BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//CERN//INDICO//EN
BEGIN:VEVENT
SUMMARY:Analytical calculation of phase bistability switching rates in dis
sipative Jaynes-Cummings model
DTSTART;VALUE=DATE-TIME:20190620T164500Z
DTEND;VALUE=DATE-TIME:20190620T170000Z
DTSTAMP;VALUE=DATE-TIME:20240809T213917Z
UID:indico-contribution-36-205@cern.ch
DESCRIPTION:Speakers: Tomáš Novotný (Charles University\, Prague)\nWe s
tudy the dynamics of a dissipative Jaynes-Cummings model subject to a stro
ng resonant drive. Above a certain drive threshold there appear two metast
able states in the stationary state with roughly the same field amplitude
but different phases which are well captured by the bifurcation in the neo
-classical approach. Their appearance is associated with the splitting of
the spectrum of the corresponding Liouvillean heralding the quantum bistab
ility. We focus on the analytical evaluation of the switching rates betwee
n the two metastable states which we achieve by a generalized Fermi-golden
-rule-like method based on a precise estimate of the character of the meta
stable states. We find simple analytical expression for the rate surprisin
gly of non-exponential (i.e.\, non-Arrhenius) form\, which nevertheless ma
tches nearly perfectly the numerical results.\n\nhttps://indico.unina.it/e
vent/18/contributions/205/
LOCATION:Strand Hotel Terme Delfini
URL:https://indico.unina.it/event/18/contributions/205/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quasiparticle transport properties in superconductor-ferromagnet-s
uperconductor trilayers
DTSTART;VALUE=DATE-TIME:20190620T163000Z
DTEND;VALUE=DATE-TIME:20190620T164500Z
DTSTAMP;VALUE=DATE-TIME:20240809T213917Z
UID:indico-contribution-36-200@cern.ch
DESCRIPTION:Speakers: Zorica Popović (University of Belgrade\, Faculty of
Physics)\nA quantitative theory describing the behaviour of current/volta
ge characteristics (CVC) and conductances (G) for both s-wave (S) and d-
wave (D) type of ballistic voltage-biased superconductor/ferromagnet (F)/
superconductor (SFS or DFD) trilayers is developed. The calculation is b
ased on the nonequilibrium microscopic theory of transport in isotropic s-
wave superconductor/normal metal (SNS) junctions by Kümmel\, Gunsenheimer
and Nikolsky [1] in the relaxation time approximation using the time-depe
ndent Bogoliubov-de Gennes equations [2-5]. The model operates for differe
nt barrier thicknesses d\, the mean free path in the barrier l>d and diffe
rent temperatures T. For given exchange energy h the shape of CVCs depends
\, first\, on the barrier thickness\, while the presence and number of non
linear structures are determined by h. The behaviour of current-voltage ch
aracteristics (CVC) in SFS junctions\, such as steep rise of the current a
nd negative differential conductance at small voltage\, as well as the exc
hange field dependent position of the peaks\, are obtained for weak exchan
ge energy h≤∆\, where ∆=∆(T) is the superconducting energy gap. Su
ch behaviour is interpreted to be induced by multiple Andreev reflections
(AR)\, modified in presence of h in F. For DFD junctions\, the AR suppress
ion due to the presence of order parameter nodes in D\, and the presence o
f h in the F barrier leads to relatively smooth CVC for any value of h and
of d in contrast to the case of isotropic pairing in superconducting elec
trodes (SFS case). This provides an indication of the superconductor order
parameter symmetry. For DFD junctions with misoriented superconducting el
ectrodes we found that at low bias the coherence in the quasiparticle tran
sport could be enhanced by magnetic field in F. For θ=π/4 (d-wave superc
onductor is oriented with its gap node facing the boundary with F)\, where
the proximity effect is the strongest\, there is an enhancement of the cu
rrent (as well as zero bias conductance)\, starting from h=0 up to a maxim
um at h≈∆(T). \nWe find that conductance curves G(V) have a rich nonli
near structure in low-voltage multiple AR region. At higher voltages\, the
curves are almost flat\, with characteristic dips whose position are not
influenced by the type of order parameter anisotropy and electrodes misori
entation\, but vary only with the h in F and temperature dependent pair po
tential in superconductor\, according to the simple law neV=2∆(T)∓h\,
with n=0\,1\,…. We suggest that from observed dip's locations at given t
emperature one could determine experimentally the value of the exchange fi
eld in the barrier. We find that temperature dependence of zero bias cond
uctance for h≤∆\, show a kink at some characteristic temperature T^*
such that ∆(T^* )=h\, what provides another reliable experimental metho
d for measurements of small exchange field.\\\\ \n\n\nReferences \n\n1. R.
Kümmel\, U. Gunsenheimer\, and R. Nicolsky\, Phys. Rev. B 42\, 3992 (199
0).\n2. Z. Popović\, L. Dobrosavljević - Grujić\, and R. Zikic\, Ph
ys. Rev. B 85\, 174510 (2012).\n3. Z. Popović\, L. Dobrosavljević -
Grujić\, and R. Zikic\, J. Phys. Soc. Jpn. 82\, 114714 (2013).\n4. Z. P
opović\, R. Zikic\, and L. Dobrosavljević - Grujić\, Prog. Theor. Exp.
Phys. 2015\, 103I01 (2015).\n5. Z. Popović\, P. Miranović\, and R. Ziki
c\, Phys. Status Solidi B 255\, 1700554 (2018).\n\nhttps://indico.unina.it
/event/18/contributions/200/
LOCATION:Strand Hotel Terme Delfini
URL:https://indico.unina.it/event/18/contributions/200/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Spinful quantum dot junctions probed by superconductivity and ther
moelectricity
DTSTART;VALUE=DATE-TIME:20190620T160000Z
DTEND;VALUE=DATE-TIME:20190620T163000Z
DTSTAMP;VALUE=DATE-TIME:20240809T213917Z
UID:indico-contribution-36-207@cern.ch
DESCRIPTION:Speakers: Clemens Winkelmann (Univ. Grenoble Alpes)\nWe invest
igate the properties of gate-tunable single quantum dot junctions\, obtain
ed by the electromigration technique\, in the spin-1/2 Kondo regime with r
ather large $U/\\Gamma$ ($U$ is the on-site interaction and $\\Gamma$ the
tunnel coupling). In the first part we investigate the device response in
the presence of superconductivity in the leads. We tune the ground state o
f the dot quantum spin from screened to unscreened\, using the gate voltag
e\, the temperature and the magnetic field. In the second part\, we invest
igate the thermoelectric device response in the normal state of the leads\
, in the presence of a thermal gradient. We find a 2e-periodic response of
the Seebeck coefficient with respect to the quantum dot charge state\, wh
ich provides a characteristic signature of the spin degeneracy of the quan
tum dot levels. A sign change of the Seebeck coefficient with increasing t
emperature in the oddly occupied state provides a hallmark of Kondo correl
ations\, in very good agreement with NRG calculations.\n\nhttps://indico.u
nina.it/event/18/contributions/207/
LOCATION:Strand Hotel Terme Delfini
URL:https://indico.unina.it/event/18/contributions/207/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Spin-dependent thermoelectric effects in superconductor/ferromagne
t hybrid structures
DTSTART;VALUE=DATE-TIME:20190620T153000Z
DTEND;VALUE=DATE-TIME:20190620T160000Z
DTSTAMP;VALUE=DATE-TIME:20240809T213917Z
UID:indico-contribution-36-217@cern.ch
DESCRIPTION:Speakers: Detlef Beckmann (KIT\, Institute of Nanotechnology)\
nWe report on the experimental observation of spin-dependent thermoelectri
c effects in superconductor-ferromagnet tunnel junctions in high magnetic
fields. The thermoelectric signals are due to a spin-dependent lifting of
particle-hole symmetry on the energy scale of the superconducting gap. Due
to the small energy scale\, the thermoelectric effects can be quite large
\, and we infer a maximum Seebeck coefficient of about 100 µV/K from our
data. Nonlocal thermoelectric effects elucidate the coupling of spin and h
eat transport in high-field superconductors.\n\nhttps://indico.unina.it/ev
ent/18/contributions/217/
LOCATION:Strand Hotel Terme Delfini
URL:https://indico.unina.it/event/18/contributions/217/
END:VEVENT
END:VCALENDAR