Anisotropic Electronic Structure of the Kondo Semiconductor CeFe<sub>2</sub>Al<sub>10</sub>Studied by Optical Conductivity

Kimura, S.; Muro, Yuji; Takabatake, Toshiro

doi:10.1143/jpsj.80.033702

Cited by 45 publications

(54 citation statements)

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“…This is also the case for CeRu 4 Sn 6 , as illustrated by temperature-dependent electrical resistivity, ρ(T ), data along the two principal axes a and c (Fig. 1, left [33]), a pronounced anisotropy is observed. The temperaturedependent energy gaps ∆(T ) for the two directions (Fig.…”

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confidence: 62%

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Anisotropic optical conductivity of the putative Kondo insulator CeRu4Sn6

et al. 2013

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Kondo insulators and in particular their non-cubic representatives have remained poorly understood. Here we report on the development of an anisotropic energy pseudogap in the tetragonal compound CeRu4Sn6 employing optical reflectivity measurements in broad frequency and temperature ranges, and local density approximation plus dynamical mean field theory calculations. The calculations provide evidence for a Kondo insulator-like response within the a − a plane and a more metallic response along the c axis and qualitatively reproduce the experimental observations, helping to identify their origin.Correlated materials with gapped or pseudo-gapped ground states continue to be of great interest. The gap in the electronic density of states (DOS) either opens gradually with decreasing temperature, as the pseudogap of high-temperature superconductors [1], or emerges at a continuous or first order phase transition [2][3][4]. In heavy fermion compounds [5] -systems in which f and conduction electrons strongly interact -a narrow hybridization gap is known to emerge gradually [6][7][8][9]. Generically, the Fermi energy is situated in one of the hybridized bands and a metallic heavy fermion ground state arises. Only for special cases the Fermi energy lies within the gap and the ground state is Kondo insulating. Metallic heavy fermion systems have been intensively investigated over the past decades and are now, at least away from quantum criticality [10], well understood [11] within the framework of Landau Fermi liquid theory. Hence, a very few parameters, most notably the effective mass, allow us to describe thermodynamic and transport properties at the lowest temperatures. In comparison, the physics of Kondo insulators has proven to be much less tractable. This is at least in part due to the fact that the gapped ground state inhibits a characterization via the above properties. Many experimental efforts have therefore focussed on the determination of the gap width from temperature dependencies, which has frequently led to conflicting results, in particular for anisotropic Kondo insulators such as CeNiSn [12]. Here the strongly anisotropic transport and magnetic properties have been interpreted phenomenologically on the basis of a V-shaped DOS [13] or by invoking a hybridization gap with nodes [14][15][16] or extrinsic effects such as impurities, off stoichiometry or strain [17,18]. To advance the field it appears mandatory to model a number of carefully chosen materials ab initio, taking all essential ingredients into account.Here we investigate a new material, CeRu 4 Sn 6 , which due to its tetragonal crystal structure is simpler than the previously studied orthorhombic materials. In a combined experimental and theoretical effort we provide direct spectroscopic evidence for the development of an anisotropic pseudogap: While weak metallicity prevails in the optical conductivity along the c axis, insulatorlike behavior without a Drude peak is observed in the a − a plane. We trace this back to a correlated band structure whic...

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confidence: 62%

“…The only other non-cubic Kondo insulator for which σ 1 (ω) results along the different crystallographic directions are available is CeFe 2 Al 10 [33]. Here a Drude-like feature appears for all three crystallographic directions; the anisotropy is thus much less pronounced than for CeRu 4 Sn 6 .…”

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Anisotropic optical conductivity of the putative Kondo insulator CeRu4Sn6

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“…For CeFe 2 Al 10 a charge gap of 55 meV was observed in all directions, but without a clear onset temperature, while for CeRu 2 Al 10 and CeOs 2 Al 10 a charge gap of 35 meV and 45 meV, respectively was observed in the a-c plane [63]. The observed excitations in the ac-plane originate from the optical transition across the c-f hybridization gap [62][63][64]. The observed peak structure at 20 meV was attributed to the formation of charge density waves (CDWs) in CeRu 2 Al 10 and CeOs 2 Al 10.…”

Section: Ins Study On Polycrystalline Cet 2 a L0mentioning

confidence: 92%

“…It is interesting to note that the high energy INS study reveals very broad magnetic excitations at 50 meV in CeFe 2 Al 10 [46], while two broad CEF excitations have been observed in CeT 2 Al 10 (T=Ru and Os) [61]. Further, it is interesting to compare the observed spin gap value in CeT 2 Al 10 with that of the charge gap estimated through the optical spectroscopy [62][63][64]. The spectrum of polarized optical conductivity, σ(T), along the b-axis differs greatly from that in the ac-plane, indicating that these materials have an anisotropic electronic structure.…”

Section: Ins Study On Polycrystalline Cet 2 a L0mentioning

confidence: 97%

“…The gap near the zone centre is about 4-5 meV, whose origin could be due to a combined effect of the single ion anisotropy and anisotropic magnetic exchange. The anisotropic exchange could arise due to the presence of strong anisotropic hybridization between 4f-electrons and conduction electrons proposed from various experimental techniques, such as optical spectroscopy [62][63][64]. The zone boundary energy is 8 meV in CeRu 2 Al 10 and 12 meV in CeOs 2 Al 10 .…”

Section: Ins Study On Single Crystals Of Cet 2 Al 10mentioning

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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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Thermal conductivity, thermoelectric power and Mössbauer investigations on atiferromagnetic CeFe1.7Ir0.3Al10

Anand

Adroja

Idczak

et al. 2022

Journal of Magnetism and Magnetic Materials

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Anisotropic Electronic Structure of the Kondo Semiconductor CeFe₂Al₁₀Studied by Optical Conductivity

Cited by 45 publications

References 30 publications

Anisotropic optical conductivity of the putative Kondo insulator CeRu4Sn6

Anisotropic optical conductivity of the putative Kondo insulator CeRu4Sn6

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Thermal conductivity, thermoelectric power and Mössbauer investigations on atiferromagnetic CeFe1.7Ir0.3Al10

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Anisotropic Electronic Structure of the Kondo Semiconductor CeFe2Al10Studied by Optical Conductivity

Cited by 45 publications

References 30 publications

Anisotropic optical conductivity of the putative Kondo insulator CeRu4Sn6

Anisotropic optical conductivity of the putative Kondo insulator CeRu4Sn6

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Thermal conductivity, thermoelectric power and Mössbauer investigations on atiferromagnetic CeFe1.7Ir0.3Al10

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Anisotropic Electronic Structure of the Kondo Semiconductor CeFe₂Al₁₀Studied by Optical Conductivity