Publications


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


Magneto-orbital ordering in the divalent A-site quadruple perovskite manganites AMn(7)O(12) (A = Sr, Cd, and Pb)

PHYSICAL REVIEW B 96 (2017) ARTN 054448

RD Johnson, DD Khalyavin, P Manuel, PG Radaelli, IS Glazkova, N Terada, AA Belik


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


Layer-by-layer epitaxial thin films of the pyrochlore Tb2Ti2O7.

Nanotechnology 28 (2017) 055708-

L Bovo, CM Rouleau, D Prabhakaran, ST Bramwell

Layer-by-layer epitaxial growth of the pyrochlore magnet Tb2Ti2O7 on the isostructural substrate Y2Ti2O7 results in high-quality single crystal films of up to 60 nm thickness. Substrate-induced strain is shown to act as a strong and controlled perturbation to the exotic magnetism of Tb2Ti2O7, opening up the general prospect of strain-engineering the diverse magnetic and electrical properties of pyrochlore oxides.


Proposal of a micromagnetic standard problem for ferromagnetic resonance simulations

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 421 (2017) 428-439

A 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


Deterministic and robust room-temperature exchange coupling in monodomain multiferroic BiFeO3 heterostructures.

Nature communications 8 (2017) 1583-1583

W Saenrang, BA Davidson, F Maccherozzi, JP Podkaminer, J Irwin, RD Johnson, JW Freeland, J Íñiguez, JL Schad, K Reierson, JC Frederick, CAF Vaz, L Howald, TH Kim, S Ryu, MV Veenendaal, PG Radaelli, SS Dhesi, MS Rzchowski, CB Eom

Exploiting multiferroic BiFeO3 thin films in spintronic devices requires deterministic and robust control of both internal magnetoelectric coupling in BiFeO3, as well as exchange coupling of its antiferromagnetic order to a ferromagnetic overlayer. Previous reports utilized approaches based on multi-step ferroelectric switching with multiple ferroelectric domains. Because domain walls can be responsible for fatigue, contain localized charges intrinsically or via defects, and present problems for device reproducibility and scaling, an alternative approach using a monodomain magnetoelectric state with single-step switching is desirable. Here we demonstrate room temperature, deterministic and robust, exchange coupling between monodomain BiFeO3 films and Co overlayer that is intrinsic (i.e., not dependent on domain walls). Direct coupling between BiFeO3 antiferromagnetic order and Co magnetization is observed, with ~ 90° in-plane Co moment rotation upon single-step switching that is reproducible for hundreds of cycles. This has important consequences for practical, low power non-volatile magnetoelectric devices utilizing BiFeO3.


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


Magnetic excitations of the charge stripe electrons below half doping in La2-xSrxNiO4 (x=0.45, 0.4)

PHYSICAL REVIEW B 95 (2017) ARTN 064403

PG Freeman, SR Giblin, K Hradil, RA Mole, P Cermak, D Prabhakaran


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


ARPES study of the epitaxially grown topological crystalline insulator SnTe(111)

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 219 (2017) 35-40

Y Zhang, Z Liu, B Zhou, Y Kim, L Yang, H Ryu, C Hwang, Y Chen, Z Hussain, Z-X Shen, S-K Mo


Signature of type-II Weyl semimetal phase in MoTe2.

Nature communications 8 (2017) 13973-

J Jiang, ZK Liu, Y Sun, HF Yang, CR Rajamathi, YP Qi, LX Yang, C Chen, H Peng, C-C Hwang, SZ Sun, S-K Mo, I Vobornik, J Fujii, SSP Parkin, C Felser, BH Yan, YL Chen

Topological Weyl semimetal (TWS), a new state of quantum matter, has sparked enormous research interest recently. Possessing unique Weyl fermions in the bulk and Fermi arcs on the surface, TWSs offer a rare platform for realizing many exotic physical phenomena. TWSs can be classified into type-I that respect Lorentz symmetry and type-II that do not. Here, we directly visualize the electronic structure of MoTe2, a recently proposed type-II TWS. Using angle-resolved photoemission spectroscopy (ARPES), we unravel the unique surface Fermi arcs, in good agreement with our ab initio calculations that have nontrivial topological nature. Our work not only leads to new understandings of the unusual properties discovered in this family of compounds, but also allows for the further exploration of exotic properties and practical applications of type-II TWSs, as well as the interplay between superconductivity (MoTe2 was discovered to be superconducting recently) and their topological order.


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


Suppression of electronic correlations by chemical pressure from FeSe to FeS

Phys. Rev. B 96, 121103(R) (2017) American Physical Society (2017)

P Reiss, MD Watson, TK Kim, AA Haghighirad, DN Woodruff, M Bruma, SJ Clarke, AI Coldea

Iron-based chalcogenides are complex superconducting systems in which orbitally-dependent electronic correlations play an important role. Here, using high-resolution angle-resolved photoemission spectroscopy, we investigate the effect of these electronic correlations outside the nematic phase in the tetragonal phase of superconducting FeSe1-xSx (x = 0; 0:18; 1). With increasing sulfur substitution, the Fermi velocities increase significantly and the band renormalizations are suppressed towards a factor of 1.5-2 for FeS. Furthermore, the chemical pressure leads to an increase in the size of the quasi-two dimensional Fermi surface, compared with that of FeSe, however, it remains smaller than the predicted one from first principle calculations for FeS. Our results show that the isoelectronic substitution is an effective way to tune electronic correlations in FeSe1-xSx, being weakened for FeS with a lower superconducting transition temperature. This suggests indirectly that electronic correlations could help to promote higher-Tc superconductivity in FeSe.


Spin Resonance Clock Transition of the Endohedral Fullerene ^{15}N@C_{60}.

Physical review letters 119 (2017) 140801-

RT Harding, S Zhou, J Zhou, T Lindvall, WK Myers, A Ardavan, GAD Briggs, K Porfyrakis, EA Laird

The endohedral fullerene ^{15}N@C_{60} has narrow electron paramagnetic resonance lines which have been proposed as the basis for a condensed-matter portable atomic clock. We measure the low-frequency spectrum of this molecule, identifying and characterizing a clock transition at which the frequency becomes insensitive to magnetic field. We infer a linewidth at the clock field of 100 kHz. Using experimental data, we are able to place a bound on the clock's projected frequency stability. We discuss ways to improve the frequency stability to be competitive with existing miniature clocks.


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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