arXiv subjects

H. Michor

Publications and source records attributed to H. Michor.

23 records · Page 2Linked to original sources

arXiv2003

Itinerant electron metamagnetism in LaCo$_9$Si$_4$

The strongly exchange enhanced Pauli paramagnet LaCo$_9$Si$_4$ is found to exhibit an itinerant metamagnetic phase transition with indications for metamagnetic quantum criticality. Our investigation comprises magnetic, specific heat, and NMR measurements as well as ab-initio electronic structure calculations. The critical field is about 3.5 T for $H||c$ and 6 T for $H\bot c$, which is the lowest value ever found for rare earth intermetallic compounds. In the ferromagnetic state there appears a moment of about 0.2 $μ_B$/Co at the $16k$ Co-sites, but sigificantly smaller moments at the 4d and $16l$ Co-sites.

cond-mat.str-el↗

arXiv2003

Heavy fermion superconductivity and magnetic order in non-centrosymmetric $CePt_3Si$

$\rm CePt_3Si$ is a novel heavy fermion superconductor, crystallising in the $\rm CePt_3B$ structure as a tetragonally distorted low symmetry variant of the $\rm AuCu_3$ structure type. $\rm CePt_3Si$ exhibits antiferromagnetic order at $T_N \approx 2.2$ K and enters into a heavy fermion superconducting state at $T_c \approx 0.75$ K. Large values of $H_{c2}' \approx -8.5$ T/K and $H_{c2}(0) \approx 5$ T refer to heavy quasiparticles forming Cooper pairs. Hitherto, $\rm CePt_3Si$ is the first heavy fermion superconductor without a center of symmetry.

cond-mat.str-el↗

arXiv2002

An unusual interplay among disorder, Kondo-effect and spin-glass behavior in the Kondo lattices, Ce$_2$Au$_{1-x}$Co$_x$Si$_3$

We report the results of magnetic measurements for the solid solution Ce$_2$Au$_{1-x}$Co$_x$Si$_3$. The results reveal that this solid solution is characterized by a magnetic phase diagram (plot of magnetic transition temperature versus $x$) unusual for Kondo lattices. In particular, the spin-glass freezing induced by disorder is observed only for the compositions at the weak coupling limit; as one approaches the quantum critical point by a gradual replacement of Au by Co, this disorder effect is surprisingly suppressed in favor of long range antiferro-magnetic ordering in contrast to expectations. This unusual interplay between disorder, spin-glass freezing and the Kondo-effect calls for further refinement of theories on competition between magnetism and the Kondo effect.

cond-mat.str-el↗

arXiv2001

Thermal conductivity of superconducting MgB2

Thermal conductivity of superconducting MgB2 was studied in both the superconducting and the normal state region. The latter is almost equally determined by the electronic - and the lattice contribution to the total thermal conductivity. In the superconducting state, however, the lattice contribution is larger. The electronic thermal conductivity below Tc was derived from the experimental data considering the Bardeen-Rickayzen-Tewordt theory together with the model of Geilikman. The analysis shows that electron scattering on static imperfections dominates.

cond-mat.supr-con↗

arXiv2001

Superconducting properties of Y_xLu_(1-x)Ni2B2C and La3Ni2B2N3: A comparison between experiment and Eliashberg theory

Specific heat and resistivity measurements were performed on polycrystalline samples of the solid-solution Y_xLu_(1-x)Ni2B2C in order to determine thermodynamic properties such as the specific-heat difference, the thermodynamic critical field H_c(T), as well as the upper critical field H_{c2}(T). These properties were analyzed within the Eliashberg theory including anisotropy effects, yielding electron-phonon coupling anisotropy parameters ranging beween 0.02 and 0.03 for the whole series, and Fermi velocity anisotropy parameters of = 0.245-0.3. Excellent agreement between theory and experiment was achieved for these parameters, the Sommerfeld constant and model phonon spectra determined from specific heat measurements. An analysis of the previously investigated boronitride La3Ni2B2N3 for comparison revealed the electron-phonon anisotropy to be of great significance in describing its thermodynamic properties and the calculations yielded \~ 0.08 and ~ 0.245. The T_c-behavior within the series Y_xLu_(1-x)Ni2B2C is discussed in terms of coupling and impurity effects, and the density of states at the Fermi level N(0).

cond-mat.supr-con↗