K2V8O16 including predictions on the outcome of future experimental studies.

Structural instability and the Mott-Peierls transition in a half-metallic hollandite :K2Cr8O16

“…K 2 Cr 8 O 16 and K x Ti 8 O 16 show magnetic transition from paramagnetic to ferromagnetic (FM) phase with varying the temperature and the carrier concentration, respectively [5][6][7]. On the other hand, K 2 V 8 O 16 has a complex ground state containing the charge ordering and the spin-singlet structure [3,8]. The possibility of Tomonaga-Luttinger liquid property has also been suggested in K 2 Ru 8 O 16 [9].…”

Metal-insulator transition in the hollanditeK2V8OShimizu1, Okai2, Itoh3 et al. 2011Phys. Rev. B23080View full textAdd to dashboardCite

“…Indeed, a Heisenberg model of the zigzag ladder predicts degenerated ground states, including nematic, 3,4 topological, 5 chiral, 6 incommensurate magnetic orders, 7 the spin-Bose metal, 8 and the field-induced orbital current. 9 In the presence of the orbital degrees of freedom with the moderate electron correlation and the electron-phonon coupling, various phase transitions have been found, such as the valence bond 10,11 and ferromagnetic 12 orders in hollandites A 2 M 8 O 16 , and the antiferromagnetic metal 13 and insulator 14 in pyroferites AM 2 O 4 , where A are alkaline metals and M are transition metals. To understand these phase transitions, the electron correlation and the orbital occupancy would be the dominant parameters, which should be revealed experimentally.…”

“…11 The tetragonal I 4/m crystal structure of K 2 V 8 O 16 consists of a framework of four double chains holding K ions in a large tunnel, as shown in Figs. 1(a) and 1(b).…”

“…The interaction within the double chain running along the c axis forms a zigzag ladder of the edge-sharing VO 6 . The 3d 1.25 electrons on average (V 3+ : V 4+ = 1 : 3) partially occupy the t 2g manifold consisting of the d yz -d zx doublet and the d xy singlet, 15,16 as schematically illustrated in Fig. 1(c), and hence the orbital degree of freedom is still active.…”

“…An alternative charge-order pattern with the nonmagnetic and paramagnetic spins was proposed theoretically. 16 Thus the microscopic spin, charge, and orbital states remain unsolved. Applying low pressures, T MI is sensitively suppressed up to 1 GPa, but turns to increase at high pressures up to 7 GPa, 17 implying the competing ground states due to the geometrical frustration.…”