In most strongly correlated electron systems superconductivity appears nearby a magnetic quantum critical point (QCP) which is believed to cause unconventional behaviors. In order to explore this physics, we present here a study of the heavy-fermion superconductors CeIrSi3 and CeRhSi3 carried out using a newly developed system for high-resolution magnetic penetration-depth measurements under pressure. Superconductivity in CeIrSi3 shows a change from an excitation spectrum with a line-nodal gap to one which is entirely gapful when pressure is close but not yet at the QCP. In contrast, CeRhSi3 does not possess a T = 0 quantum phase transition and the superconducting phase remains for all accessible pressures with a nodal gap. Combining both results suggests that in these compounds unconventional superconducting behaviors are rather connected with the coexisting antiferromagnetic order. This study provides another viewpoint on the interplay of superconductivity, magnetism, and quantum criticality in CeIrSi3 and CeRhSi3 and maybe in other heavy fermions.

A rectenna, standing for a rectifying antenna, is an apparatus which generates d.c. electricity from electric fluctuations. It is expected to realize wireless power transmission as well as energy harvesting from environmental radio waves. To realize such rectification, devices that are made up of internal atomic asymmetry such as an asymmetric junction have been necessary so far. Here we report a material that spontaneously generates electricity by rectifying environmental fluctuations without using atomic asymmetry. The sample is a common superconductor without lowered crystalline symmetry, but, just by putting it in an asymmetric magnetic environment, it turns into a rectifier and starts generating electricity. Superconducting vortex strings only annihilate and nucleate at surfaces, and this allows the bulk electrons to feel surface fluctuations in an asymmetric environment: a vortex rectenna. The rectification and generation can be switched on and off with only a slight change in temperature or external magnetic fields.

The weak itinerant‐electron ferromagnet ZrZn2 exhibits intriguing high‐pressure properties, such as non‐Fermi‐liquid behavior and the electronic topological transition (the Lifshitz transition). We report the detailed magnetic properties at high pressures and propose a novel phase diagram containing a crossover temperature that emerges from a metamagnetic critical point.

The field-orientation dependent thermal conductivity of the heavy-fermion superconductor UPt3 was measured down to very low temperatures and under magnetic fields throughout the distinct superconducting phases: B and C phases. In the C phase, a striking twofold oscillation of the thermal conductivity within the basal plane is resolved reflecting the superconducting gap structure with a line of node along the a axis. Moreover, we find an abrupt vanishing of the oscillation across a transition to the B phase, as a clear indication of a change of gap symmetries. We also identify extra two line nodes below and above the equator in both B and C phases. From these results together with the symmetry consideration, the gap function of UPt3 is determined as a E(1u) representation characterized by a combination of two line nodes at the tropics and point nodes at the poles.

Neutron diffraction experiments were performed to investigate a nature of the antiferromagnetic ordered phase below TN = 5.0 K of the pressure-induced superconductor CeIrSi3. We succeeded in observing incommensurate magnetic peaks characterized by the wave vector τ = (±0.265, 0, 0.43). In contrast to the magnetic structure of CeRhSi3, the observed magnetic structure is incommensurate both along the a and c directions. The antiferromagnetic ordered state in CeIrSi3 could be interpreted as a spin-density wave formation.

We performed nuclear-magnetic-resonance measurements on itinerant-electron metamagnet UCoAl to investigate the critical behavior of the magnetism near a metamagnetic (MM) critical endpoint (CEP). We derived c-axis magnetization M-c and its fluctuation S-c from the measurements of Knight shift and nuclear spin-lattice relaxation rate 1/T-1 as a function of the c-axis external field (H-c) and temperature (T). We developed contour plots of M-c and S-c on the H-c-T phase diagram, and observed the strong divergence of S-c at the CEP. The critical exponents of M-c and S-c near the CEP are estimated and found to be close to the universal properties of a three-dimensional Ising model. We indicate that the critical phenomena at the itinerant-electron MM CEP in UCoAl have a common feature as a gas-liquid transition.

In order to identify the gap structure of a spin-triplet superconductor UPt3, we performed field-angle-resolved specific heat (Cϕ) measurements in a magnetic field rotated around the [0001] axis. Although various theories predict fourfold symmetry of the gap in the superconducting C phase, we observed no angular variation in Cϕ in a temperature range down to 88 mK (~ 0.17Tc). This absence of the variation in Cϕ implies that the field-angle-dependent quasiparticle excitations, reflecting the gap anisotropy, are averaged out in the bulk of UPt3.

We report the first observation of the continuous Fermi surface (FS) variation from La compound (LaRu2Si2) with no f electron to Ce compound (CeRu2Si2) with itinerant f electron via the de Haas-van Alphen (dHvA) effect. The dHvA frequency smoothly varies with Ce concentration and there is no discontinuous change with Ce concentration. It is found that the effective mass and signal amplitude with Ce concentration depends strongly on the Fermi surface sheet, and the effective mass is enhanced toward xc (= 0.91) and the signal amplitude reduces around xc or somewhere between xc and x ∼ 0.8.

Measurements of low-temperature transport and thermodynamic properties have been used to characterize the non-Fermi-liquid state of the itinerant ferromagnet ZrZn2. We observe a T-5/3 temperature dependence of the electrical resistivity at zero field, which becomes T-2-like in an applied field of 9 T. In zero field, we also measured the thermal conductivity, and we see a novel linear-in-T dependence of the difference between the thermal and electrical resistivities. Heat-capacity measurements, also at zero field, reveal an upturn in the electronic contribution at low temperatures when the phonon term is subtracted. Taken together, we argue that these properties are consistent with a marginal Fermi-liquid state, which is predicted by a mean-field model of enhanced spin fluctuations on the border of ferromagnetism in three dimensions. We compare our data to quantitative predictions and establish this model as a compelling theoretical framework for understanding ZrZn2.

Superconductivity at interfaces has been investigated since the first demonstration of electric-field-tunable superconductivity in ultrathin films in 1960 1 . So far, research on interface superconductivity has focused on materials that are known to be superconductors in bulk 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 . Here, we show that electrostatic carrier doping can induce superconductivity in KTaO 3 , a material in which superconductivity has not been observed before 10 , 11 . Taking advantage of the large capacitance of the self-organized electric double layer that forms at the interface between an ionic liquid and KTaO 3 (ref. 12 ), we achieve a charge carrier density that is an order of magnitude larger than the density that can be achieved with conventional chemical doping. Superconductivity emerges in KTaO 3 at 50 mK for two-dimensional carrier densities in the range 2.3 × 10 14 to 3.7 × 10 14 cm −2 . The present result clearly shows that electrostatic carrier doping can lead to new states of matter at nanoscale interfaces.

We report the temperature dependence of the zero-field ac-susceptibility of CeRhSi3 under several pressures. We have observed a clear difference between the onset temperature of superconducting transition T-c(onset) and main shielding temperature T-c(main). T-c(main) approaches T-c(onset) with increasing pressure and merges at about 2.4 GPa at which the antiferromagnetism vanishes under zero field. In the temperatures between T-c(onset) and T-c(main), the decrease of chi' is quite small while chi '' changes largely. At T-c(main), chi' drops and chi '' peaks sharply as those of conventional superconductors. These results imply that CeRhSi3 has two different types of pinning state in the superconductivity and the appearance of them is probably associated with the antiferromagnetic state.

The two Laves phase compounds ZrZn2 and NbFe2 belong to the small group of low temperature itinerant magnets. While ZrZn2 shows a ferromagnetic (FM) transition with a small ordered moment, Nb1-yFe2+y exhibits a magnetically ordered ground state which is believed to be of spin-density-wave type for vertical bar y vertical bar < 0.015 and FM for vertical bar y vertical bar >= 0.02. Furthermore, signatures of a logarithmic Fermi-liquid breakdown suggest the existence of a quantum critical point on the Nb-rich side at y approximate to -0.015. In both systems a largely enhanced Stoner factor indicates the presence of FM correlations, which, in general, support the observability of a conduction electron spin resonance (ESR). We present our results of ESR measurements on high quality ZrZn2 single crystals and on polycrystalline samples of Nb1-yFe2+y. The ESR data of both compounds is analysed in terms of a conduction ESR being subject to strong exchange enhancement effects.

We report the temperature dependence of the electrical resistivity ρ(T) and resultant superconducting B-T phase diagram of CeRhSi3 for fields along the tetragonal c-axis. We have found a bend on the curve of upper-critical-field Bc2(T) vs. temperature. The bend emerges at pressures above 2.4 GPa where the superconducting transition temperature is comparable to or higher than the Néel temperature under zero field. Associated with the emergence of the bend, the ρ(T) curve at each field has an obvious change in the slope at a temperature under the magnetic fields.

We demonstrate an extremely high upper-critical-field, Bc2, in the noncentrosymmetric heavy-fermion superconductor CeRhSi3 for a magnetic field along the tetragonal c-axis. The robustness of the superconductivity over the magnetic field is outstanding among the known superconductors. The extremely large Bc2 is attributed to the absence of the paramagnetic pair-breaking effect characteristic of noncentrosymmetric superconductors.

We report anomalous behaviors of the de Haas – van Alphen (dHvA) oscillations in various CexLa1−xRu2Si2 samples when magnetic field is applied in the (001) plane. We argue that these behaviors can be explained by assuming that the effective mass of the conduction electron of one spin direction decreases with field while that of the opposite spin direction increases.

We report the de Haas-van Alphen (dHvA) effect studies across the first order metamagnetic transitions in samples of CexLa1-xRu2Si2 with x = 0.16, 0.51 and 0.84. It is found that the dHvA frequency and effective mass do not change across the first order metamagnetic transition. These behaviors are in striking contrast to those observed in magnetic fields across and above the metamagnetic crossover in CeRu2Si2.

We report the first observation of the de Haas-van Alphen (dHvA) oscillations in U-based alloys U1-xThxPd3 up to x = 0.5. In U0.5Th0.5Pd3, the dHvA oscillations β2 can be observed in the (1100) plane and the frequencies of the oscillations as well as their angular dependences are found to be nearly the same as those in UPd3. On the other hand, the effective mass of the β2 oscillation is found to decrease with x from 1.78m0 of UPd3 to 1.32m0 of U0.5Th0.5Pd3. From these observations we argue that the f electrons in UPd3 are nearly localized and the interactions between the f electrons and the conduction electrons are weak.

Fermi liquids and metallic ferromagnetism The low-temperature properties of conventional metals are well described by Fermi liquid theory, which treats electrons as a gas of scattering but otherwise non-interacting entities. But increasingly, examples of metallic systems are being found in which Fermi liquid theory breaks down, often in mysterious ways. Smith et al. describe one such example in which non-Fermi liquid properties can be attributed to a specific process — the long-range interactions between the electronic spins in a metal on the verge of becoming magnetic. Such a system is known as a 'marginal' Fermi liquid, and provides a conceptual link between classical metals and more exotic non-Fermi systems.

We report de Haas-van Alphen effect measurements on CeRu(2)(Si(1-x)Ge(x))(2) to reveal electronic structure change over the broad range of chemical pressure from x = 0.0 to 1.0. It is found that the Fermi surface properties change drastically across the metamagnetic crossover field (B(m)) but vary smoothly with x from those in magnetic fields above B(m) in CeRu(2)Si(2) to those in the ferromagnetic state in CeRu(2)Ge(2). Implications of the present results are discussed in conjunction with the magnetic phase diagram.