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Sun P.,CAS Institute of Physics | Steglich F.,Max Planck Institute for Chemical Physics of Solids
Physical Review Letters | Year: 2013

A distinctly temperature-dependent Nernst coefficient, ν, which is strongly enhanced over that of LaCu2Si2, is observed between T=2 and 300 K for CeCu2Si2 and Ce 0.8La0.2Cu2Si2. The enhanced ν(T) is determined by the asymmetry of the on-site Kondo (conduction electron -4f electron) scattering rate. Taking into account the measured Hall mobility, μH, the highly unusual thermopower, S, of these systems can be semiquantitatively described by S(T)=-ν(T)/μH(T), which explicitly demonstrates that the thermopower originates from the local Kondo scattering process over a wide temperature range from far above to well below the coherence temperature (≈20 K for CeCu2Si2). Our results suggest that the Nernst effect can act as a proper probe of local charge-carrier scattering. This promises to impact on exploring the unconventional enhancement of the thermopower in correlated materials suited for potential applications. © 2013 American Physical Society.

Thalmeier P.,Max Planck Institute for Chemical Physics of Solids
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

In the skutterudite compounds the anharmonic "rattling" oscillations of 4f -guest ions in the surrounding Sb12 host cages are found to have significant influence on the low-temperature properties. Recently specific-heat analysis of Pr ( Os1-x Rux) 4 Sb12 has shown that the energy of crystalline electric field singlet-triplet excitations increases strongly with Ru concentration x and crosses the almost constant rattling mode frequency ω0 at about x=0.65. Due to magnetoelastic interactions this may entail prominent nonadiabatic effects in inelastic neutron-scattering intensity and quadrupolar susceptibility. Furthermore the Ru-concentration dependence of the superconducting Tc, notably the minimum at intermediate x is explained as a crossover effect from pair-forming aspherical Coulomb scattering to pair-breaking exchange scattering. © 2010 The American Physical Society.

Felser C.,Max Planck Institute for Chemical Physics of Solids
Angewandte Chemie - International Edition | Year: 2013

Topologically stable magnetic screw-like nanostructures called skyrmions were designed by using the concept of topology and the guidance of theory. These particles in real space are found in non-centrosymmetric compounds such as MnSi. Skyrmions might have an enormous impact in the context of future spintronics applications. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sun Y.,Max Planck Institute for Chemical Physics of Solids
Nature Materials | Year: 2015

Topological Weyl semimetals (TWSs) represent a novel state of topological quantum matter which not only possesses Weyl fermions (massless chiral particles that can be viewed as magnetic monopoles in momentum space) in the bulk and unique Fermi arcs generated by topological surface states, but also exhibits appealing physical properties such as extremely large magnetoresistance and ultra-high carrier mobility. Here, by performing angle-resolved photoemission spectroscopy (ARPES) on NbP and TaP, we directly observed their band structures with characteristic Fermi arcs of TWSs. Furthermore, by systematically investigating NbP, TaP and TaAs from the same transition metal monopnictide family, we discovered their Fermiology evolution with spin–orbit coupling (SOC) strength. Our experimental findings not only reveal the mechanism to realize and fine-tune the electronic structures of TWSs, but also provide a rich material base for exploring many exotic physical phenomena (for example, chiral magnetic effects, negative magnetoresistance, and the quantum anomalous Hall effect) and novel future applications. © 2015 Nature Publishing Group

Thalmeier P.,Max Planck Institute for Chemical Physics of Solids
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

The effect of helical Dirac states on surface phonons in a topological insulators is investigated. Their coupling is derived in the continuum limit by assuming displacement-dependent Dirac cones. The resulting renormalization of sound velocity and attenuation and its dependence on the chemical potential and wave vector is calculated. At finite wave vectors a Kohn anomaly in the renormalized phonon frequency is caused by intraband transitions. It appears at wave vectors q<2k F due to a lack of backscattering for helical Dirac electrons. The wave vector and chemical potential dependence of this anomaly is calculated. © 2011 American Physical Society.

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