arXiv subjects

Tobias Foerster

Publications and source records attributed to Tobias Foerster.

4 recordsLinked to original sources

arXiv2017

Extremely high magnetoresistance and conductivity in the type-II Weyl semimetals WP2 and MoP2

The peculiar band structure of semimetals exhibiting Dirac and Weyl crossings can lead to spectacular electronic properties such as large mobilities accompanied by extremely high magnetoresistance. In particular, two closely neighbouring Weyl points of the same chirality are protected from annihilation by structural distortions or defects, thereby significantly reducing the scattering probability between them. Here we present the electronic properties of the transition metal diphosphides, WP2 and MoP2, that are type-II Weyl semimetals with robust Weyl points. We present transport and angle resolved photoemission spectroscopy measurements, and first principles calculations. Our single crystals of WP2 display an extremely low residual low-temperature resistivity of 3 nohm-cm accompanied by an enormous and highly anisotropic magnetoresistance above 200 million % at 63 T and 2.5 K. These properties are likely a consequence of the novel Weyl fermions expressed in this compound. We observe a large suppression of charge carrier backscattering in WP2 from transport measurements.

cond-mat.mtrl-sci↗

arXiv2016

Quantum phase transitions and multicriticality in Ta(Fe1-xVx)2

We present a comprehensive study of synthesis, structure analysis, transport and thermodynamic properties of the C14 Laves phase Ta(Fe1-xVx)2. Our measurements confirm the appearance of spin-density wave (SDW) order within a dome-like region of the x - T phase diagram with vanadium content 0.02 < x < 0.3. Our results indicate that on approaching TaFe2 from the vanadium-rich side, ferromagnetic (FM) correlations increase faster than the antiferromagnetic (AFM) ones. This results in an exchange-enhanced susceptibility and in the suppression of the SDW transition temperature for x < 0.13 forming the dome-like shape of the phase diagram. This effect is strictly related to a significant lattice distortion of the crystal structure manifested in the c/a ratio. At x = 0.02 both FM and AFM energy scales have similar strength and the system remains paramagnetic down to 2 K with an extremely large Stoner enhancement factor of about 400. Here, spin fluctuations dominate the temperature dependence of the resistivity ρ~ T ^ 3/2 and of the specific heat C/T ~ - log(T) which deviate from their conventional Fermi liquid forms, inferring the presence of a quantum critical point of dual nature.

cond-mat.str-el↗

arXiv2015

Large linear magnetoresistance and weak anti-localization in Y(Lu)PtBi topological insulators

Topological insulators are new kind of Dirac materials that possess bulk insulating and surface conducting behavior. They are basically known for their unique electronic properties at the surface. Here we present the magneto-transport properties of our high quality single crystalline Y(Lu)PtBi Heusler topological insulators, which belong to a group of noncentrosymmetric superconductor with Tc = 0:8 K. Both the compounds show semi-metallic behavior with low charge carrier of 6 x1018 cm^-3 for YPtBi and 8 x1019 cm^-3 for LuPtBi at 2 K. Magneto-conductivity measurements in the tilted field indicate that the charge carriers transport through quantum interference. This provide a direct evidence of weak anti-localization below 50 K, giving a strong signature of surface transport. Most importantly, these compounds show very high unsaturated linear magnetoresistance of approximately 2000% at 10 K in a magnetic field of 60 T.

cond-mat.mtrl-sci↗

arXiv2008

Relevance of ferromagnetic correlations for the Electron Spin Resonance in Kondo lattice systems

Electron Spin Resonance (ESR) measurements of the ferromagnetic Kondo lattice system CeRuPO show a well defined ESR signal which is related to the magnetic properties of the Ce3+ moment. In contrast, no ESR signal could be observed in the antiferromagnetic homologue CeOsPO. Additionally, we detect an ESR signal in a further ferromagnetic Yb compound, YbRh, while it was absent in a number of Ce or Yb intermetallic compounds with dominant antiferromagnetic exchange, independently of the presence of a strong Kondo interaction or the proximity to a (quantum) critical point. Thus, the observation of an ESR signal in a Kondo lattice is neither specific to Yb nor to the proximity of a quantum critical point, but seems to be connected to the presence of ferromagnetic fluctuations. These conclusions not only provide a basic concept to understand the ESR in Kondo lattice systems even well below the Kondo temperature as observed in the heavy fermion metal YbRh2Si2 but point out ESR as a prime method to investigate directly the spin dynamics of the Kondo ion.

cond-mat.str-el↗