Nodal multigap superconductivity in KCa2Fe4As4F2

Physical Review B 97 (2018) 060509(R)

M Smidman, FKK Kirschner, DT Adroja, AD Hillier, F Lang, Z-C Zhang, G-H Cao, SJ Blundell

Implications of bond disorder in a S=1 kagome lattice.

Scientific reports 8 (2018) 4745-4745

JL Manson, J Brambleby, PA Goddard, PM Spurgeon, JA Villa, J Liu, S Ghannadzadeh, F Foronda, J Singleton, T Lancaster, SJ Clark, IO Thomas, F Xiao, RC Williams, FL Pratt, SJ Blundell, CV Topping, C Baines, C Campana, B Noll

Strong hydrogen bonds such as F···H···F offer new strategies to fabricate molecular architectures exhibiting novel structures and properties. Along these lines and, to potentially realize hydrogen-bond mediated superexchange interactions in a frustrated material, we synthesized [H2F]2[Ni3F6(Fpy)12][SbF6]2 (Fpy = 3-fluoropyridine). It was found that positionally-disordered H2F+ ions link neutral NiF2(Fpy)4 moieties into a kagome lattice with perfect 3-fold rotational symmetry. Detailed magnetic investigations combined with density-functional theory (DFT) revealed weak antiferromagnetic interactions (J ~ 0.4 K) and a large positive-D of 8.3 K with ms = 0 lying below ms = ±1. The observed weak magnetic coupling is attributed to bond-disorder of the H2F+ ions which leads to disrupted Ni-F···H-F-H···F-Ni exchange pathways. Despite this result, we argue that networks such as this may be a way forward in designing tunable materials with varying degrees of frustration.

Extreme Sensitivity of a Topochemical Reaction to Cation Substitution: SrVO2H versus SrV1- xTi xO1.5H1.5.

Inorganic chemistry 57 (2018) 2890-2898

M Amano Patino, D Zeng, SJ Blundell, JE McGrady, MA Hayward

The anion-ordered oxide-hydride SrVO2H is an antiferromagnetic insulator due to strong correlations between vanadium d electrons. In an attempt to hole-dope SrVO2H into a metallic state, a strategy of first preparing SrV1- xTi xO3 phases and then converting them to the corresponding SrV1- xTi xO2H phases via reaction with CaH2 was followed. This revealed that the solid solution between SrVO3 and SrTiO3 is only stable at high temperature. In addition, reactions between SrV0.95Ti0.05O3 and CaH2 were observed to yield SrV0.95Ti0.05O1.5H1.5 not SrV0.95Ti0.05O2H. This dramatic change in reactivity for a very modest change in initial chemical composition is attributed to an electronic destabilization of SrVO2H on titanium substitution. Density functional theory calculations indicate that the presence of an anion-ordered, tetragonal SrMO2H phase is uniquely associated with a d2 electron count and that titanium substitution leads to an electronic destabilization of SrV1- xTi xO2H phases, which, ultimately, drives further reaction of SrV1- xTi xO2H to SrV1- xTi xO1.5H1.5. The observed sensitivity of the reaction products to the chemical composition of initial phases highlights some of the difficulties associated with electronically doping metastable materials prepared by topochemical reactions.

LaSr3 NiRuO4 H4 : A 4d Transition-Metal Oxide-Hydride Containing Metal Hydride Sheets.

Angewandte Chemie (International ed. in English) (2018)

L Jin, M Lane, D Zeng, FKK Kirschner, F Lang, P Manuel, SJ Blundell, JE McGrady, MA Hayward

The synthesis of the first 4d transition metal oxide-hydride, LaSr3 NiRuO4 H4 , is prepared via topochemical anion exchange. Neutron diffraction data show that the hydride ions occupy the equatorial anion sites in the host lattice and as a result the Ru and Ni cations are located in a plane containing only hydride ligands, a unique structural feature with obvious parallels to the CuO2 sheets present in the superconducting cuprates. DFT calculations confirm the presence of S=1/2  Ni+ and S=0, Ru2+ centers, but neutron diffraction and μSR data show no evidence for long-range magnetic order between the Ni centers down to 1.8 K. The observed weak inter-cation magnetic coupling can be attributed to poor overlap between Ni 3dz2 and H 1s in the super-exchange pathways.

Comparative study of the magnetic properties of La3Ni2B ' O-9 for B ' = Nb, Ta or Sb


C-M Chin, PD Battle, SJ Blundell, E Hunter, F Lang, M Hendrickx, RP Sena, J Hadermann

Author Correction: How to probe the spin contribution to momentum relaxation in topological insulators.

Nature communications 9 (2018) 729-

M-S Nam, BH Williams, Y Chen, S Contera, S Yao, M Lu, Y-F Chen, GA Timco, CA Muryn, REP Winpenny, A Ardavan

The original version of this Article contained an error in the spelling of the author Benjamin H. Williams, which was incorrectly given as Benjamin H. Willams. This has now been corrected in both the PDF and HTML versions of the Article.

How to probe the spin contribution to momentum relaxation in topological insulators (vol 8, 2017)


M-S Nam, BH Willams, Y Chen, S Contera, S Yao, M Lu, Y-F Chen, GA Timco, CA Muryn, REP Winpenny, A Ardavan

Author Correction: How to probe the spin contribution to momentum relaxation in topological insulators.

Nat Commun 9 (2018) 729-

M-S Nam, BH Williams, Y Chen, S Contera, S Yao, M Lu, Y-F Chen, GA Timco, CA Muryn, REP Winpenny, A Ardavan

The original version of this Article contained an error in the spelling of the author Benjamin H. Williams, which was incorrectly given as Benjamin H. Willams. This has now been corrected in both the PDF and HTML versions of the Article.

Two-gap superconductivity with line nodes in CsCa2Fe4As4F2

PHYSICAL REVIEW B 97 (2018) ARTN 060506

FKK Kirschner, DT Adroja, Z-C Wang, F Lang, M Smidman, PJ Baker, G-H Cao, SJ Blundell

Magnetic edge states and coherent manipulation of graphene nanoribbons.

Nature 557 (2018) 691-695

M Slota, A Keerthi, WK Myers, E Tretyakov, M Baumgarten, A Ardavan, H Sadeghi, CJ Lambert, A Narita, K Müllen, L Bogani

Graphene, a single-layer network of carbon atoms, has outstanding electrical and mechanical properties 1 . Graphene ribbons with nanometre-scale widths2,3 (nanoribbons) should exhibit half-metallicity 4 and quantum confinement. Magnetic edges in graphene nanoribbons5,6 have been studied extensively from a theoretical standpoint because their coherent manipulation would be a milestone for spintronic 7 and quantum computing devices 8 . However, experimental investigations have been hampered because nanoribbon edges cannot be produced with atomic precision and the graphene terminations that have been proposed are chemically unstable 9 . Here we address both of these problems, by using molecular graphene nanoribbons functionalized with stable spin-bearing radical groups. We observe the predicted delocalized magnetic edge states and test theoretical models of the spin dynamics and spin-environment interactions. Comparison with a non-graphitized reference material enables us to clearly identify the characteristic behaviour of the radical-functionalized graphene nanoribbons. We quantify the parameters of spin-orbit coupling, define the interaction patterns and determine the spin decoherence channels. Even without any optimization, the spin coherence time is in the range of microseconds at room temperature, and we perform quantum inversion operations between edge and radical spins. Our approach provides a way of testing the theory of magnetism in graphene nanoribbons experimentally. The coherence times that we observe open up encouraging prospects for the use of magnetic nanoribbons in quantum spintronic devices.

Proposal for the detection of magnetic monopoles in spin ice via nanoscale magnetometry

PHYSICAL REVIEW B 97 (2018) ARTN 140402

FKK Kirschner, F Flicker, A Yacoby, NY Yao, SJ Blundell

Endohedral Metallofullerene as Molecular High Spin Qubit: Diverse Rabi Cycles in Gd2@C79N.

Journal of the American Chemical Society 140 (2018) 1123-1130

Z Hu, B-W Dong, Z Liu, J-J Liu, J Su, C Yu, J Xiong, D-E Shi, Y Wang, B-W Wang, A Ardavan, Z Shi, S-D Jiang, S Gao

An anisotropic high-spin qubit with long coherence time could scale the quantum system up. It has been proposed that Grover's algorithm can be implemented in such systems. Dimetallic aza[80]fullerenes M2@C79N (M = Y or Gd) possess an unpaired electron located between two metal ions, offering an opportunity to manipulate spin(s) protected in the cage for quantum information processing. Herein, we report the crystallographic determination of Gd2@C79N for the first time. This molecular magnet with a collective high-spin ground state (S = 15/2) generated by strong magnetic coupling (JGd-Rad = 350 ± 20 cm-1) has been unambiguously validated by magnetic susceptibility experiments. Gd2@C79N has quantum coherence and diverse Rabi cycles, allowing arbitrary superposition state manipulation between each adjacent level. The phase memory time reaches 5 μs at 5 K by dynamic decoupling. This molecule fulfills the requirements of Grover's searching algorithm proposed by Leuenberger and Loss.

How to probe the spin contribution to momentum relaxation in topological insulators.

Nat Commun 9 (0) 56-

M-S Nam, BH Williams, Y Chen, S Contera, S Yao, M Lu, Y-F Chen, GA Timco, CA Muryn, REP Winpenny, A Ardavan

Topological insulators exhibit a metallic surface state in which the directions of the carriers' momentum and spin are locked together. This characteristic property, which lies at the heart of proposed applications of topological insulators, protects carriers in the surface state from back-scattering unless the scattering centres are time-reversal symmetry breaking (i.e. magnetic). Here, we introduce a method of probing the effect of magnetic scattering by decorating the surface of topological insulators with molecules, whose magnetic degrees of freedom can be engineered independently of their electrostatic structure. We show that this approach allows us to separate the effects of magnetic and non-magnetic scattering in the perturbative limit. We thereby confirm that the low-temperature conductivity of SmB6 is dominated by a surface state and that the momentum of quasiparticles in this state is particularly sensitive to magnetic scatterers, as expected in a topological insulator.

Comparative study of the magnetic properties of La<inf>3</inf>Ni<inf>2</inf>B′O<inf>9</inf>for B′ = Nb, Taor Sb

Journal of Solid State Chemistry 258 (2018) 825-834

CM Chin, PD Battle, SJ Blundell, E Hunter, F Lang, M Hendrickx, R Paria Sena, J Hadermann

© 2017 Elsevier Inc. Polycrystalline samples of La 3 Ni 2 NbO 9 and La 3 Ni 2 TaO 9 have been characterised by X-ray and neutron diffraction, electron microscopy, magnetometry and muon spin relaxation (µSR); the latter technique was also applied to La 3 Ni 2 SbO 9 . On the length scale of a neutron diffraction experiment, the six-coordinate sites of the monoclinic perovskite structure are occupied in a 1:1 ordered manner by Ni and a random ⅓Ni/⅔B′ mixture. Electron microscopy demonstrated that this 1:1 ordering is maintained over microscopic distances, although diffuse scattering indicative of short-range ordering on the mixed site was observed. No magnetic Bragg scattering was observed in neutron diffraction patterns collected from La 3 Ni 2 B′O 9 (B′ = Nb or Ta) at 5 K although in each case µSR identified the presence of static spins below 30 K. Magnetometry showed that La 3 Ni 2 NbO 9 behaves as a spin glass below 29 K but significant short-range interactions are present in La 3 Ni 2 TaO 9 below 85 K. The contrasting properties of these compounds are discussed in terms of their microstructure.

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

Room-temperature helimagnetism in FeGe thin films.

Scientific reports 7 (2017) 123-

SL Zhang, I Stasinopoulos, T Lancaster, F Xiao, A Bauer, F Rucker, AA Baker, AI Figueroa, Z Salman, FL Pratt, SJ Blundell, T Prokscha, A Suter, J Waizner, M Garst, D Grundler, G van der Laan, C Pfleiderer, T Hesjedal

Chiral magnets are promising materials for the realisation of high-density and low-power spintronic memory devices. For these future applications, a key requirement is the synthesis of appropriate materials in the form of thin films ordering well above room temperature. Driven by the Dzyaloshinskii-Moriya interaction, the cubic compound FeGe exhibits helimagnetism with a relatively high transition temperature of 278 K in bulk crystals. We demonstrate that this temperature can be enhanced significantly in thin films. Using x-ray scattering and ferromagnetic resonance techniques, we provide unambiguous experimental evidence for long-wavelength helimagnetic order at room temperature and magnetic properties similar to the bulk material. We obtain α intr = 0.0036 ± 0.0003 at 310 K for the intrinsic damping parameter. We probe the dynamics of the system by means of muon-spin rotation, indicating that the ground state is reached via a freezing out of slow dynamics. Our work paves the way towards the fabrication of thin films of chiral magnets that host certain spin whirls, so-called skyrmions, at room temperature and potentially offer integrability into modern electronics.

Crystal structure and magnetic modulation in beta-Ce2O2FeSe2


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

Quantum-critical spin dynamics in a Tomonaga-Luttinger liquid studied with muon-spin relaxation

PHYSICAL REVIEW B 95 (2017) ARTN 020402

JS Moller, T Lancaster, SJ Blundell, FL Pratt, PJ Baker, F Xiao, RC Williams, W Hayes, MM Turnbul, CP Landee

Emergence, causation and storytelling: Condensed matter physics and the limitations of the human mind

Philosophica 92 (2017) 139-164

SJ Blundell

The physics of matter in the condensed state is concerned with problems in which the number of constituent particles is vastly greater than can be easily comprehended. The inherent physical limitations of the human mind are fundamental and restrict the way in which we can interact with and learn about the universe. This presents challenges for developing scientific explanations that are met by emergent narratives, concepts and arguments that have a nontrivial relationship to the underlying microphysics. By examining examples within condensed matter physics, and also from cellular automata, I show how such emergent narratives efficiently describe elements of reality.

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.