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 1-3 , 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 YbRh 2 Si 2 . This finding leads to a materials-based global phase diagram -a precondition for a unified theoretical description.1 Quantum phase transitions arise in matter at zero temperature due to competing interactions. When they are continuous, the associated quantum critical points (QCPs) give rise to collective excitations which influence the physical properties over a wide range of parameters. As such, they are being explored in a variety of electronic materials, ranging from high T c cuprates to insulating magnets and quantum Hall systems 4,5 .Heavy fermion compounds are prototype materials to study quantum phase transitions. Their low energy scales allow to induce such transitions deliberately, by the variation of external parameters such as pressure or magnetic field. Microscopically, electrons in partiallyfilled f shells behave as localized magnetic moments. They interact with conduction electrons through a Kondo exchange interaction, which favors a non-magnetic ground state that entangles the local moments and the spins of the conduction electrons. They also interact among themselves through an RKKY exchange interaction, which typically induces antiferromagnetic order. It has been known that tuning external parameters changes the ratio of the Kondo coupling to the RKKY interaction. Recently, the importance of a second microscopic quantity has been suggested. This is the degree of quantum fluctuations of the local moments, parameterized by G: magnetic order weakens with increasing G, as it would with enhancing the Kondo coupling J K . These two quantities define a two-dimensional parameter space, which allows the consideration of a global phase diagram 10 . This global phase diagram is most clearly specified via the energy scale T * associated with the breakdown of the Kondo entanglement between the local moments and conduction electrons. So far T * has only been identified in tetragonal YbRh 2 Si 2 (refs. 8,11,12 ). It is believed that this energy scale no...

The increasing worldwide energy consumption calls for the design of more efficient energy systems. Thermoelectrics could be used to convert waste heat back to useful electric energy if only more efficient materials were available. The ideal thermoelectric material combines high electrical conductivity and thermopower with low thermal conductivity. In this regard, the intermetallic type-I clathrates show promise with their exceedingly low lattice thermal conductivities. Here we report the successful incorporation of cerium as a guest atom into the clathrate crystal structure. In many simpler intermetallic compounds, this rare earth element is known to lead, through the Kondo interaction, to strong correlation phenomena including the occurrence of giant thermopowers at low temperatures. Indeed, we observe a 50% enhancement of the thermopower compared with a rare-earth-free reference material. Importantly, this enhancement occurs at high temperatures and we suggest that a rattling-enhanced Kondo interaction underlies this effect.

Background: Cardiac surgery often represents the only treatment option in patients with infective endocarditis (IE). However, IE surgery may lead to a sudden release of inflammatory mediators, which is associated with the severity of postoperative organ dysfunction. We investigated the impact of hemoadsorption during IE surgery on postoperative organ dysfunction. Methods: This multi-center, randomized, non-blinded, controlled trial assigned patients undergoing cardiac surgery for IE to hemoadsorption [integration of CytoSorb® to cardiopulmonary bypass (CPB)] or control. The Primary outcome (ΔSOFA) was defined as the difference between the mean total postoperative sequential organ failure assessment score (SOFA), calculated maximally to the 9th postoperative day, and the basal SOFA score. The analysis was by modified intention-to-treat. A predefined inter-group comparison was done using a linear mixed model for ΔSOFA including surgeon and baseline SOFA as fixed effect covariates and with the surgical center as random effect. The SOFA score assesses dysfunction in six organ systems, each scored from zero to four. Higher scores indicate worsening dysfunction. Secondary outcomes were 30-day mortality, durations of mechanical ventilation, vasopressor and renal replacement therapy. Cytokines were measured in the first 50 patients. Results: Between January 17, 2018 and January 31, 2020, A total of 288 patients were randomly assigned to hemoadsorption (n=142) or control (n=146). Four patients in the hemoadsorption and two in the control group were excluded as they did not undergo surgery. The primary outcome ΔSOFA did not differ between the hemoadsorption and the control group (1.79 ± 3.75 and 1.93 ± 3.53, respectively, 95% CI: −1.30 to 0.83, p=0.6766). Mortality at 30 days (21% hemoadsorption vs 22% control, p=0.782), the durations of mechanical ventilation, vasopressor and renal replacement therapy did not differ between groups. Levels of IL-1β and IL-18 at the end of CPB were significantly lower in the hemoadsorption than in the control group. Conclusions: This randomized trial failed to demonstrate a reduction in postoperative organ dysfunction through intraoperative hemoadsorption in patients undergoing cardiac surgery for IE. Although hemoadsorption reduced plasma cytokines at the end of CPB, there was no difference in any of the clinically relevant outcome points.

Kondo insulators and in particular their non-cubic representatives have remained poorly understood. Here we report on the development of an anisotropic energy pseudogap in the tetragonal compound CeRu4Sn6 employing optical reflectivity measurements in broad frequency and temperature ranges, and local density approximation plus dynamical mean field theory calculations. The calculations provide evidence for a Kondo insulator-like response within the a − a plane and a more metallic response along the c axis and qualitatively reproduce the experimental observations, helping to identify their origin.Correlated materials with gapped or pseudo-gapped ground states continue to be of great interest. The gap in the electronic density of states (DOS) either opens gradually with decreasing temperature, as the pseudogap of high-temperature superconductors [1], or emerges at a continuous or first order phase transition [2][3][4]. In heavy fermion compounds [5] -systems in which f and conduction electrons strongly interact -a narrow hybridization gap is known to emerge gradually [6][7][8][9]. Generically, the Fermi energy is situated in one of the hybridized bands and a metallic heavy fermion ground state arises. Only for special cases the Fermi energy lies within the gap and the ground state is Kondo insulating. Metallic heavy fermion systems have been intensively investigated over the past decades and are now, at least away from quantum criticality [10], well understood [11] within the framework of Landau Fermi liquid theory. Hence, a very few parameters, most notably the effective mass, allow us to describe thermodynamic and transport properties at the lowest temperatures. In comparison, the physics of Kondo insulators has proven to be much less tractable. This is at least in part due to the fact that the gapped ground state inhibits a characterization via the above properties. Many experimental efforts have therefore focussed on the determination of the gap width from temperature dependencies, which has frequently led to conflicting results, in particular for anisotropic Kondo insulators such as CeNiSn [12]. Here the strongly anisotropic transport and magnetic properties have been interpreted phenomenologically on the basis of a V-shaped DOS [13] or by invoking a hybridization gap with nodes [14][15][16] or extrinsic effects such as impurities, off stoichiometry or strain [17,18]. To advance the field it appears mandatory to model a number of carefully chosen materials ab initio, taking all essential ingredients into account.Here we investigate a new material, CeRu 4 Sn 6 , which due to its tetragonal crystal structure is simpler than the previously studied orthorhombic materials. In a combined experimental and theoretical effort we provide direct spectroscopic evidence for the development of an anisotropic pseudogap: While weak metallicity prevails in the optical conductivity along the c axis, insulatorlike behavior without a Drude peak is observed in the a − a plane. We trace this back to a correlated band structure whic...

No abstract