arXiv subjects

Guo-Qiang Liu

Publications and source records attributed to Guo-Qiang Liu.

4 recordsLinked to original sources

arXiv2016

A first-principles study on the phonon transport in layered BiCuOSe

First-principles calculations are employed to investigate the phonon transport of BiCuOSe. Our calculations reproduce the lattice thermal conductivity of BiCuOSe. The calculated gruneisen parameter is 2.4~2.6 at room temperature, a fairly large value indicating a strong anharmonicity in BiCuOSe, which leads to its ultralow lattice thermal conductivity. The contribution to total thermal conductivity from high-frequency optical phonons, which are mostly contributed by the vibrations of O atoms, is larger than 1/3, remarkably different from the usual picture with very little contribution from high-frequency optical phonons. Our calculations show that both the high group velocities and low scattering processes involved make the high-frequency optical modes contribute considerably to the total lattice thermal conductivity. In addition, we show that the sound velocity and bulk modulus along $a$ and $c$ axes exhibit strong anisotropy, which results in the anisotropic thermal conductivity in BiCuOSe.

cond-mat.mtrl-sci↗

arXiv2011

Spin-orbit coupling induced Mott transition in Ca$_{2-x}$Sr$_{x}$RuO$_{4}$ (0<x<0.2)

We propose a new mechanism for the paramagnetic metal-insulator transition in the layered perovskite Ca$_{2-x}$Sr$_{x}$RuO$_{4}$ (0<x<0.2). The LDA+U approach including spin-orbit coupling is used to calculate the electronic structures. In Ca$_{2}$RuO$_{4}$, we show that the spin-orbit effect is strongly enhanced by the Coulomb repulsion, which leads to an insulating phase. When Ca is substituted by Sr, the effective spin-orbit splitting is reduced due to the increasing bandwidth of the degenerate $d_{xz}$ and $d_{yz}$ orbitals. For x=0.2, the compound is found to be metallic. We show that these results are in good agreement with the experimental phase diagram.

cond-mat.str-el↗

arXiv2011

Orbital-spin ordering in the striped antiferromagnetic state of iron-based superconductors

The magnetic properties of iron-arsenides are investigated using the LSDA+U approach. In addition to one high moment state, we find that a positive U also produces two low moment states with m~0.4 $μ_{B}$ and m~1.0 $μ_{B}$. The electronic structures indicate that the low moment states originate in the strong orbital hybridization between antiferromagnetic Fe neighbors. Therefore, the geometry of the FeAs4 tetrahedron is crucial to the low moment states, which is the key to understand the negative pressure coefficient of Tc in LiFeAs. Finally, our theory suggests that the superconducting phase is an orbital-spin ordered state, where the orbital spin-moments cancel each other.

cond-mat.supr-con↗

arXiv2008

Coulomb-Enhanced Spin-Orbit Splitting: The Missing Piece in the Sr2RhO4 Puzzle

The outstanding discrepancy between the measured and calculated (local-density approximation) Fermi surfaces in the well-characterized, paramagnetic Fermi liquid Sr2RhO4 is resolved by including the spin-orbit coupling and Coulomb repulsion. This results in an effective spin-orbit coupling constant enhanced 2.15 times over the bare value. A simple formalism allows discussion of other systems. For Sr2RhO4, the experimental specific-heat and mass enhancements are found to be 2.2.

cond-mat.str-el↗