A5025502158- Rare-earth and actinide compounds
- Iron-based superconductors research
- Advanced Thermoelectric Materials and Devices
- Topological Materials and Phenomena
- Magnetic and transport properties of perovskites and related materials
- Physics of Superconductivity and Magnetism
- Advanced Condensed Matter Physics
- Magnetic Properties of Alloys
- Inorganic Chemistry and Materials
- Thermal properties of materials
- Thermal Expansion and Ionic Conductivity
- Quantum and electron transport phenomena
- Graphene research and applications
- Thermodynamic and Structural Properties of Metals and Alloys
- Advanced Chemical Physics Studies
- Solid-state spectroscopy and crystallography
- Phase-change materials and chalcogenides
- Crystal Structures and Properties
- Semiconductor materials and interfaces
- Heusler alloys: electronic and magnetic properties
- Superconductivity in MgB2 and Alloys
- High-pressure geophysics and materials
- Intermetallics and Advanced Alloy Properties
- Conducting polymers and applications
- Advanced Materials Characterization Techniques
TU Wien
2016-2025
Rice University
2007-2024
Georgi Nadjakov Institute of Solid State Physics
2021
Institute of Modern Physics
2020
Zhejiang University
2020
SOLID (Austria)
2020
Christian Doppler Laboratory for Thermoelectricity
2017
University of Johannesburg
2014
University of Vienna
2014
Max Planck Institute for Chemical Physics of Solids
2000-2013
Nontrivial topology in condensed matter systems enriches quantum states of matter, to go beyond either the classification into metals and insulators terms conventional band theory or that symmetry broken phases by Landau's order parameter framework. So far, focus has been on weakly interacting systems, little is known about limit strong electron correlations. Heavy fermion are a highly versatile platform explore this regime. Here we report discovery giant spontaneous Hall effect Kondo...
${\mathrm{Eu}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30}$ is the only clathrate known so far where guest positions are fully occupied by a rare-earth element. Our investigations show that, in addition to previously synthesized modification with clathrate-I structure, there exists second clathrate-VIII structure. Polycrystalline samples of both phases behave as local-moment ferromagnets relatively low Curie temperatures (10.5 and 36 K). The charge-carrier concentrations rather small (3.8...
This paper addresses some important questions concerning hopping conduction in doped conducting polymers, i.e., dimensionality, homogeneity, adiabaticity, Coulomb interactions, and multiphonon character. It will be shown that electron transport these materials is due to correlated between polaronic clusters. We propose a model which describes quantitatively this process. Conductivity magnetoresistance measurements performed on disordered polypyrroles with polyelectrolytes are presented...
We report thermodynamic measurements in a magnetic-field-driven quantum critical point of heavy fermion metal, YbRh$_2$Si$_2$. The data provide evidence for an energy scale the equilibrium excitation spectrum, that is addition to one expected from slow fluctuations order parameter. Both scales approach zero as reached, thereby providing new class criticality.
Transport properties of ${\mathrm{Ba}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30}$ single-crystalline samples prepared with an excess Ga are presented. The does not only produces p-type transport but also a thermal conductivity (\ensuremath{\kappa}) that, unlike in any other reported the literature, is similar to that iso-structural ${\mathrm{Eu}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30}$ and ${\mathrm{Sr}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30}.$ These observations disagree commonly made...
Insulating states can be topologically nontrivial, a well-established notion that is exemplified by the quantum Hall effect and topological insulators. By contrast, metals have not been experimentally evidenced until recently. In systems with strong correlations, they yet to identified. Heavy fermion semimetals are prototype of strongly correlated and, given their spin-orbit coupling, present natural setting make progress. Here we advance Weyl-Kondo semimetal phase in periodic Anderson model...
Quantum criticality arises when a macroscopic phase of matter undergoes continuous transformation at zero temperature. While the collective fluctuations quantum-critical points are being increasingly recognized as playing an important role in wide range quantum materials, nature underlying excitations remains poorly understood. Here we report in-depth measurements Hall effect heavy-fermion metal YbRh2Si2, prototypical system for criticality. We isolate rapid crossover isothermal coefficient...
Perfectly crystalline solids are excellent heat conductors. Prominent counterexamples intermetallic clathrates, guest-host systems with a high potential for thermoelectric applications due to their ultralow thermal conductivities. Our combined experimental and theoretical investigation of the lattice dynamics particularly simple binary representative, ${\mathrm{Ba}}_{8}{\mathrm{Si}}_{46}$, identifies mechanism responsible reduction conductivity intrinsic perfect crystal structure. Above...
Engineering lattice thermal conductivity requires to control the heat carried by atomic vibration waves, phonons. The key parameter for quantifying it is phonon lifetime, limiting travelling distance, whose determination however at limits of instrumental capabilities. Here, we show achievement a direct quantitative measurement lifetimes in single crystal clathrate Ba7.81Ge40.67Au5.33, renowned its puzzling 'glass-like' conductivity. Surprisingly, transport dominated acoustic phonons with...
Quantum critical behavior occurs at low temperatures where quantum fluctuations become more important than thermal fluctuations. Of particular current interest is unconventional criticality, which lacks a classical counterpart. Angle resolved photoemission and scanning tunneling microscopy are experimental techniques that measure single-particle excitations, recently been used to probe strongly correlated metals near points Here, how the properties reflect criticality discussed, prospect for...
Recent theoretical studies of topologically nontrivial electronic states in Kondo insulators have pointed to the importance spin-orbit coupling (SOC) for stabilizing these states. However, systematic experimental that tune SOC parameter $\lambda_{\rm{SOC}}$ remain elusive. The main reason is variations (chemical) pressure or doping strongly influence $J_{\text{K}}$ and chemical potential $\mu$ -- both essential parameters determining ground state material thus possible tuning effects...
Strange-metal behavior has been observed in materials ranging from high-temperature superconductors to heavy fermion metals. In conventional metals, current is carried by quasiparticles; although it suggested that quasiparticles are absent strange direct experimental evidence lacking. We measured shot noise probe the granularity of current-carrying excitations nanowires metal YbRh
Lattice symmetries are central to the characterization of electronic topology. Recently, it was shown that Green's function eigenvectors form a representation space group. This formulation has allowed identification gapless topological states even when quasiparticles absent. Here we demonstrate profundity framework in extreme case, interactions lead Mott insulator, through solvable model with long-range interactions. We find both poles and zeros subject symmetry constraints, relate...
We present a comprehensive series of electrical transport (conductivity, magnetoresistance, and Hall effect), thermodynamic (specific heat, magnetic susceptibility, magnetization), optical (reflectivity) measurements in varying temperature ranges between 0.05 330 K on high-quality FeSi single crystals grown by vapor transport. The entire set data can consistently be described with the usual relations for (compensated $n$ type) semiconductor if an unconventional band structure is assumed....
Temperature dependent synchrotron powder diffraction and single crystal neutron data are used for probing the vibrational states disorder in type I clathrates ${\mathrm{Ba}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Si}}_{30}$, ${\mathrm{Ba}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30}$, ${\mathrm{Ba}}_{8}{\mathrm{In}}_{16}{\mathrm{Ge}}_{30}$, ${\mathrm{Sr}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30}$. If an empirical term is included, temperature dependence of atomic displacement factors (ADPs) framework...
The canonical view of heavy fermion quantum criticality assumes a single critical point separating the paramagnet from antiferromagnet. However, recent experiments on Yb-based compounds suggest presence non-Fermi liquid behavior over finite zero-temperature region. Using detailed susceptibility and transport measurements we show that classic system, Ge-substituted YbRh2Si2, also displays such behavior. We advance arguments this is not due to disorder-smeared point, but represents new class...
One of the key requirements for good thermoelectric materials is a low lattice thermal conductivity. Here we present combined neutron scattering and theoretical investigation dynamics in type I clathrate system Ba-Ge-Ni, which fulfills this requirement. We observe strong hybridization between phonons Ba guest atoms acoustic Ge-Ni host structure over wide region Brillouin zone, contrast with frequently adopted picture isolated cages. It occurs without decrease phonon lifetime, contradicts...
Abstract Some of the highest-transition-temperature superconductors across various materials classes exhibit linear-in-temperature ‘strange metal’ or ‘Planckian’ electrical resistivities in their normal state. It is thus believed by many that this behavior holds key to unlock secrets high-temperature superconductivity. However, these typically display complex phase diagrams governed competing energy scales, making an unambiguous identification physics at play difficult. Here we use...