Single crystal growth and physical properties of Kondo insulator YbB12

Iga, Fumitoshi; Shimizu, Nobujiro; Takabatake, Toshiro

doi:10.1016/s0304-8853(97)00493-9

Cited by 189 publications

(153 citation statements)

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“…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 under the base pressure of ∼2×10 −11 Torr, and the spectra were recorded using a VG Scienta R4000 analyzer.…”

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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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confidence: 99%

“…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 under the base pressure of ∼2×10 −11 Torr, and the spectra were recorded using a VG Scienta R4000 analyzer.…”

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confidence: 99%

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

et al. 2015

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“…10) Single crystals of the Pr filled skutterudite compounds PrT 4 Sb 12 and PrRu 2 Zn 20 were grown by the Sb-flux method 11) and the Zn self-flux method, 12) respectively. Raman scattering spectra were measured by a following multichannel detection system.…”

Section: Methodsmentioning

confidence: 99%

Raman Scattering Study of Lattice Dynamics in Caged Compounds

et al. 2011

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“…The nature of the narrow gap (ε g ≈ 17.8 meV [1,2]) in YbB 12 , which shares the place between antiferromagnetic metal TmB 12 [3] and superconducting LuB 12 [4] in the set of rare-earth dodecaborides RB 12 , stays a subject of discussions [1][2][3][5][6][7][8][9][10][11]. The ground state of YbB 12 identified usually as the Kondo insulator [1] seems to have a non-trivial topology of the band structure resulting in surface conductivity [5].…”

Section: Introductionmentioning

confidence: 99%

“…The ground state of YbB 12 identified usually as the Kondo insulator [1] seems to have a non-trivial topology of the band structure resulting in surface conductivity [5]. However, studies of Ludoped and Zr-doped YbB 12 show that the gap in the YbB 12 band spectrum is local and is not influenced by the onset of long-range coherence [6,7].…”

Section: Introductionmentioning

confidence: 99%

Charge Transport and Magnetism in Tm_0.03Yb_0.97B₁₂

et al. 2017

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Transport and magnetic properties of polycrystalline Tm0.03Yb0.97B12 samples were investigated at temperatures 1.8-300 K in magnetic fields up to 9 T. The activated behavior of resistivity, the Hall coefficient and thermopower is described in terms of a narrow gap εg ≈ 16.6 meV, which controls the charge transport in Tm0.03Yb0.97B12 at T > 40 K. The maximum of magnetic susceptibility found at 50 K is shown to be induced by a spin gap ∆ ≈ 4.7 meV being close to the half of the spin fluctuation energy in YbB12. Large diffusive thermopower S = AT , A = −29.1 µV/K 2 and the Pauli susceptibility χ0 ≈ 7.2 × 10 −3 emu/mol found below 20 K seem to be associated with the many-body resonance, which corresponds to states with an enhanced effective mass m * ≈ 250m0 (m0 -free electron mass). The effective parameters of magnetic centers and the analysis of anomalies favor the nonequivalent states of substitute Tm ions.

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Single crystal growth and physical properties of Kondo insulator YbB12

Cited by 189 publications

References 6 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

Raman Scattering Study of Lattice Dynamics in Caged Compounds

Charge Transport and Magnetism in Tm_0.03Yb_0.97B₁₂

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Single crystal growth and physical properties of Kondo insulator YbB12

Cited by 189 publications

References 6 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

Raman Scattering Study of Lattice Dynamics in Caged Compounds

Charge Transport and Magnetism in Tm0.03Yb0.97B12

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Charge Transport and Magnetism in Tm_0.03Yb_0.97B₁₂