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. BAUERInstitut für Festkörperphysik, Technische Universität Wien, Wien, Austria

D. K. MAUDEGrenoble 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

Outline1. Motivation2. Point contact

spectroscopy3. Results4. Conclusions

• 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

Motivation

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

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:

1. ballistic - lel, lin >> d2. diffusive – lel << d << (lel lin)1/2

3. thermal - lel, lin << d

l 10-11cm2

cm (4 K)l 1-10 nm

dV/dI curves versus V for YbCu3.5Al1.5 – YbCu3.5Al1.5 (solid line) and YbCu3.5Al1.5 – Pt (dots) at 1.5 K.

Comparison of dV/dI for heterocontact YbCu3.5Al1.5 – Pt at 0.1 and 6 K.

Results

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)]/2 dV/dI(V)as = [dV/dI(V > 0) - dV/dI(V < 0)]/2

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.

Results

Results

0 5 10 15 20 25

2.8

3.0

3.2

3.4

3.6

3.8

YbCu3.5

Al1.5

- YbCu3.5

Al1.5

T = 1.5 KI = 0.38 mA

RP

C [

]

B [T]

-20 -10 0 10 20

1.6

1.8

2.0

2.2

22 T

18 T

15 T

12 T

9 T

6 T3 T

0 TYbCu

3.5Al

1.5 - Pt

T = 1.5 K

dV/d

I(V) []

Voltage [mV]

Characteristic magnetic field behviour of dV/dIfor heterocontact YbCu3.5Al1.5 – Pt at 1.5 K.

RPC(B) for heterocontact YbCu3.5Al1.5 – Pt at1.5 K.

Results

Conclusions• needle anvil arrangement of PC• high in orders 100 cm, 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 (T, B) • asymmetry due to NFL features?• more suitable MCBJ – higher RPC

• YbRh2Si2 in orders 1 cm, 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 of QCP, Physica B 378-380 (2006) 100-101.

Oral presentation CSMAG’07: Point Contact Spectroscopy of Non-Fermi Liquid Compound YbCu5-xAlx (x = 1.3 - 1.75) In High Magnetic FieldsG.Pristáš, M.Reiffers, E.Bauer, A. G. M. Jansen, D. Maude.

-review paper - homocontacts, high magnetic fields…