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Abstracts
P1.20
PRESSURE EFFECT ON THE EINSTEIN-LIKE PHONON MODE
IN SUPERCONDUCTING YB
6
Orend´aˇc Mat´uˇs(1,2), Gab´ani Slavom´ır(1), Gaˇzo Emil(1), Prist´aˇs Gabriel(1),
Flachbart Karol(1), Mori Takao(3), Wang Shao(4), Kamenev Konstantin(4)
(1) Institute of Experimental Physics, SAS, Watsonova 47, 04001 Koˇsice,
Slovakia
(2) Institute of Physics, Faculty of Science, P.J. Safarik University, Park
Angelinum 9, 04154 Koˇsice, Slovakia
(3) Advanced Materials Laboratory, National Institute for Materials Science,
Namiki 1-1, 305 0044 Tsukuba, Japan
(4) Centre for Science at Extreme Conditions, University of Edinburgh, Mayfield
road, EH9 3JZ Edinburgh, United Kingdom
YB6 is known as a conventional type-II BCS superconductor, in which the strong
coupling superconductivity with 2∆
/k
B
T
c
≈
4
.
1 is mediated by the Einstein-like
phonon mode of Y atoms located at
~
ωE
≈
9 meV. We have investigated the
pressure effect on
ωE
by Raman scattering up to 14 GPa. A linear increase of
this phonon mode energy with pressure yields a value of the isothermal Gr¨uneisen
coefficient
γT
=
−
∂lnωE/∂lnV
= 3
.
85. Moreover, the pressure effect on the
electron-phonon interaction calculated from the McMillan-Allen-Dynes expression
for the superconducting transition temperature was determined.
P1.21
PRESSURE DEPENDENCE OF THE UPPER AND THIRD
CRITICAL FIELD IN SUPERCONDUCTING YB
6
Gab´ani Slavom´ır(1), Kuˇsn´ır J´an(2), Orend´aˇc Mat´uˇs(1,2), Gaˇzo Emil(1),
Prist´aˇs Gabriel(1), Mori Takao(3), Flachbart Karol(1)
1) Institute of Experimental Physics, SAS, Watsonova 47, 04001 Koˇsice, Slovakia
2) Institute of Physics, Faculty of Science, P.J. Safarik University, Park
Angelinum 9, 04154 Koˇsice, Slovakia
3) Advanced Materials Laboratory, National Institute for Materials Science,
Namiki 1-1, 305 0044 Tsukuba, Japan
We present measurements of the superconducting critical temperature
T
c
, the
upper critical field
H
c
2
and the third critical field
H
c
3
as a function of pressure in
BCS superconductor YB
6
(
T
c
= 7
.
5
K
,
H
c
2
(0) = 280
mT
and
H
c
3
(0) = 450
mT
)
up to 3 GPa. The magnetic susceptibility and magnetoresistivity measurement
down to 2 K have shown a negative pressure effect on Tc as well as on
H
c
2
and
H
c
3
with slopes
dlnT
c
/dp
= 6
÷
7 %/GPa,
dlnH
c
2
/dp
=
−
14 %/GPa
and
dlnH
c
3
/dp
=
−
11%
/GPa
, respectively. The positive pressure effect on the
coherence length,
dξ
(0)
/dp
= 2
nm/GPa
, together with the zero pressure effect on
the magnetic penetration depth,
dλ
(0)
/dp
≈
0, imply that the Ginzburg-Landau
parameter
κ
(0) =
λ
(0)
/ξ
(0) decreases markedly with pressure,
dκ
(0)
/dp
=
−
0
.
32
/GPa
, and moves YB
6
to the type-I direction at
p
c
≈
10
GPa
.
32