Montemurro, Domenico
(2016)
Hybrid superconducting InAs-nanowire based nanojunctions.
[Tesi di dottorato]
| Tipologia del documento: |
Tesi di dottorato
|
| Lingua: |
English |
| Titolo: |
Hybrid superconducting InAs-nanowire based nanojunctions |
| Autori: |
| Autore | Email |
|---|
| Montemurro, Domenico | domenicofisico@gmail.com |
|
| Data: |
31 Marzo 2016 |
| Numero di pagine: |
126 |
| Istituzione: |
Università degli Studi di Napoli Federico II |
| Dipartimento: |
Fisica |
| Scuola di dottorato: |
Scienze fisiche |
| Dottorato: |
Fisica fondamentale ed applicata |
| Ciclo di dottorato: |
28 |
| Coordinatore del Corso di dottorato: |
| nome | email |
|---|
| Velotta, raffaele | velotta@na.infn.it |
|
| Tutor: |
| nome | email |
|---|
| Tagliacozzo, Arturo | [non definito] | | Tafuri, Francesco | [non definito] |
|
| Data: |
31 Marzo 2016 |
| Numero di pagine: |
126 |
| Parole chiave: |
InAs nanowire, superconducting proximity e�ect, low temperature superconductor,
high temperature superconductor, hybrid nanostructures,
semiconducting barriers, mesoscopic systems, nanostructures, nanotechnology,
clean room |
| Settori scientifico-disciplinari del MIUR: |
Area 02 - Scienze fisiche > FIS/03 - Fisica della materia |
[error in script]
[error in script]
| Depositato il: |
14 Apr 2016 21:00 |
| Ultima modifica: |
31 Ott 2016 09:50 |
| URI: |
http://www.fedoa.unina.it/id/eprint/11093 |
Abstract
Semiconductor-superconductor hybrid devices have been investigated
for many years. In these devices the macroscopic quantum correlations
typical of superconductors can be induced via proximity effect
in a wide class of low-dimensional materials such as, topological insulator
, ferromagnetic barriers ], graphene and in particular
semiconducting nanowires (NWs) which o�er a
unique freedom in the design and control of quantum states. Precise
control of the geometry, composition and chemical properties enabled the NWs to be a potential building block in felds, like nanoelectronics,
photonics, mechanical and biological systems or sensors
[32]. The most intriguing consequence of such a material combination
is the possibility to give raise to novel excitations and properties that
none of the single device components originally possesses. Recently, intense
activity was aimed at arti�cially creating topologically protected
Majorana fermion states. Many proposals make use quasi-onedimensional
(quasi-1D) low critical temperature superconductors (LTS)
in contact with topological insulators or quasi-one-dimensional materials
with strong spin-orbit interactions (InAs & InSb NWs).
Efforts have been made to use unconventional barriers with LTS, which
o�er a much better compatibility and therefore nominal better interfaces,
thus limiting, by low critical magnetic felds and low gap energy,
for instance, the range parameters necessary to observe MBSs.
HTS are much harder to integrate with other systems, but present the
advantage as higher critical temperature, gap energy and huge stability
to the magnetic field. Device that combine semiconducting nanowires
(InAs-NWs) with HTS exploit both superconducting properties available
with ceramic HTS and the high-purity of InAs-NWs together with
xviii
Hybrid superconducting InAs-nanowire based nanojunctions xix
the tunability of their transport. The NWs represent the conductive
channel in a superconductor-semiconductor-superconductor �eld-e�ect
transistor (SUFET) device architecture and provide an ideal
mesoscopic system to study both quantum con�nement and interference
e�ects at low temperature, which is a promising platform to develop
novel quantum devices, and the limits of quantum suppression of superconductivity.
Nanoscale ordering and phase transition in complex
oxides, where the electrons self-organize in ways qualitatively di�erent
from those of conventional metals and insulators, is one of the most
outstanding problems in physics today, and studies of nanoscale devices
may have a formidable impact on that.
Mixing bottom-up and top-down nanofabrication approaches have allowed
building Josephson junctions in non-suspended and suspended
design. Sophisticate EBL techniques have been developed and aim to
align the InAs-NWs. Design device on which the InAs-NWs are positioned
in random and guided (Dielectrophoresis (DEP) technique)
way are fabricated. The InAs-NWs show external native oxide shell
that hampers the current
ux trough the interface, reason that procedures
that allow to remove the oxide and get a good transparency between
InAs-NWs and superconductor has been developed. Currentvoltage
measurements as function of the temperature show, for both designs,
a critical current amplitude that increases when the temperature
decrease. Novel insights on macroscopic superconducting coupling in
extreme conditions imposed by the nanostructures have been derived.
The nanotechnology platform developed for suspended LTS junctions
has represented the starting point for the integration between YBCO,
the most used HTS, and NWS. This is an extremely challenging, high
risk but extremely rewarding activity. Many designs have been developed
for this type of junction. Many nanofabrication problems due
to the complex structure of YBCO unit cell have been solved. In order
to minimize the YBCO damaging e�ects due to out-di�usion oxygen
from unit cell the nanofabrication recipe developed includes two
sessions of electron beam lithography (EBL), two e-resists (PMMA)
baking steps at low temperature and for few minutes, one dry etching
session performed at very low temperature and one fast wet etching
Hybrid superconducting InAs-nanowire based nanojunctions xx
step. Special design of devices that allows verifying electric shorts before
the InAs-NWs deposition have been developed. Innovative superconducting
hybrid devices InAs-NWs/YBCO have been characterized
with electric transport measurements as function of temperature and
show as a current injected into YBCO banks can through the InAs-NWs
that works as a weak link. I have demonstrated the feasibility of the
fabrication procedure of YBCO/suspended InAs-NW/YBCO junctions.
The �rst achievement of my work is that junctions YBCO/ suspended
InAs-NW/YBCO of length � 200nm are not insulating. Current passes
through the InAs-NWS, demonstrating the feasibility of the whole fabrication
process. The other encouraging result is that di�erently from
InAs-NWs/Aluminium junctions resistance behavior observed for InAs-
NW/YBCO devices depends on the normal length (L) of junction [43].
The work is structured in seven chapters.
The �rst chapter is dedicated to a review of the general mechanisms of
the electric transport in the normal state.
In the second chapter an introduction to superconductivity and to the
concept of Josephson coupling have been discussed.
The third chapter is dedicated to the description of the properties of
InAs material (bulk and nanostructutered).
The fourth chapter summarizes all the nanofabrication procedures developed
for the fabrication of non-suspended junction between InAsnanowire
and aluminium, suspended junction between InAs-nanowire
and aluminium and in the last sections,the e�orts accomplished for
the fabrication of the novel type of hybrid systems between InAsnanowire/
YBCO will be shown.
In the �fth chapter the cryogenic system and the measurement setup
used for the characterization of the devices builded are described.
In the sixth chapter the transport measures, and their elaboration, of
Hybrid superconducting InAs-nanowire based nanojunctions xxi
InAs-nanowires and aluminium junctions will be shown.
In the seven chapter the transport measurements of InAs-nanowires/YBCO
junctions and their comparative analysis performed with InAs-nanowires
and aluminium junctions have been performed
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