arXiv subjects

S. Horn

Publications and source records attributed to S. Horn.

44 records · Page 3Linked to original sources

arXiv2001

New magnetic phase in metallic V_{2-y}O_3 close to the metal insulator transition

We have observed two spin density wave (SDW) phases in hole doped metallic V_{2-y}O_3, one evolves from the other as a function of doping, pressure or temperature. They differ in their response to an external magnetic field, which can also induce a transition between them. The phase boundary between these two states in the temperature-, doping-, and pressure-dependent phase diagram has been determined by magnetization and magnetotransport measurements. One phase exists at high doping level and has already been described in the literature. The second phase is found in a small parameter range close to the boundary to the antiferromagnetic insulating phase (AFI). The quantum phase transitions between these states as a function of pressure and doping and the respective metamagnetic behavior observed in these phases are discussed in the light of structurally induced changes of the band structure.

cond-mat.str-el↗

arXiv2001

One-dimensional dynamics of the d-electrons in $α'$-NaV$_{2}$O$_{5}$

We have studied the electronic properties of the ladder compound $α'$-NaV$_{2}$O$_{5}$, adopting a joint experimental and theoretical approach. The momentum-dependent loss function was measured using electron energy-loss spectroscopy in transmission. The optical conductivity derived from the loss function by a Kramers-Kronig analysis agrees well with our results from LSDA+U band-structure calculations upon application of an antiferromagnetic alignment of the V~3$d_{xy}$ spins along the legs and an on-site Coulomb interaction U of between 2 and 3 eV. The decomposition of the calculated optical conductivity into contributions from transitions between selected energy regions of the DOS reveals the origin of the observed anisotropy of the optical conductivity. In addition, we have investigated the plasmon excitations related to transitions between the vanadium states within an effective 16 site vanadium cluster model. Good agreement between the theoretical and experimental loss function was obtained using the hopping parameters derived from the tight binding fit to the band-structure and moderate Coulomb interactions between the electrons within the ab plane.

cond-mat.str-el↗

arXiv2000

Heavy-Fermions in LiV2O4: Kondo-Compensation vs. Spin-Liquid Behavior?

7Li NMR measurements were performed in the metallic spinel LiV2O4. The temperature dependencies of the line width, the Knight shift and the spin-lattice relaxation rate were investigated in the temperature range 30 mK < T < 280 K. For temperatures T < 1 K we observe a spin-lattice relaxation rate which slows down exponentially. The NMR results can be explained by a spin-liquid behavior and the opening of a spin gap of the order 0.6 K.

cond-mat.str-el↗

arXiv2000

Charge Order in NaV2O5 studied by EPR

We present angular dependent EPR measurements in NaV2O5 at X-band frequencies in the temperature range 4.2 K < T < 670 K. A detailed analysis in terms of the antisymmetric Dzyaloshinski-Moriya and the anisotropic exchange interactions yields the following scheme of charge order: On decreasing temperature a quarter-filled ladder with strong charge disproportions, existing for T > 100 K, is followed by zig-zag charge-order fluctuations which become long-range and static below T_SP=34 K.

cond-mat.str-el↗

arXiv1999

Valence band excitations in V_2O_5

We present a joint theoretical and experimental investigation of the electronic and optical properties of vanadium pentoxide. Electron energy-loss spectroscopy in transmission was employed to measure the momentum-dependent loss function. This in turn was used to derive the optical conductivity, which is compared to the results of band structure calculations. A good qualitative and quantitative agreement between the theoretical and the experimental optical conductivity was observed. The experimentally observed anisotropy of the optical properties of V_2O_5 could be understood in the light of an analysis of the theoretical data involving the decomposition of the calculated optical conductivity into contributions from transitions into selected energy regions of the conduction band. In addition, based upon a tight binding fit to the band structure, values are given for the effective V3d_xy-O2p hopping terms and are compared to the corresponding values for alpha'-NaV_2O_5.

cond-mat↗

arXiv1999

Electronic structure and magnetic interactions in LiV2O4

We present results of all-electron electronic structure calculations for the recently discovered d electron heavy fermion compound LiV_2O_4. The augmented spherical wave calculations are based on density functional theory within the local density approximation. The electronic properties near the Fermi energy originate almost exclusively from V 3d t_{2g} states, which fall into two equally occupied subbands: While sigma-type metal-metal bonding leads to rather broad bands, small pi-type p-d overlap causes a narrow peak at E_F. Without the geometric frustration inherent in the crystal structure, spin-polarized calculations reveal an antiferromagnetic ground state and ferromagnetic order at slightly higher energy. Since direct d-d exchange interaction plays only a minor role, ordering of the localized vanadium moments can be attributed exclusively to a rather weak superexchange interaction. With the magnetic order suppressed by the geometric frustration, the remaining spin fluctuations suggest an explanation of the low temperature behaviour of the specific heat.

cond-mat.str-el↗

arXiv1994

Magnetic properites of the Heavy Fermion Antiferromagnets YbNiAl and YbPtAl

Measurements of electrical resistivity and Hall effect as a function of magnetic field on the Heavy Fermion Systems YbNiAl and YbPtAl are presented. Both compounds order antiferro magnetically and show metamagnetic behavior in a magnetic field. Scaling behavior of the magnetoresistance above TN suggests that the paramagnetic regime for YbNiAl can be described in terms of a single ion Kondo effect.

cond-mat↗

arXiv1994

Angular Dependent Soft X-ray Absorption Spectroscopy of V2O5 and V6O13

We have measured the V 2p3/2 and O 1s x-ray absorption spectra of single crystal V2O5 and V6O13 and compared to linear combinations of atomic orbitals (LCAO) density of states (DOS) calculations. The spectra change dramatically with incident angle. The use of polarized light and a single crystal limits the number of transitions possible, revealing spectral features that cannot be resolved on polycrystals (angle-integrated). The measured O 1s and V 2p3/2 spectra agree with the projected unoccupied O 2p and V 3d DOS respectively, indicating that atomic and solid state effects, including V-O hybridization, must be included to adequately describe the spectra.

cond-mat↗