arXiv subjects

Xiaoqiang Liu

Publications and source records attributed to Xiaoqiang Liu.

40 records · Page 3Linked to original sources

arXiv2021

A silver(II) route to unconventional superconductivity

The highly unusual divalent silver in silver difluoride (AgF$_2$) features a nearly square lattice of Ag$^{+2}$ bridged by fluorides. As a structural and electronic analogue of cuprates, its superconducting properties are yet to be examined. Our first principles electronic structure calculations reveal a striking resemblance between AgF$_2$ and the cuprates. Computed spin susceptibility shows a magnetic instability consistent with the experimentally observed antiferromagnetic transition. A linearized Eliashberg theory in fluctuation-exchange approximation shows an unconventional singlet $d$-wave superconducting pairing for bulk AgF$_2$ at an optimal electron doping. The pairing is found to strengthen with a decreasing interlayer coupling, highlighting the importance of quasi-2D nature of the crystal structure. These findings place AgF$_2$ in the category of unconventional high-$T_\text{C}$ superconductors, and its chemical uniqueness may help shed new lights on the high-$T_\text{C}$ phenomena.

cond-mat.supr-con↗

arXiv2020

Zero-energy bound states in the high-temperature superconductors at the two-dimensional limit

Majorana zero modes (MZMs) that obey the non-Abelian statistics have been intensively investigated for potential applications in topological quantum computing. The prevailing signals in tunneling experiments "fingerprinting" the existence of MZMs are the zero-energy bound states (ZEBSs). However, nearly all of the previously reported ZEBSs showing signatures of the MZMs are observed in difficult-to-fabricate heterostructures at very low temperatures and additionally require applied magnetic field. Here, by using in-situ scanning tunneling spectroscopy, we detect the ZEBSs upon the interstitial Fe adatoms deposited on two different high-temperature superconducting one-unit-cell-thick iron chalcogenides on SrTiO3(001). The spectroscopic results resemble the phenomenological characteristics of the MZMs inside the vortex cores of topological superconductors. Our experimental findings may extend the MZM explorations in connate topological superconductors towards an applicable temperature regime and down to the two-dimensional limit. While a concrete understanding of the observations is lacking, possible explanations involving novel 2D superconducting states with spin-orbit coupling, spontaneous nucleation of anomalous vortices at the magnetic sites, and noncoplanar magnetic ordering may further stimulate theoretical understandings of the scarcely captured ZEBSs in strongly correlated systems with multiband Cooper pairing.

cond-mat.supr-con↗

arXiv2017

On the charge and magnetic ordering in monolayer NbSe$_2$: a first principles study

Monolayer NbSe$_2$ has recently been shown to be a 2-dimensional superconductor, with a competing charge-density wave (CDW) order. This work investigates the electronic structure of monolayer NbSe$_2$ based on first principles calculations, focusing on charge and magnetic orders in connection to the superconductivity. It is found that decreased screening in the monolayer NbSe$_2$ with a perfect lattice exhibits magnetic instability, which is removed by the formation of CDW. Two energetically competitive but distinct $3\times3$ CDW structures are revealed computationally, which have a significant impact on the Fermi surface. The relations of the potential CDW phases with experimental structure and the coexisting superconductivity are discussed.

cond-mat.str-el↗

arXiv2017

Observation of Unusual Magnetoelastic Effects in a Quasi-1D Spiral Magnet

We present a systematic study of spin and lattice dynamics in the quasi-one-dimensional spiral magnet CuBr2, using Raman scattering in conjunction with infrared and neutron spectroscopy. Along with the development of spin correlations upon cooling, we observe a rich set of broad Raman bands at energies that correspond to phonon-dispersion energies near the one-dimensional magnetic wave vector. The low-energy bands further exhibit a distinct intensity maximum at the spiral magnetic ordering temperature. We attribute these unusual observations to two possible underlying mechanisms: (1) formation of hybrid spin-lattice excitations, and/or (2) "quadrumerization" of the lattice caused by spin-singlet entanglement in competition with the spiral magnetism.

cond-mat.str-el↗