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451 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I05-ARPES	Bonding states underpinning structural transitions in IrTe2 observed with micro-ARPES C. W. Nicholson , M. D. Watson , A. Pulkkinen , M. Rumo , G. Kremer , K. Y. Ma , F. O. Von Rohr , C. Cacho , C. Monney Physical Review B 110 DOI: 10.1103/PhysRevB.110.205123 Diamond Proposal Number(s): [25906] Open Access Show Abstract ▼ Abstract: Competing interactions in low-dimensional materials can produce nearly degenerate electronic and structural phases. We investigate structural phase transitions in layered IrTe2 for which a number of potential transition mechanisms have been postulated. The spatial coexistence of multiple phases on the micron scale has prevented a detailed analysis of the electronic structure. By exploiting micro-angle-resolved photoemission spectroscopy obtained with synchrotron radiation we extract the electronic structure of the multiple structural phases in IrTe2 in order to address the mechanism underlying the phase transitions. We find direct evidence of lowered energy states that appear in the low-temperature phases, states previously predicted by ab initio calculations and extended here. Our results validate a proposed scenario of bonding and antibonding states as the driver of the phase transitions.	Nov 2024
I11-High Resolution Powder Diffraction	Pseudo-easy-axis anisotropy in antiferromagnetic S = 1 diamond-lattice systems S. Vaidya , A. Hernández-Melián , J. P. Tidey , S. P. M. Curley , S. Sharma , P. Manuel , C. Wang , G. L. Hannaford , S. J. Blundell , Z. E. Manson , J. L. Manson , J. Singleton , T. Lancaster , R. D. Johnson , P. A. Goddard Physical Review B 110 DOI: 10.1103/PhysRevB.110.174438 Open Access Show Abstract ▼ Abstract: We investigate the magnetic properties of 𝑆=1 antiferromagnetic diamond-lattice, Ni⁢𝑋2⁢(pyrimidine)2 (𝑋=Cl, Br), hosting a single-ion anisotropy (SIA) orientation which alternates between neighboring sites. Through neutron diffraction measurements of the 𝑋=Cl compound, the ordered state spins are found to align collinearly along a pseduo-easy axis, a unique direction created by the intersection of two easy planes. Similarities in the magnetization, exhibiting spin-flop transitions, and the magnetic susceptibility in the two compounds imply that the same magnetic structure and a pseduo-easy axis is also present for 𝑋=Br. We estimate the Hamiltonian parameters by combining analytical calculations and Monte Carlo (MC) simulations of the spin-flop and saturation field. The MC simulations also reveal that the spin-flop transition occurs when the applied field is parallel to the pseduo-easy axis. Contrary to conventional easy-axis systems, there exist field directions perpendicular to the pseduo-easy axis for which the magnetic saturation is approached asymptotically and no symmetry-breaking phase transition is observed at finite fields.	Nov 2024
I10-Beamline for Advanced Dichroism - scattering	Switching of ferrotoroidal domains via an intermediate mixed state in the multiferroic Y-type hexaferrite Ba0.5Sr1.5Mg2Fe12O22 Jiahao Chen , Francis Chmiel , Jieyi Liu , Dharmalingam Prabhakaran , Paolo G. Radaelli , Roger Johnson Physical Review B 110 DOI: 10.1103/PhysRevB.110.134410 Diamond Proposal Number(s): [17388] Open Access Show Abstract ▼ Abstract: We report a detailed study of the magnetic field switching of ferrotoroidal/multiferroic domains in the Y-type hexaferrite compound Ba0.5⁢Sr1.5⁢Mg2⁢Fe12⁢O22. By combining data from superconducting quantum interference device (SQUID) magnetometry, magnetocurrent measurements, and resonant x-ray scattering experiments, we arrive at a complete description of the deterministic switching, which involves the formation of a temperature-dependent mixed state in low magnetic fields. This mechanism is likely to be shared by other members of the hexaferrite family, and presents a challenge for the development of high-speed read-write memory devices based on these materials.	Oct 2024
I06-Nanoscience (XPEEM)	Near-room-temperature ferrimagnetism and half-metallicity in disordered Ca1.5La0.5MnRuO6 A. G. Silva , R. B. Pontes , M. Boldrin , H. V. S. Pessoni , L. S. I. Veiga , J. R. Jesus , H. Fabrelli , A. R. C. Gonzaga , E. M. Bittar , L. Bufaiçal Physical Review B 110 DOI: 10.1103/PhysRevB.110.144415 Diamond Proposal Number(s): [31735] Show Abstract ▼ Abstract: The electron spin polarization on half-metallic double perovskites is usually conditioned to the ordered rock-salt arrangement of the transition-metal ions along the lattice. In this work, we investigate a polycrystalline sample of the Ca1.5⁢La0.5⁢MnRuO6 compound by employing x-ray powder diffraction, high-resolution transmission electron microscopy, x-ray absorption and magnetic circular dichroism at the Mn 𝐿2,3 and Ru 𝑀2,3 edges, magnetometry, electrical transport, and first-principles calculations in order to show that this is a fully disordered material exhibiting near-room-temperature ferrimagnetism and half-metallic conductivity, with significant intergrain tunneling magnetoresistance. These unprecedented results are compared to those of archetypical ordered double perovskites, and discussed in terms of the Mn and Ru valences and their orbital hybridization.	Oct 2024
I09-Surface and Interface Structural Analysis	Electronic structure and surface band bending of Sn-doped 𝛽-Ga2O3 thin films studied by X-ray photoemission spectroscopy and ab initio calculations Jiaye Zhang , Zhenni Yang , Siliang Kuang , Ziqi Zhang , Shenglong Wei , Joe Willis , Tien-Lin Lee , Piero Mazzolini , Oliver Bierwagen , Shanquan Chen , Zuhuang Chen , Duanyang Chen , Hongji Qi , David Scanlon , Kelvin H. L. Zhang Physical Review B 110 DOI: 10.1103/PhysRevB.110.115120 Diamond Proposal Number(s): [31069, 31681] Show Abstract ▼ Abstract: The bulk and surface electronic structures of Sn-doped 𝛽−Ga2⁢O3 thin films have been studied by soft and hard x-ray photoemission spectroscopy (soft PES at 1486.6 eV and HAXPES at 5920 eV). The experimental spectra are compared with density functional theory calculated density of states in the valence band and conduction band. Excellent agreement was found between experimental spectra and calculated density of states by taking into account the photoionization cross section of different orbitals involved in the valence and conduction bands. The electronic states derived from Ga 4⁢𝑠 character are selectively enhanced by HAXPES. This allows us to infer that the states at the conduction band and bottom of the valence band contain pronounced Ga 4⁢𝑠 character. The occupation of the lower conduction band in degenerately Sn-doped Ga2⁢O3 is clearly observed by HAXPES, which allows for direct measurement of Burstein-Moss shift and band-gap renormalization as a function of Sn doping. A comparison of the valence band spectra of Sn-doped Ga2⁢O3 films with Si-doped samples suggests that Sn doping has different effects on the electronic structure than Si doping. An in-gap electronic state is observed for Sn-doped Ga2⁢O3, which is attributed to self-compensating S⁢n2+ related defects. Furthermore, a larger band-gap renormalization is found in Sn-doped samples, because the Sn 5⁢𝑠 dopant orbital mixes strongly with the host Ga 4⁢𝑠 derived conduction band. Finally, a comparison of the valence band and core-level spectra excited with soft and hard x rays allows us to identify an upward band bending at the surface region of Sn-doped Ga2⁢O3 films.	Sep 2024
I05-ARPES	Novel electronic structures from anomalous stackings in NbS2 and MoS2 Matthew D. Watson , Mihir Date , Alex Louat , Niels B. M. Schroeter Physical Review B 110 DOI: 10.1103/PhysRevB.110.L121121 Diamond Proposal Number(s): [31067, 31222, 31407] Open Access Show Abstract ▼ Abstract: We show that in some transition metal dichalcogenides, minority regions of the cleaved sample surfaces show—unexpectedly and anomalously—a finite number of 2D electronic states instead of the expected 3D valence bands. In the case of NbS2, in addition to the typical spectrum associated with bulk 2Ha stacking, we also find minority regions with electronic structures consistent with few layers of 3R stacking. In MoS2, we find areas of both bulk 2Hc and 3R stackings, and regions exhibiting finite-layer quantization of both types. We further find evidence for a more exotic 4Ha stacking of MoS2, in which the valence band maximum is quasi-2D. The results highlight how variation of the interlayer stacking of van der Waals materials beyond the commonly reported bulk polytypes can yield novel electronic structures.	Sep 2024
I16-Materials and Magnetism	Anisotropic resonant scattering from uranium systems at the U 𝑀4edge E. Lawrence Bright , E. N. Ovchinnikova , L. M. Harding , D. G. Porter , R. Springell , V. E. Dmitrienko , R. Caciuffo , G. H. Lander Physical Review B 110 DOI: 10.1103/PhysRevB.110.125138 Diamond Proposal Number(s): [27807, 34651] Show Abstract ▼ Abstract: We have conducted a series of scattering experiments at the uranium 𝑀4 absorption edge on low-symmetry uranium compounds (U2⁢N3 and U3⁢O8) produced as epitaxial films. At weak and forbidden reflections, we find a resonant signal, independent of temperature, with an energy dependence resembling the imaginary part 𝑓″ of the scattering factor. The theory, using the fdmnes code, shows that these results can be reliably reproduced assuming that they originate from aspherical 5⁢𝑓 electron charge distributions around the U nucleus. Such effects arise from the intrinsic anisotropy of the 5⁢𝑓 shell and from the mixing of the 5⁢𝑓 electrons of uranium with the outer 2⁢𝑝 electrons of the anions. The good agreement between theory and experiment includes azimuthal scattering dependences, as well as polarization states of the scattered photons. The methodology reported here opens the way for a deeper understanding of the role the 5⁢𝑓 electrons in the bonding in actinide compounds.	Sep 2024
I16-Materials and Magnetism	Strain-induced antiferromagnetic domain switching via the spin Jahn-Teller effect Dylan Behr , Leonid S. Taran , Daniel G. Porter , Alessandro Bombardi , Dharmalingam Prabhakaran , Sergey V. Streltsov , Roger D. Johnson Physical Review B 110 DOI: 10.1103/PhysRevB.110.L060408 Diamond Proposal Number(s): [32034] Open Access Show Abstract ▼ Abstract: The spin Jahn-Teller effect, where a degeneracy of magnetic ground states is spontaneously lifted by structural distortions, lends itself to exploitation by the implied magnetoelastic coupling. CoTi2⁢O5 hosts a frustrated topology of magnetic interactions that could realize such coupling, since the observed magnetic ground state requires a spontaneous monoclinic distortion of the crystal. Using resonant elastic x-ray scattering to simultaneously probe the magnetic structure and lattice distortion of CoTi2⁢O5, we demonstrate near complete magnetic domain switching by an applied uniaxial stress that is conjugate to the monoclinic strain. Our results, supported by density functional theory calculations, confirm that CoTi2⁢O5 displays spin Jahn-Teller effects that can be understood in terms of modulated Heisenberg exchange interactions, and demonstrate the potential functionality of spin Jahn-Teller materials in spintronic devices sensitive to uniaxial strain.	Aug 2024
I21-Resonant Inelastic X-ray Scattering (RIXS)	Investigation of spin excitations and charge order in bulk crystals of the infinite-layer nickelate LaNiO 2 S. Hayashida , V. Sundaramurthy , P. Puphal , M. Garcia-Fernandez , K.-J. Zhou , B. Fenk , M. Isobe , M. Minola , Y.-M. Wu , Y. E. Suyolcu , P. A. Van Aken , B. Keimer , M. Hepting Physical Review B 109 DOI: 10.1103/PhysRevB.109.235106 Diamond Proposal Number(s): [33241] Open Access Show Abstract ▼ Abstract: Recent x-ray spectroscopic studies have revealed spin excitations and charge density waves in thin films of infinite-layer (IL) nickelates. However, clarifying whether the origin of these phenomena is intrinsic to the material class or attributable to impurity phases in the films has presented a major challenge. Here we utilize topotactic methods to synthesize bulk crystals of the IL nickelate LaNiO2 with crystallographically oriented surfaces. We examine these crystals using resonant inelastic x-ray scattering (RIXS) at the Ni 𝐿3-edge to elucidate the spin and charge correlations in the bulk of the material. While we detect the presence of prominent spin excitations in the crystals, fingerprints of charge order are absent at the ordering vectors identified in previous thin-film studies. These results contribute to the understanding of the bulk properties of LaNiO2 and establish topotactically synthesized crystals as viable complementary specimens for spectroscopic investigations.	Jun 2024
I21-Resonant Inelastic X-ray Scattering (RIXS)	Spin fluctuations sufficient to mediate superconductivity in nickelates Paul Worm , Qisi Wang , Motoharu Kitatani , Izabela Bialo , Qiang Gao , Xiaolin Ren , Jaewon Choi , Diana Csontosová , Ke-Jin Zhou , Xingjiang Zhou , Zhihai Zhu , Liang Si , Johan Chang , Jan M. Tomczak , Karsten Held Physical Review B 109 DOI: 10.1103/PhysRevB.109.235126 Diamond Proposal Number(s): [30189] Show Abstract ▼ Abstract: Infinite-layer nickelates show high-temperature superconductivity, and the experimental phase diagram agrees well with the one simulated within the dynamical vertex approximation (D⁢Γ⁢A). Here, we compare the spin-fluctuation spectrum behind these calculations to resonant inelastic x-ray scattering experiments. The overall agreement is good. This independent cross validation of the strength of spin fluctuations strongly supports the scenario, advanced by D⁢Γ⁢A, that spin fluctuations are the mediator of the superconductivity observed in nickelates.	Jun 2024

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