Indications of flat bands driving the to volume collapse of plutonium.

On cooling from the melt, plutonium (Pu) undergoes a series of structural transformations accompanied by a ≈ 28% reduction in volume from its phase to its phase at low temperatures. While Pu's partially filled 5-electron shells are known to be involved, their precise role in the transformations has remained unclear. By using calorimetry measurements on -Pu and gallium-stabilized -Pu combined with resonant ultrasound and X-ray scattering data to account for the anomalously large softening of the lattice with temperature, we show here that the difference in electronic entropy between the and phases dominates over the difference in phonon entropy.

The structure of CeAlGe refined for the first time from single-crystal X-ray diffraction data.

Single crystals of dicerium trialuminium tetragermanide, CeAlGe, have been synthesized from a high-temperature reaction using an eutectic mixture of Al and Ge as a metal flux. Through single-crystal X-ray diffraction it was established that CeAlGe crystallizes in the centrosymmetric space group Cmce (No. 64) with the BaCdBi structure type (Pearson code oC36).

Phase stabilization by electronic entropy in plutonium.

Plutonium metal undergoes an anomalously large 25% collapse in volume from its largest volume δ phase (δ-Pu) to its low temperature α phase, yet the underlying thermodynamic mechanism has largely remained a mystery. Here we use magnetostriction measurements to isolate a previously hidden yet substantial electronic contribution to the entropy of δ-Pu, which we show to be crucial for the stabilization of this phase. The entropy originates from two competing instabilities of the 5f-electron shell, which we show to drive the volume of Pu in opposing directions, depending on the temperature and volume.

Avoided valence transition in a plutonium superconductor.

The d and f electrons in correlated metals are often neither fully localized around their host nuclei nor fully itinerant. This localized/itinerant duality underlies the correlated electronic states of the high-Tc cuprate superconductors and the heavy-fermion intermetallics and is nowhere more apparent than in the 5f valence electrons of plutonium. Here, we report the full set of symmetry-resolved elastic moduli of PuCoGa5--the highest Tc superconductor of the heavy fermions (Tc = 18.

Emergent antiferromagnetism out of the "hidden-order" state in URu2Si2: high magnetic field nuclear magnetic resonance to 40 T.

Very high field (29)Si-NMR measurements using a fully (29)Si-enriched URu(2)Si(2) single crystal were carried out in order to microscopically investigate the "hidden order" (HO) state and adjacent magnetic phases in the high field limit. At the lowest measured temperature of 0.4 K, a clear anomaly reflecting a Fermi surface instability near 22 T inside the HO state is detected by the (29)Si shift, (29)K(c).

Weak itinerant antiferromagnetism in PuIn3 explored using 115In nuclear quadrupole resonance.

The results of (115)In nuclear quadrupole resonance (NQR) measurements on PuIn3 are reported. Three of the four NQR lines of (115)In expected for nuclear spin I = 9/2 are observed. The equal spacing of these lines at 20 K yields the NQR frequency of νQ = 10.

Synthesis, structural characterization, and physical properties of the early rare-earth metal digermanides REGe(2-x) (x ≈ 1/4) [RE = La-Nd, Sm]. A case study of commensurately and incommensurately modulated structures.

Rare-earth metal germanides with the general formula RE(4)Ge(7) (RE = La, Ce, Pr, Nd, Sm) have been synthesized using the In-flux technique. Their structures have been established from single-crystal and powder X-ray diffraction, and the structural elucidation has been aided by electron diffraction. These compounds represent superstructures of the α-ThSi(2) structure type through the long- and/or short-range vacancy ordering.

Electronic tuning and uniform superconductivity in CeCoIn5.

We report a globally reversible effect of electronic tuning on the magnetic phase diagram in CeCoIn(5) driven by electron (Pt and Sn) and hole (Cd, Hg) doping. Consequently, we are able to extract the superconducting pair breaking component for hole and electron dopants with pressure and codoping studies, respectively. We find that these nominally nonmagnetic dopants have a remarkably weak pair breaking effect for a d-wave superconductor.

Observation of the hybridization gap and Fano resonance in the Kondo lattice URu2Si2.

The nature of the second-order phase transition that occurs in URu2Si2 at 17.5 K remains puzzling despite intensive research. A key question emerging in the field is whether a hybridization gap between the renormalized bands can be identified as the "hidden" order parameter.

Controllable chirality-induced geometrical Hall effect in a frustrated highly correlated metal.

A current of electrons traversing a landscape of localized spins possessing non-coplanar magnetic order gains a geometrical (Berry) phase, which can lead to a Hall voltage independent of the spin-orbit coupling within the material-a geometrical Hall effect. Here we show that the highly correlated metal UCu(5) possesses an unusually large controllable geometrical Hall effect at T<1.2 K due to its frustration-induced magnetic order.

Multiconfigurational nature of 5f orbitals in uranium and plutonium intermetallics.

Uranium and plutonium's 5f electrons are tenuously poised between strongly bonding with ligand spd-states and residing close to the nucleus. The unusual properties of these elements and their compounds (e.g.

Superconducting pairs with extreme uniaxial anisotropy in URu2Si2.

We report magnetic field orientation-dependent measurements of the superconducting upper critical field in high quality single crystals of URu(2)Si(2) and find the effective g factor estimated from the Pauli limit to agree remarkably well with that found in quantum oscillation experiments, both quantitatively and in the extreme anisotropy (≈10(3)) of the spin susceptibility. Rather than a strictly itinerant or purely local f-electron picture being applicable, the latter suggests the quasiparticles subject to pairing in URu(2)Si(2) to be "composite heavy fermions" formed from bound states between conduction electrons and local moments with a protected Ising behavior. Non-Kramers doublet local magnetic degrees of freedom suggested by the extreme anisotropy favor a local pairing mechanism.

Localized 5f electrons in superconducting PuCoIn₅: consequences for superconductivity in PuCoGa₅.

The physical properties of the first In analog of the PuMGa(5) (M = Co, Rh) family of superconductors, PuCoIn(5), are reported. With its unit cell volume being 28% larger than that of PuCoGa(5), the characteristic spin-fluctuation energy scale of PuCoIn(5) is three to four times smaller than that of PuCoGa(5), which suggests that the Pu 5f electrons are in a more localized state relative to PuCoGa(5). This raises the possibility that the high superconducting transition temperature T(c) = 18.

Single crystal study of the heavy-fermion antiferromagnet CePt₂In₇.

We report the synthesis, structure, and physical properties of single crystals of CePt(2)In(7). Single crystal x-ray diffraction analysis confirms the tetragonal I4/mmm structure of CePt(2)In(7) with unit cell parameters a = 4.5886(6) Å, c = 21.

Anisotropic critical magnetic fluctuations in the ferromagnetic superconductor UCoGe.

We report neutron scattering measurements of critical magnetic excitations in the weakly ferromagnetic superconductor UCoGe. The strong non-Landau damping of the excitations we observe, although unusual, has been found in another related ferromagnet, UGe(2) at zero pressure. However, we also find that there is a significant anisotropy of the magnetic correlation length in UCoGe that contrasts with an almost isotropic length for UGe(2).

Nanorod Self-Assembly in High J YBa₂Cu₃O₇ Films with Ru-Based Double Perovskites.

Many second phase additions to YBa₂Cu₃O (YBCO) films, in particular those that self-assemble into aligned nanorod and nanoparticle structures, enhance performance in self and applied fields. Of particular interest for additions are Ba-containing perovskites that are compatible with YBCO. In this report, we discuss the addition of Ba₂YRuO₆ to bulk and thick-film YBCO.

Sequential spin polarization of the Fermi surface pockets in URu2Si2 and its implications for the hidden order.

Using Shubnikov-de Haas oscillations measured in URu2Si2 over a broad range in a magnetic field of 11-45 T, we find a cascade of field-induced Fermi surface changes within the hidden order phase I and further signatures of oscillations within field-induced phases III and V [previously discovered by Kim et al., [Phys. Rev.

Synthesis, structure and physical properties of YbNi3Al9.23.

The physical properties of YbNi(3)Al(9.23(1)), including the crystal structure, magnetization, specific heat, valence, and electrical resistivity, are reported. Single crystal x-ray diffraction reveals that the compound crystallizes with the rhombohedral space group R32 and has unit cell parameters a = 7.

Magnetic order in Pu₂M₃Si₅ (M = Co, Ni).

The physical properties including magnetic susceptibility, specific heat, and electrical resistivity of two new plutonium compounds Pu2M3Si5 (M = Co, Ni) are reported. Pu2Ni3Si5 crystallizes in the orthorhombic U2Co3Si5 structure type, which can be considered a variant of the BaAl4 tetragonal structure, while Pu2Co3Si5 adopts the closely related monoclinic Lu2Co3Si5 type. Magnetic order is observed in both compounds, with Pu2Ni3Si5 ordering ferromagnetically at T(C) = 65 K then undergoing a transition into an antiferromagnetic state below T(N) = 35 K.

Mixed cations and structural complexity in (Eu(1-x)Ca(x))(4)In(3)Ge(4) and (Eu(1-x)Ca(x))(3)In(2)Ge(3)--the first two members of the homologous series A(2[n+m])In(2n+m)Ge(2[n+m]) (n, m = 1, 2, ...infinity; A = Ca, Sr, Ba, Eu, or Yb).

Reported are the synthesis and the structural characterization of two members of a new homologous series of polar intermetallic compounds, which exist only with mixed alkaline-earth and rare-earth metal cations. Crystals of (Eu(1-x)Ca(x))(4)In(3)Ge(4) (0.35(1) View Article and Find Full Text PDF

Magnesium substitutions in rare-earth metal germanides with the orthorhombic Gd5Si4-type structure. Synthesis, crystal chemistry, and magnetic properties of RE(5-x)Mg(x)Ge4 (RE = Gd-Tm, Lu, and Y).

A series of magnesium-substituted rare-earth metal germanides with a general formula RE(5-x)Mg(x)Ge(4) (x approximately = 1.0-2.3; RE = Gd-Tm, Lu, Y) have been synthesized by high-temperature reactions and structurally characterized by single-crystal X-ray diffraction.

Structure and properties of Gd3Ge4: the orthorhombic RE3Ge4 structures revisited (RE = Y, Tb-Tm).

The new binary compound Gd(3)Ge(4) has been synthesized and its structure has been determined from single-crystal X-ray diffraction. Gd(3)Ge(4) crystallizes in the orthorhombic space group Cmcm (No. 63) with unit cell parameters a = 4.

Vacancy ordering in SmGe2-x and GdGe2-x (x = 0.33): structure and properties of two Sm3Ge5 polymorphs and of Gd3Ge5.

The crystal structures and the magnetic properties of three new binary rare-earth intermetallic phases are reported. alpha-Sm3Ge5 and beta-Sm3Ge5 and Gd3Ge5 have been prepared from the corresponding elements through high-temperature reactions using the flux-growth method. The structures of the three compounds have been established using single-crystal X-ray diffraction: alpha-Sm3Ge5 crystallizes with its own type in the hexagonal space group P2c (No.

Structure and bonding in Yb4MgGe4: Yb2+/Yb3+ mixed-valency and charge separation.

Reported are the synthesis and the structural characterization of a new derivative of the RE5Tt4 family (RE = Rare-earth; Tt = Tetrel, = Si, Ge, i.e., group 14 element), Yb5-xMgxGe4 (x approximately 1).