Possible Octupole Ordering in Phase II of SmRu<sub>4</sub>P<sub>12</sub> Suggested from Elastic Constants

Yoshizawa, Michito; Nakanishi, Y.; Oikawa, Masafumi; Sekine, Chihiro; Shirotani, Ichimin; Saha, Shanta; Sugawara, Hitoshi; Sato, Hideyuki

doi:10.1143/jpsj.74.2141

Cited by 104 publications

(78 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…If it is possible to increase ∆ experimentally for Nd-and Sm-based filled skutterudites, we expect exotic electronic properties to result from octupolar fluctuations, including Γ 2u and Γ 5u . In fact, for SmRu 4 P 12 , signs of octupolar ordering have been suggested by elastic constant measurements 26 and µSR experiments. 27 When we turn our attention to actinides, quite recently, NpFe 4 P 12 has been successfully synthesized.…”

mentioning

confidence: 89%

Magnetic and orbital fluctuations in filled skutterudites

Hotta¹

2006

Physica B: Condensed Matter

View full text Add to dashboard Cite

In order to clarify exotic multipole properties of filled skutterudites, we evaluate multipole susceptibility for n=1∼5, where n is the local f -electron number, on the basis of a multiorbital Anderson model constructed using the j-j coupling scheme. For n=1, magnetic fluctuations dominate over lowtemperature electronic properties, while for n=2 and 4, electronic states are dominated by both magnetic and quadrupole fluctuations. For n=3 and 5, octupole fluctuations are found to be significant, depending on the crystalline electric field potential. We discuss possible relevance of the results to actual materials.KEYWORDS: Multipole susceptibility, Filled skutterudites, Multiorbital Anderson model, j-j coupling scheme, Numerical renormalization group method Recent discovery of heavy-fermion superconductivity in PrOs 4 Sb 12 has triggered a rapid increase of research activities on filled skutterudite compounds. 1, 2 This material is believed to belong to the group of strongly correlated electron systems, but the superconductivity cannot be simply understood in terms of d-wave pairing mediated by antiferromagnetic spin fluctuations, since the inverse of the nuclear spinlattice relaxation time for PrOs 4 Sb 12 does not show the T 3 behavior at low temperature T characteristic of a line-node gap. 3 In addition, PrOs 4 Sb 12 exhibits several exotic superconducting features such as multiple superconducting phases, 4 point-node behavior in the gap function, 4, 5 and the breaking of time-reversal symmetry as detected by µSR experiments. 6 It is premature to settle on the mechanism of superconductivity in PrOs 4 Sb 12 , but recently, the possibility of exotic pairing due to quadrupole fluctuations has been suggested experimentally 7 and theoretically. 8 In fact, neutron scattering experiments have revealed that a quadrupole ordered state is induced by a magnetic field in the vicinity of the superconducting phase of PrOs 4 Sb 12 , 9 implying a potential role for quadrupole fluctuations in superconducting pair formation. Moreover, PrFe 4 P 12 exhibits a second-order phase transition at 6.5K, 10 but this transition is considered to be due to antiferro-quadrupolar ordering from neutron scattering experiments 11 and theoretical efforts. 12, 13 It has been gradually recognized that the quadrupolar degree of freedom plays a crucial role in filled skutterudite compounds.From the theoretical viewpoint, multipole phenomena in felectron systems have been investigated phenomenologically on the basis of the LS coupling scheme. This Heisenberglike model for relevant multipole moments could successfully explain some of the experimental results for filled skutterudites. In particular, the phase diagram for PrOs 4 Sb 12 has been reproduced 14 in a quasi-quartet system with Γ 1 ground and Γ (2) 4 excited states with a very small excitation energy 15 for a crystalline electric field (CEF) potential with T h symmetry. 16 However, the microscopic approach to electronic properties of filled skutterudites has been very limited mainly due to the ...

show abstract

mentioning

confidence: 89%

Magnetic and orbital fluctuations in filled skutterudites

Hotta¹

2006

Physica B: Condensed Matter

View full text Add to dashboard Cite

show abstract

“…Second, by application of magnetic fields, the specific heat anomaly of AFQ ordering in CeB 6 is enhanced, while that at T MI in SmRu 4 P 12 changes only slighy; meanwhile, the anomaly at T N in CeB 6 is weakened, whereas it is enhanced in SmRu 4 P 12 [7,13]. Recently, the possibility of octupole ordering was proposed for the MI transition [14]. This proposition is based on the appearance of elastic softening in phase II toward T N and the indistinctness of the subsequent magnetic ordering at T N , because these facts suggest a new coupling of ΨM ǫ (Ψ: probable octupole OP in phase II; M : dipole OP in phase III; ǫ: elastic strain induced by ultrasound) and indicate breakdown of the time reversal symmetry (TRS) in phase II.…”

Section: Introductionmentioning

confidence: 99%

Anomalous elastic softening ofSmRu4P12under high pressure

et al. 2007

Self Cite

View full text Add to dashboard Cite

The filled skutterudite compound SmRu4P12 undergoes a complex evolution from a paramagnetic metal (phase I) to a probable multipolar ordering insulator (phase II) at TMI ∼ 16.5 K, then to a magnetically ordered phase (phase III) at TN ∼ 14 K. Elastic properties under hydrostatic pressures were investigated to study the nature of the ordering phases. We found that distinct elastic softening above TMI is induced by pressure, giving evidence of quadrupole degeneracy of the ground state in the crystalline electric field. It also suggests that quadrupole moment may be one of the order parameters below TMI under pressure. Strangely, the largest degree of softening is found in the transverse elastic constant CT at around 0.5-0.6 GPa, presumably having relevancy to the competing and very different Grüneisen parameters Ω of TMI and TN. Interplay between the two phase transitions is also verified by the rapid increase of TMI under pressure with a considerably large Ω of 9. Our results can be understood on the basis of the proposed octupole scenario for SmRu4P12.

show abstract

“…I, quite recently, a possibility of octupole ordering in filled skutterudite compound SmRu 4 P 12 has been suggested experimentally. 21,22 In the filled skutterudite structure, rare-earth ion surrounded by pnictogens form the bcc lattice. Moreover, the Γ 8 CEF ground state has been reported in the Smbased filled skutterudite.…”

Section: B Bcc Latticementioning

confidence: 99%

“…Very recently, a possibility of octupole ordering has been proposed also for SmRu 4 P 12 . 21,22 It is noted that in these materials, crystalline electric field (CEF) ground states are Γ 8 quartets with large degeneracy even under a CEF potential. 23,24,25 In the Γ 8 ground-state multiplet, octupoles exist as independent moments besides dipole and quadrupole moments.…”

Section: Introductionmentioning

confidence: 99%

Multipole ordering inf-electron systems on the basis of aj−jcoupling scheme

Kubo

Hotta

2005

Phys. Rev. B

View full text Add to dashboard Cite

We investigate microscopic aspects of multipole ordering in f -electron systems with emphasis on the effect of lattice structure. For the purpose, first we construct f -electron models on three kinds of lattices, simple cubic (sc), bcc, and fcc, by including f -electron hopping through (f f σ) bonding in a tight-binding approximation on the basis of a j-j coupling scheme. Then, an effective model is derived in the strong-coupling limit for each lattice structure with the use of second-order perturbation theory with respect to (f f σ). By applying mean-field theory to such effective models, we find different types of multipole ordered state depending on the lattice structure. For the sc lattice, a Γ3g antiferro-quadrupole transition occurs at a finite temperature and as further lowering temperature, we find another transition to a ferromagnetic state. For the bcc lattice, a Γ2u antiferrooctupole ordering occurs first, and then, a ferromagnetic phase transition follows it. Finally, for the fcc lattice, we find a single phase transition to the longitudinal triple-q Γ5u octupole ordering.

show abstract

Possible Octupole Ordering in Phase II of SmRu₄P₁₂ Suggested from Elastic Constants

Cited by 104 publications

References 12 publications

Magnetic and orbital fluctuations in filled skutterudites

Magnetic and orbital fluctuations in filled skutterudites

Anomalous elastic softening ofSmRu4P12under high pressure

Multipole ordering inf-electron systems on the basis of aj−jcoupling scheme

Contact Info

Product

Resources

About

Possible Octupole Ordering in Phase II of SmRu4P12 Suggested from Elastic Constants

Cited by 104 publications

References 12 publications

Magnetic and orbital fluctuations in filled skutterudites

Magnetic and orbital fluctuations in filled skutterudites

Anomalous elastic softening ofSmRu4P12under high pressure

Multipole ordering inf-electron systems on the basis of aj−jcoupling scheme

Contact Info

Product

Resources

About

Possible Octupole Ordering in Phase II of SmRu₄P₁₂ Suggested from Elastic Constants