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Point contact properties of intermetallic compound YbCu (5-x) Al x (x = 1.3 – 1.75)

Point contact properties of intermetallic compound YbCu (5-x) Al x (x = 1.3 – 1.75). G. PRISTÁŠ , M. REIFFERS Institute of Exp. Physics, Center of Low Temperature Physics, Košice, Slovakia E. BAUER Institut für Festkörperphysik, Technische Universität Wien, Wien, Austria D. K. MAUDE

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Point contact properties of intermetallic compound YbCu (5-x) Al x (x = 1.3 – 1.75)

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  1. Point contact properties of intermetallic compound YbCu(5-x)Alx (x = 1.3 – 1.75) G. PRISTÁŠ, M. REIFFERS Institute of Exp. Physics, Center of Low Temperature Physics, Košice, Slovakia E. BAUER Institut für Festkörperphysik, Technische Universität Wien, Wien, Austria D. K. MAUDE Grenoble High Magnetic Field Laboratory (CNRS), BP 166, 38042 Grenoble Cedex 9, France A. G. M. JANSEN Service de Physique Statistique, Magnétisme, et Supraconductivité, CEA-Grenoble, 38054 Grenoble Cedex 9, France • Outline • Motivation • Point contact spectroscopy • Results • Conclusions

  2. Motivation • •YbCu3.5Al1.5 is a well-known example of a non-Fermi liquid (NFL) system • crystallizing in the hexagonal CaCu5 structure • • major characteristic NFL features of this compound (our sample) • - negative logarithmic contribution to the specific heat • - substantial deviations of the electrical resistivity from a T2 dependence, Tn where n < 2 • were proven in E. Bauer et al., Phys. Rev. B60 (1999) 1238 • • proximity to a quantum critical point was demonstrated considering • the self consistent renormalization model – preference to spin fluctuations • Ch. Seuring et al., J. Low Temp. Physics 123 (2001) 25 • • magnetic field suppresses the NFL behaviour - 12 T probably sufficient to recover • a FL state • • NFL behaviour of point contacts (PC) between YbCu3.5Al1.5 and Cu first in • M. Reiffers et al., J. Magn. Magn. Mater. 272-276 (2004) 625 • only a few reports of PCS of NFL systems

  3. E. Bauer et al., Phys. Rev. B60, 2 (1999) 1238 x = 1.3 – Kondo lattice TK = 31 K x = 1.4 – NFL behaviour xcr = 1.5 - NFL behaviour x = 1.6 – magnetic ordering TN = 0.25 K X = 1.75 – magnetic ordering TN = 1 K

  4. Point contact spectroscopy • PC means a metallic constriction with size d smaller than mean scattering length l of conduction electrons • Applying of voltage to the contact – conduction electrons gain an energy ~ eV • PC spectroscopy - scattering of conduction electrons with other quasiparticles in metals • First derivative dV/dI(V) of I-V characteristic – dynamic resistance • Second derivative d2V/dI2(V) of I-V characteristic – directly proportional to the electron quasiparticle interaction (EQI) Wexler formula: rl 10-11Wcm2 r = 100 mWcm (4 K) l  1-10 nm 1. ballistic - lel, lin >> d 2. diffusive – lel << d << (lellin)1/2 3. thermal - lel, lin << d

  5. Results Comparison of dV/dI for heterocontact YbCu3.5Al1.5 – Pt at 0.1 and 6 K. dV/dI curves versus V for YbCu3.5Al1.5 – YbCu3.5Al1.5 (solid line) and YbCu3.5Al1.5 – Pt (dots) at 1.5 K.

  6. Results Comparison of dV/dI for homocontact YbCu3.5Al1.5 – YbCu3.5Al1.5 (solid line) vs. symmetric part of heterocontact YbCu3.5Al1.5 – Pt (dash line) at 1.5 K. dV/dI curves versus V for YbCu3.5Al1.5 – Pt (solid line), symmetric part of dV/dI (dash line) and asymmetric part of dV/dI (dash dot line) at 1.5 K. dV/dI(V)s = [dV/dI(V > 0) + dV/dI(V < 0)]/2dV/dI(V)as = [dV/dI(V > 0) - dV/dI(V < 0)]/2

  7. Results

  8. Results Characteristic magnetic field behviour of dV/dI for heterocontact YbCu3.5Al1.5 – Pt at 1.5 K. RPC(B) for heterocontact YbCu3.5Al1.5 – Pt at 1.5 K.

  9. Conclusions • needle anvil arrangement of PC • high rin orders 100 mWcm, short mean free path • maximu close to zero; homocontact – origin YbCu5-xAlx • contradiction to thermal regime(calculated) • in magnetic field – dV/dI(V, B) similar to r(T, B) • asymmetry due to NFL features? • more suitable MCBJ – higher RPC • YbRh2Si2r in orders 1 mWcm, single crystal • G.Pristáš, M.Reiffers, E.Bauer: Point-contact properties of non-Fermi liquid compounds YbCu5-xAlx • (x = 1.3, 1.4 and 1.6) in the vicinity ofQCP, Physica B378-380(2006)100-101. • Oral presentation CSMAG’07: PointContact Spectroscopy of Non-Fermi • Liquid Compound YbCu5-xAlx (x = 1.3 - 1.75) In High Magnetic Fields • G.Pristáš, M.Reiffers, E.Bauer, A. G. M. Jansen, D. Maude. • -review paper - homocontacts, high magnetic fields…

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