NMR Investigation of Energy Gap Formation in the Valence Fluctuating Compound CeNiSn

Kyogaku, Masafumi; Kitaoka, Y.; Nakamura, Hiroyuki; Takabatake, Toshiro; Teshima, F.; Fujii, H.

doi:10.1143/jpsj.59.1728

Cited by 99 publications

(44 citation statements)

References 7 publications

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“…To account for this unusual behavior, Ikeda and Miyake proposed a hybridization model for this Kondo lattice system [10], treating it as a Kondo insulator in which the hybridization gap contains a node along the crystallographic a-axis. The presence of this node leads to a "V"-shaped electronic density of states, a feature which is consistent with both tunneling and NMR measurements [14][15][16][17].…”

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Giant Isotropic Nernst Effect in an Anisotropic Kondo Semimetal

et al. 2016

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The "failed Kondo insulator" CeNiSn has long been suspected to be a nodal metal, with a node in the hybridization matrix elements. Here we carry out a series of Nernst effect experiments to delineate whether the severely anisotropic magnetotransport coefficients do indeed derive from a nodal metal or can simply be explained by a highly anisotropic Fermi surface. Our experiments reveal that despite an almost 20-fold anisotropy in the Hall conductivity, the large Nernst signal is isotropic. Taken in conjunction with the magnetotransport anisotropy, these results provide strong support for an isotropic Fermi surface with a large anisotropy in quasiparticle mass derived from a nodal hybridization.There is a wide and growing interest in electron materials with topologically protected excitation spectra, including Z 2 topological insulators and topological superconductors [1][2][3] and, most recently, topologically protected Weyl semimetals [4,5]. Rare earth heavy fermion systems have recently emerged as a new venue to explore the interplay of strong correlations with topology [6][7][8][9]: the strong electron-electron interactions and spinorbit coupling make these systems ideal candidates for research in this area. The class of Kondo insulators, such as SmB 6 , has received much attention as candidate strongly interacting Z 2 topological insulators. The littleknown family of Kondo semimetals [10-13] may provide a second example of such topological protection. These compounds are considered to be failed Kondo insulators, in which the hybridization gap contains a node that closes the gap in certain directions, giving rise to a semimetal with a pseudogap. Transport studies on these materials have confirmed the presence of a large anisotropy in the magnetotransport, but such anisotropies are not in themselves an indication of a nodal hybridization, and could derive from anisotropic Fermi surface geometries.In this paper we carry out a series of magnetothermoelectric measurements on the Kondo semimetal CeNiSn. They reveal that unlike the Hall conductivity, which is highly anisotropic, the large Nernst effect is essentially isotropic. We show how this unexpected isotropy rules out an anisotropic Fermi surface geometry and is a natural consequence of cancellations between mean free path and mass anisotropies expected in a nodal semimetal. This definite understanding of the material's bulk properties is an important prelude to any future studies of putative surface contributions.CeNiSn is a heavy electron material with emergent semimetallic properties. When it develops coherence at low temperatures, a pseudogap opens in its electronic density of states, as revealed by both tunneling [14,15] and nuclear magnetic resonance [16,17] studies. Modest magnetic fields are sufficient to remove the pseudogap [15]. The material exhibits marked anisotropy in its magnetotransport properties [18][19][20][21]. To account for this unusual behavior, Ikeda and Miyake proposed a hybridization model for this Kondo lattice system [10], treating ...

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confidence: 83%

Giant Isotropic Nernst Effect in an Anisotropic Kondo Semimetal

et al. 2016

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“…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.…”

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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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“…The fitting is satisfactory, which indicates that the broad peak results from the narrow pseudogap and that the temperature-independent value at low temperatures comes from the finite DOS in the gap. Although we tried to fit the susceptibility by assuming a Lorentzian-shaped band separated by a V-shaped gap, as has been proposed for CeNiSn, 20) the result was not satisfactory. The Knight shift is, in general, proportional to the intrinsic susceptibility.…”

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confidence: 99%