C. Geibel
Max Planck Society
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Featured researches published by C. Geibel.
Nature Communications | 2014
A. Chikina; M. Höppner; S. Seiro; Kurt Kummer; S. Danzenbächer; S. Patil; Alexander V. Generalov; M. Güttler; Yu. Kucherenko; E. V. Chulkov; Yu. M. Koroteev; K. Koepernik; C. Geibel; M. Shi; M. Radovic; C. Laubschat; D. V. Vyalikh
Carrying a large, pure spin magnetic moment of 7 μB per atom in the half-filled 4f shell, divalent europium is an outstanding element for assembling novel magnetic devices in which a two-dimensional electron gas may be polarized due to exchange interaction with an underlying magnetically-active Eu layer. Here we show that the Si-Rh-Si surface trilayer of the antiferromagnet EuRh2Si2 bears a surface state, which exhibits an unexpected and large spin splitting controllable by temperature. The splitting sets in below ~32.5 K, well above the ordering temperature of the Eu 4f moments (~24.5 K) in the bulk, indicating a larger ordering temperature in the topmost Eu layers. The driving force for the itinerant ferromagnetism at the surface is the aforementioned exchange interaction. Such a splitting may also be induced into states of functional surface layers deposited onto the surface of EuRh2Si2 or similarly ordered magnetic materials with metallic or semiconducting properties.
Nature | 2003
J. Custers; P. Gegenwart; H. Wilhelm; K. Neumaier; Yoshi Tokiwa; O. Trovarelli; C. Geibel; F. Steglich; C. Pepin; Piers Coleman
The point at absolute zero where matter becomes unstable to new forms of order is called a quantum critical point (QCP). The quantum fluctuations between order and disorder that develop at this point induce profound transformations in the finite temperature electronic properties of the material. Magnetic fields are ideal for tuning a material as close as possible to a QCP, where the most intense effects of criticality can be studied. A previous study on the heavy-electron material YbRh2Si2 found that near a field-induced QCP electrons move ever more slowly and scatter off one another with ever increasing probability, as indicated by a divergence to infinity of the electron effective mass and scattering cross-section. But these studies could not shed light on whether these properties were an artefact of the applied field, or a more general feature of field-free QCPs. Here we report that, when germanium-doped YbRh2Si2 is tuned away from a chemically induced QCP by magnetic fields, there is a universal behaviour in the temperature dependence of the specific heat and resistivity: the characteristic kinetic energy of electrons is directly proportional to the strength of the applied field. We infer that all ballistic motion of electrons vanishes at a QCP, forming a new class of conductor in which individual electrons decay into collective current-carrying motions of the electron fluid.
Nature | 2004
S. Paschen; T. Lühmann; Steffen Wirth; P. Gegenwart; O. Trovarelli; C. Geibel; F. Steglich; P. Coleman; Qimiao Si
A quantum critical point (QCP) develops in a material at absolute zero when a new form of order smoothly emerges in its ground state. QCPs are of great current interest because of their singular ability to influence the finite temperature properties of materials. Recently, heavy-fermion metals have played a key role in the study of antiferromagnetic QCPs. To accommodate the heavy electrons, the Fermi surface of the heavy-fermion paramagnet is larger than that of an antiferromagnet. An important unsolved question is whether the Fermi surface transformation at the QCP develops gradually, as expected if the magnetism is of spin-density-wave (SDW) type, or suddenly, as expected if the heavy electrons are abruptly localized by magnetism. Here we report measurements of the low-temperature Hall coefficient (RH)—a measure of the Fermi surface volume—in the heavy-fermion metal YbRh2Si2 upon field-tuning it from an antiferromagnetic to a paramagnetic state. RH undergoes an increasingly rapid change near the QCP as the temperature is lowered, extrapolating to a sudden jump in the zero temperature limit. We interpret these results in terms of a collapse of the large Fermi surface and of the heavy-fermion state itself precisely at the QCP.
Physical Review Letters | 2002
P. Gegenwart; J. Custers; C. Geibel; K. Neumaier; T. Tayama; Kenichi Tenya; O. Trovarelli; F. Steglich
We report low-temperature calorimetric, magnetic, and resistivity measurements on the antiferromagnetic (AF) heavy-fermion metal YbRh(2)Si(2) ( T(N)=70 mK) as a function of magnetic field B. While for fields exceeding the critical value B(c0) at which T(N)-->0 the low-temperature resistivity shows an AT2 dependence, a 1/(B-B(c0)) divergence of A(B) upon reducing B to B(c0) suggests singular scattering at the whole Fermi surface and a divergence of the heavy quasiparticle mass. The observations are interpreted in terms of a new type of quantum critical point separating a weakly AF ordered from a weakly polarized heavy Landau-Fermi liquid state.
European Physical Journal B | 1992
A. Krimmel; Peter Fischer; B. Roessli; H. Maletta; C. Geibel; C. Schank; A. Grauel; A. Loidl; F. Steglich
An elastic neutron scattering study was performed on the new superconducting heavy fermion systems UPd2Al3 and UNi2Al3. The neutron diffraction patterns reveal unambiguously long range antiferromagnetic order in UPd2Al3 with an ordered magnetic momentμU = (0.85±0.03)μB, which coexists with the superconducting state. This is by far the largestμU value observed for any heavy fermion superconductor. For UNi2Al3, no long-range magnetic order could be observed for temperaturesT≧1.5 K, yielding an upper limit of the ordered moment of 0.2μB.
Physical Review Letters | 2003
R. Kuchler; N. Oeschler; P. Gegenwart; T. Cichorek; K. Neumaier; O. Tegus; C. Geibel; J. A. Mydosh; F. Steglich; L. Zhu; Qimiao Si
We present low-temperature volume thermal expansion, beta, and specific heat, C, measurements on high-quality single crystals of CeNi2Ge2 and YbRh2(Si0.95Ge0.05)(2) which are located very near to quantum critical points. For both systems, beta shows a more singular temperature dependence than C, and thus the Grüneisen ratio Gamma proportional to beta/C diverges as T-->0. For CeNi2Ge2, our results are in accordance with the spin-density wave (SDW) scenario for three-dimensional critical spin fluctuations. By contrast, the observed singularity in YbRh2(Si0.95Ge0.05)(2) cannot be explained by the itinerant SDW theory but is qualitatively consistent with a locally quantum critical picture.
Physical Review B | 2008
C. Krellner; N. Caroca-Canales; A. Jesche; H. Rosner; Alim Ormeci; C. Geibel
Resistivity, specific-heat, and magnetic-susceptibility measurements performed on
New Journal of Physics | 2006
P. Gegenwart; Y. Tokiwa; T. Westerkamp; Franziska Weickert; J. Custers; J. Ferstl; C. Krellner; C. Geibel; P. Kerschl; Klaus Muller; F. Steglich
{\text{SrFe}}_{2}{\text{As}}_{2}
Physical Review Letters | 2008
Andreas Leithe-Jasper; Walter Schnelle; C. Geibel; H. Rosner
samples evidence a behavior very similar to that observed in LaFeAsO and
Nature | 2011
S. Ernst; Stefan Kirchner; C. Krellner; C. Geibel; Gertrud Zwicknagl; F. Steglich; S. Wirth
{\text{BaFe}}_{2}{\text{As}}_{2}