Intermetallic compounds containing $f$-electron elements display a wealth of superconducting phases, which are prime candidates for unconventional pairing with complex order parameter symmetries. For instance, superconductivity has been found at the border of magnetic order as well as deep within ferromagnetically and antiferromagnetically ordered states, suggesting that magnetism may promote rather than destroy superconductivity. Superconducting phases near valence transitions or in the vicinity of magnetopolar order are candidates for new superconductive pairing interactions such as fluctuations of the conduction electron density or the crystal electric field, respectively. The experimental status of the study of the superconducting phases of $f$-electron compounds is reviewed.

Superconducting phases of f -electron compounds

The concept of quantum criticality is proving to be central to attempts to understand the physics of strongly correlated electrons. Here, we argue that observations on the itinerant metamagnet Sr3Ru2O7 represent good evidence for a new class of quantum critical point, arising when the critical end point terminating a line of first-order transitions is depressed toward zero temperature. This is of interest both in its own right and because of the convenience of having a quantum critical point for which the tuning parameter is the magnetic field. The relationship between the resultant critical fluctuations and novel behavior very near the critical field is discussed.

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Magnetic field-tuned quantum criticality in the metallic ruthenate Sr3Ru2O7.

We carried out the de Haas–van Alphen (dHvA) experiment for an antiferromagnet CeRhIn 5 at high pressures up to 3 GPa. The cross-sectional areas of the Fermi surfaces due to main dHvA branches α i and β 2 at ambient pressure, which are well explained by two kinds of nearly cylindrical Fermi surfaces of a non-4 f reference compound LaRhIn 5 , are unchanged up to about 2.3 GPa, while the corresponding cyclotron masses m c * increase steeply above a pressure P * = 1.6 GPa where pressure-induced superconductivity sets in : m * c = 5.5 m 0 at ambient pressure, 20 m 0 at 1.6 GPa and 60 m 0 at 2.2 GPa for branch β 2 , for example. Above 2.4 GPa, new dHvA branches appear, which are in good agreement with the corresponding dHvA branches of a 4 f -itinerant heavy fermion superconductor CeCoIn 5 , indicating that the 4 f electron of CeRhIn 5 becomes itinerant and significantly contributes to the volume of the Fermi surface. The 4 f -electron character is thus changed from localized to itinerant at a critical pressur...

A Drastic Change of the Fermi Surface at a Critical Pressure in CeRhIn5: dHvA Study under Pressure

We have studied Fermi surface properties of LaRhIn 5 and CeTIn 5 (T: Co, Rh and Ir) via the de Haas–van Alphen (dHvA) experiment. The Fermi surface of a non-4 f reference compound LaRhIn 5 is quasi...

Fermi Surface, Magnetic and Superconducting Properties of LaRhIn5 and CeTIn5 (T: Co, Rh and Ir)

In order to discuss superconductivity in orbital degenerate systems, a microscopic Hamiltonian is introduced. Based on the degenerate model, a strong-coupling theory of superconductivity is developed within the fluctuation exchange (FLEX) approximation where spin and orbital fluctuations, spectra of electron, and superconducting gap function are self-consistently determined. Applying the FLEX approximation to the orbital degenerate model, it is shown that the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave superconducting phase is induced by increasing the orbital splitting energy which leads to the development and suppression of the spin and orbital fluctuations, respectively. It is proposed that the orbital splitting energy is a controlling parameter changing from the paramagnetic to the antiferromagnetic phase with the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave superconducting phase in between.

https://arxiv.org/pdf/cond-mat/0309575.pdf

Strong-coupling theory of superconductivity in a degenerate Hubbard model

We studied the magnetic properties in a non-magnetic heavy-fermion compound CeIrIn 5 and an antiferromagnetic compound CeRhIn 5 with the tetragonal structure. High-field magnetization of CeIrIn 5 s...

Magnetic and Thermal Properties of CeIrIn5 and CeRhIn5

We performed DC-magnetization and neutron scattering experiments under pressure P for a pressure-induced superconductor UGe 2 . We found that the magnetic moment is enhanced at a characteristic temperature T * in the ferromagnetic state, where T * is smaller than a Curie temperature T C . This enhancement becomes remarkable in the vicinity of P C * =1.20 GPa, where T * becomes 0 K and the superconducting transition temperature T SC shows a maximum. The characteristic temperature T * , which decreases with increasing pressure, also depends on the magnetic field.

Magnetic properties of a pressure-induced superconductor UGe2

We performed the DC-magnetization and neutron scattering experiments under pressure {\it P} for a pressure-induced superconductor UGe$_2$. We found that the magnetic moment is enhanced at a characteristic temperature {\it T}$^{*}$ in the ferromagnetic state, where {\it T}$^{*}$ is smaller than a Curie temperature {\it T}$_{\rm C}$. This enhancement becomes remarkable in the vicinity of {\it P}$_{\rm C}^{*}$ = 1.20 GPa, where {\it T}$^{*}$ becomes 0 K and the superconducting transition temperature {\it T}$_{\rm SC}$ shows a maximum. The characteristic temperature {\it T}$^{*}$, which decreases with increasing pressure, also depends on the magnetic field.

https://arxiv.org/pdf/cond-mat/0107075.pdf

Magnetic Properties of a Pressure-induced Superconductor UGe$_2$

We succeeded in growing a high-quality single crystal of an antiferromagnet UNiGa 5 by the self-flux method, and measured the de Haas-van Alphen (dHvA) effect, together with the electrical resistiv...

Quasi-Two Dimensional Fermi Surface Properties of the Antiferromagnet UNiGa5.

We have grown a single crystal with the residual resistivity ratio of 81, and studied its electronic properties of the cubic antiferromagnetic compound UGa 3 . From the transverse magnetoresistance...

Tetsutaro Inoue

Papers

Magnetic and Thermal Properties of CeIrIn5 and CeRhIn5

Magnetic properties of a pressure-induced superconductor UGe2

Magnetic Properties of a Pressure-induced Superconductor UGe$_2$

Quasi-Two Dimensional Fermi Surface Properties of the Antiferromagnet UNiGa5.

Electronic States of the Antiferromagnet UGa3