Spin gap formation in SmB6

Ġlushkov, V. V.; Kuznetsov, A. V.; Churkin, O. A.; Demishev, S. V.; Paderno, Yu. B.; Shitsevalova, N. Yu.; Sluchanko, N. E.

doi:10.1016/j.physb.2006.01.167

Cited by 17 publications

(8 citation statements)

References 10 publications

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“…[15]). While the low T resistivity of SmB 6 saturates below 4 K, which is attributed to the topological surface states, the onset of the in-gap states in the susceptibility 12 , in inelastic neutron scattering 9 , the NMR Knight shift and relaxation 15 and Raman spectroscopy 8 occurs at higher T , of the order of 25 -30 K. This is shown in Fig. 2.…”

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confidence: 90%

NMR relaxation in the topological Kondo insulatorSmB6

Schlottmann¹

2014

Phys. Rev. B

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SmB6 has been predicted to be a strong topological Kondo insulator and experimentally it has been confirmed that at low temperatures the electrical conductivity only takes place at the surfaces of the crystal. We study the temperature and magnetic field dependence of the NMR Knight shift and relaxation rate arising from the topological conduction states. For the clean surface the Landau quantization of the surface states gives rise to highly degenerate discrete levels for which the Knight shift is proportional to the magnetic field B and inversely proportional to the temperature T . The relaxation rate, 1/T1, is not Korringa-like. For the more realistic case of a surface with a low concentration of defects (dirty limit) the scattering of the electrons leads to a broadening of the Landau levels and hence to a finite density of states. The mildly dirty surface case leads to a T -independent Knight shift proportional to B and a Korringa-like 1/T1 at low T . The wave functions of the surface states are expected to fall off exponentially with distance from the surface giving rise to a superposition of relaxation times, i.e. a stretched exponential. It is questionable that the experimental 11 B Knight shift and relaxation rate arise from the surface states of the TKI. An alternative explanation is that the bulk susceptibility and the 11 B NMR properties are the consequence of the in-gap bulk states originating from magnetic exciton bound states proposed by Riseborough [Phys. Rev. B 68, 235213 (2003)].

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confidence: 90%

NMR relaxation in the topological Kondo insulatorSmB6

Schlottmann¹

2014

Phys. Rev. B

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“…11 Recently, it has been argued that there is some residual bulk electrical conductivity in SmB 6 below 4 K. 12 There also exists significant bulk acconduction arising from low-energy states in the Kondo gap. 13 Nuclear magnetic resonance (NMR) Knight shift and spin-lattice relaxation rate (1/T 1 ) measurements, 14 bulk magnetic susceptibility, 15 Raman spectroscopy, 16,17 and inelastic neutron scattering (INS) 18,19 studies of SmB 6 reveal the emergence of bulk in-gap bound states of a different origin below T ∼ 20-30 K. The sharp dispersive magnetic excitations observed at 14 meV within the hybridization gap by INS have been attributed to a bulk collective spin exciton resonance mode due to residual antiferromagnetic (AFM) quasiparticle interactions. 20,21 These bound magnetic quasiparticle states are robust due to the protection provided by the hybridization gap, and there is evidence that the spin excitons couple to bulk in-gap states introduced by disorder.…”

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confidence: 99%

Quantum spin fluctuations in the bulk insulating state of pure and Fe-doped SmB6

et al. 2017

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The intermediate-valence compound SmB6 is a well-known Kondo insulator, in which hybridization of itinerant 5d electrons with localized 4f electrons leads to a transition from metallic to insulating behavior at low temperatures. Recent studies suggest that SmB6 is a topological insulator, with topological metallic surface states emerging from a fully insulating hybridized bulk band structure. Here we locally probe the bulk magnetic properties of pure and 0.5 % Fe-doped SmB6 by muon spin rotation/relaxation (µSR) methods. Below 6 K the Fe impurity induces simultaneous changes in the bulk local magnetism and the electrical conductivity. In the low-T insulating bulk state we observe a temperature-independent dynamic relaxation rate indicative of low-lying magnetic excitations driven primarily by quantum fluctuations.Topological insulators are exotic quantum states of matter characterized by an electrically insulating bulk and topologically-protected metallic surface states. Due to an interplay of strong correlations and strong spinorbit coupling of the 4f electrons, SmB 6 is predicted to develop a non-trivial Z 2 topological insulating state. 1 Angle-resolved photoemission 2 and point-contact spectroscopy 3 measurements show that the crossover from the bulk high-T metallic state to the low-T Kondo insulating phase occurs gradually over a fairly wide temperature range (30 K < T < 110 K). Transport measurements show that surface electrical conduction occurs below T ∼ 5 to 6 K with a resistance that saturates at lower temperature. 4-6 The low-T conduction arises from twodimensional states 7 that occur in the hybridization gap exclusively at the surface, 3,4,8 as expected for metallic surface states of topological origin. 9 Yet the ground state of SmB 6 is still unclear, in part because not all bulk properties at low T are that of a conventional band-gapped insulator. Despite the loss of bulk electrical conduction, quantum oscillations consistent with a bulk Fermi surface have been observed, 10 and the low-temperature specific heat exhibits a significant bulk residual T -linear term typical of a metallic state. 11 Recently, it has been argued that there is some residual bulk electrical conductivity in SmB 6 below 4 K. 12 There also exists significant bulk acconduction arising from low-energy states in the Kondo gap. 13Nuclear magnetic resonance (NMR) Knight shift and spin-lattice relaxation rate (1/T 1 ) measurements, 14 bulk magnetic susceptibility, 15 Raman spectroscopy, 16,17 and inelastic neutron scattering (INS) 18,19 studies of SmB 6 reveal the emergence of bulk in-gap bound states of a different origin below T ∼ 20-30 K. The sharp dispersive magnetic excitations observed at 14 meV within the hybridization gap by INS have been attributed to a bulk collective spin exciton resonance mode due to residual antiferromagnetic (AFM) quasiparticle interactions. 20,21 These bound magnetic quasiparticle states are robust due to the protection provided by the hybridization gap, and there is evidence that the spin excitons co...

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“…2a). At T > 40 K the χ(T ) data can be well fitted by the spin gap model χ S (T ) = χ S0 + C S /T exp(−∆/T ) applied earlier for the relative compound SmB 6 [12]. The spin gap size ∆ ≈ 54.7 K is approximately equal to the half of the spin fluctuations temperature in YbB 12 (T sf ≈ 100 K) [11] and is comparable with the binding energies of in-gap manybody states (E a = 65 ± 10 K) detected in Tm 1−x Yb x B 12 (x < 0.19) [9].…”

Section: Resultsmentioning

confidence: 70%

“…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]. Recent studies of Tm x Yb 1−x B 12 single crystals [8][9][10] pointed out that the rise of Yb content results in a metal-insulator transition, a bulk narrow many-body resonance (∆ ≈ 6 meV) appears at the Fermi level.…”

Section: Introductionmentioning

confidence: 99%

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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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Spin gap formation in SmB6

Cited by 17 publications

References 10 publications

NMR relaxation in the topological Kondo insulatorSmB6

NMR relaxation in the topological Kondo insulatorSmB6

Quantum spin fluctuations in the bulk insulating state of pure and Fe-doped SmB6

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

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Spin gap formation in SmB6

Cited by 17 publications

References 10 publications

NMR relaxation in the topological Kondo insulatorSmB6

NMR relaxation in the topological Kondo insulatorSmB6

Quantum spin fluctuations in the bulk insulating state of pure and Fe-doped SmB6

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

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