Quantum magnetism and quantum phase transitions

Research group

Research theme

Sub department

About

Origin of the insulating state in the honeycomb iridate Cu2IrO3

Physical Review B American Physical Society 111:24 (2025) 245122

Authors:

Ying Li, Roger D Johnson, Yogesh Singh, Radu Coldea, Roser Valent铆

Abstract:

Through a combination of crystal symmetry analysis and density functional theory calculations we unveil a possible microscopic origin of the unexpected insulating behavior reported in the honeycomb Kitaev material Cu2鈦谤翱3. Our study suggests that this material hosts an instability towards charge ordering of the Ir ions, with alternating magnetic Ir4+ and nonmagnetic Ir3+ ions arranged on the honeycomb lattice. In this case, the next-nearest-neighbor interactions that couple magnetic Ir4+ ions form an enlarged triangular lattice, instead of the expected honeycomb lattice. The magnetic Cu2+ ions located at the center of the iridium honeycomb voids also form a triangular lattice, and additionally contribute to the magnetization of the system. Together, the interpenetrated Ir4+ and Cu2+ triangular lattices present a novel type of honeycomb Kitaev lattice composed of two types of magnetic ion.

From continuum excitations to sharp magnons via transverse magnetic field in the spin-1/2 Ising-like triangular lattice antiferromagnet Na2BaCo(PO4)2

(2025)

Authors:

Leonie Woodland, Ryutaro Okuma, J Ross Stewart, Christian Balz, Radu Coldea

Superconductivity in Hexagonal Zr6CoAl2-Type Zr6RuBi2 and Zr6FeBi2

Journal of the Physical Society of Japan 94:1 (2025)

Authors:

K Yuchi, D Nishio-Hamane, K Kojima, K Moriyama, R Okuma, Y Okamoto

Abstract:

We report the synthesis and electronic properties of polycrystalline samples of Zr6MBi2 (M = Ru and Fe) crystallizing in the hexagonal Zr6CoAl2-type structure. Based on their electrical resistivity, magnetization, and heat capacity data, Zr6RuBi2 and Zr6FeBi2 are found to exhibit bulk superconductivity below Tc = 4.9 and 1.4 K, respectively. Although Zr6RuBi2 is most likely a conventional superconductor, the considerably higher Tc for M = Ru compared with that for M = Fe differs from the trend in Tc for Zr6CoAl2-type superconductors reported to date. The superconductivity of an amorphous solid-solution phase, which may hinder elucidation of the superconducting properties of Zr6MBi2, is also discussed.

Topological Semimetal KAlGe with Novel Electronic Instability

Chemistry of Materials American Chemical Society (ACS) 37:1 (2025) 189-197

Authors:

Toshiya Ikenobe, Takahiro Yamada, Jun-ichi Yamaura, Tamio Oguchi, Ryutaro Okuma, Daigorou Hirai, Hajime Sagayama, Yoshihiko Okamoto, Zenji Hiroi

From continuum excitations to sharp magnons via transverse magnetic field in the spin-1/2 Ising-like triangular lattice antiferromagnet Na2BaCo(PO4)2 : data archive

University of Oxford (2025)

Authors:

Leonie Woodland, Ryutaro Okuma, J Ross Stewart, Christian Balz, Radu Coldea

Abstract:

The deposited package contains experimental single crystal inelastic neutron scattering data probing the spin dynamics in the quantum Ising-like triangular lattice antiferromagnet Na2BaCo(PO4)2 in in-plane magnetic field together with corresponding theoretical calculations of the spin dynamics, as well as single crystal x-ray diffraction data from the same material. A Matlab script to read and plot all data in ASCII files is also supplied.