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Neutron imaging is one of the most powerful tools for nondestructive inspection owing to the unique characteristics of neutron beams, such as high permeability for many heavy metals, high sensitivity for certain light elements, and isotope selectivity owing to a specific nuclear reaction between an isotope and neutrons. In this study, we employed a superconducting detector, current-biased kinetic-inductance detector (CB-KID) for neutron imaging using a pulsed neutron source. We employed the delay-line method, and high spatial resolution imaging with only four reading channels was achieved. We also performed wavelength-resolved neutron imaging by the time-of-flight method for the pulsed neutron source. We obtained the neutron transmission images of a Gd-Al alloy sample, inside which single crystals of GdAl3 were grown, using the delay-line CB-KID. Single crystals were well imaged, in both shapes and distributions, throughout the Al-Gd alloy. We identified Gd nuclei via neutron transmissions that exhibited characteristic suppression above the neutron wavelength of 0.03 nm. In addition, the ^{155}Gd resonance dip, a dip structure of the transmission caused by the nuclear reaction between an isotope and neutrons, was observed even when the number of events was summed over a limited area of 15 X 12 um^2. Gd selective imaging was performed using the resonance dip of ^{155}Gd, and it showed clear Gd distribution even with a limited neutron wavelength range of 1 pm., 7 pages, 6 figures, Accepted in Journal of IEEE transactions of Applied Superconductivity

We report a vector-scanning SQUID microscope for probing a vector magnetic field. We designed and fabricated a vector [three-dimensional (3-D)] SQUID sensor with the aid of Nb multilayer fabrication technology. Our vector SQUID sensor on a single chip is composed of a vector sensor with three orthogonal pick-up coils, which catch the X , Y, and Z magnetic field components. We improved both the sensitivity and the spatial resolution not only by reducing the inner diameter but also by increasing the number of pick-up-coil windings within the framework of the multilayer technique. Our SQUID sensors operated properly, and the characteristics showed a good agreement with our design parameters. Since the sensor is suitable for our SQUID microscope, we are constructing our scanning microscope platform by using a Gifford-McMahon cryocooler for allowing long-time measurements. We also succeeded in connecting our vector SQUID sensor to a commercial flux-locked loop readout circuit (Magnicon Inc., Model XXF-1) to generate the voltage outputs, which are proportional to the XYZ components of the external magnetic field. We also use an XYZ piezo-driven scanner for the precise control of the pick-up-coil positions over the 3-D range of 5 × 5 × 5 mm 3 with a step size of 10 nm at 4 K.

We investigated vortex states in small star-shaped Mo 80 Ge 20 plates both theoretically and experimentally. The numerical calculations of the Ginzburg–Landau equation have been carried out with the aid of the finite element method, which is convenient to treat an arbitrarily shaped superconductor. The experimental results were observed by using a scanning SQUID microscope. Through systematic measurements, we figured out how vortices form symmetric configuration with increasing the magnetic field. The vortex distribution tends to adapt to one of five mirror symmetric lines when vortices were located at the five triangular horns of a star-shaped plate. The crystalline homogeneity of a sample was confirmed by the X-ray diffraction and the superconducting properties so that vortices are easily able to move for accommodating vortices in the geometric symmetry of the star-shaped plate. The experimental vortex configurations obtained for a star-shaped plate are in good agreement with theoretical predictions from the nonlinear Ginzburg–Landau equation.

A superconducting nanowire detector with a 10 B conversion layer is useful for sensing a single neutron at a high operation rate. We use 7 Li ion and 4 He ion emitted as two independent heat sources in opposite direction, which are associated with nuclear reaction 10 B(n, 4 He) 7 Li to identify the XV position of neutron arrival. We probe a change rate in the kinetic inductance L k originating from kinetic inertia of the Cooper pairs. Our detector is different from a well-known microwave kinetic inductance detector and, hence, is named as a current-biased kinetic inductance detector. We use two sets of meanderlines made of Nb nanowires with superconducting readout taps to monitor local signals. In between the X meander and the V meander, we sandwiched a 10 B layer acting as a neutron conversion layer to two charged particles. We succeeded in observing signal induced by nuclear reaction. We plan to build a megapixel neutron imager by coupling 10-bit linear position-sensitive arrays with single-flux quantum circuits to read (X,V) position of neutron arrival in the future.

We succeeded in demonstrating a neutron detector based on a Nb superconducting meander line with a 10B conversion layer for a neutron imager based on superconductor devices. We use a current-biased kinetic inductance detector (CB-KID), which is composed of a meander line, for detection of a neutron with high spatial resolution and fast response time. The thickness of Nb meander lines is 40 nm and the line width is narrower than 3 mu m. The area of 8 mm × 8 mm is covered by CB-KIDs, which are assembled at the center of the Si chip of the size 22 mm × 22 mm. The Nb CB-KIDs with a 10B conversion layer output the voltage by irradiating pulsed neutrons. We have investigated γ/n discrimination of a Nb-based CB-KID with 10B conversion layer using a Cd plate, which indicates that a CB-KID can operate as a neutron detector under the strong γ-ray fields.

The amorphous superconducting films, which tend to have weakened pinning centers, are remarkably useful as model substance in studying nanostructured superconductors. The amorphous Mo 80 Ge 20 films have been deposited by a sputtering apparatus using a Mo 80 Ge 20 target and the small Mo 80 Ge 20 plates were fabricated with the aid of photolithography. The vortex distribution in a Mo 80 Ge 20 disk has been investigated by means of a scanning SQUID microscope. We found that vortices form different configurations as well as shell structures, which evolves with the increase in applied magnetic fields. The observed results are in good agreement with theoretical studies predicted for vortices in mesoscopic circular disks. We also applied a novel numerical method to improve the spatial resolution of the scanning SQUID microscope.

The heavy-fermion compound URu2Si2 has mystified researchers since the superconducting state (Tc = 1.45 K) is embedded within the enigmatic ‘‘hidden order” phase (Th = 17.5 K). Here, we report charge and thermal transport measurements on ultraclean single crystals of URu2Si2 with very large residual-resistivity-ratio down to 30 m K (∼Tc/50), which reveal a number of unprecedented superconducting properties. The results provide strong evidence for a new type of unconventional superconductivity with two distinct gaps having different nodal topology. We propose a gap function with chiral d-wave form Δ(k) = Δ0kz(kx + iky). We also demonstrate that a distinct flux line lattice melting transition with outstanding characters occurs well below the upper critical fields even at sub-Kelvin temperature. The intriguing superconducting state of URu2Si2 adds a unique and exciting example to the list of unconventional superconductors.

CeCoIn 5 is a heavy fermion superconductor with the transition temperature T c = 2.3 K, while in a related material CeRhIn 5 the superconductivity is highly suppressed and an incommensurate antiferromagnetic (AFM) order characterized by the propagation vector q h = (1/2, 1/2, 0.297) appears below T N = 3.8 K. From the elastic neutron diffraction measurements on mixed compounds CeRh 1―x Co x In 5 , it was found that the superconductivity is strongly suppressed by the incommensurate AFM order while it coexists with the commensurate AFM order with q c = (1/2, 1/2, 1/2) in the intermediate x region. This is in sharp contrast to the CeRh 1―x Ir x In 5 system, where both the commensurate and incommensurate AFM orders coexist with the superconductivity. These results reveal that particular areas on the Fermi surface nested by q h play an active role in forming the superconducting state in CeCoIn 5 .

The most fascinating phenomenon of vortex matter is the first-order melting transition from flux line lattice to liquid. In low- T c superconductors, the transition is extremely difficult to observe, because it occurs in the immediate vicinity of the mean field upper critical field H c2 . In contrast, the melting transition is established in high- T c cuprates at several tens of Kelvin, owing to large thermal fluctuations. Here we find that in ultraclean heavy-fermion superconductor URu 2 Si 2 ( T c = 1.45 K) a distinct melting transition with outstanding characters occurs well below H c2 . We show that very low carrier number with heavy mass results in exceptionally large fluctuations even at subkelvin temperatures. We also find a thermal conductivity anomaly below the melting transition, indicating enhancement of the quasiparticle mean free path possibly due to the formation of a quasiparticle Bloch state.

Revolution of the pressure-induced heavy fermion state and superconductivity in an antiferromagnet CeRhIn5 have been established by high-pressure Fermi surface studies using the de Haas–van Alphen technique. A marked change of the 4f-electron nature from localized to itinerant is realized at a critical pressure P c ≃ 2.35 GPa under magnetic fields, together with a divergent tendency of the cyclotron mass at P c . The electronic state of CeIrSi3 with the non-centrosymmetric tetragonal structure is also tuned from the antiferromagnetic state to the superconducting state as a function of pressure. The upper critical field H c 2 ( 0 ) at pressure of 2.65 GPa is found to be highly anisotropic: H c 2 ( 0 ) = 95 kOe for H ∥ [ 1 1 0 ] and H c 2 ( 0 ) ≃ 300 kOe for H ∥ [ 0 0 1 ] , with the superconducting transition temperature T sc = 1.6 K . A large magnitude of H c 2 ( 0 ) and a large anisotropy of H c 2 ( 0 ) are characteristic, which reveals a new type of superconductivity closely related to the spin–orbit interaction based on the non-centrosymmetric crystal structure.

We report our measurements of transport coefficients of quasi-2D HF CeRIn5 in the normal state, in the vicinity of a QCP and in the superconducting state. In the normal state, we observed a T-linear resistivity, a T2-dependence of cot θH (θH is the Hall angle), the violation of Kohler’s rule, and a giant Nernst coefficient. In the superconducting state, on the other hand, we found a rapid increase of the quasiparticle (QP) mean free path as the temperatures is reduced below Tc. The density of states (DOS) of delocalized QPs obtained from the thermal Hall coefficient is consistent with a d-wave pairing symmetry. Moreover, the angular dependence of thermal conductivity indicates that the gap function has a d-wave symmetry with line nodes perpendicular to the ab-plane. These results bear a striking resemblance to those obtained for the high-Tc cuprates. This similarity implies that the fluctuation and excitation spectrum near a 2D antiferromagnetic QCP could be universal.

We studied the change of the Fermi surface properties in antiferromagnets CeIn 3 and CeRhIn 5 via the dHvA experiments under pressure. We found the abrupt change of the Fermi surface at the critical pressure P c , where the magnetic ordering state changes to the paramagnetic one. The change of the Fermi surface indicates that the 4f-electron character is changed from localized to itinerant in CeIn 3 and CeRhIn 5 at P c . Namely, the 4f-electron contributes to the volume of the Fermi surface above P c . Interestingly, the pressure-induced heavy fermion state with large effective mass was observed around P c , where the pressure-induced superconductivity appears. We also discuss the Fermi surface properties in the system without inversion symmetry in the crystal structure as in CePt 3 Si and CeTX 3 (T:Co, Ir, Rh, X:Si, Ge). The spin–orbit interaction due to the lack of inversion symmetry brings about a splitting of the Fermi surface, which is important for considering the formation of Cooper pair.

We have studied the superlattices with alternating block layers (BLs) of heavy-fermion superconductor CeCoIn5 and conventional-metal YbCoIn5 by site-selective nuclear magnetic resonance(NMR) spectroscopy, which uniquely offers spatially-resolved dynamical magnetic information. We find that the presence of antiferromagnetic fluctuations is confined to the Ce-BLs, indicating that magnetic degrees of freedom of f-electrons are quenched inside the Yb-BLs. Contrary to simple expectations that the two-dimensionalization enhances fluctuations, we observe that antiferromagnetic fluctuations are rapidly suppressed with decreasing Ce-BL thickness. Moreover, the suppression is more prominent near the interfaces between the BLs. These results imply significant effects of local inversion-symmetry breaking at the interfaces., 5 pages, 4 figures, accepted for publication as a Rapid Communication in Physical Review B

We have measured the ultrasound velocity of quasi-two-dimensional superconductor CeCoIn 5 with extremely large Pauli paramagnetic susceptibility. The results indicate that the new high field superconducting phase, which is revealed by the recent heat capacity measurements, is characterized by the unusual softening of flux line lattice. The softening is most likely due to the collapse of the flux line lattice tilt modulus and transition to quasi-two-dimensional vortex state. These results provide a strong evidence that the high field phase is the Fulde–Ferrell–Larkin–Ovchinnikov phase, in which the order parameter is spatially modulated and has planar nodes aligned perpendicularly to the vortices.

When pressure is applied to cerium and uranium compounds, the magnetic ordering temperature is suppressed and becomes zero at a critical pressure P c . Around P c , non-Fermi liquid and/or superconductivity are observed. We clarified a change of the electronic state via a de Haas–van Alphen (dHvA) experiment when pressure crosses P c . The dHvA experiment under pressure was done for the antiferromagnets CeRh 2 Si 2 and CeRhIn 5 , and for a ferromagnet UGe 2 . We found an abrupt change of the Fermi surface for CeRh 2 Si 2 and UGe2 when crossing P c , indicating a first-order like phase transition. For CeRhIn 5 , the topology of the Fermi surface was unchanged, but the cyclotron mass increased steeply above 1.6 Gpa, where superconductivity sets in.

We present the In-NQR results under pressure ( P ) in CeIr ( In 1 - x Cd x ) 5 . In CeCoIn 5 and CeRhIn 5 , the occurrence of superconductivity (SC) is related with the antiferromagnetic spin fluctuations (AFM-SFs) originating from the antiferromagnetic quantum-critical point (AFM-QCP). The high- T c SC ( T cmax > 2 K ) is realized in both compounds. However, in CeIrIn 5 which is apart from the AFM-QCP, SC occurs even without AFM-SFs and the quite small value of T cmax (∼1 K) is observed around P = 3 GPa . The mechanism of SC in CeIrIn 5 may be different from that in CeCoIn 5 and CeRhIn 5 .

The present NMR study indicates an appearance of finite hyperfine fields coupled to incommensurate antiferromagnetic order of the Ce moments in CeCoIn 5 . The magnetic order is never observed in the normal state and also in the BCS state, but appears only inside the novel superconducting phase. Strong field dependence of the ordered magnetic moments indicates the coexistence of the incommensurate SDW order and an modulated SC (FFLO) state.

The observation of cyclotron resonance in ultra-clean crystals of URu2Si2 [S. Tonegawa et al., PRL 109, 036401 (2012)] provides another route besides quantum oscillations to the determination of the bulk electronic structure in the hidden order phase. We report detailed analyses of the resonance lines, which fully resolve the cyclotron mass structure of the main Fermi surface sheets. A particular focus is given to the anomalous splitting of the sharpest resonance line near the [110] direction under in-plane magnetic-field rotation, which implies peculiar electronic structure in the hidden order phase. The results under the field rotation from [110] toward [001] direction reveal that the splitting is a robust feature against field tilting from the basal plane. This is in sharp contrast to the reported frequency branch alpha in the quantum oscillation experiments showing a three-fold splitting that disappears by a small field tilt, which can be explained by the magnetic breakdown between the large hole sphere and small electron pockets. Our analysis of the cyclotron resonance profiles reveals that the heavier branch of the split line has a larger scattering rate, providing evidence for the existence of hot-spot regions along the [110] direction. These results are consistent with the broken fourfold rotational symmetry in the hidden-order phase, which can modify the interband scattering in an asymmetric manner. We also extend our measurements down to 0.7 K, which results in the observation of cyclotron resonance in the superconducting state, where novel effects of vortex dynamics may enter. We find that the cyclotron mass undergoes no change in the superconducting state. In contrast, the quasiparticle scattering rate shows a rapid decrease below the vortex-lattice melting transition temperature, which supports the formation of quasiparticle Bloch state in the vortex lattice phase.

We report on the pressure (P)-induced phase diagram of antiferromagnetism (AFM) and superconductivity (SC) which emerges at their border at zero magnetic field. The nuclear-quadrupole-resonance (NQR) measurements have revealed that AFM can take place in the superconducting state with T c ∼ 2.1 K at P = 2.05 GPa and the AFM quantum phase transition (QPT) occurs near P = 2.1 GPa . These results reveal the existence of the tetracritical point in the P–T phase diagram of AFM and SC in CeRnIn 5 . We also found the gapless nature in the uniformly coexisting phase of AFM and SC, indicating an intimate relationship between AFM and SC.

We measured the local magnetization in CeCoIn5 with a micro-Hall probe for magnetic fields H along the [0 0 1] and [1 0 0] directions. We observed a sharp jump in the local magnetization at T c ( H ) below 0.77 K for H ∥ [0 0 1] and 0.79 K for H ∥ [1 0 0], indicating the first-order phase transitions at upper critical fields. We also observed a dip structure in the local magnetization at the first-order phase transitions for H ∥ [0 0 1], below which the FFLO state is realized. We infer that the dip structure is consistent with the development of planar nodes in the FFLO state.

We studied systematically a series of the ternary compounds RRhIn 5 (R: rare earth) which were grown in the single crystalline form by means of the flux method. Most of these compounds order antiferromagnetically at low temperatures, except for R = Y, La, Pr and Yb. The observed temperature dependence of the specific heat and the anisotropic features in the magnetic susceptibility and magnetization have been analyzed on the basis of the crystalline electric field (CEF) model, and an interesting relationship between the anisotropic exchange interaction and the CEF effect is obtained for RRhIn 5 compounds.

To investigate the quasiparticle dynamics in the superconducting state of quasi-two dimensional heavy fermion superconductor CeCoIn 5 , thermal conductivity tensor is measured. We obtained the quasiparticle mean free path and the density of states separately by using the combination of longitudinal thermal conductivity and thermal Hall angle. The quasiparticle mean free path increases dramatically below T c in zero magnetic field. The density of states and the scaling relation of thermal Hall conductivity are consistent with d-wave symmetry. We also argue that CeCoIn 5 is in the superclean regime. These results highlight the anomalous superconducting state in CeCoIn 5 with striking similarities with high- T c cuprates.

We report on the pressure ( P ) -induced phase diagram of antiferromagnetism (AFM) and superconductivity (SC) which emerges at their border at zero magnetic field. The nuclear-quadrupole-resonance (NQR) measurements have revealed that AFM can take place in the superconducting state with T c ∼ 2.1 K at P = 2.05 GPa . The present experiments have, for the first time, demonstrated that AFM phase, AFM + SC uniformly coexisting phase, SC phase and paramagnetic phase all contact with each other at T tetra ∼ 2.1 K and P tetra ∼ 2 GPa which evidence the existence of the tetracritical point in the P – T phase diagram of AFM and SC in CeRnIn 5 .

We report on pressure-induced evolutions of antiferromagnetic spin fluctuations (AFM-SFs) and unconventional superconductivity on the x = 0.6 sample in a series of compounds CeRh 1 - x Ir x In 5 via the 115In nuclear-quadrupole-resonance (NQR) experiment. The In-NQR 1 / T 1 measurements have revealed that the slight application of pressure makes T c = 0.9 K at P = 0 increase up to T c = 1.06 K at P = 0.47 GPa . Concomitantly, the character of AFM-SF evolves from an isotropic regime to an anisotropic one as P increases. These results suggest that AFM-SFs play vital role in mediating the strong-coupling superconductivity in CeRh 1 - x Ir x In 5 .

We measured the electrical resistivity in antiferromagnets CeIrSi 3 (a Neel temperature T N = 5.0 K ) and CeIrGe 3 ( T N 1 = 8.7 K , T N 2 = 4.7 K ) under pressure. In CeIrSi 3 , superconductivity was found in a wide pressure region from 1.8 GPa to about 3.5 GPa, where the superconducting transition temperature is T sc = 1.6 K at a critical pressure P c ≃ 2.5 GPa at which the Neel temperature becomes zero. On the other hand, the antiferromagnetic ordering of CeIrGe 3 is stable up to 8 GPa.

The Josephson effect between a single-crystal CeIrIn 5 and an s -wave superconductor has been investigated for current flows parallel to the [1 0 0] and [1 1 0] axes of CeIrIn 5 . The magnetic-field modulation of the Josephson critical current has shown a nearly ideal Fraunhofer pattern in the [1 0 0] direction and a small deviation from that pattern in the [1 1 0] direction. The clear anisotropy, which has been reported for YBa 2 Cu 3 O 7 - δ indicating the d -wave superconductivity, was not observed in this study.

We succeeded in growing single crystals of RRhIn 5 (R: rare earth) and measured the magnetic susceptibility and magnetization. The lattice constants of RRhIn 5 with the tetragonal structure are well understood from a viewpoint of the lanthanide contraction, except YbRhIn 5 with the divalent Yb ion. Most of RRhIn 5 compounds order antiferromagnetically. NdRhIn 5 indicates two metamagnetic transitions at H m 1 = 7.2 and H m 2 = 9.6 T below T N for the magnetic field along the [0 0 1] direction. The saturation moment of 2.5 μ B / Nd is in good agreement with a staggered Nd moment determined by the neutron scattering experiment. The similar metamagnetic transitions were observed in TbRhIn 5 , DyRhIn 5 and HoRhIn 5 .

We report on the evolution of the Hall effect in heavy fermion compounds CeMIn 5 (M=Co, Rh), ranging from antiferromagnetic metal to Fermi liquid regime through non-Fermi liquid regime by applying pressure. We found that anomalous transport properties of CeMIn 5 are strikingly similar to that of high- T c cuprates. We also found that the magnitude of Hall coefficient appears to diverge near an antiferromagnetic quantum critical point. These results strongly suggest that unusual transport properties of CeMIn 5 are dominated by anisotropic scattering due to strong spin fluctuations.

The topology of the Fermi surface in CePt 3 Si is most likely similar to that in LaPt 3 Si. In fact, one small Fermi surface in CePt 3 Si is the same as that in LaPt 3 Si, where the main Fermi surface in LaPt 3 Si consists of three-dimensional multiply-connected Fermi surfaces. With increasing pressure, the topology of the Fermi surface in CePt 3 Si is approximately unchanged but the cyclotron effective mass is found to be reduced, together with a steep decrease of the Neel temperature and superconducting transition temperature. These results indicate that the heavy fermion state in CePt 3 Si, which is closely correlated with superconductivity, is stable at ambient pressure.

We have measured the de Haas–van Alphen (dHvA) effect in PrFe 4 P 12 under high pressures up to 3.0 GPa, and found that both the dHvA frequency and cyclotron mass of ψ -branch considerably decrease with increasing pressure.

We have carried out the de Haas–van Alphen (dHvA) experiment of an antiferromagnet CeRhIn 5 under pressure. The detected dHvA branches α i ( i = 1 , 2 , 3 ) and β 2 at ambient pressure are well explained by the corresponding dHvA branches in LaRhIn 5 , indicating that the f electron is localized at ambient pressure. At 2.9 GPa, where the antiferromagnetic ordering disappears completely, a new branch α i ( i = 1 , 2 , 3 ) appears. This is approximately the same as that of 4f-itinerant Fermi surface in CeCoIn 5 , suggesting that the 4f electronic state is changed into an itinerant one.

We report on a systematic evolution of the superconducting (SC) characteristics of 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). The marked suppression of AFM SFs leads to the reduction in the size of SC energy gap. Nevertheless, T c increases with the pressure due to the increase in HF bandwidth. This is expected to make the lifetime of quasi-particles sufficiently long.

We report the discovery of novel phases in CeIn3 on the verge of antiferromagnetism (AFM) through the In-nuclear quadrupole resonance (NQR) measurements. We have found that even though a pressure (P)-induced phase separation into AFM and paramagnetism (PM) takes place, a novel superconductivity (SC), which is induced without strong spin fluctuations, has been found to coexist with AFM on a microscopic level. 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 measured the magnetic susceptibility and magnetization of an antiferromagnet Ce3Sn7 with the orthorhombic crystal structure. The experimental data are found to be well explained on the basis of the crystalline electric field (CEF) 4f-scheme under the assumption that two Ce atoms in the 2(a) site possess a magnetic moment of 0.36 μ B / Ce and one Ce atom in the 4(i) site possesses no magnetic moment as in a valence fluctuating compound CeSn3, which was previously proposed by Bonnet et al. Furthermore, we carried out the de Haas–van Alphen experiment. The detected Fermi surfaces are many in number but are extremely small in volume, indicating that Ce3Sn7 is a semimetal.

We have investigated a change of the electronic state in CeIn 3 via de Haas–van Alphen (dHvA) experiments under pressure up to 2.72 GPa for the magnetic field along 〈 1 1 0 〉 . A main Fermi surface with the dHvA frequency F = 9.4 × 10 7 Oe and a large cyclotron mass m c * = 53 m 0 was observed at 2.72 GPa in the vicinity of the critical pressure where the Neel temperature is suppressed to zero.

We report systematic evolution of superconducting (SC) characteristic of heavy-fermion superconductor CeCoIn 5 via the nuclear-quadrupole-resonance (NQR) measurement under pressure ( P ). The temperature dependence of nuclear spin–lattice relaxation rate (1/ T 1 ) below T C has revealed that once the value of SC energy gap (2 Δ 0 / k B T C ) slightly increases in P P , it decreases significantly. By contrast, T C increases monotonously up to 2.6 K as P increases up to 1 GPa, exhibiting a saturation in P =1.0–1.5 GPa.

We report the first successful observation of the de Haas–van Alphen effect in the filled skutterudite LaRu4P12. Observed Fermi surfaces (FSs) are close to those expected from the band calculation. The effective mass m c ∗ is roughly twice compared to the calculated band mass. Assuming the similarity of FS between LaRu4P12 and PrRu4P12, the FS nesting with q=(1,0,0) as a possible origin of the M–I transition in PrRu4P12 is discussed.

We present the quasi-two-dimensional Fermi surface studies in RTIn5 (R: rare earth, T: Co, Rh and Ir), together with UTGa5. The present quasi-two dimensionality is closely related to the unique crystal structure elongated along the [0 0 1] direction, which brings about a flat Brillouin zone and produces cylindrical but highly corrugated Fermi surfaces along [0 0 1] .

We observed the de Haas–van Alphen (dHvA) oscillation both in the normal and superconducting mixed states in a heavy fermion superconductor CeCoIn 5 . The dHvA oscillation due to a main Fermi surface is observed in the mixed state just below the upper critical field H c2 , indicating a large scattering rate of quasi-particles. We determined the Dingle temperatures both in the normal and the mixed states.

The normal-state charge transport is studied systematically in high-quality single crystals of ${\text{BaFe}}_{2}{({\text{As}}_{1\ensuremath{-}x}{\text{P}}_{x})}_{2}$ $(0\ensuremath{\le}x\ensuremath{\le}0.71)$. By substituting isovalent P for As, the spin-density-wave (SDW) state is suppressed and the dome-shaped superconducting phase $({T}_{c}\ensuremath{\lesssim}31\text{ }\text{K})$ appears. Near the SDW end point $(x\ensuremath{\approx}0.3)$, we observe striking linear temperature $(T)$ dependence of resistivity in a wide $T$ range, and remarkable low-$T$ enhancement of Hall-coefficient magnitude from the carrier number estimates. We also find that the magnetoresistance apparently violates the Kohler's rule and is well scaled by the Hall angle ${\ensuremath{\Theta}}_{H}$ as $\ensuremath{\Delta}{\ensuremath{\rho}}_{xx}/{\ensuremath{\rho}}_{xx}\ensuremath{\propto}{\text{tan}}^{2}\text{ }{\ensuremath{\Theta}}_{H}$. These non-Fermi-liquid transport anomalies cannot be attributed to the simple multiband effects. These results capture universal features of correlated electron systems in the presence of strong antiferromagnetic fluctuations.

We present a phase diagram for the antiferromagnetism and superconductivity in ${\text{Ce}}_{2}{\text{RhIn}}_{8}$ probed by In-NQR studies under pressure $(P)$. The quasi-two-dimensional character of antiferromagnetic spin fluctuations in the paramagnetic state at $P=0$ evolves into a three-dimensional character because of the suppression of antiferromagnetic order for $Pg{P}_{\text{QCP}}\ensuremath{\sim}1.36\text{ }\text{GPa}$ (QCP: quantum critical point). Nuclear-spin-lattice relaxation rate $1/{T}_{1}$ measurements revealed that the superconducting order occurs in the $P$ range 1.36--1.84 GPa, with maximum ${T}_{c}\ensuremath{\sim}0.9\text{ }\text{K}$ around ${P}_{\text{QCP}}\ensuremath{\sim}1.36\text{ }\text{GPa}$.

2 pages; International audience; Crystalline disorder in the pnictide superconductor PrFeAsO1−y is studied using magneto-optical visualisation of flux penetration, Transmission Electron Microscopy, and X-ray diffraction using synchrotron radiation. Critical-state like flux distributions and the magnitude and temperature dependence of the critical current demonstrate bulk vortex pinning by oxygen vacancies at all temperatures.

We report on a pressure $(P)$-induced evolution of magnetism and superconductivity (SC) in a helical magnet ${\text{CeRhIn}}_{5}$ with an incommensurate wave vector ${Q}_{i}=(\frac{1}{2},\frac{1}{2},0.297)$ through the $^{115}\text{I}\text{n}$ nuclear quadrupole resonance (NQR) measurements under $P$. Systematic measurements of the $^{115}\text{I}\text{n}$-NQR spectrum reveal that the commensurate antiferromagnetism (AFM) with ${Q}_{c}=(\frac{1}{2},\frac{1}{2},\frac{1}{2})$ is realized above ${P}_{m}\ensuremath{\sim}1.7\text{ }\text{GPa}$. An important finding is that the size of SC gap and ${T}_{c}$ increase as the magnitude of the AFM moment decreases in the $P$ region, where SC uniformly coexists with the commensurate AFM. This result provides evidence of strong coupling between the commensurate AFM order parameter (OP) and SC OP.

We have studied the lower critical fields ${H}_{c1}$ of superconducting iron oxipnictide ${\text{PrFeAsO}}_{1\ensuremath{-}y}$ single crystals for $\mathbit{H}$ parallel and perpendicular to the $ab$ planes. Measurements of the local magnetic induction at positions straddling the sample edge by using a miniature Hall-sensor array clearly resolve the first flux penetration from the Meissner state. The temperature dependence of ${H}_{c1}$ for $\mathbit{H}\ensuremath{\parallel}c$ is well scaled by the in-plane penetration depth without showing any unusual behavior, in contrast to previous reports. The anisotropy of penetration lengths at low temperatures is estimated to be $\ensuremath{\simeq}2.5$, which is considerably smaller than the anisotropy of the coherence lengths. This is indicative of multiband superconductivity in this system in which the active band for superconductivity is more anisotropic. We also point out that the local induction measured at a position near the center of the crystal, which has been used in a number of reports for the determination of ${H}_{c1}$, might seriously overestimate the obtained ${H}_{c1}$ value.

In quasi-two-dimensional $\text{Ce}(\text{Ir},\text{Rh}){\text{In}}_{5}$ system, it has been suggested that the phase diagram contains two distinct domes with different heavy-fermion superconducting states. Here, we report the systematic pressure dependence of the electron transport properties in the normal state of ${\text{CeRh}}_{0.2}{\text{Ir}}_{0.8}{\text{In}}_{5}$ and ${\text{CeIrIn}}_{5}$, which locates in first and second superconducting domes, respectively. We observed non-Fermi liquid behavior at low temperatures in both compounds, including nonquadratic $T$ dependence of the resistivity, large enhancement of the Hall coefficient, and the violation of the Kohler rule in the magnetoresistance. We show that the cotangent of the Hall angle $\text{cot}\text{ }{\ensuremath{\Theta}}_{H}$ varies as ${T}^{2}$, and the magnetoresistance is quite scaled well by the Hall angle as $\ensuremath{\Delta}{\ensuremath{\rho}}_{xx}/{\ensuremath{\rho}}_{xx}\ensuremath{\propto}{\text{tan}}^{2}\text{ }{\ensuremath{\Theta}}_{H}$. The observed transport anomalies are common features of $\text{Ce}M{\text{In}}_{5}$ ($M=\text{Co}$, Rh, and Ir) and high-${T}_{c}$ cuprates, which suggest that the anomalous transport properties observed in ${\text{CeIrIn}}_{5}$ are mainly governed by the antiferromagnetic spin fluctuations not by the Ce-valence fluctuations, which have been proposed to be the possible origin for the second superconducting dome.

We report on pressure-induced unconventional superconductivity (SC) in the heavy-fermion (HF) antiferromagnet ${\mathrm{CeIn}}_{3}$ by means of nuclear-quadrupole-resonance (NQR) studies conducted under a high pressure. The temperature $(T)$ and pressure $(P)$ dependences of the In-NQR spectra have revealed a first-order quantum-phase transition (QPT) from antiferromagnetism (AFM) to paramagnetism (PM) at a critical pressure ${P}_{\mathrm{c}}=2.46\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ at which AFM disappears with a minimum value of ${T}_{\mathrm{N}}({P}_{\mathrm{c}})=1.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. High-energy x-ray scattering measurements under $P$ show a progressive decrease in the lattice density without any change in the crystal structure, whereas an increase in the NQR frequency $({\ensuremath{\nu}}_{\mathrm{Q}})$ indicates an increase in the hybridization between $4f$ electrons and conduction electrons, which stabilizes the HF-PM state. This competition between the AFM phase where ${T}_{\mathrm{N}}$ is reduced and the formation of the HF-PM phase triggers the first-order QPT at ${P}_{\mathrm{c}}=2.46\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. Despite the lack of an AFM quantum critical point in the $P\text{\ensuremath{-}}T$ phase diagram, we highlight the fact that unconventional SC occurs in both phases of AFM and PM. The measurements of the nuclear spin-lattice relaxation rate $1∕{T}_{1}$ in the AFM phase have provided evidence for the uniformly coexisting $\mathrm{AFM}+\mathrm{SC}$ phase. Remarkably, the significant increase in $1∕{T}_{1}$ upon cooling in the AFM phase has revealed the development of low-lying magnetic excitations down to ${T}_{\mathrm{c}}$ in the AFM phase; it is indeed relevant to the onset of the uniformly coexisting AFM+SC phase. In the HF-PM phase where AFM fluctuations are not developed, $1∕{T}_{1}$ decreases without the coherence peak just below ${T}_{\mathrm{c}}$, followed by a power-law-like $T$ dependence that indicates an unconventional SC with a line-node gap. Remarkably, ${T}_{\mathrm{c}}$ has a peak around ${P}_{\mathrm{c}}$ in the HF-PM phase as well as in the AFM phase. In other words, an SC dome exists with a maximum value of ${T}_{\mathrm{c}}=230\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ around ${P}_{\mathrm{c}}$, indicating that the origin of the pressure-induced HF SC in ${\mathrm{CeIn}}_{3}$ is not relevant to AFM spin fluctuations but to the emergence of the first-order QPT in ${\mathrm{CeIn}}_{3}$. These phenomena observed in ${\mathrm{CeIn}}_{3}$ should be understood in terms of the first-order QPT because these new phases of matter are induced by applying $P$. When the AFM critical temperature is suppressed at the termination point of the first-order QPT, ${P}_{\mathrm{c}}=2.46\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, the diverging AFM spin-density fluctuations emerge at the critical point from AFM to PM. The results with ${\mathrm{CeIn}}_{3}$ leading to a new type of quantum criticality deserve further theoretical investigations.

To investigate the unusual normal-superconducting phase transition near the upper critical fields at low temperatures of the quasi-two-dimensional heavy fermion compound CeCoIn5, local magnetic induction measurements have been performed by using a micro Hall probe for both H||c and H||a. The local magnetic induction as a function of temperature displays a discontinuous jump at the superconducting phase boundary below the critical temperature T0 approximate to 0.8 K for both field directions, indicating a change from the second- to first-order transition and confirming previously reported bulk measurements on CeCoIn5. The magnetic induction data display an unexpected undershoot behavior just below the jump down, which has never been reported in the bulk measurements. This undershoot is observed at the phase boundary between the normal state and the high-field superconducting phase, which has been attributed to the spatially inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov state. Possible origins of this unusual undershoot behavior are discussed.

Elastic neutron diffraction measurements were performed on the quasi-two-dimensional heavy-fermion system $\mathrm{Ce}{\mathrm{Rh}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{In}}_{5}$, ranging from an incommensurate antiferromagnet for low Co composition $x$ to an unconventional superconductor on the Co-rich end of the phase diagram. We found that the superconductivity competes with the incommensurate antiferromagnetic (AFM) order characterized by ${\mathbit{q}}_{I}=(1∕2,1∕2,\ensuremath{\delta})$ with $\ensuremath{\delta}=0.298$, while it coexists with the commensurate AFM order with ${\mathbit{q}}_{c}=(1∕2,1∕2,1∕2)$. This is in sharp contrast to the $\mathrm{Ce}{\mathrm{Rh}}_{1\ensuremath{-}x}{\mathrm{Ir}}_{x}{\mathrm{In}}_{5}$ system, where both the commensurate and incommensurate magnetic orders coexist with the superconductivity. These results reveal that particular areas on the Fermi surface nested by ${\mathbit{q}}_{I}$ play an active role in forming the superconducting state in $\mathrm{Ce}\mathrm{Co}{\mathrm{In}}_{5}$.