ABSTRACT
We report point-contact spectroscopy measurements on heavy fermion cousins CeCoIn5, Ce2PdIn8and Ce3PdIn11to systematically study the hybridization betweenfand conduction electrons. Below a temperatureT*, the spectrum of each compound exhibits an evolving Fano-like conductance shape, superimposed on a sloping background, that suggests the development of hybridization between localfand itinerant conduction electrons in the coherent heavy fermion state belowT*. We present a quantitative analysis of the conductance curves with a two-channel model to compare the tunneling process between normal metallic silver particles in our soft point-contact and heavy-fermion single crystals CeCoIn5, Ce2PdIn8and Ce3PdIn11.
ABSTRACT
CeIn3, a prototypical antiferromagnet, is an ideal candidate for investigating the relationship between magnetism and superconductivity, as superconductivity is induced as the magnetic transition temperature (T N) is lowered to 0 K by applying pressure. When La is substituted for Ce, T N of CeIn3 decreases to 0 K owing to the Ce dilution effects, thereby providing an alternative route to the zero-temperature quantum phase transition. In this study, we report a combinatorial approach to gain access to the critical point by applying external pressure to 20% La-doped CeIn3. Electrical resistivity measurements of La0.2Ce0.8In3 show that the T N of 8.4 K at 1 bar is gradually suppressed under pressure and can be extrapolated to 0 K at approximately 2.47 GPa, thereby showing a similar pressure dependence of T N as shown by undoped CeIn3. The kink-like feature in resistivity at T N of CeIn3 changed to an obvious jump in the doped compound for pressures higher than 1.64 GPa, indicating depletion in the carrier density due to a gap opening. AC calorimetry measurements under applied pressure show that the size of the specific heat jump at T N decreases with increasing pressure, but any signatures associated with the gap opening are not obvious, suggesting that the pressure-induced kink-to-jump change at T N in the resistivity is not a phase transition, but rather a gradual crossover. The low-temperature specific heat divided by temperature, C/T, does not strongly diverge with decreasing temperature, but is almost saturated near the projected quantum critical point, which can be attributed to a weak enhancement in the effective mass up to 2.6 GPa.
ABSTRACT
A wide range of metals exhibit anomalous electrical and thermodynamic properties when tuned to a quantum critical point (QCP), although the origins of such strange metals have posed a long-standing mystery. The frequent association of strange metals with unconventional superconductivity and antiferromagnetic QCPs1-4 has led to the belief that they are highly entangled quantum states5. By contrast, ferromagnets are regarded as an unlikely setting for strange metals, because they are weakly entangled and their QCPs are often interrupted by competing phases or first-order phase transitions6-8. Here we provide evidence that the pure ferromagnetic Kondo lattice9,10 CeRh6Ge4 becomes a strange metal at a pressure-induced QCP. Measurements of the specific heat and resistivity under pressure demonstrate that the ferromagnetic transition is continuously suppressed to zero temperature, revealing a strange-metal behaviour around the QCP. We argue that strong magnetic anisotropy has a key role in this process, injecting entanglement in the form of triplet resonating valence bonds into the ordered ferromagnet. We show that a singular transformation in the patterns of the entanglement between local moments and conduction electrons, from triplet resonating valence bonds to Kondo-entangled singlet pairs at the QCP, causes a jump in the Fermi surface volume-a key driver of strange-metallic behaviour. Our results open up a direction for research into ferromagnetic quantum criticality and establish an alternative setting for the strange-metal phenomenon. Most importantly, strange-metal behaviour at a ferromagnetic QCP suggests that quantum entanglement-not the destruction of antiferromagnetism-is the common driver of the varied behaviours of strange metals.
ABSTRACT
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
ABSTRACT
We have synthesized high quality single crystals of Sm4Co3Ga16 with gallium flux and investigated its physical properties with electrical resistivity, magnetization and specific-heat measurements. Antiferromagnetic transition below 6.7 K has been detected. No superconducting transitions have been dectected down to 0.5 K from our single crystals. Based on our experimental result, Sm3+ state in Sm4Co3Ga16 is likely well localized, in which stable magnetic moment in its doubly degenerated ground state contributes to the magnetic order with little interference of Kondo type of interaction.
ABSTRACT
The nature of the pairing symmetry of the first heavy fermion superconductor CeCu2Si2 has recently become the subject of controversy. While CeCu2Si2 was generally believed to be a d-wave superconductor, recent low-temperature specific heat measurements showed evidence for fully gapped superconductivity, contrary to the nodal behavior inferred from earlier results. Here, we report London penetration depth measurements, which also reveal fully gapped behavior at very low temperatures. To explain these seemingly conflicting results, we propose a fully gapped [Formula: see text] band-mixing pairing state for CeCu2Si2, which yields very good fits to both the superfluid density and specific heat, as well as accounting for a sign change of the superconducting order parameter, as previously concluded from inelastic neutron scattering results.
ABSTRACT
Generally, studies of the critical current Ic are necessary if superconductors are to be of practical use, because Ic sets the current limit below which there is a zero-resistance state. Here, we report a peak in the pressure dependence of the zero-field Ic, Ic(0), at a hidden quantum critical point (QCP), where a continuous antiferromagnetic transition temperature is suppressed by pressure toward 0 K in CeRhIn5 and 4.4% Sn-doped CeRhIn5. The Ic(0)s of these Ce-based compounds under pressure exhibit a universal temperature dependence, underlining that the peak in zero-field Ic(P) is determined predominantly by critical fluctuations associated with the hidden QCP. The dc conductivity σdc is a minimum at the QCP, showing anti-correlation with Ic(0). These discoveries demonstrate that a quantum critical point hidden inside the superconducting phase in strongly correlated materials can be exposed by the zero-field Ic, therefore providing a direct link between a QCP and unconventional superconductivity.
ABSTRACT
Conventional, thermally driven continuous phase transitions are described by universal critical behavior that is independent of the specific microscopic details of a material. However, many current studies focus on materials that exhibit quantum-driven continuous phase transitions (quantum critical points, or QCPs) at absolute zero temperature. The classification of such QCPs and the question of whether they show universal behavior remain open issues. Here we report measurements of heat capacity and de Haas-van Alphen (dHvA) oscillations at low temperatures across a field-induced antiferromagnetic QCP (Bc0 ≈ 50 T) in the heavy-fermion metal CeRhIn5. A sharp, magnetic-field-induced change in Fermi surface is detected both in the dHvA effect and Hall resistivity at B0* ≈ 30 T, well inside the antiferromagnetic phase. Comparisons with band-structure calculations and properties of isostructural CeCoIn5 suggest that the Fermi-surface change at B0* is associated with a localized-to-itinerant transition of the Ce-4f electrons in CeRhIn5. Taken in conjunction with pressure experiments, our results demonstrate that at least two distinct classes of QCP are observable in CeRhIn5, a significant step toward the derivation of a universal phase diagram for QCPs.
ABSTRACT
We use heat-capacity measurements as a function of field rotation to identify the nodal gap structure of CeIrIn(5) at pressures to 2.05 GPa, deep inside its superconducting dome. A fourfold oscillation in the heat capacity at 0.3 K is observed for all pressures, but with its sign reversed between 1.50 and 0.90 GPa. On the basis of recent theoretical models for the field-angle-dependent specific heat, all data, including the sign reversal, imply a d(x(2)-y(2)) order parameter with nodes along [110], which constrains theoretical models of the pairing mechanism in CeIrIn(5).
ABSTRACT
Magnetic susceptibility, magnetization, specific heat, and electrical resistivity studies on single crystals of Ce4Pt12Sn25 reveal an antiferromagnetic transition at T(N) = 0.19 K, which develops from a paramagnetic state with a very large specific heat coefficient (C/T) of 14 J mol(-1) K(-2)-Ce just above T(N). On the basis of its crystal structure and these measurements, we argue that a weak magnetic exchange interaction in Ce4Pt12Sn25 is responsible for its low ordering temperature and a negligible Kondo-derived contribution to physical properties above T(N). The anomalous enhancement of specific heat above T(N) is suggested to be related, in part, to weak geometric frustration of f-moments in this compound.
ABSTRACT
Pressure- and temperature-dependent heat capacity and electrical resistivity experiments on Sn- and La-doped CeRhIn5 are reported for two samples with specific concentrations, Ce(0.90)La(0.10)RhIn5 and CeRhIn(4.84)Sn(0.16), which present the same TN=2.8 K. The obtained P-T phase diagrams for doped CeRhIn5 compared to that for the pure compound show that Sn doping shifts the diagram to lower pressures while La doping does exactly the opposite, indicating that the important energy scale to define the pressure range for superconductivity in CeRhIn5 is the strength of the on-site Kondo coupling.
ABSTRACT
The origin of magnetic order in metals has two extremes: an instability in a liquid of local magnetic moments interacting through conduction electrons, and a spin-density wave instability in a Fermi liquid of itinerant electrons. This dichotomy between 'local-moment' magnetism and 'itinerant-electron' magnetism is reminiscent of the valence bond/molecular orbital dichotomy present in studies of chemical bonding. The class of heavy-electron intermetallic compounds of cerium, ytterbium and various 5f elements bridges the extremes, with itinerant-electron magnetic characteristics at low temperatures that grow out of a high-temperature local-moment state. Describing this transition quantitatively has proved difficult, and one of the main unsolved problems is finding what determines the temperature scale for the evolution of this behaviour. Here we present a simple, semi-quantitative solution to this problem that provides a basic framework for interpreting the physics of heavy-electron materials and offers the prospect of a quantitative determination of the physical origin of their magnetic ordering and superconductivity. It also reveals the difference between the temperature scales that distinguish the conduction electrons' response to a single magnetic impurity and their response to a lattice of local moments, and provides an updated version of the well-known Doniach diagram.
ABSTRACT
A new polymorph of CeNiSb3 has been grown from a Sn flux and characterized by single-crystal X-ray diffraction. beta-CeNiSb3 crystallizes in the orthorhombic space group Pbcm (No. 57) with Z = 8. The unit cell parameters are a = 12.9170(2) A, b = 6.1210(5) A, c = 12.0930(6) A, and V = 956.13(9) A3. Its layered structure contains structural motifs similar to that of the first form of CeNiSb3 and consists of Ce atoms inserted between anionic layers of nearly square infinity2[Sb] nets and distorted infinity2[NiSb2] octahedra. We report the synthesis, magnetization, electrical resistivity, and specific heat of the new form of CeNiSb3 and compare the structures and physical properties of both polymorphs.
Subject(s)
Alloys/chemistry , Antimony/chemistry , Cerium/chemistry , Lanthanum/chemistry , Magnetics , Nickel/chemistry , Alloys/chemical synthesis , Crystallography, X-Ray , Electric Impedance , Models, Molecular , Phase Transition , Temperature , ThermodynamicsABSTRACT
A new rare earth metal Zintl phase, Eu(3)In(2)P(4), was synthesized by utilizing a metal flux method. The compound crystallizes in the orthorhombic space group Pnnm with the cell parameters a = 16.097(3) A, b = 6.6992(13) A, c = 4.2712(9) A, and Z = 2 (T = 90(2) K, R1 = 0.0159, wR2 = 0.0418 for all data). It is isostructural to Sr(3)In(2)P(4). The structure consists of tetrahedral dimers, [In(2)P(2)P(4/2)](6-), that form a one-dimensional chain along the c axis. Three europium atoms interact via a Eu-Eu distance of 3.7401(6) A to form a straight line triplet. Single-crystal magnetic measurements show anisotropy at 30 K and a magnetic transition at 14.5 K. High-temperature data give a positive Weiss constant, which suggests ferromagnetism, while the shape of susceptibility curves (chi vs T) suggests antiferromagnetism. Heat capacity shows a magnetic transition at 14.5 K that is suppressed with field. This compound is a semiconductor according to the temperature-dependent resistivity measurements with a room-temperature resistivity of 0.005(1) Omega m and E(g) = 0.452(4) eV. It shows negative magnetoresistance below the magnetic ordering temperature. The maximum magnetoresistance (Deltarho/rho(H)) is 30% at 2 K with H = 5 T.
Subject(s)
Europium/chemistry , Indium/chemistry , Magnetics , Phosphorus Compounds/chemistry , Crystallography, X-Ray , Models, Molecular , Phosphorus Compounds/chemical synthesis , Semiconductors , Surface Properties , TemperatureABSTRACT
Eu3InP3 has been prepared as large single crystals with an indium flux reaction. The structure of the new compound is isotypic to Sr3InP3 and crystallizes in the orthorhombic space group Pnma with unit cell dimensions of a = 12.6517(15) A, b = 4.2683(5) A, and c = 13.5643(14) A (Z = 4, T = 140 K, R1 = 0.0404, wR2 = 0.0971 for all data). The structure consists of one-dimensional chains of corner-shared distorted [InP2P2/2]6- tetrahedra separated by rows of Eu2+ ions. Two of the three crystallographically distinct europium sites have a short Eu(1)-Eu(2) distance of 3.5954(7) A, which yields Eu-Eu dimers. The Eu-P bond distances range from 2.974(2) to 3.166(2) A. The temperature dependence of the conductivity indicates that Eu3InP3 is a small band gap semiconductor. Both magnetization and Eu-151 Mossbauer spectral measurements indicate that the europium in Eu3InP3 is divalent and that at least two magnetic transitions occur. Magnetization studies reveal magnetic transitions at 14, 10.4, and approximately 5 K. These transitions are also observed in heat capacity studies of Eu3InP3. The Mossbauer spectra indicate that the two europium sites are ordered at 12 K and that all three europium sites are ordered at 8 K.
