M. Klemm

Physical properties of FeSe0.5Te0.5 single crystals grown under different conditions

AbstractnWe report on structural, magnetic, conductivity, and thermodynamic studies of FeSe0.5Te0.5 single crystals grown by self-flux and Bridgman methods. The lowest values of the susceptibility in thennormal state, the highest transition temperature Tc of 14.4xa0K, and the largest heat-capacity anomaly at Tc were obtained for pure (oxygen-free) samples. The criticalncurrent density jc of 8.6 × 104nA/cm2 (at 2xa0K) achieved in pure samples is attributed to intrinsic inhomogeneity due to disorder at the anion sites. The samples containing an impurity phase of Fe3O4 show increased jc up ton2.3 × 105nA/cm2 due to additional pinning centers. The upper critical fieldn

Angle dependent soft-X-ray absorption spectroscopy of V2O5

H_{c2}

Angular-resolved photoemission on V2O3 and VO2

nof ~500xa0kOe is estimated from the resistivity studynin magnetic fields parallel to the c-axis using a criterion of a 50%ndrop of the normal state resistivity Rn. The anisotropy ofnthe upper critical fieldnγH c2 =nHabc2/Hc2cnreaches a value ~6 atn

Angular-dependent soft X-ray absorption spectroscopy of V2O5 and V6O13

Tlongrightarrow T_c

Structural precursor to the metal-insulator transition in V{sub 2}O{sub 3}

. Extremely low values of the residualnSommerfeld coefficient

Magnetic properties of geometrically frustrated ZnxLi1−xV2O4

gamma_r

Elimination of self-absorption in fluorescence hard-x-ray absorption spectra

of about 1xa0mJ/mol K2,ncompared to the normal state Sommerfeld coefficient γn = 25nmJ/molxa0K2 for pure samples indicate a high volume fraction of thensuperconducting phase (up to 97%). The electronic contribution to the specific heat in thensuperconducting state is well described within a single-band BCS model with a temperature dependent gapnΔ(0 K) = 27(1) K. A broad cusp-like anomaly in the electronic specific heat observed at low temperatures in samples with suppressed bulk superconductivity is ascribed to a splitting of the ground state of the Fe2+ ions at the 2c sites. This contribution is fully suppressed in the ordered state in samples with bulk superconductivity.n

Spectroscopy of metallic and insulating V{sub 2}O{sub 3}

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

Dramatic Change of the Magnetic Response in LiV2O4: Possible Heavy Fermion to Itinerant d-Metal Transition

Abstract We present photoemission measurements on in situ oriented and characterized single crystals of V2O3 and VO2. The (1 1 0) surface of VO2 and the (0001) surface of V2O3 show high quality LEED pattern consistent with the bulk structure. Photoemission spectra were measured in normal emission on the (1 1 0) surface of VO2 and the (0001) surface of V2O3. For both materials, the measured V 3d band dispersion was less than that predicted by band structure calculations, and the photoemission features were twice as broad as those of other oxides, such as V2O5 and MoO2, the latter of which is isostructural to the insulating phase of VO2. A possible mechanism for this broadening is suggested, based on strong coupling of electronic and lattice degrees of freedom.

LEED and photoemission study of the stability of VO{sub 2} surfaces

Abstract We have measured the V 2 p 3 2 and O 1st 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 2 p 3 2 spectra agree with the projected unoccupied O 2p and V 3d DOS, respectively, indicating that atomic and solid state effects, including Vue5f8O hybridization, must be included to describe adequately the spectra.