Investigation of novel high T<SUB>c</SUB> superconducting oxides

Our results of microscopic and macroscopic studies of novel high Tc superconductors are discussed. They permit a straightforward comparison of the nature of the superconductivity in 40 K range (La2CuO4 type) and 90 K range (YBa2Cu3O7type) superconductors

Role of Nonplanar Peptide Unit in Regular Polypeptide Helices - New Model for Pply-Beta-Benzyl-L-Aspartate

The effect of non-planarity of the peptide unit on helical structures stabilized by intrachain hydrogen bonds is discussed. While the present calculations generally agree with those already reported in the literature for right-handed helical structures, it is found that the most stable left-handed structure is a novel helix, called the delta-helix. Its helical parameters are close to these reported for poly-beta-benzyl-L -aspartate. Conformational energy calculations show that poly-beta-benzyl-L -aspartate with the delta-helical structure is considerably more stable than the structure it is generally believed to take up (the omega-helix) by about 15 kcal/mol-residue

Heat capacity and magnetic susceptibility of mixed valent YbPt<SUB>2</SUB>Si<SUB>2</SUB>

From heat capacity and magnetic susceptibility results, we conclude that YbPt2Si2 is a homogeneously mixed valent compound

Investigation of 4f-magnetism in CeNi<SUB>2</SUB>P<SUB>2</SUB>, EuNi<SUB>2</SUB>P<SUB>2</SUB> and YbNi<SUB>2</SUB>P<SUB>2</SUB> by susceptibility and NMR studies

The results of 31P NMR Knight shift (KS) and spin-lattice relaxation time (T1) as well as magnetic susceptibility (&#958;) measurements in the temperature interval 4.2-300K are reported for the compounds RENi2P2(RE = Ce, EuandYb) in order to understand the nature of the 41 magnetism in these compounds. The KS results conclusively establish that all these compounds exhibit non-magnetic ground states. There is a low-temperature upturn in &#958; for CeNi2P2 and YbNi2P2 presumably due to magnetic impurities. The estimated spin fluctuation temperatures (Tsf) for EuNi2P2 above 50K agree qualitatively with those obtained earlier from M&#246;ssbauer and &#958; data employing ionic interconfigurational fluctuation model, but seem to disagree at low temperatures. Implications of this result are discussed

Knight shift of <SUP>115</SUP>In in REInAg<SUB>2</SUB> alloys and mixed valent YbInAu<SUB>2</SUB>

Large temperature dependent Knight shift (KS) of <SUP>115</SUP>In has been measured in REInAg<SUB>2</SUB> alloys with the Heusler structure, usually found in compounds of transition metals. In SmInAg<SUB>2</SUB>, interaction of the excited state | J=7/2 &gt; with the ground state | J=5/2 &gt; is clearly observed. In mixed valent YbInAu<SUB>2</SUB>, a weak maximum in KS at ~100 K is discernible

Characterization of the valence transition in Yb<SUB>x</SUB>In<SUB>1−x</SUB>Cu<SUB>2</SUB> and anomalous <SUP>115</SUP>In Knight-shift behavior

115In nuclear-magnetic-resonance Knight shift studies in YbxIn1&#8722;xCu2 microscopically confirm the existence of an anomalous valence transition of Yb ions for some values of x. The rate of variation, as well as the overall variation of the Knight shifts is the largest ever observed in any Yb system. The Knight shifts do not track the susceptibility at low temperatures, the possible implications of which are discussed. Specific-heat results prove the intermediate-valence character of Yb ions in the ground state of these compounds

The effect of Ni and Pt substitution in CeRh<SUB>2</SUB>Si<SUB>2</SUB>

A small replacement of Rh by Ni or Pt (about 10%) results in the destruction of anomalous magnetism (TN=36 K) of CeRh2Si2, leading to a heavy fermion ground state. Further substitution of Ni for Rh stabilizes the strong mixed valent state