Browsing by Author "Ditusa, J. F."
Now showing 1 - 2 of 2
- Results Per Page
- Sort Options
Item Fermi Surface, Possible Unconventional Fermions, and Unusually Robust Resistive Critical Fields in the Chiral-Structured Superconductor AuBe(American Physical Society) Rebar, D. J.; Birnbaum, S. M.; Singleton, J.; Khan, M.; Ball, J. C.; Adams, P. W.; Chan, Julia Y.; Young, D. P.; Browne, D. A.; Ditusa, J. F.; 0000-0003-4434-2160 (Chan, JY); Chan, Julia Y.The noncentrosymmetric superconductor (NCS) AuBe is investigated using a variety of thermodynamic and resistive probes in magnetic fields of up to 65 T and temperatures down to 0.3 K. Despite the polycrystalline nature of the samples, the observation of a complex series of de Haas-van Alphen (dHvA) oscillations has allowed the calculated band structure for AuBe to be validated. This permits a variety of BCS parameters describing the superconductivity to be estimated, despite the complexity of the measured Fermi surface. In addition, AuBe displays a nonstandard field dependence of the phase of dHvA oscillations associated with a band thought to host unconventional fermions in this chiral lattice. This result demonstrates the power of the dHvA effect to establish the properties of a single band despite the presence of other electronic bands with a larger density of states, even in polycrystalline samples. In common with several other NCSs, we find that the resistive upper critical field exceeds that measured by heat capacity and magnetization by a considerable factor. We suggest that our data exclude mechanisms for such an effect associated with disorder, implying that topologically protected superconducting surface states may be involved. ©2019 American Physical Society.Item Magnetic, Thermodynamic, and Electrical Transport Properties of the Noncentrosymmetric B20 Germanides MnGe and CoGe(American Physical Society, 2014-10-03) Ditusa, J. F.; Zhang, S. B.; Yamaura, K.; Xiong, Y.; Prestigiacomo, J. C.; Fulfer, B. W.; Adams, P. W.; Brickson, M. I.; Browne, D. A.; Capan, C.; Fisk, Z.; Chan, Julia Y.; C-5392-2008 (Chan, JY)We present magnetization, specific heat, resistivity, and Hall effect measurements on the cubic B20 phase of MnGe and CoGe and compare to measurements of isostructural FeGe and electronic-structure calculations. In MnGe, we observe a transition to a magnetic state at Tc=275K as identified by a sharp peak in the ac magnetic susceptibility, as well as second phase transition at lower temperature that becomes apparent only at finite magnetic field. We discover two phase transitions in the specific heat at temperatures much below the Curie temperature, one of which we associate with changes to the magnetic structure. A magnetic field reduces the temperature of this transition which corresponds closely to the sharp peak observed in the ac susceptibility at fields above 5 kOe. The second of these transitions is not affected by the application of field and has no signature in the magnetic properties or our crystal-structure parameters. Transport measurements indicate that MnGe is metallic with a negative magnetoresistance similar to that seen in isostructural FeGe and MnSi. Hall effect measurements reveal a carrier concentration of about 0.5 carriers per formula unit, also similar to that found in FeGe and MnSi. CoGe is shown to be a low carrier density metal with a very small, nearly temperature-independent diamagnetic susceptibility.