Magnetic excitations observed by means of inelastic neutron scattering in polycrystalline

Bouvet, A.; Kasuya, T.; Bonnet, Michel; Regnault, L.P.; Rossat‐Mignod, J.; Fumitoshi, Iga; Fåk, B.; Severing, A.

doi:10.1088/0953-8984/10/25/016

Cited by 56 publications

(70 citation statements)

References 17 publications

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“…The quasiparticle spectrum of SmB 6 is significantly renormalized by interactions in a temperaturedependent manner 13 . Even more strikingly, inelastic neutron scattering (INS) 5,9,14,15 has identified a coherent collective mode in SmB 6 . The energy of this mode is smaller than the quasiparticle excitation gap (charge gap), and thus protects it from decay.…”

Section: Introductionmentioning

confidence: 99%

In-gap collective mode spectrum of the topological Kondo insulatorSmB6

Fuhrman

Nikolić

2014

Phys. Rev. B

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Samarium hexaboride (SmB6) is the first strongly correlated material with a recognized nontrivial band-structure topology. Its electron correlations are seen by inelastic neutron scattering as a coherent collective excitation at the energy of 14 meV. Here we calculate the spectrum of this mode using a perturbative slave boson method. Our starting point is the recently constructed Anderson model that properly captures the band-structure topology of SmB6. Most self-consistent renormalization effects are captured by a few phenomenological parameters whose values are fitted to match the calculated and experimentally measured mode spectrum in the first Brillouin zone. A simple band-structure of low-energy quasiparticles in SmB6 is also modeled through this fitting procedure, because the important renormalization effects due to Coulomb interactions are hard to calculate by ab-initio methods. Despite involving uncontrolled approximations, the slave boson calculation is capable of producing a fairly good quantitative match of the energy spectrum, and a qualitative match of the spectral weight throughout the first Brillouin zone. We find that the "fitted" band-structure required for this match indeed puts SmB6 in the class of strong topological insulators. Our analysis thus provides a detailed physical picture of how the SmB6 band topology arises from strong electron interactions, and paints the collective mode as magnetically active exciton.

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Section: Introductionmentioning

confidence: 99%

In-gap collective mode spectrum of the topological Kondo insulatorSmB6

Fuhrman

Nikolić

2014

Phys. Rev. B

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“…7 In-gap states are also known to exist for FeSi and YbB 12 and are thought to be a common feature in all Kondo insulators. 3,14,21,22 In-gap states can be intrinsic or arise from defects. Inherent to hexaboride crystals is a boron deficiency, which plays a significant role when the cation is divalent, e.g., for the semimetal EuB 6 , the insulator CaB 6 , 23 and the semiconductor SmB 6 .…”

Section: Introductionmentioning

confidence: 99%

High-field suppression of in-gap states in the Kondo insulatorSmB6

et al. 2007

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The controversial ground-state properties of the Kondo insulator SmB 6 have been investigated using 11 B NMR in very high magnetic fields up to 37 T. We find evidence that, following the development of a gap in the conduction-band density of states below 100 K, the in-gap states dominate the nuclear relaxation at temperatures less than 10 K. The Korringa product 1 / K 2 T 1 T exhibits anomalous behavior in this range and the application of high magnetic fields leads to suppression of nuclear relaxation. The hybridization gap, however, remains open up to 37 T. The behavior of the relaxation at low temperatures suggests a strong field dependence of the in-gap states and rules out the possibility that bound states arise from B 6 vacancies. A simple densityof-states model and a band scheme are introduced to account for these observations.

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“…The electron band-structure itself is renormalized and effectively shows temperature dependence 34 . More importantly, coherent collective modes of the paramagnon type have been seen in Kondo insulators 14,18,35,36 like SmB 6 . These modes can be understood as excitons of hybridized particle-hole pairs 13,20 whose binding is mediated by the quantum fluctuations of Kondo singlets, as illustrated by the Feynman diagrams in Fig.2.…”

Section: B Correlations Due To Coulomb Interactionsmentioning

confidence: 99%

“…[10][11][12][13][14][15][16][17][18][19][20] and iridium oxides (Pr 2 Ir 2 O 7 , Sr 2 IrO 4 , Na 2 IrO 3 , etc.) [21][22][23][24][25][26][27] .…”

Section: Introductionmentioning

confidence: 99%

“…The Fermi energy of a Kondo insulator lies within a small temperature-dependent bandgap 34 . Neutron scattering experiments have revealed a gapped coherent collective mode with a fairly narrow dispersion that also resides inside the bandgap 14,18,35,36 . The slave boson theory of Kondo materials views this mode as an exciton, which is created by the Coulomb interactions among the narrow-band f electrons and protected against decay by the material's bandgap 13,20 .…”

Section: Introductionmentioning

confidence: 99%

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Two-dimensional heavy fermions on the strongly correlated boundaries of Kondo topological insulators

Nikolić¹

2014

Phys. Rev. B

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Samarium hexaboride (SmB6), a representative Kondo insulator, has been characterized recently as a likely topological insulator. It is also a material with strong electron correlations, evident by the temperature dependence of its bandgap and the existence of a nearly flat collective mode whose energy lies within the bandgap. Similar strong correlations can affect or even destabilize the two-dimensional metallic state of topological origin at the crystal boundary. Here we construct the minimal lattice model of the correlated boundary of topological Kondo insulators, and make phenomenological predictions for its possible ground states. Depending on the microscopic properties of the interface between the topological Kondo material and a conventional insulator, the boundary metal can exhibit a varied degree of hybridization between the d and f orbitals of the rare earth element, yielding a rich two-dimensional heavy fermion phenomenology. A pronounced participation of the f orbitals is expected to create a heavy fermion Dirac metal, possibly unstable to a spin density wave, electron localization or even superconductivity. The opposite limit of "localized magnetic moments" helped by the partial Kondo screening on the crystal boundary can bring about a non-Fermi liquid of d electrons that exhibits two-dimensional quantum electrodynamics, or other unconventional states. In addition, ultra-thin films made from topological Kondo insulators could open the possibility of creating exotic incompressible quantum liquids with non-Abelian fractional excitations, whose dynamics shaped by the strong Rashba spin-orbit coupling resembles that of fractional quantum Hall systems.

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Magnetic excitations observed by means of inelastic neutron scattering in polycrystalline

Cited by 56 publications

References 17 publications

In-gap collective mode spectrum of the topological Kondo insulatorSmB6

In-gap collective mode spectrum of the topological Kondo insulatorSmB6

High-field suppression of in-gap states in the Kondo insulatorSmB6

Two-dimensional heavy fermions on the strongly correlated boundaries of Kondo topological insulators

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