Kharkiv

1
Where I came from
B. Verkin Institute for Low Temperature Physics
and Engineering, National Academy of Sciences
of Ukraine, 47 Lenin Ave., 61103, Kharkiv,
Ukraine
Poland
Kharkiv
Kyiv
Kharkiv Uni on the largest square in the Europe
L gt 1000 km
Kishinev
Uni
Naidycuk Yu. G. 2004 ?
2
Realization of an N-shaped IVC of nanoscale
metal- lic junctions using the antiferromagnetic
transition.
Yu. G. Naidyuk, K. Gloos, I. K. Yanson
B. Verkin Institute for Low Temperature Physics
and Engineering, National Academy of Sciences
of Ukraine, Kharkiv, Ukraine
Nano-Science Center, Niels Bohr Institute fAFG,
Universitetsparken 5, DK-2100 Copenhagen, Denmark
3
Model of point contact with electron trajectories
Naidyuk Yu. G. 2003 ?
4
Fermi distribution function for ballistic
point-contact
Distribution function splits into two parts with
energy difference defined by the bias voltage V
Naidyuk Yu. G. 2003 ?
5
Regimes of current flow in point contacts
ballistic
diffusive
thermal
Naidyuk Yu. G. 2003 ?
6
Current regimes in point contacts

• Ballistic d gtgt li ,le
• Diffusive (li le)1/2gtd gtli
• Thermal d gtgt li le
• Tunnel (STM)

????????
impurities
electron
phonons
electron
?1
EF
Naidycuk Yu. G. 2002 ?
?2
Study of EDOS and inelastic excita- tions in
(near) the barrier
eV
t
7
Thermal regime in ferromagnetic metals
Naidyuk 2004
Low voltage ? ballistic
High voltage ? thermal
Calculation of r(T) in NiCu alloy from PC spectra
by above Eq.
Phonon DOS
Phonon DOS
Phonon DOS
8
Methods of point-contact preparation
Thin films
Needle-anvil
Sliding
Nanotechnology
notch
Naidyuk Yu. G. 2003 ?
Break junction
9


Structure and properties of UPd2Al3 .
Heavy fermion superconductor (Tc1.5-2K) with AFM
order (TN14.5K)
RRR45
?0 3.5 ?? cm
C-axis
Polycr.
Single
Naidyuk Yu. G. 2003 ?
U-ion 0.85 ?B
? Abulk T2
10

IVC and its derivative for MCBJ of UPd2Al3 .
Naidyuk Yu. G. 2004 ?
11

Calculations of IVC for UPd2Al3 PCs in thermal
regime
I(V)Vd ??-1(T?1-x2)dx TV/2?L
RPC(T)
Naidyuk Yu. G. 2003 ?
12

Comparison of exp. and calculated IVC for
UPd2Al3 .
calcul. exp.
exp.
calcul.
exp.
calcul.
Naidyuk Yu. G. 2003 ?
13

Conclusion and outlook .
For metallic break-junction point contacts on the
heavy-fermion compound UPd2Al3 we observed at low
temperatures hysteretic IVC. We show that these
highly nonlinear IVC can be reproduced by
calculation assuming realization of the thermal
regime in the constriction. Anomalous behavior
of IVC is due to peculiar ?(T) dependence of
UPd2Al3, namely, is due to the sharp increase of
?(T) near the Neel temperature connected with the
AFM transition. Investigated PCs represent a
nonlinear element with N -shaped IVC. Thus, they
have a negative differential resistance and can
serve as an analog of Esaki tunnel diode or Gunn
diode for amplifying, generating and switching
units. Estimated thermal relaxation time is 100
ps for d100nm. From general considerations each
material with suchlike ?(T) is suitable to
produce N-shaped IVC, therefore from this point
of view UPd2Al3 is not unique material.
Naidyuk Yu. G. 2003 ?
14
Calculated IVC for prospective La0.75Sr0.25MnO3
contacts

Rare-earth manganite La1-xAxMnO3 (ASr, Ca) are
known as colossal magneto-resistance (CMR)
systems. Here metallic phases with a fully
spin-polarized conduction band occurs.
Manganite structural, magnetic and transport
properties are intrinsical-ly related. The CMR
effects are promising for potential applications.
I-V curves for 100-nm-size constriction
Naidyuk Yu. G. 2004 ?