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Presents a study that reported transport experiments on CeAl[sub3] samples under quasihydrostatic pressure. Background on the CeAl[sub3] compound; Characteristics of the samples used; Evidence of the failure to scale with a single parameter.

Deals with a study which measured the resistivity of europium molybdenum[sub 6] sulphur[sub 8] and europium molybdenum[sub 5] tungsten sulphur[sub 8] single crystals. Details of the experiment; Results; Discussion.

Deals with a study which described the thermoelectric power of 4f instability compounds in very low temperatures. Information on materials with unstable 4f shells; Behavior of heavy fermion compounds; model used for explaining the main feaures of the thermoelectric power of the compounds.

Examines the magnetic and transport measurements on fermion compounds CeAl[sub3], CeCu[sub2]Si[sub2] and CeRu[sub2]Si[sub2]. Resistivity and thermoelectric power of the compounds; Annealing of the cerium compounds.

Presents a study which examined the upper critical field H[subc2](T) of the heavy fermion superconductor UPt[sub3], for a magnetic field applied in the basal plane. Basis of the existence of the multi component superconducting phase diagram proposed for UPt[sub3]; Application of resistivity measurements on mono crystalline whiskers; Description of the distinct kink in H[subc2](T) at ambient pressure.

Presents a study which reported thermal-expansion measurements in the field for heavy-fermion CeRu[sub2]Si[sub2] samples. Method used in growing the samples; Calculation of the Grüneisen parameters; Test on the validity of the scaling ansatz.

Recently there is renewed interest in quantum critical phase transitions (QCPT) at T = 0 K in metallic strongly correlated electron systems. From early experimental results, the QCPT in the Kondo-lattice compound YbRh2Si2 is not a case of the ordinary spin density wave (SDW) instability observed in Ce-based Kondo lattices, but a candidate for a novel locally critical case. Here, we observe that coexisting, static Fermi liquid (FL) and non-Fermi liquid (NFL) states are a key feature of the QCPT in YbRh2Si2. By means of nuclear magnetic resonance (NMR) spin-lattice relaxation time (T1) measurements on a single-crystalline sample, we find that the FL and NFL states are invariant, whereas their ratio in a crossover is field dependent near the QCPT. Such a pair of states has remained hidden in Ce compounds, owing presumably to the short lifetimes of the two states. We derive a scaling law for the occupation ratio of the two states, which could be widely applicable to Kondo-lattice systems. [ABSTRACT FROM AUTHOR]

Pressure is the cleanest way to tune heavy fermion systems to a quantum phase transition in order to study the rich physics and competing phases, and the comparison between ytterbium and cerium systems is particularly fruitful. We briefly review the mechanisms in play and show some examples of expected and unexpected behaviour. We emphasise the importance of the valence changes under pressure and show how modern synchrotron techniques can accurately determine this, including at low temperature. [ABSTRACT FROM AUTHOR]

Emphasis is given on the observation of a convergence to a critical value of the effective mass of a heavy fermion compound by tuning it through a quantum instability either by applying pressure or magnetic field from an antiferromagnetic (AF) to a paramagnetic (PM) ground state. Macroscopic and microscopic results are discussed and the main message is to rush to the discovery of an ideal material whose Fermi surface could be fully observed on both sides of each quantum phase transition. [ABSTRACT FROM AUTHOR]

The interpretation of the magnetic phase diagrams of strongly correlated electron systems remains controversial. In particular, the physics of quantum phase transitions, which occur at zero temperature, is still enigmatic. Heavy-fermion compounds are textbook examples of quantum criticality, as doping, or the application of pressure or a magnetic field can lead to a quantum phase transition between a magnetically ordered state and a paramagnetic regime. A central question concerns the microscopic nature of the critical quantum fluctuations. Are they antiferromagnetic or of local origin? Here we demonstrate, using inelastic neutron scattering experiments, that the quantum phase transition in the heavy-fermion system Ce1−xLaxRu2Si2 is controlled by fluctuations of the antiferromagnetic order parameter. At least for this heavy-fermion family, the Hertz–Millis–Moriya spin fluctuation approach seems to be a sound basis for describing the quantum antiferromagnetic–paramagnetic instability. [ABSTRACT FROM AUTHOR]

We report on tunneling spectroscopy measurements using a scanning tunneling microscope (STM) on the spin triplet superconductor Sr2RuO4. A fully open gap, close to the Bardeen-Cooper-Schrieffer (BCS) value, is found, which disappears at the bulk Tc = 1.5 K. The results are discussed in the framework of recent multigap scenarios for an unconventional spin triplet superconductor. [ABSTRACT FROM AUTHOR]

Combining old and new de Haas-van Alphen (dHvA) and magnetoresistance data, we arrive at a detailed picture of the Fermi surface of the heavy fermion superconductor UPt3. Our work was partially motivated by a new proposal that two 5f valence electrons per formula unit in UPt3 are localized by correlation effects-agreement with previous dHvA measurements of the Fermi surface was invoked in its support. Comprehensive comparison with our new observations shows that this 'partially localized' model fails to predict the existence of a major sheet of the Fermi surface, and is therefore less compatible with experiment than the originally proposed 'fully itinerant' model of the electronic structure of UPt3. In support of this conclusion, we offer a more complete analysis of the fully itinerant band structure calculation, where we find a number of previously unrecognized extremal orbits on the Fermi surface. [ABSTRACT FROM AUTHOR]

We present transport and specific heat measurements on high quality single crystals of UPt[sub 3] before and after irradiation by high energy electrons. The induced changes of the superconducting critical temperature are found to depend strongly on the distance from the irradiated surface. The dramatic effects of the irradiation on the specific heat in the superconducting state can then be simply explained in terms of an inhomogeneous distribution of superconducting transition temperatures. The question of the failure of the "universal limit" in the heat transport of UPt[sub 3] is reexamined, and the conditions for a clean experimental test are established. [ABSTRACT FROM AUTHOR]

The superconducting critical current along the c-axis of the unconventional superconductor UPt[sub 3] has been determined as a function of magnetic field direction in the basal (a-a[sup *]) plane in the three (A, B and C) phases of the mixed state. The critical current has maxima for field directions parallel to both the a- and a[sup *]-axis in the superconducting C phase, but has maxima only parallel to the a-axis in the A and B phases. Our experiments thus show that the anisotropy of the superconducting critical current in UPt[sub 3] changes at the same field at which the symmetry of the order parameter changes. This demonstrates for the first time that the critical current is sensitive to the symmetry of the superconducting order parameter. [ABSTRACT FROM AUTHOR]

We report resistivity measurements performed on a high quality single crystal of CePd2Si2 under hydrostatic pressure. At ambient pressure the de Haas–van Alphen effect has been also studied. Two different frequencies with weak angular dependence were detected with magnetic field lying in the basal plane, while another frequency was found with magnetic field parallel to the tetragonal c axis. Near the critical pressure, Pc∼27 kbar, where the antiferromagnetic transition vanishes, the normal state resistivity does not follow the usual Fermi-liquid (FL) behavior and is described by a T1.3 law, while just below Pc, the resistivity shows clearly separated spin wave and electron–electron contributions. At Pc, the FL form of ρ(T) is not restored even at magnetic field up to 6T. The first appearance of superconductivity is observed at P=19 kbar, and the critical temperature increases with pressure up to 27 kbar. The analysis of the upper critical field at Pc shows that the superconducting state is well described by a weak coupling, clean limit model with a slightly anisotropic orbital limit and a strongly anisotropic paramagnetic one. [ABSTRACT FROM AUTHOR]

Reports the observation of superconductivity on the border of ferromagnetism in a pure system, UGe..., which is known to be qualitatively similar to the classic d-electron ferromagnets. Measurement of and band magnetism in UGe...; Role of magnetic interactions; Topic of lattice interactions; Details of spin-triplet superconductivity; Methods.

We have implemented AC calorimetric measurements in diamond anvil pressure cells. The range of pressure (0–20 GPa), the excellent hydrostatic conditions of solid 4He used as the pressure transmitting medium associated with the possibility of continuously tuning the pressure at low temperature makes this experiment ideally suited for investigating phase diagrams under pressure and in particular for studying the thermodynamics of correlated metals around a Quantum Critical Point (QCP) where magnetic order is suppressed at absolute zero temperature. We present here results on the heavy fermion compound CeRu2Ge2 up to 8 GPa and down to 2 K. The specific heat anomalies associated with the different magnetic phase transitions are clearly resolved, allowing a precise determination of the magnetic phase diagram. On approaching the QCP close to 7 GPa, we observe a striking broadening of the antiferromagnetic transition associated with an anomalous behavior of the signal phase which could correspond to a change in the nature of this transition. [ABSTRACT FROM AUTHOR]

Superconducting and normal state properties of a single crystal of CeCu2Si2 have been investigated by resistivity measurements under hydrostatic pressure and magnetic field. The low temperature resistivity behaviour ( ρ = ρ0 + AT2, which is observed up to a temperature TA) is considered within the self-consistent renormalized (SCR) spin fluctuation model. Contrary to the model predictions, the product AT2 A increases on approaching the quantum critical point (QCP). The temperature dependence of the upper critical field is analyzed assuming strong coupling and an intermediate regime between the clean and dirty limits. Both the low temperature resistivity behaviour at high pressure and the parameters deduced from the fits of H c2 point to a pressure induced decrease of the quasi-particle effective mass m*. The anisotropy of the initial slope of H c2( T) and therefore that of the effective mass was found to change under pressure. [ABSTRACT FROM AUTHOR]

Thermal conductivity has been measured from 0.03 K to 0.8 K in single crystal CeNi2 Ge2 which is quite near the quantum critical point (QCP). The Wiedemann–Franz law is observed at low temperatures (T< 0.1 K) for both directions (j⊥c and j ∥ c ), indicating that quasiparticles are scattered elastically as T→ 0 K. With increasing temperature, a deviation from the Wiedemann–Franz law due to inelastic spin-fluctuation contributions is observed. The effect of proximity to the QCP in CeNi2 Ge2 appears in the spin-fluctuation contributions to the thermal and electrical conductivities. [ABSTRACT FROM AUTHOR]

The superconducting properties of the heavy fermion UPt3 have been changed by irradiation with high energy electrons which creates point defects in a reproducible and controled way. Measurements of the residual resistivity, critical temperature, upper critical field and thermal conductivity have been realized on these irradiated samples. The strong suppresion of superconductivity with increasing defect concentration is in agreement with the theory of unconventional superconductivity. However, our thermal conductivity data contradicts the simple predictions derived from the most popular modelsE 1g and E 2u) of the superconducting order parameter in UPt3 . [ABSTRACT FROM AUTHOR]

Inelastic neutron scattering experiments were performed to study the spin dynamics of the heavy fermion compound Ce0,925La0.075Ru2Si2. This composition corresponds to the borderline of the magnetic-non magnetic transition in the family of alloys Ce1−xLaxRu2Si2. Short range magnetic correlations of an inelastic nature characterize this system in addition to a small ordered moment of the order of 0.02μB which appears below 2 K. Comparison with the magnetic excitation spectrum of the Pauli paramagnet CeRu2Si2 is given from the viewpoint of recent work on phase transitions near the magnetic instability point. [ABSTRACT FROM AUTHOR]

Inelastic neutron scattering experiments were performed to study the spin dynamics of the heavy fermion compound Ce0.925La0.075Ru2Si2. This composition corresponds to the borderline of the magnetic-non magnetic transition in the family of alloys Ce1 − xLaxRu2Si2. Short range magnetic correlations of an inelastic nature characterize this system in addition to a small ordered moment of the order of 0.02µB which appears below 2 K. Comparison with the magnetic excitation spectrum of the Pauli paramagnet CeRu2Si2 is given from the viewpoint of recent work on phase transitions near the magnetic instability point. [ABSTRACT FROM AUTHOR]

The effect of spin fluctuations on the thermal properties of strongly correlated itinerant fermion systems is discussed based on the self-consistent renormalized (SCR) spin fluctuation model. Specific heat and magnetic susceptibility in the normal phase of liquid-3He and heavy electron compounds at finite temperatures are well described by the unified SCR picture including the mode-mode coupling of spin fluctuations beyond the random phase approximation (RPA). [ABSTRACT FROM AUTHOR]

We present new measurements of the thermal conductivity (κ) of UPt3 down to very low temperatures (16 mK) and under magnetic fields (up to 4 T) which cover all the superconducting phases of UPt3. The measurements in zero field are compared with recent theoretical predictions for the thermal conductivity, which is dominated by impurity states at the lowest temperatures studied. The measurements under magnetic field at low temperatures are surprising since they don’t show the expected low field square root dependence, $$\kappa \propto \sqrt {\rm B} $$ . The discontinuity of dκ/ dT at T c changes drastically when passing from the high field low temperature C phase to the low field high temperature A phase: this is related to the change of the symmetry of the superconducting order parameter when crossing the A→ C phase transition. [ABSTRACT FROM AUTHOR]

Focuses on a study which characterized the normal and superconducting states of uranium platinum[sub 3] (UPt) in terms of magnetoresistivity and thermoelectric power. Description of Upt as a superconducting heavy fermion compound; Results of virgin magnetization measurements; Details of thermal conductivity experiments.

Presents information on a study which compared the magnetization, neutron diffraction and resistivity measurements of compounds TmSe and TmS with dilute alloys (tm, Y)Se and (Tm,Y)S. Resistivity and susceptibility of the compounds; Difference between the compounds; Conclusions.

The nearly ferromagnetic superconductor UTe2 shows several intriguing phenomena, including an extraordinary reinforcement of superconductivity in very strong magnetic fields. Here we show that pressure tunes the system to a more correlated state and probable magnetic order. The superconducting critical temperature is also strongly enhanced, reaching almost 3 K, a new record for U-based heavy fermion superconductors. Most spectacularly under pressure we find a transition within the superconducting state, putting UTe2 among the very rare systems having multiple superconducting phases. UTe2 under pressure is a treasure trove of several of the most fascinating phenomena in unconventional superconductivity and may well be a keystone in their understanding. The recent discovery of superconductivity with an unusually high upper critical field in the heavy fermion system UTe2 has incited enormous interest in this material as one of the rare known spin-triplet superconductors with potentials for topological superconductivity and quantum computing. In this work, the authors report evidence for enhanced superconductivity and multiple superconducting phases in UTe2 under hydrostatic pressure, revealing a very rich phase landscape in this material. [ABSTRACT FROM AUTHOR]

reports on the magnetization measurements performed on a single crystal of Ce[sub0.8]La[sub0.2]Ru[sub2]Si[sub2]. Anomalies observed; Effect of the application of a hydrostatic pressure.