Evolution of magnetic, transport, and thermal properties inNa4−xIr3O8 (original) (raw)

Topological Spin Liquid on the Hyperkagome Lattice of Na4Ir3O8

Physical Review Letters, 2008

Recent experiments on the "hyper-kagome" lattice system Na4Ir3O8 have demonstrated that it is a rare example of a three dimensional spin-1/2 frustrated antiferromagnet. We investigate the role of quantum fluctuations as the primary mechanism lifting the macroscopic degeneracy inherited by classical spins on this lattice. In the semi-classical limit we predict, based on large-N calculations, that an unusual q = 0 coplaner magnetically ordered ground state is stabilized with no local "weather vane" modes. This phase melts in the quantum limit and a gapped topological Z2 spin liquid phase emerges. In the vicinity of this quantum phase transition, we study the dynamic spin structure factor and comment on the relevance of our results for future neutron scattering experiments.

Spin liquid close to a quantum critical point in Na4Ir3O8

Physical Review B, 2013

Na4Ir3O8 is a candidate material for a 3-dimensional quantum spin-liquid on the hyperkagome lattice. We present thermodynamic measurements of heat capacity C and thermal conductivity κ on high quality polycrystalline samples of Na4Ir3O8 down to T = 500 mK and 75 mK, respectively. Absence of long-range magnetic order down to T = 75 mK strongly supports claims of a spin-liquid ground state. The constant magnetic susceptibility χ below T ≈ 25 K and the presence of a small but finite linear-T term in C(T) suggest the presence of gapless spin excitations. Additionally, the magnetic Grüneisen ratio shows a divergence as T → 0 K and a scaling behavior which clearly demonstrates that Na4Ir3O8 is situated close to a zero-field QCP.

Spin liquids and spin dynamics in kagome antiferromagnets

2006

Among all the corner sharing highly frustrated magnets, only a few experimental systems are good candidates for a low-T fluctuating state, ie fulfilling the important conditions of the pure Heisenberg lattice with nn couplings. The combination of the weakness of the single-ion anisotropy and of a direct overlap antiferromagnetic exchange are certainly the major advantages of the chromate S=3/2 kagome bilayer Ba 2 Sn 2 ZnGa 10−7p Cr 7p O 22-BSZCGO(p)-and the long studied SrCr 9p Ga 12−9p O 19-SCGO(p). Beyond the absence of ordering well below the Curie-Weiss temperature, the unusual large value of the specific heat unveils a high density of low lying excitations and its field independence suggests that the excited states are mostly singlets. Moreover, their ground state is found essentially fluctuating although an intrinsic spin glass (SG) signature is observed in susceptibility measurements. Through a review of our past years work, I'll illustrate all the potential of local studies (NMR and µSR) to reveal some key aspects of the physics of these compounds: susceptibility, fluctuations, impact of dilution defects which generate an extended response of the spin-lattice ... as well as the puzzling spin-glass state. More recently we also investigated new series of compounds, among them volborthite and delafossites which feature S=1/2 spins on a corner sharing antiferromagnetic lattice. I'll introduce these compounds and shortly discuss their relation to ideal Hamiltonians and novel features.-D. Bono et al.

Quantum-spin-liquid states in the two-dimensional kagome antiferromagnets ZnxCu4−x(OD)6Cl2

Nature Materials, 2007

A three-dimensional system of interacting spins typically develops static longrange order when it is cooled. If the spins are quantum (S = 1/2), however, novel quantum paramagnetic states may appear. The most highly sought state among them is the resonating valence bond (RVB) state 1,2 in which every pair of neighboring quantum spins form entangled spin singlets ↑↓ − ↓↑ () (valence bonds) and the singlets are quantum mechanically resonating amongst all the possible highly degenerate pairing states. Here we provide experimental evidence for such quantum paramagnetic states existing in frustrated antiferromagnets, Zn x Cu 4-x (OD) 6 Cl 2 , where the S = 1/2 magnetic Cu 2+ moments form layers of a twodimensional kagomé lattice. We find that in Cu 4 (OD) 6 Cl 2 , where distorted kagomé planes are weakly coupled to each other, a dispersionless excitation mode appears in the magnetic excitation spectrum below ~ 20 K, whose characteristics resemble those of quantum spin singlets in a solid state, known as a valence bond solid

Magnetic Mushy Sea Ice Like Phase in Kagomé Antiferromagnets

We report magnetization and neutron scattering measurements down to 60 mK on a new family of Fe based kagome antiferromagnets, in which a strong local spin anisotropy combined with a low exchange path network connectivity lead to domain walls intersecting the kagome planes through strings of free spins. These produce unfamiliar slow spin dynamics in the ordered phase, evolving from exchange-released spin-flips towards a cooperative behavior on decreasing the temperature, probably due to the onset of long-range dipolar interaction. A domain structure of independent magnetic grains is obtained that could be generic to other frustrated magnets.

Realization of the kagome spin ice state in a frustrated intermetallic compound

Science

Spin ices are exotic phases of matter characterized by frustrated spins obeying local “ice rules,” in analogy with the electric dipoles in water ice. In two dimensions, one can similarly define ice rules for in-plane Ising-like spins arranged on a kagome lattice. These ice rules require each triangle plaquette to have a single monopole and can lead to different types of orders and excitations. Using experimental and theoretical approaches including magnetometry, thermodynamic measurements, neutron scattering, and Monte Carlo simulations, we establish HoAgGe as a crystalline (i.e., nonartificial) system that realizes the kagome spin ice state. The system features a variety of partially and fully ordered states and a sequence of field-induced phases at low temperatures, all consistent with the kagome ice rule.

Gapless Spin Liquids on the Three-Dimensional Hyperkagome Lattice of Na4Ir3O8

Physical Review Letters, 2008

Recent experiments indicate that Na4Ir3O8, a material in which s=1/2 Ir local moments form a three dimensional network of corner-sharing triangles, may have a quantum spin liquid ground state with gapless spin excitations. Using a combination of exact diagonalization, symmetry analysis of fermionic mean field ground states and Gutzwiller projected variational wavefunction studies, we propose a quantum spin liquid with spinon Fermi surfaces as a favorable candidate for the ground state of the Heisenberg model on the hyper-kagome lattice of Na4Ir3O8. We present a renormalized mean field theory of the specific heat of this spin liquid and also discuss possible low temperature instabilities of the spinon Fermi surfaces.