arXiv subjects

R. G. Buckley

Publications and source records attributed to R. G. Buckley.

6 recordsLinked to original sources

arXiv2026

Van Hove singularities at the $L$-face of the lutetium nitride phonon dispersion

We report the structural and vibrational properties of the prototypical 4$f$-filled nonmagnetic member LuN of the lanthanide nitrides, \textit{Ln}N, with elastic and inelastic neutron scattering data at $4$~K. We find a peak in the generalized density of states which, through input from a DFT+$U$ computation, we ascribe to a van Hove singularity on the fourfold-degenerate $L$-face of the Brillouin zone. This work advances the understanding of phonon dynamics in \textit{Ln}N beyond the $Γ$-point.

cond-mat.mtrl-sci↗

arXiv2026

Optical, vibrational, and electronic properties of semiconducting YbN

We investigate the vibrational, optical, and electronic properties of insulating YbN thin films using Raman spectroscopy, Fourier-transform infrared spectroscopy, and electrical transport measurements, supported by density functional theory. Raman spectra reveal the LO($Γ$) phonon and a cation-vacancy mode, while the optical conductivity identifies the TO phonon and an absorption edge corresponding to a 1.7 eV N 2p{$\rightarrow$}Yb 5d transition. The films exhibit thermally activated resistivity consistent with an insulating ground state. An additional defect induced absorption tail below the intrinsic band gap is observed, which in combination with the electrical measurements indicates the Fermi energy resides in a disordered conduction band minimum.

cond-mat.mtrl-sci↗

arXiv2024

Spin polarisation and non-isotropic effective mass in the conduction band of GdN

GdN is a ferromagnetic semiconductor which has seen increasing interest in the preceding decades particularly in the areas of spin- and superconducting- based electronics. Here we report a detailed computational study and optical spectroscopy study of the electronic structure of stoichiometric and nitrogen vacancy doped GdN. Based on our calculations we provide the effective mass tensor for undoped GdN, and some indicative values for electron doped GdN. Such a property is valuable as it can directly affect device design, and be directly measured experimentally to validate the existing computation results.

cond-mat.mtrl-sci↗

arXiv2023

Unconventional superconductivity and quantum criticality in SmN

Nitrogen vacancy doped SmN$_{1-δ}$ is a semiconductor which lies in the intermediary between insulating-ferromagnetic SmN and metallic-anti-ferromagnetic Sm. The dopant electrons resulting from nitrogen vacancies have recently been predicted to lie in a band precipitated by a majority-spin 4$f$ level on the six Sm ions neighbouring each nitrogen vacancy, an in-gap state $\sim$1 eV below the 4$f$ states in stoichiometric SmN. Optical data reported here corroborate the prediction along with an extended computational study. Electrical transport measurements show the transition from an insulating to metallic state with a hopping type conductivity in dilutely doped films. We provide strong evidence that electron transport is mediated by a dispersion-less majority spin defect band implying triplet type superconductivity, the location of which in the SmN-Sm phase diagram suggests the location of a quantum critical point.

cond-mat.supr-con↗

arXiv2019

4f Conduction in the Magnetic Semiconductor NdN

We report the growth of films of the intrinsic ferromagnetic semiconductor NdN, and an investigation of their optical and transport properties. There is clear evidence of a strong anomalous Hall effect as expected from a 4f conduction channel, supported by an optical absorption into a 4f or 4f/5d hybridized tail at the base of the conduction band. The results reveal a heavy-fermion 4f/5d band lying where it can be occupied at controllable levels with nitrogen-vacancy donors.

cond-mat.str-el↗

arXiv2019

Optical Spectroscopy of SmN: Evidence for 4f Transport

The rare-earth nitride ferromagnetic semiconductors owe their varying magnetic properties to the progressive filling of 4f shell across the series. Recent electrical transport measurements on samarium nitride, including the observation of superconductivity, have been understood in terms of a contribution from a 4f transport channel. Band structure calculations generally locate an empty majority 4f-band within the conduction band although over a wide range of possible energies. Here we report optical reflection and transmission measurements on samarium nitride between 0.01 eV to 4 eV, that demonstrate clearly that the 4f band forms the bottom of the conduction band. Results at the lowest energies show no free carrier absorption, indicating a semiconducting ground state, and supporting earlier conclusions based on transport measurements.

cond-mat.str-el↗