Polarized-Neutron Study of Spin Dynamics in the Kondo Insulator<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>YbB</mml:mi><mml:mn>12</mml:mn></mml:msub></mml:math>

Nemkovski, K. S.; Mignot, J.-M.; Alekseev, P. A.; Ivanov, A.; Nefeodova, E. V.; Rybina, A. V.; Regnault, L.P.; Iga, Fumitoshi; Takabatake, Toshiro

doi:10.1103/physrevlett.99.137204

Cited by 56 publications

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“…YbB 12 is a typical Kondo insulator [2,3] with a fluctuating Yb valence around 2.9+ [4,5]. According to infrared spectroscopy studies [6], the Drude response is sharply decreased below ∼80 K and an indirect gap of ∼15 meV opens at 8 K. Inelastic neutron scattering studies reported the spin gap of 15 meV in the insulating state [7,8]. This crossover is frequently explained by a narrow-gap formation due to hybridization between the conduction band electrons and the localized f electrons (c-f hybridization) within the scheme of the periodic Anderson model.…”

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Hybridization gap formation in the Kondo insulatorYbB12observed using time-resolved photoemission spectroscopy

et al. 2015

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A detailed low-energy electronic structure of a Kondo insulator YbB12 was revealed by a synergetic combination of ultrahigh-resolution laser photoemission spectroscopy (PES) and time-resolved PES. The former confirmed a 25-meV pseudogap corresponding to the Kondo temperature of this material, and more importantly, it revealed that a 15-meV gap and a Kondo-peak feature developed below a crossover temperature T * ∼ 110 K. In harmony with this, the latter discovered a very long recombination time exceeding 100 ps below ∼T * . This is a clear manifestation of photoexcited carriers due to the bottleneck in the recovery dynamics, which is interpreted as a developing hybridization gap of a hard gap. [4,5]. According to infrared spectroscopy studies [6], the Drude response is sharply decreased below ∼80 K and an indirect gap of ∼15 meV opens at 8 K. Inelastic neutron scattering studies reported the spin gap of 15 meV in the insulating state [7,8]. This crossover is frequently explained by a narrow-gap formation due to hybridization between the conduction band electrons and the localized f electrons (c-f hybridization) within the scheme of the periodic Anderson model. However, there is increasing evidence that some metallic states persist within the gap of many Kondo insulators, making elusive whether the low-temperature (T ) gap is a real charge gap or a pseudogap. For example, the resistivity is still as low as ∼1 Ω cm at low T in high-quality single crystals of some Kondo insulators, such as YbB 12 [3] and SmB 6 [9]. Photoemission spectroscopy (PES) studies [10][11][12][13][14] reported a pseudogap feature (<20 meV) that can be interpreted as a hybridization gap, but the finite spectral weight still remained around the Fermi level E F . In addition, tunneling spectra in YbB 12 exhibit that a finite state persists at the zero-bias voltage [15,16].In this Rapid Communication, to settle the above controversy, we investigate the electronic states within the * Present address: Department of Physics, University of Tokyo, Kashiwa, Chiba 277-8561, Japan pseudogap as well as its evolution on cooling by an unprecedented energy resolution set to 1 meV using ultrahigh-resolution laser PES [17]. Furthermore, we employed time-resolved PES (TrPES) with a pump-probe method and investigate the nonequilibrium electron dynamics of YbB 12 at various temperatures. The recovery time from photoexcited nonequilibrium states is the measure of a charge gap: If there is a gap as in insulators, semiconductors, or nodeless superconductors, the electronic recovery time will become exceedingly long in comparison with a typical metal [18]. Such behavior was reported in past TrPES studies on typical semiconducting materials, such as GaAs and Si [19]. Since TrPES provides direct information of the electron-hole recombination, it is particularly appropriate to investigate such dynamics.Single crystals of YbB 12 were grown by the floating zone method [3]. In both ultra-high-resolution laser PES and TrPES measurements, the samples were fractured in situ...

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Hybridization gap formation in the Kondo insulatorYbB12observed using time-resolved photoemission spectroscopy

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“…The INS study of YbB 12 reveals two spin gap type excitations near 15.5 meV and 20 meV [70]. From the Q and temperature dependence it was found that the origin of 15.5 meV peak in YbB 12 is very similar to 14 meV peak in SmB 6 .…”

Section: (B) Hybridization Gap Study In the Kondo Insulator Cefe 2 Al 10mentioning

confidence: 67%

“…From the Q and temperature dependence it was found that the origin of 15.5 meV peak in YbB 12 is very similar to 14 meV peak in SmB 6 . The 20 meV peak in YbB 12 was identified as manifesting a transition from a localized Kondo singlet with a gap to a magnetic state [70]. Further two spin gaps at 27 meV and 50 meV have been also observed through INS study on TKI CeOs 4 Sb 12 , which been interpreted as indirect (or spin gap) and direct (or charge gap) [75].…”

Section: (B) Hybridization Gap Study In the Kondo Insulator Cefe 2 Al 10mentioning

confidence: 88%

“…We now compare the magnetic excitations in CeFe 2 Al 10 with those observed in the mixed valence Kondo insulators SmB 6 and YbB 12 [68][69][70]. It is interesting to note that the various surface techniques, such as angle-resolved photoemission spectroscopy (ARPES) have shown that SmB 6 and YbB 6 exhibit a topological Kondo insulator (TKI) behaviour [71,72].…”

Section: (B) Hybridization Gap Study In the Kondo Insulator Cefe 2 Al 10mentioning

confidence: 99%

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Adroja¹,

Muro²,

Takabatake³

et al. 2016

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Abstract. 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 CeT 2 Al 10 (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 CeRu 2 Al 10 (T N =27 K) and CeOs 2 Al 10 (T N =28.5 K) and the Kondo insulating behaviour observed in the valence fluctuating compound CeFe 2 Al 10 with 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 CeRu 2 Al 10 and CeOs 2 Al 10 revealed dispersive gapped spin wave excitations below T N . 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 CeFe 2 Al 10 , 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 CeFe 2 Al 10 based on theoretical models of heavy-fermion semiconductors.

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“…The spin resonance is a common phenomenon in the gap of, e.g. heavy fermion (HF) unconventional superconductors [23][24][25][26][27][28] , but it may also exist in the hybridization or hidden order gap of non-superconducting Kondo compounds [29][30][31][32][33] (for a review see Ref. 34).…”

Section: Introductionmentioning

confidence: 99%

Collective spin resonance excitation in the gapped itinerant multipole hidden order phase ofURu2Si2

Akbari

Thalmeier

2015

Phys. Rev. B

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An attractive proposal for the hidden order (HO) in the heavy electron compound URu2Si2 is an itinerant multipole order of high rank. It is due to the pairing of electrons and holes centered on zone center and boundary, respectively in states that have maximally different total angular momentum components. Due to the pairing with commensurate zone boundary ordering vector the translational symmetry is broken and a HO quasiparticle gap opens below the transition temperature THO. Inelastic neutron scattering (INS) has demonstrated that for T < THO the collective magnetic response is dominated by a sharp spin exciton resonance at the ordering vector Q that is reminiscent of spin exciton modes found inside the gap of unconventional superconductors and Kondo insulators. We use an effective two-orbital tight binding model incorporating the crystalline electric field effect to derive closed expressions for quasiparticle bands reconstructed by the multipolar pairing terms. We show that the magnetic response calculated within that model exhibits the salient features of the resonance found in INS. We also use the calculated dynamical susceptibility to explain the low temperature NMR relaxation rate.

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Polarized-Neutron Study of Spin Dynamics in the Kondo InsulatorYbB12

Cited by 56 publications

References 17 publications

Hybridization gap formation in the Kondo insulatorYbB12observed using time-resolved photoemission spectroscopy

Hybridization gap formation in the Kondo insulatorYbB12observed using time-resolved photoemission spectroscopy

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Collective spin resonance excitation in the gapped itinerant multipole hidden order phase ofURu2Si2

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