Publications


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


Probing the Topological Surface State in Bi2Se3 Thin Films Using Temperature-Dependent Terahertz Spectroscopy

ACS PHOTONICS 4 (2017) 2711-2718

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


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


Quasiparticle Breakdown and Spin Hamiltonian of the Frustrated Quantum Pyrochlore Yb_{2}Ti_{2}O_{7} in a Magnetic Field.

Physical review letters 119 (2017) 057203-

JD Thompson, PA McClarty, D Prabhakaran, I Cabrera, T Guidi, R Coldea

The frustrated pyrochlore magnet Yb_{2}Ti_{2}O_{7} has the remarkable property that it orders magnetically but has no propagating magnons over wide regions of the Brillouin zone. Here we use inelastic neutron scattering to follow how the spectrum evolves in cubic-axis magnetic fields. At high fields we observe, in addition to dispersive magnons, a two-magnon continuum, which grows in intensity upon reducing the field and overlaps with the one-magnon states at intermediate fields leading to strong renormalization of the dispersion relations, and magnon decays. Using heat capacity measurements we find that the low- and high-field regions are smoothly connected with no sharp phase transition, with the spin gap increasing monotonically in field. Through fits to an extensive data set of dispersion relations combined with magnetization measurements, we reevaluate the spin Hamiltonian, finding dominant quantum exchange terms, which we propose are responsible for the anomalously strong fluctuations and quasiparticle breakdown effects observed at low fields.


Low-field spin dynamics of Cr7Ni and Cr7Ni-Cu-Cr7Ni molecular rings as detected by mu SR

PHYSICAL REVIEW B 96 (2017) ARTN 184403

S Sanna, P Arosio, L Bordonali, F Adelnia, M Mariani, E Garlatti, C Baines, A Amato, KPV Sabareesh, G Timco, REP Winpenny, SJ Blundell, A Lascialfari


Spectroscopic evidence for the gapless electronic structure in bulk ZrTe5

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 219 (2017) 45-52

L Shen, MX Wang, SC Sun, J Jiang, X Xu, T Zhang, QH Zhang, YY Lv, SH Yao, YB Chen, MH Lu, YF Chen, C Felser, BH Yan, ZK Liu, LX Yang, YL Chen


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


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


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

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 422 (2017) 93-99

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


Quantum Griffiths Phase Inside the Ferromagnetic Phase of Ni_{1-x}V_{x}.

Physical review letters 118 (2017) 267202-267202

R Wang, A Gebretsadik, S Ubaid-Kassis, A Schroeder, T Vojta, PJ Baker, FL Pratt, SJ Blundell, T Lancaster, I Franke, JS Möller, K Page

We study by means of bulk and local probes the d-metal alloy Ni_{1-x}V_{x} close to the quantum critical concentration, x_{c}≈11.6%, where the ferromagnetic transition temperature vanishes. The magnetization-field curve in the ferromagnetic phase takes an anomalous power-law form with a nonuniversal exponent that is strongly x dependent and mirrors the behavior in the paramagnetic phase. Muon spin rotation experiments demonstrate inhomogeneous magnetic order and indicate the presence of dynamic fluctuating magnetic clusters. These results provide strong evidence for a quantum Griffiths phase on the ferromagnetic side of the quantum phase transition.


Local magnetism and spin dynamics of the frustrated honeycomb rhodate Li2RhO3

PHYSICAL REVIEW B 96 (2017) ARTN 094432

P Khuntia, S Manni, FR Foronda, T Lancaster, SJ Blundell, P Gegenwart, M Baenitz


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.


Direct experimental determination of spiral spin structures via the dichroism extinction effect in resonant elastic soft x-ray scattering

PHYSICAL REVIEW B 96 (2017) ARTN 094401

SL Zhang, G van der Laan, T Hesjedal


Perfect quintuple layer Bi2Te3 nanowires: Growth and thermoelectric properties

APL MATERIALS 5 (2017) ARTN 086110

P Schonherr, D Kojda, V Srot, SF Fischer, PA van Aken, T Hesjedal


Topological origin of the type-II Dirac fermions in PtSe2

PHYSICAL REVIEW MATERIALS 1 (2017) ARTN 074202

Y Li, Y Xia, SA Ekahana, N Kumar, J Jiang, L Yang, C Chen, C Liu, B Yan, C Felser, G Li, Z Liu, Y Chen


Topological triplon modes and bound states in a Shastry-Sutherland magnet

NATURE PHYSICS 13 (2017) 736-+

PA McClarty, F Krueger, T Guidi, SF Parker, K Refson, AW Parker, D Prabhakaran, R Coldea


Magnetic Field Dependence of Excitations Near Spin-Orbital Quantum Criticality.

Physical review letters 118 (2017) 067205-

A Biffin, C Rüegg, J Embs, T Guidi, D Cheptiakov, A Loidl, V Tsurkan, R Coldea

The spinel FeSc_{2}S_{4} has been proposed to realize a near-critical spin-orbital singlet (SOS) state, where entangled spin and orbital moments fluctuate in a global singlet state on the verge of spin and orbital order. Here we report powder inelastic neutron scattering measurements that observe the full bandwidth of magnetic excitations and we find that spin-orbital triplon excitations of an SOS state can capture well key aspects of the spectrum in both zero and applied magnetic fields up to 8.5 T. The observed shift of low-energy spectral weight to higher energies upon increasing applied field is naturally explained by the entangled spin-orbital character of the magnetic states, a behavior that is in strong contrast to spin-only singlet ground state systems, where the spin gap decreases upon increasing applied field.


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.

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