Search

We grew single crystals of PrCoIn 5 , PrRhIn 5 , and PrIrIn 5 with the tetragonal crystal structure and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization and de Haas–van Alphen effect. These Pr compounds reveal no magnetic ordering. The topology of the Fermi surfaces is the same as that of a non-4 f reference compound LaRhIn 5 . The cyclotron mass and/or the electronic specific heat coefficient are also approximately the same as those of LaRhIn 5 . The magnetic susceptibility and magnetization are anisotropic, reflecting the crystal structure, which are well explained by the tetragonal crystalline electric field scheme with the singlet ground state.

We have succeeded in growing a high-quality single crystal of ThIn 3 with the cubic structure by the In-flux method and measured the electrical resistivity, magnetic susceptibility and de Haas–van ...

We have studied a change of the Fermi surface in an antiferromagnet CeIn 3 via the de Haas–van Alphen experiment under pressure up to 3 GPa. With increasing pressure P , the Neel temperature T N =10 K decreases and becomes zero at a critical pressure P c ≃2.6 GPa. In the pressure region P > P c , we have observed a large main Fermi surface named a , which indicates that the electronic state of 4 f electron in CeIn 3 changes from localized to itinerant at P c , as observed in the similar antiferromagnets CeRh 2 Si 2 and CeRhIn 5 . The cyclotron effective mass m c * of this main Fermi surface is extremely enhanced around P c : m c * ≃60 m 0 at 2.7 GPa for the magnetic field along the direction.

We have succeeded in growing a high-quality single crystal of an antiferromagnet UPdGa 5 by the Ga-flux method with the off-stoichiometric composition of U : Pd : Ga = 1 : 2 : 7.3. The Neel temperature T N = 30.5 K is found to increase with increasing the residual resistivity ratio (RRR) and becomes constant for a high-quality single crystal sample whose RRR is larger than 50. The electronic state has been investigated by the de Haas–van Alphen experiment, indicating the similar cylindrical Fermi surfaces as in an antiferromagnet UPtGa 5 . We have also studied the pressure effect by measuring the electrical resistivity. The Neel temperature decreases with increasing pressure and becomes zero at 3.1 GPa. The antiferromagnetic state is changed into the paramagnetic state above 3.1 GPa.

We have succeeded in growing a high-quality single crystal of UCu 2 Si 2 with the tetragonal structure by the Sn-flux method and measured the electrical resistivity, magnetic susceptibility, magnetization and specific heat. UCu 2 Si 2 is found to order antiferromagnetically below T N =106 K, and follows a successive ferromagnetic ordering at T C =100 K. The magnetic properties are highly anisotropic, reflecting the crystal structure. An easy-axis of magnetization is found to be the [001] direction ( c -axis) both in the antiferromagnetic and ferromagnetic phases, while the [100] direction ( a -axis) corresponds to the hard-axis in magnetization. The magnetization curve in the antiferromagnetic phase indicates a clear metamagnetic transition at a low field of about 1 kOe and changes into a ferromagnetic magnetization curve below T C =100 K. The saturation moment is determined as 1.75 µ B /U at 2 K. The electronic specific heat coefficient is also determined as 20 mJ/(K 2 ·mol).

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...

The pressure dependence of the first-order phase transition (FOPT) at the upper critical field H c2 in CeCoIn 5 has been studied by magnetization measurements. The FOPT is found to persist at pressures at least up to 1.5 GPa in the c axis and up to 1.38 GPa in the a axis. With increasing pressure, the anisotropy of H c2 becomes stronger, and the condensation energy decreases significantly. We also observed a notable peak effect near H c2 under pressure. Our results suggest that the FOPT cannot be accounted for by Pauli limiting alone.

We report the systematic evolution of the superconducting (SC) characteristics of the heavy-fermion (HF) superconductor CeCoIn 5 via nuclear-quadrupole-resonance (NQR) measurement under pressure ( P ). The application of P significantly suppresses the nuclear spin–lattice relaxation rate 1/ T 1 that is dominated by antiferromagnetic (AFM) spin fluctuations (SFs) specific to a quantum critical point (QCP). It is demonstrated that the marked suppression of AFM SFs leads to a reduction in the SC energy gap or in the coupling strength of the Cooper pair. T c , nevertheless, increases with increasing P due to the increase in HF bandwidth. This is expected to make the lifetime of quasi-particles sufficiently long.

We measured the electrical resistivity, specific heat, magnetic susceptibility, high-field magnetization, thermal expansion and magnetostriction of an antiferromagnet Ce 3 Sn 7 with the orthorhombic crystal structure. The experimental data are found to be well explained on the basis of the crystalline electric field (CEF) 4 f -scheme previously proposed by Bonnet et al. in which the two Ce atoms at the 2(a) site possess a magnetic moment of 0.36 µ B /Ce and the one Ce atom at the 4(i) site possesses no magnetic moment as in a valence fluctuating compound CeSn 3 . We also constructed the antiferromagnetic phase diagram for the three principal directions. Furthermore, we carried out the de Haas–van Alphen experiment. Fermi surfaces are many in number but extremely small in volumes, indicating that Ce 3 Sn 7 is a semimetal.

We report the discovery of new superconducting and novel magnetic phases in CeIn$_3$ on the verge of antiferromagnetism (AFM) under pressure ($P$) through the In-nuclear quadrupole resonance (NQR) measurements. We have found a $P$-induced phase separation of AFM and paramagnetism (PM) without any trace for a quantum phase transition in CeIn$_3$. A new type of superconductivity (SC) was found in $P=2.28-2.5$ GPa to coexist with AFM that is magnetically separated from PM where the heavy fermion SC takes place. We propose that the magnetic excitations such as spin-density fluctuations induced by the first-order magnetic phase transition might mediate attractive interaction to form Cooper pairs.

We have studied the superconducting property by measuring the electrical resistivity under the magnetic field and pressure for CePt 3 Si, which is the first antiferromagnetic heavy fermion superconductor without inversion symmetry in its tetragonal crystal structure. The upper critical field H c2 (0) is found to be approximately isotropic: H c2 (0) = 2.7 T for H ∥[100] and 3.2 T for H ∥[001]. The Neel temperature T N = 2.3 K and the zero resistivity superconducting transition temperature T sc ≃0.65 K decrease markedly with increasing pressure, suggesting that the present superconductivity is correlated to the antiferromagnetic state.

We have measured the electrical resistivity, magnetic susceptibility, high-field magnetization, specific heat and de Haas–van Alphen (dHvA) oscillation of Ce 2 RhIn 8 , together with the dHvA oscillation of La 2 RhIn 8 . In La 2 RhIn 8 we detected three kinds of dHvA branches showing cylindrical Fermi surfaces, which are well explained by the result of FLAPW energy band calculations. The corresponding two dHvA branches were detected in Ce 2 RhIn 8 , indicating that the topology of the Fermi surface in Ce 2 RhIn 8 is approximately the same as that of La 2 RhIn 8 . The magnetic susceptibility and magnetization of Ce 2 RhIn 8 were analyzed on the basis of the crystalline electric field scheme of localized-4 f energy levels. Pressure-induced superconductivity was confirmed above 1.2 GPa from the resistivity and ac-susceptibility measurements.

We have succeeded in growing a single crystal of CeNiIn 4 with the orthorhombic crystal structure by the In-flux method. CeNiIn 4 is found to order antiferromagnetically below 1.4 K, with a successive change of the magnetic structure below 0.75 K. The magnetic phase diagram was formed by the specific heat and magnetization measurements. The electronic specific heat coefficient is determined as 80 mJ/K 2 ·mol. From these experimental results it is concluded that CeNiIn 4 is a usual 4 f -localized compound.

We report that the muon spin relaxation rate under zero-external field in the heavy-fermion compound Ce Tr In 5 ( Tr =Ir, Co) is independent of temperature down to 20 mK, demonstrating the absence of magnetism due to long-range magnetic order and/or to the breakdown of time-reversal symmetry in the superconducting state. The magnetic penetration depth deduced by the muon spin relaxation rate under a transverse field is λ∼6700 A for CeIrIn 5 at 402 G and ∼5500 A for CeCoIn 5 at 3 kG.

The pressure dependence of transport properties in CeRhIn5 was studied up to 8.5 GPa by using a diamond-anvil cell. The electrical resistivity does not follow the T 2 -dependecne of a Fermi liquid nature under any pressure. In this non-Fermi liquid state, superconductivity was observed in a wide pressure range of 1:5 GPa

We measured the low-temperature specific heat in magnetic fields up to 80 kOe, together with the magnetization for the heavy-fermion superconductor CeCoIn 5 with the transition temperature T c = 2....

We measured the high-field magnetization of TmCu 2 with the orthorhombic structure. A metamagnetic transition with a large hysteresis was observed for the field along the a -axis. This metamagnetic transition is not related to the antiferromagnetic order, which was observed even above the Neel temperature of 6.3 K. After the metamagnetic transition, the magnetization curve is not similar to the easy-axis ( b -axis) magnetization, but is similar to the magnetization for the field tilted by 60° from the a -axis. Except this result, the character of this metamagnetism is similar to the previous metamagnetism of RCu 2 (R = Ce, Pr, Dy, Tb) based on the quadrupole moment.

By using a sensitive superconducting cavity resonator, we measure the temperature dependence of in-plane microwave penetration depth λ a b in underdoped single crystals of the iron-pnictide superconductor PrFeAsO 1- y ( T c ∼35 K). At low temperatures, λ a b ( T ) shows very flat temperature dependence, which indicates that the superconducting gap function Δ( k ) is non-zero all over the Fermi surface.

The effect of pressure on the electronic states in antiferromagnets CeRhSi 3 , CeIrSi 3 , CePtSi 3 , CeRhGe 3 , CeIrGe 3 , and CeCoGe 3 were studied under pressures up to 8 GPa. Superconductivity was found in CeRhSi 3 , CeIrSi 3 , and CeCoGe 3 at a critical pressure where the corresponding Neel temperature becomes zero.

We have succeeded in growing a high-quality single crystal of UCu 2 Si 2 with a tetragonal structure by the Sn-flux method and measured the de Haas–van Alphen effect. UCu 2 Si 2 orders antiferromagnetically below T N =106 K and follows a successive ferromagnetic ordering at T C =100 K. Several de Haas–van Alphen branches are observed in the ferromagnetic state, ranging from 5×10 6 to 7×10 7 Oe. The corresponding cyclotron effective masses are moderately large, ranging from 1.4 to 4.2 m 0 , consistent with the electronic specific heat coefficient γ=20 mJ/(K 2 ·mol). These experimental results are approximately explained by the 5 f -itinerant spin- and orbital-polarized energy band model.

To investigate a mysterious superconducting state of URu_2Si_2 embedded in the so-called hidden order state, the lower critical field H_{c1} is precisely determined down to 55 mK for H || a and H || c. For this purpose, the positional dependence of the local magnetic induction is measured on ultraclean single crystals (T_c = 1.4 K) with residual resistivity ratio exceeding 700. We find that the temperature dependence of H_{c1} significantly differs from that of any other superconductors. The whole H_{c1}(T) for H || a are well explained by the two superconducting gap structures with line and point nodes, which have been suggested by the recent thermal conductivity and specific heat measurements. On the other hand, for H || c, a change of slope with a distinct kink in H_{c1}(T), which cannot be accounted for by two gaps, is observed. This behavior for H || c sharply contrasts with the cusp behavior of H_{c1}(T) associated with a transition into another superconducting phase found in UPt_3 and U_{1-x}Th_xBe_{13}. The observed anomalous low-field diamagnetic response is possibly related to a peculiar vortex dynamics associated with chiral domains due to the multicomponent superconducting order parameter with broken time reversal symmetry., Comment: 7 pages, 4 figures; accepted in J. Phys. Soc. Jpn

The electronic properties in SmFe 4 P 12 have been investigated by means of the de Haas–van Alphen effect, transverse magnetoresistance, Hall effect, and band structure calculation. We have found a markedly large anisotropy in the cyclotron effective mass of the 47th band Fermi surface despite its nearly spherical shape. Moreover, this mass enhancement in SmFe 4 P 12 is robust against magnetic field. The transverse magnetoresistance increases nearly quadratically with magnetic field for all field directions; this is unexpected for an ordinary uncompensated metal. The Hall coefficient is found to be 4-fold enhanced at low temperature compared with that at room temperature. These anomalies in transport properties are ascribed to the stronger enhancement of the cyclotron effective mass of the 48th band Fermi surface.

We succeeded in growing a high-quality single crystal of LuCoGa 5 with the HoCoGa 5 -type tetragonal crystal structure by the Ga self-flux method. The lattice parameters, fractional coordinates, and thermal parameters were determined from single-crystal x-ray diffraction measurements. We also measured the electrical resistivity, specific heat, and the de Haas–van Alphen (dHvA) effect. The Fermi surface mainly consists of two nearly cylindrical Fermi surfaces, which are well explained by the results of full-potential linearized augmented plane wave (FLAPW) energy band calculations.

Flux line lattice (FLL) of a quasi-two-dimensional heavy fermion superconductor CeCoIn 5 in perpendicular field was investigated by small-angle neutron scattering technique. A square FLL was observed in magnetic fields up to 3 T and at 4 T a splitting of diffraction spots was observed, indicating reorganization of the FLL toward a triangular (rhombic) FLL. The FLL form factor is nearly field-independent up to 4 T. This is in sharp contrast to conventional superconductors, in which the form factor rapidly decays with increasing magnetic field. This behavior of the form factor, which indicates the anomalous field distribution around the vortex cores, can be attributed to strong Pauli paramagnetic effects and to field-tuned quantum critical point effects.

A series of ternary compounds RRhIn 5 (R: rare earth) has been grown in the single crystalline form by means of the flux method. The magnetic properties of these compounds were investigated by meas...

We succeeded in growing a high-quality single crystal of ThRhIn 5 with the HoCoGa 5 -type tetragonal crystal structure by the In-flux method. The lattice parameters, positional parameters and thermal parameters were determined from single-crystal x-ray diffraction measurements. We also measured the electrical resistivity and de Haas–van Alphen (dHvA) effect. Main dHvA branches are very similar to those of the 4 f -itinerant heavy fermion superconductor CeCoIn 5 , but the cyclotron effective masses are by one to two orders of magnitude smaller than those of CeCoIn 5 . These Fermi surface properties are well explained by the FLAPW energy band calculations.

We present a systematic study of the dc-resistivity, Hall effect, and magnetoresistance in the normal state of quasi 2D heavy fermion superconductors CeMIn5 (M: Rh and Co) under pressure. Here the electronic system evolves with pressure from an antiferromagnetic (AF) metal, through a highly unconventional non-Fermi liquid, and finally into a Fermi-liquid state. The amplitude of the Hall coefficient increases dramatically with decreasing T, reaching at low temperatures a value significantly larger than 1/ne. Furthermore, the magnetoresistance is characterized by T- and H-dependence which clearly violate Kohler's rule. We found that the Hall angle cot\Theta varies as T^2, and the magnetoresistance is well scaled by the Hall angle as \Delta \rho_{xx}/\rho_{xx}\propto \tan^2\Theta. These non-Fermi liquid properties in the electron transport are remarkably pronounced when the AF fluctuations are enhanced in the vicinity of the QCP. We lay particular emphasis on the striking resemblance of these anomalous magnetotransport with those of the high-Tc cuprates. We argue that features commonly observed in quasi 2D heavy fermion and cuprates very likely capture universal features of strongly correlated electron systems.

Specific heat and de Haas–van Alphen (dHvA) measurements were performed on a high-quality single crystal of CePt 3 Si without inversion symmetry in the tetragonal crystal structure. We observed distinct peaks in the specific heat C at the superconducting transition temperature T c =0.46 K and the antiferromagnetic ordering temperature T N =2.25 K, compared to the previous data, indicating an improvement of the sample quality. The temperature dependence of the electronic specific heat coefficient C e / T below about 0.3 K is well described by the equation of C e / T =γ s +β s T with γ s =34.1 mJ/(K 2 ·mol) and β s =1290 mJ/(K 3 ·mol), evidencing the existence of line nodes in the superconducting energy gap. Furthermore, the electronic specific heat coefficient γ s in the superconducting state indicates a nonlinear magnetic field dependence \(\gamma_{\text{s}}(H)\propto\sqrt{H}\), which also supports the presence of line nodes. We did not observe a discontinuous change of the Fermi surface at P AF =0.6 GPa ...

We succeeded in growing a single crystal of CePtSi 3 with the tetragonal BaNiSn 3 -type crystal structure by the Sn-flux method. CePtSi 3 is found to be an antiferromagnet with successive two trans...

We grew single crystals of NdRhIn 5 , TbRhIn 5 , DyRhIn 5 , and HoRhIn 5 with the tetragonal crystal structure and measured the magnetic susceptibility and magnetization. NdRhIn 5 is an antiferromagnet with a Neel temperature T N = 11.6 K. Below T N , magnetization reveals two metamagnetic transitions at H m1 = 70 kOe and H m2 = 93 kOe for the magnetic field along the [001] direction. The saturation moment of 2.5 µ B /Nd is in good agreement with the staggered Nd moment determined by the neutron diffraction experiment. These metamagnetic transitions correspond to the change of the magnetic structure. TbRhIn 5 , DyRhIn 5 and HoRhIn 5 are found to be antiferromagnets with T N = 47.3, 28.1, and 15.8 K, respectively. The magnetization curves of these compounds are also quite similar to those of NdRhIn 5 , revealing two metamagnetic transitions. The magnetic structures in magnetic fields are proposed by considering the exchange interactions based on the crystal structure.

We carried out the de Haas–van Alphen (dHvA) experiment of an antiferromagnet CeCoGe 3 and its reference compound LaCoGe 3 without inversion symmetry in the tetragonal crystal structure. The detect...

We report the discovery of pressure-induced superconductivity in an antiferromagnet CeIrSi 3 , which lacks inversion symmetry in the tetragonal crystal structure. The Neel temperature T N = 5.0 K at ambient pressure decreases monotonically with increasing pressure, and becomes zero at about 2.5 GPa. Superconductivity appears in a wide pressure region from 1.8 GPa to about 3.5 GPa, with a relatively large superconduting transition temperature T sc = 1.6 K and a large upper critical field H c2 (0) = 11.1 T at 2.5 GPa, indicating heavy-fermion superconductivity.