Publications


The science and art of seeing: Scope: monograph. Level: general reader

Contemporary Physics (2015)

SJ Blundell


Magnetic ground state of the two isostructual polymeric quantum magnets [Cu(HF2)(pyrazine)(2)]SbF6 and [Co(HF2)(pyrazine)(2)]SbF6 investigated with neutron powder diffraction

PHYSICAL REVIEW B 92 (2015) ARTN 134406

J Brambleby, PA Goddard, RD Johnson, J Liu, D Kaminski, A Ardavan, AJ Steele, SJ Blundell, T Lancaster, P Manuel, PJ Baker, J Singleton, SG Schwalbe, PM Spurgeon, HE Tran, PK Peterson, JF Corbey, JL Manson


New constraints on electron-beam induced halogen migration in apatite

AMERICAN MINERALOGIST 100 (2015) 281-293

MJ Stock, MCS Humphreys, VC Smith, RD Johnson, DM Pyle, EIMF


Weyl semimetal phase in the non-centrosymmetric compound TaAs

Nature Physics Nature Publishing Group 11 (2015) 728-732

Y Chen

Three-dimensional (3D) topologicalWeyl semimetals (TWSs) represent a state of quantum matter with unusual electronic structures that resemble both a ‘3D graphene’ and a topological insulator. Their electronic structure displays pairs of Weyl points (through which the electronic bands disperse linearly along all three momentum directions) connected by topological surface states, forming a unique arc-like Fermi surface (FS). Each Weyl point is chiral and contains half the degrees of freedom of a Dirac point, and can be viewed as a magnetic monopole in momentum space. By performing angle-resolved photoemission spectroscopy on the non-centrosymmetric compound TaAs, here we report its complete band structure, including the unique Fermi-arc FS and linear bulk band dispersion across the Weyl points, in agreement with the theoretical calculations1, 2. This discovery not only confirms TaAs as a 3DTWS, but also provides an ideal platform for realizing exotic physical phenomena (for example, negative magnetoresistance, chiral magnetic effects and the quantum anomalous Hall effect) which may also lead to novel future applications.


Two-dimensional Cs-vacancy superstructure in iron-based superconductor Cs0.8Fe1.6Se2

PHYSICAL REVIEW B 91 (2015) ARTN 144114

DG Porter, E Cemal, DJ Voneshen, K Refson, MJ Gutmann, A Bombardi, AT Boothroyd, A Krzton-Maziopa, E Pomjakushina, K Conder, JP Goff


Strong (pi, 0) spin fluctuations in beta-FeSe observed by neutron spectroscopy

PHYSICAL REVIEW B 91 (2015) ARTN 180501

MC Rahn, RA Ewings, SJ Sedlmaier, SJ Clarke, AT Boothroyd


Monoclinic crystal structure of alpha-RuCl3 and the zigzag antiferromagnetic ground state

PHYSICAL REVIEW B 92 (2015) ARTN 235119

RD Johnson, SC Williams, AA Haghighirad, J Singleton, V Zapf, P Manuel, II Mazin, Y Li, HO Jeschke, R Valenti, R Coldea


Magnetic proximity-enhanced Curie temperature of Cr-doped Bi2Se3 thin films

PHYSICAL REVIEW B 92 (2015) ARTN 094420

AA Baker, AI Figueroa, K Kummer, LJ Collins-McIntyre, T Hesjedal, G van der Laan


Massive Dirac Fermion Observed in Lanthanide-Doped Topological Insulator Thin Films.

Scientific reports 5 (2015) 15767-

SE Harrison, LJ Collins-McIntyre, P Schönherr, A Vailionis, V Srot, PA van Aken, AJ Kellock, A Pushp, SSP Parkin, JS Harris, B Zhou, YL Chen, T Hesjedal

The breaking of time reversal symmetry (TRS) in three-dimensional (3D) topological insulators (TIs), and thus the opening of a 'Dirac-mass gap' in the linearly dispersed Dirac surface state, is a prerequisite for unlocking exotic physical states. Introducing ferromagnetic long-range order by transition metal doping has been shown to break TRS. Here, we present the study of lanthanide (Ln) doped Bi2Te3, where the magnetic doping with high-moment lanthanides promises large energy gaps. Using molecular beam epitaxy, single-crystalline, rhombohedral thin films with Ln concentrations of up to ~35%, substituting on Bi sites, were achieved for Dy, Gd, and Ho doping. Angle-resolved photoemission spectroscopy shows the characteristic Dirac cone for Gd and Ho doping. In contrast, for Dy doping above a critical doping concentration, a gap opening is observed via the decreased spectral intensity at the Dirac point, indicating a topological quantum phase transition persisting up to room-temperature.


Spin pumping in ferromagnet-topological insulator-ferromagnet heterostructures.

Scientific Reports 5 (2015) 7907-

AA Baker, AI Figueroa, LJ Collins-McIntyre, G van der Laan, T Hesjedal

Topological insulators (TIs) are enticing prospects for the future of spintronics due to their large spin-orbit coupling and dissipationless, counter-propagating conduction channels in the surface state. However, a means to interact with and exploit the topological surface state remains elusive. Here, we report a study of spin pumping at the TI-ferromagnet interface, investigating spin transfer dynamics in a spin-valve like structure using element specific time-resolved x-ray magnetic circular dichroism, and ferromagnetic resonance. Gilbert damping increases approximately linearly with increasing TI thickness, indicating efficient behaviour as a spin sink. However, layer-resolved measurements suggest that a dynamic coupling is limited. These results shed new light on the spin dynamics of this novel material class, and suggest great potential for TIs in spintronic devices, through their novel magnetodynamics that persist even up to room temperature.


Robustness of superconductivity to structural disorder in Sr-0.3(NH2)(y)(NH3)(1-y)Fe2Se2

PHYSICAL REVIEW B 92 (2015) ARTN 134517

FR Foronda, S Ghannadzadeh, SJ Sedlmaier, JD Wright, K Burns, SJ Cassidy, PA Goddard, T Lancaster, SJ Clarke, SJ Blundell


Topological computation based on direct magnetic logic communication.

Scientific reports 5 (2015) 15773-

S Zhang, AA Baker, S Komineas, T Hesjedal

Non-uniform magnetic domains with non-trivial topology, such as vortices and skyrmions, are proposed as superior state variables for nonvolatile information storage. So far, the possibility of logic operations using topological objects has not been considered. Here, we demonstrate numerically that the topology of the system plays a significant role for its dynamics, using the example of vortex-antivortex pairs in a planar ferromagnetic film. Utilising the dynamical properties and geometrical confinement, direct logic communication between the topological memory carriers is realised. This way, no additional magnetic-to-electrical conversion is required. More importantly, the information carriers can spontaneously travel up to ~300 nm, for which no spin-polarised current is required. The derived logic scheme enables topological spintronics, which can be integrated into large-scale memory and logic networks capable of complex computations.


Transverse field muon-spin rotation signature of the skyrmion-lattice phase in Cu2OSeO3

Phys Rev B. Solid State 91 (2015) 224408

T Lancaster, RC Williams, IO Thomas, F Xiao, FL Pratt, SJ Blundell, JC Loudon, T Hesjedal, SJ Clark, PD Hatton, M Ciomaga Hatnean, DS Keeble, G Balakrishnan

We present the results of transverse field (TF) muon-spin rotation (μ+SR) measurements on Cu2OSeO3, which has a skyrmion-lattice (SL) phase. We measure the response of the TF μ+SR signal in that phase along with the surrounding ones, and suggest how the phases might be distinguished using the results of these measurements. Dipole field simulations support the conclusion that the muon is sensitive to the SL via the TF line shape and, based on this interpretation, our measurements suggest that the SL is quasistatic on a time scale τ>100 ns.


Crystal field states of Tb3+ in the pyrochlore spin liquid Tb2Ti2O7 from neutron spectroscopy

PHYSICAL REVIEW B 91 (2015) ARTN 224430

AJ Princep, HC Walker, DT Adroja, D Prabhakaran, AT Boothroyd


Suppression of orbital ordering by chemical pressure in FeSe1-xSx

Phys. Rev. B 92, 121108(R) (2015) (2015)

MD Watson, TK Kim, AA Haghighirad, SF Blake, NR Davies, M Hoesch, T Wolf, AI Coldea

We report a high-resolution angle-resolved photo-emission spectroscopy study of the evolution of the electronic structure of FeSe1-xSx single crystals. Isovalent S substitution onto the Se site constitutes a chemical pressure which subtly modifies the electronic structure of FeSe at high temperatures and induces a suppression of the tetragonal-symmetry-breaking structural transition temperature from 87K to 58K for x=0.15. With increasing S substitution, we find smaller splitting between bands with dyz and dxz orbital character and weaker anisotropic distortions of the low temperature Fermi surfaces. These effects evolve systematically as a function of both S substitution and temperature, providing strong evidence that an orbital ordering is the underlying order parameter of the structural transition in FeSe1-xSx. Finally, we detect the small inner hole pocket for x=0.12, which is pushed below the Fermi level in the orbitally-ordered low temperature Fermi surface of FeSe.


Structural properties and growth mechanism of Cd3As2 nanowires

APPLIED PHYSICS LETTERS 106 (2015) ARTN 013115

P Schoenherr, T Hesjedal


Dichotomy between the hole and electrons behavior in the multiband FeSe probed by ultra high magnetic fields

Phys. Rev. Lett. 115, 027006 (2015) (2015)

MD Watson, T Yamashita, S Kasahara, W Knafo, M Nardone, J Beard, F Hardy, A McCollam, A Narayanan, SF Blake, T Wolf, AA Haghighirad, C Meingast, AJ Schofield, HV Lohneysen, Y Matsuda, AI Coldea, T Shibauchi

Magnetoresistivity \r{ho}xx and Hall resistivity \r{ho}xy in ultra high magnetic fields up to 88T are measured down to 0.15K to clarify the multiband electronic structure in high-quality single crystals of superconducting FeSe. At low temperatures and high fields we observe quantum oscillations in both resistivity and Hall effect, confirming the multiband Fermi surface with small volumes. We propose a novel and independent approach to identify the sign of corresponding cyclotron orbit in a compensated metal from magnetotransport measurements. The observed significant differences in the relative amplitudes of the quantum oscillations between the \r{ho}xx and \r{ho}xy components, together with the positive sign of the high-field \r{ho}xy , reveal that the largest pocket should correspond to the hole band. The low-field magnetotransport data in the normal state suggest that, in addition to one hole and one almost compensated electron bands, the orthorhombic phase of FeSe exhibits an additional tiny electron pocket with a high mobility.


Unified theory of spiral magnetism in the harmonic-honeycomb iridates alpha, beta, and gamma Li2IrO3

PHYSICAL REVIEW B 91 (2015) ARTN 245134

I Kimchi, R Coldea, A Vishwanath


Study of Ho-doped Bi2Te3 topological insulator thin films

APPLIED PHYSICS LETTERS 107 (2015) ARTN 182406

SE Harrison, LJ Collins-McIntyre, SL Zhang, AA Baker, AI Figueroa, AJ Kellock, A Pushp, YL Chen, SSP Parkin, JS Harris, G van der Laan, T Hesjedal


Erratum: Emergence of the nematic electronic state in FeSe (Physical Review B - Condensed Matter and Materials Physics (2015) 91 (155106))

Physical Review B - Condensed Matter and Materials Physics 91 (2015)

MD Watson, TK Kim, AA Haghighirad, NR Davies, A McCollam, A Narayanan, SF Blake, YL Chen, S Ghannadzadeh, AJ Schofield, M Hoesch, C Meingast, T Wolf, AI Coldea

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