Zhihao Hao

Nematicity in stripe-ordered cuprates probed via resonant x-ray scattering

Disentangling intertwined orders In copper oxide superconductors, several types of order compete for supremacy. In addition to superconductivity, researchers have found periodic patterns in charge density (CDW order), as well as an asymmetry in the electronic density within the unit cell of some cuprates (nematicity). CDW order has been detected in the underdoped regime of all major cuprate families, but the ubiquity of nematicity is less clear. Achkar et al. used resonant x-ray scattering to find that, in the copper oxide planes of three lanthanum-based cuprates, nematicity has a temperature dependence distinct from that of a related structural distortion. This implies that there are additional, electronic mechanisms for nematicity Science, this issue p. 576 Nematicity has a temperature dependence that is distinct from that of a related structural distortion in lanthanum-based cuprates. In underdoped cuprate superconductors, a rich competition occurs between superconductivity and charge density wave (CDW) order. Whether rotational symmetry-breaking (nematicity) occurs intrinsically and generically or as a consequence of other orders is under debate. Here, we employ resonant x-ray scattering in stripe-ordered superconductors (La,M)2CuO4 to probe the relationship between electronic nematicity of the Cu 3d orbitals, structure of the (La,M)2O2 layers, and CDW order. We find distinct temperature dependences for the structure of the (La,M)2O2 layers and the electronic nematicity of the CuO2 planes, with only the latter being enhanced by the onset of CDW order. These results identify electronic nematicity as an order parameter that is distinct from a purely structural order parameter in underdoped striped cuprates.

Bosonic many-body theory of quantum spin ice

We carry out an analytical study of quantum spin ice, a U(1) quantum spin liquid close to the classical spin-ice solution for an effective spin- 1 model with anisotropic exchange couplings Jzz, J± ,a ndJz± on the pyrochlore lattice. Starting from the quantum rotor model introduced by Savary and Balents [ Phys. Rev. Lett.108, 037202 (2012)], we retain the dynamics of both the spinons and gauge field sectors in our treatment. The spinons are described by a bosonic representation of quantum XY rotors, while the dynamics of the gauge field is captured by a phenomenological Hamiltonian. By calculating the one-loop spinon self-energy, which is proportional to J 2 z±, we determine the stability region of the U(1) quantum spin-liquid phase in the J±/Jzz versus Jz±/Jzz zero-temperature phase diagram. From these results, we estimate the location of the boundaries between the spin-liquid phase and classical long-range ordered phases.

Order-by-disorder near criticality inXYpyrochlore magnets

We consider a system of spins on the sites of a three-dimensional pyrochlore lattice of corner-sharing tetrahedra interacting with a predominant effective

Ground state phase diagram of genericXYpyrochlore magnets with quantum fluctuations

xy

Refrustration and competing orders in the prototypical Dy2Ti2O7 spin ice material

exchange. In particular, we investigate the selection of a long-range ordered state with broken discrete symmetry induced by thermal fluctuations near the critical region. At the standard mean-field theory (s-MFT) level, in a region of the parameter space of this Hamiltonian that we refer to as

Fluctuation-driven selection at criticality in a frustrated magnetic system: the case of multiple-k partial order on the pyrochlore lattice.

\Gamma_5

Half-metallic magnetization plateaux

region, the ordered state possesses an accidental

Nematicity in Stripe Ordered Cuprates Probed via Resonant X-Ray Scattering

U(1)

Flucutation driven selection at crticality: the case of multi-k partial order on the pyrochlore lattice

degeneracy. In this paper, we show that fluctuations beyond s-MFT lift this degeneracy by selecting one of two states (so-called

Thermal Order-by-Disorder at Criticality in XY Pyrochlore Magnets

\psi_2