Localized and delocalized superconducting states controlled by non-uniform magnetic field Alexei Yu. Aladyshkin

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Nov 15, 2013 (3 years and 7 months ago)

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Localized and delocalized superconducting states controlled by non
-
uniform magnetic field


Alexei Yu. Aladyshkin
.

Department of Superconductivity,
Institute for Physics of Microstructures of Russian Academy of
Sciences, Nizhny Novgorod, Russia


Abstract:

W
e
consider

the effect of
a

static inhomogeneous magnetic field

on the thermodynamic
and transport properties of thin superconducting films
, produced
either
by ferromagnetic elements
(dots, domains etc.) or
by
current
-
carrying wire
s
.
The condition for the n
ucleation of superconductivity
is known to strongly depend on temperature
T
, the external magnetic field
H
ext
,
and the parameters of
the “internal” magnetic field such as the amplitude of the perpendicular
z
-
component of the
nonuniform magnetic field
B
0

an
d the mean width of the magnetic domains
L
.

For
planar
superconductor
-
ferromagnet

(S/F)

structures

at rather high magnetic field
(|
H
ext
|>
B
0
)
,

t
he superconducting state

first
appears
only
above
the domains of opposite polarity with
respect to the
H
ext

sign
; in these regions,

the local magnetic field (of the order of
H
ext

-

B
0
) is less tha
n
the field above the parallel domain
s

(of the order of
H
ext
+

B
0
). This inhomogeneous superconducting
state can be
called
reverse
-
domain superconductivity

(RDS). We observe

the increase (decrease) in
the maximal critical temperature for the developed RDS regime

at the compensation field,
|
H
ext
|

B
0
,
as the mean width of the magnetic domains

L

increases (decreases);

this effect
can be interpreted as
the

analog of
the
quantum
-
size effect for superconducting wave function in non
-
uniform magnetic
field
.

If

H
c2
<B
0
<H
c3

and
|
H
ext
|≈0

(
H
c2

is the
bulk upp
er critical field, and

H
c3
≈1.69
H
c2

is the critical field
of
the appearance of
surface superconductivity
)
,
the discontinuity of the
z
-
component of the magnetic
field can
stimulate

the formation of
a bound

superconducting state
localized
near the domain wall

(
domain
-
wall superconductivity
, DWS)
. The DWS

state
is similar to surface superconductivity
, which
develops

near the sample edges
at
H
c2
<|H
ext
|<H
c3
.

The transition between RDS and DWS states upon
sweeping
H
ext

w
as

studied theoretically and experimentally
for various
S/F
hybrid
s

by global resistive
measurements

and eventually
it

was confirmed directly by low
-
temperature scanning laser
microscopy

for the Pb/BaFeO system with
a
laminar domain pattern
.

For superconductor
-
elec
t
romagnet
(S/Em)
hybrids
the ampli
tude of the
“internal”
field can be
precisely

tuned by external sources, which

makes it possible to control the vortex matter and the
localized superconducting states
.
As
S/Em

system
,

we
fabricated
a

plain Al superconducting
strip in
the presence of a sing
le straight cur
rent
-
carrying Nb wire

oriented perpendicular to the
superconducting strip
. W
e demonstrate

that the discrete change in the number of
p
inned
vortices/antivortices inside the narrow and long strip nearby the current
-
carrying wire
,

results in a
peculiar oscillatory dependence of the critical current
I
c

on the control current
I
w

in the wire
.


Main relevant publications:

1.

A.Yu. Aladyshkin, A.V. Silhanek, W. Gillijns, and V.V. Moshchalkov, "Nucleation of
supercondu
c
tivity and vortex matter in superc
onductor
-
ferromagnet hybrids (topical review)" //,
Superconductor Science and Technology, vol.
22
, 053001 (2009).

2.

A.Yu. Aladyshkin A.I. Buzdin, A.A. Fraerman
et al
., Phys. R
e
v. B
68
, 184508 (2003).

3.

W. Gillijns, A.Yu. Aladyshkin, M. Lange

et al
.,
Phys
.

Rev
.

Lett.
95
, 227003 (2005).

4.

A.Yu. Aladyshkin and V.V. Moshchalkov, Phys
.

Rev
.

B

74
, 064503 (2006).

5.

W. Gillijns, A.Yu. Aladyshkin, A.V. Silhanek, and V.V. Moshchalkov, Phys
.

R
e
v
.

B

76
, 060503(R)
(2007).

6.

A.Yu. Aladyshkin, J. Fritzsche, and V.V. Moshchalkov,
Appl
.

Phys
.

Lett.
94
, 222503 (2009).

7.

A.Yu. Aladyshkin, G.W. Ataklti, W. Gillijns

et al
.,

Phys
.

R
e
v
.

B

83
, 144509 (2011).

8.

R. Werner, A.Yu. Aladyshkin, S. Guénon

et al
.,
Phys
.

Rev
.

B
84
, 020505(R) (2011).

9.

A.Yu. Aladyshkin, J. Fritzsche, R.B.G. Kramer

et al
.,
Phys
.

Rev
.

B

84
, 094523 (2011).

10.

A.Yu. Aladyshkin, A.S. Melnikov, D.A. Savinov

et al
.,
Phys
.

Rev
.

B, in press (2012)
; arXiv
:

1205.3992

(2012).