The full magnon spectrum of yttrium iron garnet

npj Quantum Materials 2 (2017)

AJ Princep, RA Ewings, S Ward, S Tóth, C Dubs, D Prabhakaran, AT Boothroyd

The Full Magnon Spectrum of Yttrium Iron Garnet

npj Quantum Materials (2017)

Princep, RA Ewings, S Ward, S Toth, C Dubs, D Prabhakaran, AT Boothroyd

Ultrahigh magnetic field spectroscopy reveals the band structure of the three-dimensional topological insulator Bi2Se3

PHYSICAL REVIEW B 96 (2017) ARTN 121111

A Miyata, Z Yang, A Surrente, O Drachenko, DK Maude, O Portugall, LB Duffy, T Hesjedal, P Plochocka, RJ Nicholas

Coexistence of magnetism and superconductivity in separate layers of the iron-based superconductor Li1-xFex(OH)Fe1-ySe

PHYSICAL REVIEW B 95 (2017) ARTN 134419

CV Topping, FKK Kirschner, SJ Blundell, PJ Baker, DN Woodruff, F Schild, H Sun, SJ Clarke

Crystal growth of the triangular-lattice antiferromagnet Ba3CoSb2O9

JOURNAL OF CRYSTAL GROWTH 468 (2017) 345-348

D Prabhakaran, AT Boothroyd

Proposal of a micromagnetic standard problem for ferromagnetic resonance simulations

Journal of Magnetism and Magnetic Materials 421 (2017) 428

AA Baker, M Beg, G Ashton, M Albert, D Chernyshenko, W Wang, S Zhang, M-A Bisotti, M Franchin, CL Hu, R Stamps, T Hesjedal, H Fangohr

Nowadays, micromagnetic simulations are a common tool for studying a wide range of different magnetic phenomena, including the ferromagnetic resonance. A technique for evaluating reliability and validity of different micromagnetic simulation tools is the simulation of proposed standard problems. We propose a new standard problem by providing a detailed specification and analysis of a sufficiently simple problem. By analyzing the magnetization dynamics in a thin permalloy square sample, triggered by a well defined excitation, we obtain the ferromagnetic resonance spectrum and identify the resonance modes via Fourier transform. Simulations are performed using both finite difference and finite element numerical methods, with OOMMF and Nmag simulators, respectively. We report the effects of initial conditions and simulation parameters on the character of the observed resonance modes for this standard problem. We provide detailed instructions and code to assist in using the results for evaluation of new simulator tools, and to help with numerical calculation of ferromagnetic resonance spectra and modes in general.

Synthesis of Superconductor-Topological Insulator Hybrid Nanoribbon Structures

NANO 12 (2017) ARTN 1750095

P Schonherr, F Zhang, V Srot, P van Aken, T Hesjedal

Temperature evolution of topological surface states in Bi2Se3 thin films studied using terahertz spectroscopy


VS Kamboj, A Singh, HE Beere, T Hesjedal, CHW Barnes, DA Ritchie

Andreev bound states in superconductor/ferromagnet point contact Andreev reflection spectra

PHYSICAL REVIEW B 95 (2017) ARTN 094516

KA Yates, LABO Olthof, ME Vickers, D Prabhakaran, M Egilmez, JWA Robinson, LF Cohen

X-ray magnetic circular dichroism study of Dy-doped Bi2Te3 topological insulator thin films


AI Figueroa, AA Baker, SE Harrison, K Kummer, G van der Laan, T Hesjedal

Anomalous behavior of displacement correlation function and strain in lanthanum cobalt oxide analyzed both from X-ray powder diffraction and EXAFS data

POWDER DIFFRACTION 32 (2017) S151-S154

V Efimov, V Sikolenko, IO Troyanchuk, D Karpinsky, E Efimova, SI Tiutiunnikov, BN Savenko, D Novoselov, D Prabhakaran

Doping Dependence of Collective Spin and Orbital Excitations in the Spin-1 Quantum Antiferromagnet La_{2-x}Sr_{x}NiO_{4} Observed by X Rays.

Physical review letters 118 (2017) 156402-

G Fabbris, D Meyers, L Xu, VM Katukuri, L Hozoi, X Liu, Z-Y Chen, J Okamoto, T Schmitt, A Uldry, B Delley, GD Gu, D Prabhakaran, AT Boothroyd, J van den Brink, DJ Huang, MPM Dean

We report the first empirical demonstration that resonant inelastic x-ray scattering (RIXS) is sensitive to collective magnetic excitations in S=1 systems by probing the Ni L_{3} edge of La_{2-x}Sr_{x}NiO_{4} (x=0, 0.33, 0.45). The magnetic excitation peak is asymmetric, indicating the presence of single and multi-spin-flip excitations. As the hole doping level is increased, the zone boundary magnon energy is suppressed at a much larger rate than that in hole doped cuprates. Based on the analysis of the orbital and charge excitations observed by RIXS, we argue that this difference is related to the orbital character of the doped holes in these two families. This work establishes RIXS as a probe of fundamental magnetic interactions in nickelates opening the way towards studies of heterostructures and ultrafast pump-probe experiments.

Terahertz spectroscopy of anisotropic materials using beams with rotatable polarization.

Scientific Reports 7 (2017) 12337-

CDW Mosley, M Failla, D Prabhakaran, J Lloyd-Hughes

We introduce a polarization-resolved terahertz time-domain spectrometer with a broadband (0.3-2.5 THz), rotatable THz polarization state, and which exhibits minimal change in the electric field amplitude and polarization state upon rotation. This was achieved by rotating an interdigitated photoconductive emitter, and by detecting the orthogonal components of the generated THz pulse via electro-optic sampling. The high precision (<0.1°) and accuracy (<1.0°) of this approach is beneficial for the study of anisotropic materials without rotating the sample, which can be impractical, for instance for samples held in a cryostat. The versatility of this method was demonstrated by studying the anisotropic THz optical properties of uniaxial and biaxial oxide crystals. For uniaxial ZnO and LaAlO3, which have minimal THz absorption across the measurement bandwidth, the orientations of the eigenmodes of propagation were conveniently identified as the orientation angles that produced a transmitted THz pulse with zero ellipticity, and the birefringence was quantified. In CuO, a multiferroic with improper ferroelectricity, the anisotropic THz absorption created by an electromagnon was investigated, mapping its selection rule precisely. For this biaxial crystal, which has phonon and electromagnon absorption, the polarization eigenvectors exhibited chromatic dispersion, as a result of the monoclinic crystal structure and the frequency-dependent complex refractive index.

Van der Waals epitaxy between the highly lattice mismatched Cu-doped FeSe and Bi2Te3


A Ghasemi, D Kepaptsoglou, PL Galindo, QM Ramasse, T Hesjedal, VK Lazarov

Strong Coupling of Microwave Photons to Antiferromagnetic Fluctuations in an Organic Magnet.

Physical review letters 119 (2017) 147701-

M Mergenthaler, J Liu, JJ Le Roy, N Ares, AL Thompson, L Bogani, F Luis, SJ Blundell, T Lancaster, A Ardavan, GAD Briggs, PJ Leek, EA Laird

Coupling between a crystal of di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium radicals and a superconducting microwave resonator is investigated in a circuit quantum electrodynamics (circuit QED) architecture. The crystal exhibits paramagnetic behavior above 4 K, with antiferromagnetic correlations appearing below this temperature, and we demonstrate strong coupling at base temperature. The magnetic resonance acquires a field angle dependence as the crystal is cooled down, indicating anisotropy of the exchange interactions. These results show that multispin modes in organic crystals are suitable for circuit QED, offering a platform for their coherent manipulation. They also utilize the circuit QED architecture as a way to probe spin correlations at low temperature.

Spin dynamics in the antiferromagnetic phases of the Dirac metals AMnBi(2) (A = Sr, Ca)

PHYSICAL REVIEW B 95 (2017) ARTN 134405

MC Rahn, AJ Princep, A Piovano, J Kulda, YF Guo, YG Shi, AT Boothroyd

Anisotropic magnetic switching along hard [110]-type axes in Er-doped DyFe2/YFe2 thin films


GBG Stenning, GJ Bowden, G van der Laan, AI Figueroa, P Bencok, P Steadman, T Hesjedal

Magnetic proximity coupling to Cr-doped Sb2Te3 thin films

PHYSICAL REVIEW B 95 (2017) ARTN 224422

LB Duffy, AI Figueroa, L Gladczuk, N-J Steinke, K Kummer, G van der Laan, T Hesjedal

Observation of nodal line in non-symmorphic topological semimetal InBi


SA Ekahana, S-C Wu, J Jiang, K Okawa, D Prabhakaran, C-C Hwang, S-K Mo, T Sasagawa, C Felser, B Yan, Z Liu, Y Chen

Emergence of Dirac-like bands in the monolayer limit of epitaxial Ge films on Au(1 1 1)

2D Materials 4 (2017) 031005

NBM Schröter, MD Watson, LB Duffy, M Hoesch, Y Chen, T Hesjedal, TK Kim

After the discovery of Dirac fermions in graphene, it has become a natural question to ask whether it is possible to realize Dirac fermions in other two-dimensional (2D) materials as well. In this work, we report the discovery of multiple Dirac-like electronic bands in ultrathin Ge flms grown on Au(1 1 1) by angle-resolved photoelectron spectroscopy. By tuning the thickness of the flms, we are able to observe the evolution of their electronic structure when passing through the monolayer limit. Our discovery may signify the synthesis of germanene, a 2D honeycomb structure made of Ge, which is a promising platform for exploring exotic topological phenomena and enabling potential applications.