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Josephson critical current I c between a single crystal CePt 3 Si and Al has been measured for the junctions on the CePt 3 Si surface perpendicular to the a and c axes. In the magnetic-field dependence of I c , a dominant maximum peak at zero field has been observed only for the junction on the a -axis face thus far, indicating that the Josephson effect is allowed at least for current flow parallel to the a axis. This result places a restriction on the representations of the order parameter in the noncentrosymmetric superconductor CePt 3 Si.

Josephson critical current density J c between a single crystal URu 2 Si 2 and an s -wave superconductor has been investigated for URu 2 Si 2 –Cu–Nb(SNS') and URu 2 Si 2 –Nb(SS') junctions. In cont...

We performed dc-magnetization and ac-susceptibility measurements to clarify how the magnetic properties of CeAgSb2, which shows ferromagnetic order along the c-axis below 9.6 K, evolve with the application of a transverse magnetic field (Hab). The Curie temperature (TC) is suppressed to zero by the application of Hab, and the ac-susceptibility measured along the c-axis \(\chi '_{c}\) under Hab continuously shows a critical-divergence-like anomaly at TC, indicating the presence of a field-induced ferromagnetic quantum critical point in this compound. On the other hand, the magnitude of \(\chi '_{c}\) at TC rapidly decreases with increasing Hab up to around 0.5 T. This result suggests that the magnetic properties around TC rapidly change with Hab in the relatively lower Hab range.

Josephson critical current I c between a single crystal UPt 3 and Al has been measured for a corner junction on the UPt 3 faces perpendicular to the a [11 2 0] and b [10 1 0] axes. The magnetic field dependence of I c has shown a global maximum at zero magnetic field like the junctions on a single face. We have not observed a behavior indicating the phase shift of the order parameter between the a - and b -axis directions thus far.

The thickness of the Meissner region ρ in Au of Au-clad Nb wire has been measured down to 50 mK, in order to investigate the superconductivity in a normal metal induced by the proximity effect. The magnetic field dependence of ρ and the Josephson critical current I C through a SNS junction made of an Au-clad Nb wire have been also measured to estimate the coherence length ξ N in Au. Above 150 mK, ρ and ξ N increase in proportion to T -1 , and are independent of the mean free path l N in Au. Although Au is in the clean limit ( l N > ξ N ), these results can be qualitatively interpreted by the dirty limit theory with a modification using ξ N derived in the clean limit.

The maximum supercurrent I c passing through the S(Nb)-N(Cu doped with Mn)-S(Nb) junction made of Cu-clad Nb wire has been measured down to 30 mK, in order to investigate the relation between the superconducting proximity effect and the Kondo effect. The maximum supercurrent becomes small with an increase in Mn concentration and remarkably with a decrease in electronic mean free path in Cu. The electronic mean free path dependence of I c may be explained qualitatively in consideration of the spin flip scattering and the RKKY interaction of Mn impurities. The Meissner effect induced by the proximity effect in Cu-clad Nb wire can be understood through the behavior of the coherence length ξ N in Cu which is derived from I c .

The magnetization change ΔM at the superconducting transition of LaIrSi3 has been measured in various magnetic fields H. The observed ΔM in H = 0 is within the range of the Meissner effect induced by the possible residual field, suggesting that the spontaneous magnetization, if it exists, is below the experimental accuracy. This result is in agreement with the results of μSR experiments, in which no spontaneous magnetic field has been observed in the superconducting state.

The proximity effect in Cu clad Nb wires of which Cu is doped with dilute magnetic impurities, has first been investigated in relation to the Kondo effect. As for Cu doped with dilute Fe, Co and Ni impurities, the probability of the spin flip scattering of conduction electrons, α, by Fe, Co and Ni impurities decreases linearly with decreasing temperature. As for Cu doped with dilute Mn impurities, the probability, α, by Mn impurities is concluded to be suppressed by the RKKY interaction between Mn impurities which depends on the electronic mean free path. The temperature dependence of the resistivity of the Mn alloy may be understood as a result of the coexistence of the dilute Kondo effect and the RKKY interaction between Mn impurities.

The anomalous behavior of the heavy-fermion superconductor UBe13, which appears below the superconducting transition temperature Tc ∼ 0.9 K, has been investigated by point-contact spectroscopy and the Josephson effect. An abrupt increase in the temperature dependence of the Josephson critical current is observed below 0.7 K between UBe13 and conventional superconductors. The zero-bias resistance of the point contacts between UBe13 and Pt decreases continuously below Tc and shows an abrupt drop at 0.5–0.6 K. These results suggest that the anomaly originates from superconductivity rather than magnetism, which has been considered as one of the origins of the anomaly.

We have measured the magnetization of single crystals of the non-centrosymmetric superconductor LaNiC2, which is considered to break time-reversal symmetry by μSR measurements. Below the transition temperature Tc ∼ 3 K, the emergence of magnetization on the order of 10−5 G is observed in zero magnetic field along the c-axis but not along the a-axis. This spontaneous magnetization is larger than the Meissner effect induced by the possible residual field and did not change after applying magnetic fields of up to 15 mOe or after warming to room temperature. The results that the direction is related to the lack of inversion symmetry and that the magnitude is sensitive to the crystallinity of the sample suggest some analogy with pyroelectricity.

The Josephson critical current I c between a single-crystal UPt 3 and Al has been measured for the junctions on the UPt 3 surface perpendicular to the hexagonal a [11\bar20], b [10\bar10], and c [0001] axes. The magnetic field dependence of I c shows a Fraunhofer diffraction pattern for a current flow parallel to the c -axis, suggesting that the Josephson coupling is uniform throughout the junction. Small modifications applied to the Fraunhofer pattern have been observed for a current flow parallel to the a - and b -axes. These results contradict the E 2 u scenario for the odd-parity order parameter in UPt 3 , in which the Josephson effect is forbidden in the three directions, whereas the recently proposed E 1 u scenario permits, at least, the a - and c -axis Josephson couplings.

We have developed a new method to perform point-contact spectroscopy PCS under pressure, in which a thin-film deposition technique is used for making a point contact. We investigated a pressure dependence of the point-contact spectra of the heavy-fermion superconductor URu 2 Si 2 single crystal. In PCS of URu 2 Si 2 , two characteristic components evolve at low temperatures: one is a symmetric structure with respect to zero bias voltage suggesting a gap of the density of states at the Fermi surface, and the other is an anti-symmetric structure. We observed little change of two components between hidden order and antiferromagnetic phases.

We report the superconducting properties of LaPt 3 Si poly and single crystals with non-centrosymmetric structure. We have measured ac magnetic susceptibility, χ ac = χ' + iχ'', under sweeping magnetic fields. On the χ', a peak ascribed to the differential paramagnetic effect DPE is observed just below critical fields, where the superconducting state of LaPt 3 Si collapses completely by an external magnetic field. However this DPE behavior disappears below 0.40 K. Additionally, in this temperature range, the width of the magnetic field of collapsing superconductivity becomes broader and the superconducting domains survive even in higher magnetic fields.

We have measured specific heat of poly and single crystalline LaPt 3 Si samples under various magnetic fields. For zero magnetic field, we observed a distinct peak and jump in the specific heat at the superconducting transition temperature T c ∼0.64 and 0.61 K for the poly and single crystals, respectively. Temperature dependences of the specific heat of both samples below T c can be well-described by a exponential equation for a conventional superconductor at zero magnetic field. The jump at T c of single crystal is still distinct under magnetic fields. On the other hand, the peak of the poly crystal becomes broad above 40 G. The broad additional specific heat tail appears at higher temperatures than the T c expected from the results of the single crystal. We show, for the first time, the temperature dependence of superconducting critical magnetic field H c ( T ) obtained from the specific heat measurement. Small anisotropy of H c ( T ) was observed for the single crystal, with H c (0) = 66 and 61 G for ...

We have fabricated a 3-axes magnetometer that can reduce the residual magnetic field below 50 µG for each direction. Josephson critical current I c between a noncentrosymmetric superconductor (CePt 3 Si or LaPt 3 Si) and Al has been investigated inside it to avoid the magnetic-flux trapping during the superconducting transition and found to show a magnetic field H dependence similar to the previous one obtained using one-axis magnetometer; asymmetric patterns with respect to H =0 are commonly observed for CePt 3 Si and LaPt 3 Si. This suggests that the residual-field components perpendicular to H applied for I c ( H ) measurements does not basically affect the I c ( H ) patterns.

The Josephson effect between LaPt 3 Si and Al has been investigated for junctions on the (100) and (001) faces of LaPt 3 Si single crystals and a polycrystal. In the magnetic-field dependence of the Josephson critical current, the anomaly previously reported for CePt 3 Si appeared; an oscillating pattern without a dominant maximum peak at zero field was observed for the junction on the (001) face. This cannot be interpreted as the Josephson effect between conventional s -wave superconductors and suggests that the origin of the anomaly lies in the noncentrosymmetric crystal structure.

We carried out simultaneous measurements of electrical resistivity and thermal expansion of the heavy-fermion compound URu2Si2 under pressure using a single crystal. We observed a phase transition anomaly between hidden (HO) and antiferromagnetic (AFM) ordered states at TM in the temperature dependence of both measurements. For the electrical resistivity, the anomaly at TM was very small compared with the distinct hump anomaly at the phase transition temperature T0 between the paramagnetic state (PM) and HO, and exhibited only a slight increase and decrease for the I // a-axis and c-axis, respectively. We estimated each excitation gap of HO, Delta_HO, and AFM, Delta_AFM, from the temperature dependence of electrical resistivity; Delta_HO and Delta_AFM have different pressure dependences from each other. On the other hand, the temperature dependence of thermal expansion exhibited a small anomaly at T0 and a large anomaly at TM. The pressure dependence of the phase boundaries of T0 and TM indicates that there is no critical end point and the two phase boundaries meet at the critical point., Comment: 4 pages, 4 figures

Fig. 1. (a) Temperature dependence of specific heat of Ce1:01Pt3Si, which was measured using the same sample as that in this study. (b) Temperature dependences of magnetization under several pressures of 0.00, 0.19, 0.22, 0.24, 0.27, 0.29, 0.50, and 0.66 GPa and (c) lowtemperature part of magnetization of selected pressures. Experimental data in (c) are shifted to avoid overlap.

We have investigated ac and dc magnetic susceptibilities (χ ac and χ dc ) of the heavy-fermion superconductor CePt 3 Si ( T c + ∼0.75 K) for two single crystals that show a specific heat anomaly at T c - ∼0.4 K. One crystal shows a double transition at T c + and T c - in the form of structures in the out-of-phase component of χ ac and in χ dc measured in the cooling process. The magnetic field dependence of χ ac suggests that the lower transition also originates in superconductivity. In contrast, only the higher transition has been detected in susceptibility measurements of the other crystal whose specific heat has a less dominant peak near T c - and a broad peak at T c + . These results suggest that CePt 3 Si consists of two superconducting phases with different T c 's, whose volume fraction varies from sample to sample.