Ordered Phases and Quantum Criticality in Cubic Heavy Fermion Compounds

Quantum criticality in cubic heavy fermion compounds remains much less explored than in quasi-two-dimensional systems. However, such materials are needed to broadly test the recently suggested global phase diagram for heavy fermion quantum criticality. Thus, to boost these activities, we review the field, with focus on Ce-based systems with temperature-magnetic field or temperature-pressure phase diagrams that may host a quantum critical point. To date, CeIn3 and Ce3Pd20Si6 are the only two among these compounds where quantum critical behaviour has been systematically investigated. Interestingly, both show Fermi surface reconstructions as function of the magnetic field that may be understood in terms of Kondo destruction quantum criticality.Comment: invited review paper, 3 figures, 102 references, to appear in J. Phys. Soc. Jpn., Section: Special Topics "Advances in Physics of Strongly Correlated Electron Systems

Exploring the role of servitization to overcome barriers for innovative energy efficiency technologies – the case of public LED street lighting in German municipalities

In this paper we analyse the case for public application of LED street lighting. Drawing from the energy services literature and transaction cost economics, we compare modes of lighting governance for modernisation. We argue that servitization can accelerate the commercialisation and diffusion of end-use energy demand reduction (EUED) technologies in the public sector if third party energy service companies (ESCo) overcome technological, institutional and economic barriers that accompany the introduction of such technologies resulting in transaction costs. This can only succeed with a supportive policy framework and an environment conducive towards the dissemination of specific technological and commercial knowledge required for the diffusion process

Quasiparticles near quantum phase transition in heavy fermion metals

We have shown that the Landau paradigm based upon both the quasiparticle concept and the notion of the order parameter can be used to explain the anomalous behavior of heavy fermion metals. Exploiting this paradigm and the fermion condensation quantum phase transition (FCQPT) we show that this anomalous behavior is universal and can be used to capture the essential aspects of recent experiments on the heavy-fermion metals at low temperatures. Behind FCQPT a tunneling conductivity between a heavy fermion metal and a simple metallic point can be noticeably dissymmetrical with respect to the change of voltage bias. We show that at T=0 and beyond FCQPT the Hall coefficient undergoes a jump upon magnetic-field tuning HF metals.Comment: 2 pages, 1 figure, submitted to the SCES'0

Effect of chemical substitution and pressure on YbRh2Si2

We carried out electrical resistivity experiments on (Yb,La)Rh2Si2 and on Yb(Rh,Ir)2Si2 under pressure and in magnetic fields. YbRh2Si2 exhibits a weak antiferromagnetic transition at atmospheric pressure with a N\'eel temperature of only T_N = 70 mK. By applying a small magnetic field T_N can be continuously suppressed to T=0 at B_c = 60 mT (B_|_c) driving the system to a quantum critical point (QCP). On applying external pressure the magnetic phase is stabilized and T_N(p) is increasing as usually observed in Yb-based heavy-fermion metals. Substituting Yb by La or Rh by Ir allows to create a negative chemical pressure, La (Ir) being smaller than Yb (Rh), and eventually to drive YbRh2Si2 to a pressure controlled QCP. In this paper we compare the effect of external hydrostatic pressure and chemical substitution on the ground-state properties of YbRh2Si2.Comment: 4 pages, 5 figures, proceedings paper of the QCNP0

Thin n-in-p planar pixel sensors and active edge sensors for the ATLAS upgrade at HL-LHC

Silicon pixel modules employing n-in-p planar sensors with an active thickness of 200 $\mu$m, produced at CiS, and 100-200 $\mu$m thin active/slim edge sensor devices, produced at VTT in Finland have been interconnected to ATLAS FE-I3 and FE-I4 read-out chips. The thin sensors are designed for high energy physics collider experiments to ensure radiation hardness at high fluences. Moreover, the active edge technology of the VTT production maximizes the sensitive region of the assembly, allowing for a reduced overlap of the modules in the pixel layer close to the beam pipe. The CiS production includes also four chip sensors according to the module geometry planned for the outer layers of the upgraded ATLAS pixel detector to be operated at the HL-LHC. The modules have been characterized using radioactive sources in the laboratory and with high precision measurements at beam tests to investigate the hit efficiency and charge collection properties at different bias voltages and particle incidence angles. The performance of the different sensor thicknesses and edge designs are compared before and after irradiation up to a fluence of $1.4\times10^{16}n_{eq}/cm^{2}$.Comment: In proceedings of the 10th International Conference on Position Sensitive Detectors, PSD10 201

Fermi-surface collapse and dynamical scaling near a quantum critical point

Quantum criticality arises when a macroscopic phase of matter undergoes a continuous transformation at zero temperature. While the collective fluctuations at quantum-critical points are being increasingly recognized as playing an important role in a wide range of quantum materials, the nature of the underlying quantum-critical excitations remains poorly understood. Here we report in-depth measurements of the Hall effect in the heavy-fermion metal YbRh2Si2, a prototypical system for quantum criticality. We isolate a rapid crossover of the isothermal Hall coefficient clearly connected to the quantum-critical point from a smooth background contribution; the latter exists away from the quantum-critical point and is detectable through our studies only over a wide range of magnetic field. Importantly, the width of the critical crossover is proportional to temperature, which violates the predictions of conventional theory and is instead consistent with an energy over temperature, E/T, scaling of the quantum-critical single-electron fluctuation spectrum. Our results provide evidence that the quantum-dynamical scaling and a critical Kondo breakdown simultaneously operate in the same material. Correspondingly, we infer that macroscopic scale-invariant fluctuations emerge from the microscopic many-body excitations associated with a collapsing Fermi-surface. This insight is expected to be relevant to the unconventional finite-temperature behavior in a broad range of strongly correlated quantum systems.Comment: 5 pages, plus supporting materia

Field-Dependent Hall Effect in Single Crystal Heavy Fermion YbAgGe below 1K

We report the results of a low temperature (T >= 50 mK) and high field (H <= 180 kOe) study of the Hall resistivity in single crystals of YbAgGe, a heavy fermion compound that demonstrates field-induced non-Fermi-liquid behavior near its field-induced quantum critical point. Distinct features in the anisotropic, field-dependent Hall resistivity sharpen on cooling down and at the base temperature are close to the respective critical fields for the field-induced quantum critical point. The field range of the non-Fermi-liquid region decreases on cooling but remains finite at the base temperature with no indication of its conversion to a point for T -> 0. At the base temperature, the functional form of the field-dependent Hall coefficient is field direction dependent and complex beyond existing simple models thus reflecting the multi-component Fermi surface of the material and its non-trivial modification at the quantum critical point

Spectroscopic Constraints on the Surface Magnetic Field of the Accreting Neutron Star EXO 0748-676

Gravitationally redshifted absorption lines of Fe XXVI, Fe XXV, and O VIII were inferred recently in the X-ray spectrum of the bursting neutron star EXO 0748-676. We place an upper limit on the stellar magnetic field based on the iron lines. The oxygen absorption feature shows a multiple component profile that is consistent with Zeeman splitting in a magnetic field of ~(1-2)x10^9 gauss, and for which the corresponding Zeeman components of the iron lines are expected to be blended together. In other systems, a field strength >5x10^{10} gauss could induce a blueshift of the line centroids that would counteract gravitational redshift and complicate the derivation of constraints on the equation of state of the neutron star.Comment: 5 pages, submitted to Phys. Rev. Let