A. Prokofiev

Destruction of the Kondo effect in the cubic heavy-fermion compound Ce3Pd20Si6

How ground states of quantum matter transform between one another reveals deep insights into the mechanisms stabilizing them. Correspondingly, quantum phase transitions are explored in numerous materials classes, with heavy-fermion compounds being among the most prominent ones. Recent studies in an anisotropic heavy-fermion compound have shown that different types of transitions are induced by variations of chemical or external pressure, raising the question of the extent to which heavy-fermion quantum criticality is universal. To make progress, it is essential to broaden both the materials basis and the microscopic parameter variety. Here, we identify a cubic heavy-fermion material as exhibiting a field-induced quantum phase transition, and show how the material can be used to explore one extreme of the dimensionality axis. The transition between two different ordered phases is accompanied by an abrupt change of Fermi surface, reminiscent of what happens across the field-induced antiferromagnetic to paramagnetic transition in the anisotropic YbRh2Si2. This finding leads to a materials-based global phase diagram--a precondition for a unified theoretical description.

Magnetocaloric effect and magnetic cooling near a field-induced quantum-critical point

The presence of a quantum-critical point (QCP) can significantly affect the thermodynamic properties of a material at finite temperatures T. This is reflected, e.g., in the entropy landscape S(T,r) in the vicinity of a QCP, yielding particularly strong variations for varying the tuning parameter r such as pressure or magnetic field B. Here we report on the determination of the critical enhancement of ∂S/∂B near a B-induced QCP via absolute measurements of the magnetocaloric effect (MCE), (∂T/∂B)S and demonstrate that the accumulation of entropy around the QCP can be used for efficient low-temperature magnetic cooling. Our proof of principle is based on measurements and theoretical calculations of the MCE and the cooling performance for a Cu2+-containing coordination polymer, which is a very good realization of a spin-½ antiferromagnetic Heisenberg chain—one of the simplest quantum-critical systems.

Search for a spin-nematic phase in the quasi-one-dimensional frustrated magnet LiCuVO 4

Hsat. For the field range Hc2 41.4 T, indicating that the majority of magnetic moments in LiCuVO4 are already saturated in this field range. This result is inconsistent with the previously observed linear field dependence of the magnetization M(H) for Hc3 < H < Hsat with µ0Hsat = 45 T [L. E. Svistov et al., JETP Letters 93, 21 (2011)]. We argue that the discrepancy is due to non-magnetic defects in the samples. The results of the spin–lattice relaxation rate of 7 Li nuclei indicate an energy gap which grows with field twice as fast as the Zeeman energy of a single spin, therefore, suggesting that the two–magnon bound state is the lowest energy excitation. The energy gap tends to close at µ0H ≈ 41 T. Our results suggest that the theoretically predicted spin–nematic phase, if it exists in LiCuVO4, can be established only within the narrow field range 40.5 < µ0H < 41.4 T .

CeRu4Sn6: a strongly correlated material with nontrivial topology.

Topological insulators form a novel state of matter that provides new opportunities to create unique quantum phenomena. While the materials used so far are based on semiconductors, recent theoretical studies predict that also strongly correlated systems can show non-trivial topological properties, thereby allowing even the emergence of surface phenomena that are not possible with topological band insulators. From a practical point of view, it is also expected that strong correlations will reduce the disturbing impact of defects or impurities, and at the same increase the Fermi velocities of the topological surface states. The challenge is now to discover such correlated materials. Here, using advanced x-ray spectroscopies in combination with band structure calculations, we infer that CeRu4Sn6 is a strongly correlated material with non-trivial topology.

Anisotropic optical conductivity of the putative Kondo insulator CeRu4Sn6

Physics Department, University of Johannesburg, Auckland Park 2006, South Africa(Dated: September 14, 2012)Kondo insulators and in particular their non-cubic representatives have remained poorly under-stood. Here we report on the development of an anisotropic energypseudogap in the tetragonalcompound CeRu

High-Pressure Torsion to Improve Thermoelectric Efficiency of Clathrates?

High-pressure torsion (HPT), as a technique to produce severe plastic deformation, has been proven effective to improve the thermoelectric performance of skutterudites. In this report, we present microstructural and thermoelectric properties of the clathrate Ba8Cu3.5Ge41In1.5 processed by HPT. The sample was synthesized from high-purity elements, subsequently annealed, ball milled, and hot pressed, and finally subject to HPT. Compared with the ball-milled and hot-pressed sample, the HPT-processed sample has higher electrical resistivity and Seebeck coefficient, and lower thermal conductivity, electron concentration, and mobility, which is attributed to the reduced grain size and increased density of dislocations, point defects, and cracks. No essential improvement of the dimensionless thermoelectric figure of merit is observed in the investigated temperature range, questioning the universal versatility of this technique for improvement of thermoelectric materials.

NMR study of the high-field magnetic phase of LiCuVO 4

We report on NMR studies of the quasi--1D antiferromagnetic

Kondo Insulator to Semimetal Transformation Tuned by Spin-Orbit Coupling

S=1/2

Dielectric properties and electrical switching behaviour of the spin-driven multiferroic LiCuVO4

chain cuprate LiCuVO

Structural, Magnetic and Transport Properties of the Rare-Earth Cage Compound Ce4Pd12Sn25

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