Publications


Observation of the topological surface state in the nonsymmorphic topological insulator KHgSb

PHYSICAL REVIEW B 96 (2017) ARTN 165143

AJ Liang, J Jiang, MX Wang, Y Sun, N Kumar, C Shekhar, C Chen, H Peng, CW Wang, X Xu, HF Yang, ST Cui, GH Hong, Y-Y Xia, S-K Mo, Q Gao, XJ Zhou, LX Yang, C Felser, BH Yan, ZK Liu, YL Chen


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


Inelastic neutron scattering investigations of an anisotropic hybridization gap in the kondo insulators: CeT<inf>2</inf>Al<inf>10</inf>(T=Fe, Ru and Os)

Solid State Phenomena 257 (2017) 11-25

DT Adroja, Y Muro, T Takabatake, MD Le, HC Walker, KA McEwen, AT Boothroyd

� 2017 Trans Tech Publications, Switzerland. The recent discovery of topological Kondo insulating behaviour in strongly correlated electron systems has generated considerable interest in Kondo insulators both experimentally and theoretically. The Kondo semiconductors CeT2Al10(T=Fe, Ru and Os) possessing a c-f hybridization gap have received considerable attention recently because of the unexpected high magnetic ordering temperature of CeRu2Al10(TN=27 K) and CeOs2Al10(TN=28.5 K) and the Kondo insulating behaviour observed in the valence fluctuating compound CeFe2Al10with a paramagnetic ground state down to 50 mK. We are investigating this family of compounds, both in polycrystalline and single crystal form, using inelastic neutron scattering to understand the role of anisotropic c-f hybridization on the spin gap formation as well as on their magnetic properties. We have observed a clear sign of a spin gap in all three compounds from our polycrystalline study as well as the existence of a spin gap above the magnetic ordering temperature in T=Ru and Os. Our inelastic neutron scattering studies on single crystals of CeRu2Al10and CeOs2Al10revealed dispersive gapped spin wave excitations below TN. Analysis of the spin wave spectrum reveals the presence of strong anisotropic exchange, along the c-axis (or z-axis) stronger than in the ab-plane. These anisotropic exchange interactions force the magnetic moment to align along the c-axis, competing with the single ion crystal field anisotropy, which prefers moments along the a-axis. In the paramagnetic state (below 50 K) of the Kondo insulator CeFe2Al10, we have also observed dispersive gapped magnetic excitations which transform into quasi-elastic scattering on heating to 100 K. We will discuss the origin of the anisotropic hybridization gap in CeFe2Al10based on theoretical models of heavy-fermion semiconductors.


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


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.


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


Crystal structure and magnetic modulation in beta-Ce2O2FeSe2

PHYSICAL REVIEW MATERIALS 1 (2017) ARTN 034403

C-H Wang, CM Ainsworth, SD Champion, GA Stewart, MC Worsdale, T Lancaster, SJ Blundell, HEA Brand, JSO Evans


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


Lifshitz Transitions Induced by Temperature and Surface Doping in Type-II Weyl Semimetal Candidate T-d-WTe2

PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS 11 (2017) ARTN 1700209

Q Zhang, Z Liu, Y Sun, H Yang, J Jiang, S-K Mo, Z Hussain, X Qian, L Fu, S Yao, M Lu, C Felser, B Yan, Y Chen, L Yang


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.


Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-point fluctuations, and possible two-dimensional universal behavior

PHYSICAL REVIEW B 95 (2017) ARTN 024404

J Brambleby, PA Goddard, J Singleton, M Jaime, T Lancaster, L Huang, J Wosnitza, CV Topping, KE Carreiro, HE Tran, ZE Manson, JL Manson


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


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.


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


Strain and Magnetic Field Induced Spin-Structure Transitions in Multiferroic BiFeO3

ADVANCED MATERIALS 29 (2017) UNSP 1602327

A Agbelele, D Sando, C Toulouse, C Paillard, RD Johnson, R Ruffer, AF Popkov, C Carretero, P Rovillain, J-M Le Breton, B Dkhil, M Cazayous, Y Gallais, M-A Measson, A Sacuto, P Manuel, AK Zvezdin, A Barthelemy, J Juraszek, M Bibes


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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