Heavy Fermion Superconductivity in the Filled Skutterudite Compound PrOs₄Sb₁₂

Superconductivity and the high-field ordered phase in the heavy-fermion compound PrOs4Sb12

“…As far as we know, PrOs 4 Sb 12 is the first example of a heavy fermion superconductor based on Pr; all of the other known heavy fermion superconductors are compounds of Ce or U. The superconducting state appears to be unconventional in nature and may consist of two distinct superconducting phases [7,8]. An ordered phase, presumably of magnetic or quadrupolar origin, occurs at high fields > 4.5 tesla and low temperatures < 1.5 K [7,9,10,11,12,13], suggesting that the superconductivity may occur in the vicinity of a magnetic or quadrupolar quantum critical point (QCP).…”

“…The superconducting state appears to be unconventional in nature and may consist of two distinct superconducting phases [7,8]. An ordered phase, presumably of magnetic or quadrupolar origin, occurs at high fields > 4.5 tesla and low temperatures < 1.5 K [7,9,10,11,12,13], suggesting that the superconductivity may occur in the vicinity of a magnetic or quadrupolar quantum critical point (QCP). In an effort to obtain information about the interactions that are responsible for the heavy fermion state and superconductivity in PrOs 4 Sb 12 , we have performed measurements of various normal and superconducting state properties of this compound as a function of temperature, pressure, and magnetic field [5,6,7,9].…”

“…An ordered phase, presumably of magnetic or quadrupolar origin, occurs at high fields > 4.5 tesla and low temperatures < 1.5 K [7,9,10,11,12,13], suggesting that the superconductivity may occur in the vicinity of a magnetic or quadrupolar quantum critical point (QCP). In an effort to obtain information about the interactions that are responsible for the heavy fermion state and superconductivity in PrOs 4 Sb 12 , we have performed measurements of various normal and superconducting state properties of this compound as a function of temperature, pressure, and magnetic field [5,6,7,9]. Analysis of magnetic susceptibility χ(T ), specific heat C(T ), electrical resistivity ρ(T ), and inelastic neutron scattering measurements within the context of a cubic crystalline electric field (CEF) yields a Pr 3+ energy level scheme that consists of a Γ 3 nonmagnetic doublet ground state that carries an electric quadrupole moment, a low lying Γ 5 triplet excited state at ∼ 10 K, and Γ 4 triplet and Γ 1 singlet excited states at much higher temperatures (∼ 130 K and ∼ 313 K, respectively) [5,6,7,9].…”

“…In an effort to obtain information about the interactions that are responsible for the heavy fermion state and superconductivity in PrOs 4 Sb 12 , we have performed measurements of various normal and superconducting state properties of this compound as a function of temperature, pressure, and magnetic field [5,6,7,9]. Analysis of magnetic susceptibility χ(T ), specific heat C(T ), electrical resistivity ρ(T ), and inelastic neutron scattering measurements within the context of a cubic crystalline electric field (CEF) yields a Pr 3+ energy level scheme that consists of a Γ 3 nonmagnetic doublet ground state that carries an electric quadrupole moment, a low lying Γ 5 triplet excited state at ∼ 10 K, and Γ 4 triplet and Γ 1 singlet excited states at much higher temperatures (∼ 130 K and ∼ 313 K, respectively) [5,6,7,9]. This scenario suggests that the underlying mechanism for the heavy fermion behavior in PrOs 4 Sb 12 may involve the interaction of Pr 3+ electric quadrupole moments with the charges of the conduction electrons, rather than Pr 3+ magnetic dipole moments with the spins of the conduction electrons.…”

NMR Observation of Ferro-Quadrupole Order in PrTi2Al20

“…[1][2][3][4] In particular, non-Kramers rare-earth ions with an even number of f electrons in a cubic environment have been attracting strong interest recently. [5][6][7][8][9][10][11] In these systems, it is possible that the ground states of the J multiplet split by the cubic crystalline electric field (CEF) are nonmagnetic, i.e., the matrix elements of the magnetic dipole J are identically zero, yet have a degeneracy that allows active higher-order multipoles such as electric quadrupoles or magnetic octupoles. Then various interesting phenomena such as multipole orders [12][13][14] or multichannel Kondo effects 15,16) are expected at low temperatures.…”