Here, a novel synthesis for near monodisperse, sub‐10 nm Bi2Te3 nanoparticles is reported. A new reduction route to bismuth nanoparticles is described, which are then applied as starting materials in the formation of rhombohedral Bi2Te3 nanoparticles. After ligand removal by a novel hydrazine hydrate etching procedure, the nanoparticle powder is spark plasma sintered to a pellet with preserved crystal grain sizes. Unlike previous works on the properties of Bi2Te3 nanoparticles, the full thermoelectric characterization of such sintered pellets shows a highly reduced thermal conductivity and the same electric conductivity as bulk n‐type Bi2Te3.

A continuous phase transition driven to zero temperature by a non-thermal parameter, such as pressure, terminates in a quantum critical point (QCP). At present, two main theoretical approaches are available for antiferromagnetic QCPs in heavyfermion systems. The conventional one is the quantum generalization of finite-temperature phase transitions, which reproduces the physical properties in many cases 1-5 . More recent unconventional models incorporate a breakdown of the Kondo effect, giving rise to a Fermi-surface reconstruction 6-8 -YbRh 2 Si 2 is a prototype of this category 5,9-11 . In YbRh 2 Si 2 , the antiferromagnetic transition temperature merges with the Kondo breakdown at the QCP. Here, we study the evolution of the quantum criticality in YbRh 2 Si 2 under chemical pressure. Surprisingly, for positive pressure we find the signature of the Kondo breakdown within the magnetically ordered phase, whereas negative pressure induces their separation, leaving an intermediate spin-liquid-type ground state over an extended range. This behaviour suggests a new quantum phase arising from the interplay of the Kondo breakdown and the antiferromagnetic QCP.In heavy-fermion systems, the Kondo effect leads to the formation of composite quasiparticles of the f and conductionelectron states with largely renormalized masses forming a Landau Fermi-liquid ground state in the paramagnetic regime well below the Kondo temperature T K . These quasiparticles are assumed to stay intact at the quantum critical point (QCP) in the conventional models in which magnetic order arises through a spin-densitywave (SDW) instability. However, the observation of magnetic correlations in CeCu 5.9 Au 0.1 being of local character 11 prompted a series of theoretical descriptions that discard this basic assumption. Rather, they focus on the breakdown of the Kondo effect, which causes the f states to become localized and decoupled from the conduction-band states at the QCP where one expects the Fermi surface to be reconstructed 7 . Consequently, a new energy scale T is predicted reflecting the finite-temperature T crossover of the Fermi-surface volume. This picture has been scrutinized in tetragonal YbRh 2 Si 2 (T K ≈ 25 K; ref. 12), a stoichiometric and very clean heavy-fermion metal that seems to be ideally suited for this kind of study 9,12 : antiferromagnetic order sets in at a very low temperature T N = 0.07 K and can easily be suppressed by a small magnetic field of µ 0 H N = 60 mT (H ⊥ c, with c being the magnetically hard axis). Hall-effect experiments 13 have detected a rapid change of the Hall coefficient along a line T (H ) that converges with H N , the width of the Hall crossover extrapolating LETTERS NATURE PHYSICS

The superconducting phase transition in heavy fermion CeCoIn5 (T(c)=2.3 K in zero field) becomes first order when the magnetic field H parallel [001] is greater than 4.7 T, and the transition temperature is below T0 approximately 0.31T(c). The change from second order at lower fields is reflected in strong sharpening of both specific heat and thermal expansion anomalies associated with the phase transition, a strong magnetocaloric effect, and a steplike change in the sample volume. This effect is due to Pauli limiting in a type-II superconductor, and was predicted theoretically in the mid-1960s.

We present low-temperature volume thermal expansion, β, and specific heat, C, measurements on high-quality single crystals of CeNi 2 Ge 2 and YbRh 2 (Si 0.95 Ge 0.05 ) 2 which are located very near to quantum critical points. For both systems, β shows a more singular temperature dependence than C, and thus the Grüneisen ratio Γ ∝ β/C diverges as T → 0. For CeNi 2 Ge 2 , our results are in accordance with the spin-density wave (SDW) scenario for three-dimensional critical spinfluctuations. By contrast, the observed singularity in YbRh 2 (Si 0.95 Ge 0.05 ) 2 cannot be explained by the itinerant SDW theory but is qualitatively consistent with a locally quantum critical picture.