Cren, Tristan
Overview
Works:  16 works in 19 publications in 2 languages and 468 library holdings 

Roles:  Other, Thesis advisor, Author 
Classifications:  TK7872.S8, 621.35 
Publication Timeline
.
Most widely held works by
Tristan Cren
Superconductors at the nanoscale : from basic research to applications by
Roger Wördenweber(
)
3 editions published in 2017 in English and held by 446 WorldCat member libraries worldwide
By covering theory, design, and fabrication of nanostructured superconducting materials, this monograph is an invaluable resource for research and development. Examples are energy saving solutions, healthcare, and communication technologies. Key ingredients are nanopatterned materials which help to improve the superconducting critical parameters and performance of superconducting devices, and lead to novel functionalities. ContentsTutorial on nanostructured superconductorsImaging vortices in superconductors: from the atomic scale to macroscopic distancesProbing vortex dynamics on a single vortex level by scanning acsusceptibility microscopySTM studies of vortex cores in strongly confined nanoscale superconductorsType1.5 superconductivityDirect visualization of vortex patterns in superconductors with competing vortexvortex interactionsVortex dynamics in nanofabricated chemical solution deposition hightemperature superconducting filmsArtificial pinning sites and their applicationsVortices at microwave frequenciesPhysics and operation of superconducting singlephoton devicesJosephson and charging effect in mesoscopic superconducting devicesNanoSQUIDs: Basics & recent advancesBi2Sr2CaCu2O8 intrinsic Josephson junction stacks as emitters of terahertz radiation
3 editions published in 2017 in English and held by 446 WorldCat member libraries worldwide
By covering theory, design, and fabrication of nanostructured superconducting materials, this monograph is an invaluable resource for research and development. Examples are energy saving solutions, healthcare, and communication technologies. Key ingredients are nanopatterned materials which help to improve the superconducting critical parameters and performance of superconducting devices, and lead to novel functionalities. ContentsTutorial on nanostructured superconductorsImaging vortices in superconductors: from the atomic scale to macroscopic distancesProbing vortex dynamics on a single vortex level by scanning acsusceptibility microscopySTM studies of vortex cores in strongly confined nanoscale superconductorsType1.5 superconductivityDirect visualization of vortex patterns in superconductors with competing vortexvortex interactionsVortex dynamics in nanofabricated chemical solution deposition hightemperature superconducting filmsArtificial pinning sites and their applicationsVortices at microwave frequenciesPhysics and operation of superconducting singlephoton devicesJosephson and charging effect in mesoscopic superconducting devicesNanoSQUIDs: Basics & recent advancesBi2Sr2CaCu2O8 intrinsic Josephson junction stacks as emitters of terahertz radiation
Expansion of a superconducting vortex core into a diffusive metal by Vasily S Stolyarov(
)
1 edition published in 2018 in English and held by 2 WorldCat member libraries worldwide
1 edition published in 2018 in English and held by 2 WorldCat member libraries worldwide
Electric field induced avalanche breakdown and nonvolatile resistive switching in the Mott Insulators AM4Q8 by B Corraze(
)
1 edition published in 2013 in English and held by 2 WorldCat member libraries worldwide
1 edition published in 2013 in English and held by 2 WorldCat member libraries worldwide
Isolated pairs of Majorana zero modes in a disordered superconducting lead monolayer by Gerbold C Ménard(
)
1 edition published in 2019 in English and held by 2 WorldCat member libraries worldwide
1 edition published in 2019 in English and held by 2 WorldCat member libraries worldwide
Signatures of a 4pi periodic Andreev bound state in topological Josephson junctions by
Kévin Le calvez(
)
1 edition published in 2017 in English and held by 2 WorldCat member libraries worldwide
Three dimensional topological insulators (3D TI) are a new state of matter composedof an electrically insulating bulk covered by metallic surface states. Theoretically, a topological Josephson junction composed of these surface states can host an Andreev Boundstate (ABS) that has twice the periodicity of the conventional 2p periodic ABSs. The4p periodic ABS is expected to be the building block of topological quantum computing.Therefore, we study the dynamic of this particular ABS by performing Shapiro measurement on Josephson junctions built with bismuth based 3D TI.To identify the e?ects of a 4p periodic ABS in a Shapiro measurement, we use a phenomenological model that simulates the voltagecurrent characteristics of a TJJ. We predicttwo signatures of the 4p periodic ABS and estimate their robustness against Joule heatingand thermally activated quasiparticle poisoning of the 4p periodic mode.We study the Josephson junctions dynamics by performing Shapiro measurements onjunctions built on Bi2Se3. We observe the two previously anticipated signatures, whichare the nonconventional appearance order of the Shapiro steps and the remaining of asupercurrent at the closing of the Shapiro step n = 0. They prove the presence of a 4pperiodic ABS.We also study the topological insulator BiSbTeSe2 that we have grown by using themelting growth method. By superconducting interferometric measurements, we show asuperconducting surface transport without bulk electronic conduction
1 edition published in 2017 in English and held by 2 WorldCat member libraries worldwide
Three dimensional topological insulators (3D TI) are a new state of matter composedof an electrically insulating bulk covered by metallic surface states. Theoretically, a topological Josephson junction composed of these surface states can host an Andreev Boundstate (ABS) that has twice the periodicity of the conventional 2p periodic ABSs. The4p periodic ABS is expected to be the building block of topological quantum computing.Therefore, we study the dynamic of this particular ABS by performing Shapiro measurement on Josephson junctions built with bismuth based 3D TI.To identify the e?ects of a 4p periodic ABS in a Shapiro measurement, we use a phenomenological model that simulates the voltagecurrent characteristics of a TJJ. We predicttwo signatures of the 4p periodic ABS and estimate their robustness against Joule heatingand thermally activated quasiparticle poisoning of the 4p periodic mode.We study the Josephson junctions dynamics by performing Shapiro measurements onjunctions built on Bi2Se3. We observe the two previously anticipated signatures, whichare the nonconventional appearance order of the Shapiro steps and the remaining of asupercurrent at the closing of the Shapiro step n = 0. They prove the presence of a 4pperiodic ABS.We also study the topological insulator BiSbTeSe2 that we have grown by using themelting growth method. By superconducting interferometric measurements, we show asuperconducting surface transport without bulk electronic conduction
ETUDE DES CUPRATES SUPRACONDUCTEURS PAR MICROSCOPIE/SPECTROSCOPIE TUNNEL by
Tristan Cren(
Book
)
2 editions published in 2000 in French and held by 2 WorldCat member libraries worldwide
Ce travail porte sur la spectroscopie tunnel locale sur les cuprates supraconducteurs. Apres quelques rappels sur le succes de la spectroscopie tunnel sur les supraconducteurs conventionnels, nous montrons en quoi les cuprates se distinguent. Nous decrivons ensuite la mise au point d'un nouveau microscope a effet tunnel a basse temperature. Nous detaillons en particulier la mise au point d'une acquisition spectroscopique permetant de mesurer la densite d'etats electronique en tout point d'une image. Nous montrons les premiers resultats spectroscopiques sur des films minces de cuprates ybco et bisrcacuo. Nous mettons en evidence les caracteristiques communes aux spectres des excitations dans ces deux composes. Grace a la spectroscopie tunnel resolue spatialement, nous realisons la cartographie complete de la densite d'etats de cuprates supraconducteurs. Ces mesures montrent qu'en presence d'un desordre modere, il y a coexistence de zones supraconductrices et nonsupraconductrices. De maniere surprenante, la densite d'etats des zones nonsupraconductrices est identique au pseudogap precedemment observe au dessus de la temperature critique et au coeur des vortex. Nous montrerons aussi comment la structure fine des spectres tunnel est liee a l'apparition de l'ordre supraconducteur a grande echelle. Cela nous conduit a proposer un nouveau parametre d'ordre gouvernant la transition etat supraconducteur  pseudogap qui explique bien la forme des spectres des excitations
2 editions published in 2000 in French and held by 2 WorldCat member libraries worldwide
Ce travail porte sur la spectroscopie tunnel locale sur les cuprates supraconducteurs. Apres quelques rappels sur le succes de la spectroscopie tunnel sur les supraconducteurs conventionnels, nous montrons en quoi les cuprates se distinguent. Nous decrivons ensuite la mise au point d'un nouveau microscope a effet tunnel a basse temperature. Nous detaillons en particulier la mise au point d'une acquisition spectroscopique permetant de mesurer la densite d'etats electronique en tout point d'une image. Nous montrons les premiers resultats spectroscopiques sur des films minces de cuprates ybco et bisrcacuo. Nous mettons en evidence les caracteristiques communes aux spectres des excitations dans ces deux composes. Grace a la spectroscopie tunnel resolue spatialement, nous realisons la cartographie complete de la densite d'etats de cuprates supraconducteurs. Ces mesures montrent qu'en presence d'un desordre modere, il y a coexistence de zones supraconductrices et nonsupraconductrices. De maniere surprenante, la densite d'etats des zones nonsupraconductrices est identique au pseudogap precedemment observe au dessus de la temperature critique et au coeur des vortex. Nous montrerons aussi comment la structure fine des spectres tunnel est liee a l'apparition de l'ordre supraconducteur a grande echelle. Cela nous conduit a proposer un nouveau parametre d'ordre gouvernant la transition etat supraconducteur  pseudogap qui explique bien la forme des spectres des excitations
YuShibaRusinov bound states versus topological edge states in Pb/Si(111) by Gerbold C Ménard(
)
1 edition published in 2019 in English and held by 2 WorldCat member libraries worldwide
1 edition published in 2019 in English and held by 2 WorldCat member libraries worldwide
Imagerie directe de champ électrique par microscopie à balayage d'un transistor à électron unique by
Jorge P Nacenta Mendivil(
)
1 edition published in 2019 in English and held by 2 WorldCat member libraries worldwide
In this doctoral work, we have developed a new scanning single electron transistor (SET) microscope that works at very low temperatures (T = 50 mK) and high magnetic fields (B = 18 T). A SET consists of a small metallic island connected to source and drain electrodes through two tunnel junctions. In the Coulomb blockade regime at low temperature regime (T 5 K), an external electric field tunes the current circulating through the SET. In addition,small electric field variations lead to large SET current changes that makes the device a highly sensitive charge detector, able to detect charges smaller than 0.01 e. Thus, when the SET scans above a surface, it maps the electrostatic properties of the sample. However, the implementation of a scanning SET microscope is extremely challenging since it combines scanning probe microscopy, low temperatures and sensitive nanoscopic devices. For thisreason, only a few groups have succeeded its realization. Our technological choices to build the microscope improve certain aspects with respect to the already existing instruments. The breakthrough is that we fabricate the SET probe using standard lithographic techniques on commercial silicon wafers.For that reason, batch fabrication of SET probes is possible. Furthermore, by a combination of dicing and etching techniques, the SET is engineered extremely close to the edge of the Si chip (< 1 micrometer). In this way, the SET can be approached to a few nanometer from the sample surface by means of a atomic force distance control. Additionally, an onprobe gate electrode fabricated close to the island can be used to tune the operating point of the SET. Anovelty of our instrument is that with this onprobe gate and a feedback loop we have been able to map directly the local electric field. We demonstrate this new feedback scanning method by imaging an interdigitated array of nanometer scale electrodes. Moreover, the SET is an ideal tool for the study of the localization of electronic states. In the future, our scanning SET will be used for the study of twodimensional electron systems in the quantum Hall regime, topological insulators and the metal insulator transition
1 edition published in 2019 in English and held by 2 WorldCat member libraries worldwide
In this doctoral work, we have developed a new scanning single electron transistor (SET) microscope that works at very low temperatures (T = 50 mK) and high magnetic fields (B = 18 T). A SET consists of a small metallic island connected to source and drain electrodes through two tunnel junctions. In the Coulomb blockade regime at low temperature regime (T 5 K), an external electric field tunes the current circulating through the SET. In addition,small electric field variations lead to large SET current changes that makes the device a highly sensitive charge detector, able to detect charges smaller than 0.01 e. Thus, when the SET scans above a surface, it maps the electrostatic properties of the sample. However, the implementation of a scanning SET microscope is extremely challenging since it combines scanning probe microscopy, low temperatures and sensitive nanoscopic devices. For thisreason, only a few groups have succeeded its realization. Our technological choices to build the microscope improve certain aspects with respect to the already existing instruments. The breakthrough is that we fabricate the SET probe using standard lithographic techniques on commercial silicon wafers.For that reason, batch fabrication of SET probes is possible. Furthermore, by a combination of dicing and etching techniques, the SET is engineered extremely close to the edge of the Si chip (< 1 micrometer). In this way, the SET can be approached to a few nanometer from the sample surface by means of a atomic force distance control. Additionally, an onprobe gate electrode fabricated close to the island can be used to tune the operating point of the SET. Anovelty of our instrument is that with this onprobe gate and a feedback loop we have been able to map directly the local electric field. We demonstrate this new feedback scanning method by imaging an interdigitated array of nanometer scale electrodes. Moreover, the SET is an ideal tool for the study of the localization of electronic states. In the future, our scanning SET will be used for the study of twodimensional electron systems in the quantum Hall regime, topological insulators and the metal insulator transition
Modulation de la supraconductivité hors équilibre avec un STM by
Thomas Jalabert(
)
1 edition published in 2020 in English and held by 1 WorldCat member library worldwide
Quasiparticles dynamics often governs the ultimate performances of superconducting devices. Outofequilibrium superconductivity has therefore attracted a longstanding interest. In order to probe the microscopic mechanisms at play, injection of quasiparticles with the help of a tunnel junction has already been employed at the mesoscopic scale, thanks to the outstanding progress in modern nanotechnology. However, lithographed tunnel junctions lack spatial resolution and do not allow to vary the bias voltage and the tunneling current independently. In order to overcome these two limitations the novelty of this PhD work is to use a Scanning Tunneling Microscope (STM) working at very low temperature (50 mK) to tune the critical current of superconducting nanowires as a function of the tip position and the tunneling setpoint.In thin niobium nanowires capped with gold, we measured a drastic reduction of the critical current by injecting a tunnelling current of quasiparticles that is six orders of magnitude lower. We interpret this observation as a local increase of the electronic temperature. We also suggest that the same mechanism is at play in superconducting Field Effect Transistors (SuFETs). The critical current depends strongly on the injection position along the nanowire, the injection rate and the energy of the quasiparticles. At large energies compared to the superconducting gap, the reduction of the critical current is controlled by the injected power. Our measurements show that the diffusion of heat by quasiparticles and phonons explains the injection power and position dependencies, and allow to probe the electronphonon coupling in our samples. By contrast, when reducing the energy at constant injection rate, the critical current sharply decreases close to the gap energy, signalling the breakdown of the quasiequilibrium model. We explain this behaviour as a non Fermi Dirac out of equilibrium energy distribution of the quasiparticles, and this allows to estimate the relaxation rate of the quasiparticles. We also probed the spectral properties of current carrying nanowires, and induced magnetic vortices to create spatial variations in the density of states. We thus evidenced the effect of quasiparticle trapping by vortices at the nanometer scale, which is of particular interest since until now the only experiments that allow investigating the dynamics of an inhomogeneous superconducting system necessarily probed a macroscopic volume of the superconductor, rendering explanation of the measurements in terms of the inhomogeneity difficult.Therefore, this experimental work opens a new perspective to investigate the competition between diffusion, relaxation and recombination of quasiparticles in strongly disordered superconductors with various applications such as in photon detection and superconducting electronics
1 edition published in 2020 in English and held by 1 WorldCat member library worldwide
Quasiparticles dynamics often governs the ultimate performances of superconducting devices. Outofequilibrium superconductivity has therefore attracted a longstanding interest. In order to probe the microscopic mechanisms at play, injection of quasiparticles with the help of a tunnel junction has already been employed at the mesoscopic scale, thanks to the outstanding progress in modern nanotechnology. However, lithographed tunnel junctions lack spatial resolution and do not allow to vary the bias voltage and the tunneling current independently. In order to overcome these two limitations the novelty of this PhD work is to use a Scanning Tunneling Microscope (STM) working at very low temperature (50 mK) to tune the critical current of superconducting nanowires as a function of the tip position and the tunneling setpoint.In thin niobium nanowires capped with gold, we measured a drastic reduction of the critical current by injecting a tunnelling current of quasiparticles that is six orders of magnitude lower. We interpret this observation as a local increase of the electronic temperature. We also suggest that the same mechanism is at play in superconducting Field Effect Transistors (SuFETs). The critical current depends strongly on the injection position along the nanowire, the injection rate and the energy of the quasiparticles. At large energies compared to the superconducting gap, the reduction of the critical current is controlled by the injected power. Our measurements show that the diffusion of heat by quasiparticles and phonons explains the injection power and position dependencies, and allow to probe the electronphonon coupling in our samples. By contrast, when reducing the energy at constant injection rate, the critical current sharply decreases close to the gap energy, signalling the breakdown of the quasiequilibrium model. We explain this behaviour as a non Fermi Dirac out of equilibrium energy distribution of the quasiparticles, and this allows to estimate the relaxation rate of the quasiparticles. We also probed the spectral properties of current carrying nanowires, and induced magnetic vortices to create spatial variations in the density of states. We thus evidenced the effect of quasiparticle trapping by vortices at the nanometer scale, which is of particular interest since until now the only experiments that allow investigating the dynamics of an inhomogeneous superconducting system necessarily probed a macroscopic volume of the superconductor, rendering explanation of the measurements in terms of the inhomogeneity difficult.Therefore, this experimental work opens a new perspective to investigate the competition between diffusion, relaxation and recombination of quasiparticles in strongly disordered superconductors with various applications such as in photon detection and superconducting electronics
Engineering topological states in arrays of magnetic molecules in interaction with a 2D superconductor by
Danilo Longo(
)
1 edition published in 2019 in English and held by 1 WorldCat member library worldwide
Recent studies predicted that the interaction between a 2D superconductor and local magnetism could induce topological superconductivity accompanied by Majorana edge states. To address this challenge, we have studied a system based on the interaction between selfassemblies of molecular magnets, i.e. manganese phthalocyanines (MnPcs), and thin films of lead (1 and 3 monolayers) grown on Si(111) surfaces that show 2D superconductivity.Our Scanning Tunneling Microscopy (STM) experiments revealed that, adsorption of a tiny amount of MnPcs on a Pb monolayer is accompanied by a very small charge transfer inducing a macroscopic structural phase transition of the surface itself. Scanning Tunneling Spectroscopy (STS) experiments at 300mK on 3 monolayers thick islands of Pb/Si(111) showed the presence of nontrivial effects responsible for the spatial fluctuation of the coherence peaks amplitude on a length scale much smaller than the superconducting coherence length. Furthermore, contrary to what shown on bulk Pb substrates, STS experiments strongly suggest that isolated MnPcs are always found in a weak interaction regime with the 3 monolayers thick Pb islands. Our results together with the observation of an ingap spectroscopic feature located at the edge of a selfassembled 2D domain of MnPcs pave the route to future studies for the engineering of superconducting topological phases
1 edition published in 2019 in English and held by 1 WorldCat member library worldwide
Recent studies predicted that the interaction between a 2D superconductor and local magnetism could induce topological superconductivity accompanied by Majorana edge states. To address this challenge, we have studied a system based on the interaction between selfassemblies of molecular magnets, i.e. manganese phthalocyanines (MnPcs), and thin films of lead (1 and 3 monolayers) grown on Si(111) surfaces that show 2D superconductivity.Our Scanning Tunneling Microscopy (STM) experiments revealed that, adsorption of a tiny amount of MnPcs on a Pb monolayer is accompanied by a very small charge transfer inducing a macroscopic structural phase transition of the surface itself. Scanning Tunneling Spectroscopy (STS) experiments at 300mK on 3 monolayers thick islands of Pb/Si(111) showed the presence of nontrivial effects responsible for the spatial fluctuation of the coherence peaks amplitude on a length scale much smaller than the superconducting coherence length. Furthermore, contrary to what shown on bulk Pb substrates, STS experiments strongly suggest that isolated MnPcs are always found in a weak interaction regime with the 3 monolayers thick Pb islands. Our results together with the observation of an ingap spectroscopic feature located at the edge of a selfassembled 2D domain of MnPcs pave the route to future studies for the engineering of superconducting topological phases
Phase diagram and fluctuations in two dimensional space charge doped Bi2Sr2CaCu2O8+x by
Edoardo Sterpetti(
)
1 edition published in 2018 in English and held by 1 WorldCat member library worldwide
The phase diagram of holedoped high critical temperature superconductors as a function of doping and temperature has been intensively studied with chemical variation of doping. Chemical doping can provoke structural changes and disorder, masking intrinsic effects. Alternatively, electrostatically doped ultrathin samples can be used through FieldEffect Transistor (FET) devices. The electrostatic modulation of charge carrier density in 2D materials is an elegant and clean approach that presents many technological challenges when high temperature superconductors are concerned. In this thesis we overcome these technological obstacles by using proprietary techniques developed in our laboratory for the study of 2D materials, and we focus on the high temperature superconductor BSCCO2212, whose phase diagram has so far never been studied via electrostatic effect. Notably we fabricate ultrathin high quality superconducting BSCCO2212 devices and use an original electrostatic method called space charge doping to measure transport characteristics from 330~K to low temperature. We extract parameters and characteristic temperatures over a large doping range and establish a comprehensive phase diagram for oneunitcellthick BSCCO2212 samples as a function of doping, temperature and disorder. We also identify the critical doping range where a quantum phase transition is predicted. Finally we take a closer look at the superconducting transition in the two dimensional limit. Fluctuations and extrinsic effects are accounted for using appropriate theoretical formalism and the two dimensional character of the superconducting transition of BSCCO2212 is analysed
1 edition published in 2018 in English and held by 1 WorldCat member library worldwide
The phase diagram of holedoped high critical temperature superconductors as a function of doping and temperature has been intensively studied with chemical variation of doping. Chemical doping can provoke structural changes and disorder, masking intrinsic effects. Alternatively, electrostatically doped ultrathin samples can be used through FieldEffect Transistor (FET) devices. The electrostatic modulation of charge carrier density in 2D materials is an elegant and clean approach that presents many technological challenges when high temperature superconductors are concerned. In this thesis we overcome these technological obstacles by using proprietary techniques developed in our laboratory for the study of 2D materials, and we focus on the high temperature superconductor BSCCO2212, whose phase diagram has so far never been studied via electrostatic effect. Notably we fabricate ultrathin high quality superconducting BSCCO2212 devices and use an original electrostatic method called space charge doping to measure transport characteristics from 330~K to low temperature. We extract parameters and characteristic temperatures over a large doping range and establish a comprehensive phase diagram for oneunitcellthick BSCCO2212 samples as a function of doping, temperature and disorder. We also identify the critical doping range where a quantum phase transition is predicted. Finally we take a closer look at the superconducting transition in the two dimensional limit. Fluctuations and extrinsic effects are accounted for using appropriate theoretical formalism and the two dimensional character of the superconducting transition of BSCCO2212 is analysed
Unconventional superconductivity in quasi2D materials with strong spinorbit coupling by
Raphaël Leriche(
)
1 edition published in 2019 in English and held by 1 WorldCat member library worldwide
The realization of topological superconductors is one of the main current goals of condensed matter physics. It was indeed predicted that such systems should host Majorana fermions. These Majorana fermions possess both a nonAbelian statistics and, because of their topological origin, a certain robustness against local disorder, which makes them attractive for quantum computing applications. One approach likely to lead to topological superconductivity consists in considering superconducting systems with strong spinorbit coupling and with broken inversion symmetry. It is in this framework that, during this thesis, I performed scanning tunneling microscopy and spectroscopy measurements on quasi2D materials : (LaSe)1,14(NbSe2)2 and Sr2IrO4. I first studied the electronic properties of misfit compound LaNb2Se5, which is a parent of transition metal dichalcogenide 2HNbSe2. (LaSe)1,14(NbSe2)2 is a heterostructure made out of alternations of NbSe2 bilayers with trigonal prismatic geometry and LaSe bilayers with rocksalt structure. (LaSe)1,14(NbSe2)2 is a potential candidate for topological superconductivity because of the presence of both a strong spinorbit coupling and of broken inversion symmetry in NbSe2 planes. Here, I present spectroscopic results showing that the electronic structure of(LaSe)1,14(NbSe2)2 is very similar to the one of electrondoped monolayer NbSe2 with a shift of the chemical potential of 0,3 eV, priorly never reached. I could also demonstrate the quasi 2D nature of (LaSe)1,14(NbSe2)2 and more particularly the presence of a strong Ising spinorbit coupling. Moreover, the observed weakness of superconductivity against nonmagnetic disorder combined with quasiparticle interferences measurements allowed me to exhibit the unconventional nature of (LaSe)1,14(NbSe2)2 superconducting order parameter. This study opens the possibility to use misfit heterostructures such as (LaSe)1,14(NbSe2)2 to study thephysics of transition metal dichalcogenides in the 2D limit, for which many theoretical studies predict topological superconductivity. In this thesis, I also present a study on the effects of doping on the electronic properties of iridate compound Sr2IrO4. Sr2IrO4 is a spinorbit induced Mott insulator. Because inversion symmetry is locally broken in Sr2IrO4, some theoretical predictions suggest that Sr2IrO4 should turn into a topological superconductor once doped. Here, I exhibit a nanometerscaleinhomogeneous dopingdriven Mott insulator to pseudometallic phase transition. This work further justifies the importance of using a local probe such as scanning tunnelling microscopy in order to complete results on Mott physics obtained by integrative methods like angleresolved photoemission spectroscopy
1 edition published in 2019 in English and held by 1 WorldCat member library worldwide
The realization of topological superconductors is one of the main current goals of condensed matter physics. It was indeed predicted that such systems should host Majorana fermions. These Majorana fermions possess both a nonAbelian statistics and, because of their topological origin, a certain robustness against local disorder, which makes them attractive for quantum computing applications. One approach likely to lead to topological superconductivity consists in considering superconducting systems with strong spinorbit coupling and with broken inversion symmetry. It is in this framework that, during this thesis, I performed scanning tunneling microscopy and spectroscopy measurements on quasi2D materials : (LaSe)1,14(NbSe2)2 and Sr2IrO4. I first studied the electronic properties of misfit compound LaNb2Se5, which is a parent of transition metal dichalcogenide 2HNbSe2. (LaSe)1,14(NbSe2)2 is a heterostructure made out of alternations of NbSe2 bilayers with trigonal prismatic geometry and LaSe bilayers with rocksalt structure. (LaSe)1,14(NbSe2)2 is a potential candidate for topological superconductivity because of the presence of both a strong spinorbit coupling and of broken inversion symmetry in NbSe2 planes. Here, I present spectroscopic results showing that the electronic structure of(LaSe)1,14(NbSe2)2 is very similar to the one of electrondoped monolayer NbSe2 with a shift of the chemical potential of 0,3 eV, priorly never reached. I could also demonstrate the quasi 2D nature of (LaSe)1,14(NbSe2)2 and more particularly the presence of a strong Ising spinorbit coupling. Moreover, the observed weakness of superconductivity against nonmagnetic disorder combined with quasiparticle interferences measurements allowed me to exhibit the unconventional nature of (LaSe)1,14(NbSe2)2 superconducting order parameter. This study opens the possibility to use misfit heterostructures such as (LaSe)1,14(NbSe2)2 to study thephysics of transition metal dichalcogenides in the 2D limit, for which many theoretical studies predict topological superconductivity. In this thesis, I also present a study on the effects of doping on the electronic properties of iridate compound Sr2IrO4. Sr2IrO4 is a spinorbit induced Mott insulator. Because inversion symmetry is locally broken in Sr2IrO4, some theoretical predictions suggest that Sr2IrO4 should turn into a topological superconductor once doped. Here, I exhibit a nanometerscaleinhomogeneous dopingdriven Mott insulator to pseudometallic phase transition. This work further justifies the importance of using a local probe such as scanning tunnelling microscopy in order to complete results on Mott physics obtained by integrative methods like angleresolved photoemission spectroscopy
On surface spin detection and doping of metallocenes by
Nicolas Bachellier(
)
1 edition published in 2016 in English and held by 1 WorldCat member library worldwide
Le sujet principal de cette thèse est l'étude de métallocènes déposés sur une surface de cuivre. Leurs adsorptions et propriétés électroniques sont expérimentalement étudiées par microscopie à effet tunnel (STM) et spectroscopie par effet tunnel (STS). Nos résultats ont été validés par des calculs se basant sur la théorie de la fonctionnelle de la densité (DFT). Plus précisément, nous avons étudié la façon dont le ferrocène FeC10H10 et le nickelocène NiC10H10s'adsorbent sur le cuivre. Nous avons découvert que ces métallocènes forment spontanément des réseaux alternant molécules horizontales et verticales. Nous avons ensuite modifié la structure du ferrocène par l'ajout d'un atome de cobalt et caractérisé les propriétés magnétiques de la nouvelle molécule ainsi créée, notamment l'apparition d'un effet Kondo témoignant de l'apparition de propriétés magnétiques au sein de la molécule. L'étude spectroscopique du nickelocène a révélé une excitation de la molécule à basse énergie.Cette excitation se traduit par une réorientation du moment de spin de la molécule, passant d'une orientation perpendiculaire à l'axe principal de la molécule à une orientation parallèle à cet axe.Nous avons finalement transféré un nickelocène sur la pointe STM et utilisé cette pointe moléculaire pour sonder les états d'une seconde molécule. Nous avons alors obtenu une double excitation de spin dans notre jonction tunnel, avec une augmentation significative de la conductance due aux excitations
1 edition published in 2016 in English and held by 1 WorldCat member library worldwide
Le sujet principal de cette thèse est l'étude de métallocènes déposés sur une surface de cuivre. Leurs adsorptions et propriétés électroniques sont expérimentalement étudiées par microscopie à effet tunnel (STM) et spectroscopie par effet tunnel (STS). Nos résultats ont été validés par des calculs se basant sur la théorie de la fonctionnelle de la densité (DFT). Plus précisément, nous avons étudié la façon dont le ferrocène FeC10H10 et le nickelocène NiC10H10s'adsorbent sur le cuivre. Nous avons découvert que ces métallocènes forment spontanément des réseaux alternant molécules horizontales et verticales. Nous avons ensuite modifié la structure du ferrocène par l'ajout d'un atome de cobalt et caractérisé les propriétés magnétiques de la nouvelle molécule ainsi créée, notamment l'apparition d'un effet Kondo témoignant de l'apparition de propriétés magnétiques au sein de la molécule. L'étude spectroscopique du nickelocène a révélé une excitation de la molécule à basse énergie.Cette excitation se traduit par une réorientation du moment de spin de la molécule, passant d'une orientation perpendiculaire à l'axe principal de la molécule à une orientation parallèle à cet axe.Nous avons finalement transféré un nickelocène sur la pointe STM et utilisé cette pointe moléculaire pour sonder les états d'une seconde molécule. Nous avons alors obtenu une double excitation de spin dans notre jonction tunnel, avec une augmentation significative de la conductance due aux excitations
2D superconductors perturbed by local magnetism : from YuShibaRusinov bound states to Majorana quasiparticles by
Gerbold, Christophe, Bertrand Ménard(
)
1 edition published in 2016 in English and held by 1 WorldCat member library worldwide
One of the present days goals of condensed matter physics is to create new systems with topological properties, especially in the field of superconductivity. One of the ways envisioned to create topological superconductors is to locally induce a magnetic interaction in the form of chains of magnetic impurities, vortices or magnetic clusters of ordered magnetic impurities. In this thesis we studied a set of effects from individual impurities to organized clusters interacting with twodimensional superconductors. Using scanning tunneling microscopy and spectroscopy we considered two systems, monocrystals of 2HNbSe2 and monolayers of Pb/Si(111). Thanks to the twodimensional electronic behavior of these two systems we show how the spatial extent of the bound states induced by magnetic impurities is considerably enhanced compared to the case of a threedimensional superconductor. By combining these magnetic atoms using a selfassembly method we were able to create ferromagnetic clusters that lead to a topological superconductivity in Pb monolayers. In particular we present here measurement of topological edge states at the interface Pb/Si(111) and Pb/Co/Si(111). We also present the measurement of zero bias peaks in the center of larger magnetic clusters that sign the presence of Majorana fermions in these systems. Our results show that an adequate patterning of surfaces could realize topological patches and call for a pursuit of the efforts in the subject in order to be able to control Majorana fermions that could eventually lead to breakthrough in quantum computation
1 edition published in 2016 in English and held by 1 WorldCat member library worldwide
One of the present days goals of condensed matter physics is to create new systems with topological properties, especially in the field of superconductivity. One of the ways envisioned to create topological superconductors is to locally induce a magnetic interaction in the form of chains of magnetic impurities, vortices or magnetic clusters of ordered magnetic impurities. In this thesis we studied a set of effects from individual impurities to organized clusters interacting with twodimensional superconductors. Using scanning tunneling microscopy and spectroscopy we considered two systems, monocrystals of 2HNbSe2 and monolayers of Pb/Si(111). Thanks to the twodimensional electronic behavior of these two systems we show how the spatial extent of the bound states induced by magnetic impurities is considerably enhanced compared to the case of a threedimensional superconductor. By combining these magnetic atoms using a selfassembly method we were able to create ferromagnetic clusters that lead to a topological superconductivity in Pb monolayers. In particular we present here measurement of topological edge states at the interface Pb/Si(111) and Pb/Co/Si(111). We also present the measurement of zero bias peaks in the center of larger magnetic clusters that sign the presence of Majorana fermions in these systems. Our results show that an adequate patterning of surfaces could realize topological patches and call for a pursuit of the efforts in the subject in order to be able to control Majorana fermions that could eventually lead to breakthrough in quantum computation
Intrinsic vibrational angular momentum driven by nonadiabatic effects in noncollinear magnetic systems by
Oliviero Bistoni(
)
1 edition published in 2022 in English and held by 1 WorldCat member library worldwide
In absence of external fields, vibrational modes of periodic systems are usually considered as linearly polarized and, as such, they do not carry angular momentum. Our work proves that nonadiabatic effects due to the electronphonon coupling are timereversal symmetry breaking interactions for the vibrational field in systems with noncollinear magnetism and large spinorbit coupling. Since in these systems the deformation potential matrix elements are necessarily complex, a nonzero synthetic gauge field (Berry curvature) arises in the dynamic equations of the ionic motion. As a result, phonon modes are elliptically polarized in the nonadiabatic framework and intrinsic vibrational angular momenta occur even for nondegenerate modes and without external probes. These results are validated by performing fully relativistic abinitio calculations on two insulating platinum clusters and a metallic manganese compound, with noncollinear magnetism.In both cases, nonadiabatic vibrational modes carry sizeable angular momenta comparable to the orbital electronic ones in itinerant ferromagnets
1 edition published in 2022 in English and held by 1 WorldCat member library worldwide
In absence of external fields, vibrational modes of periodic systems are usually considered as linearly polarized and, as such, they do not carry angular momentum. Our work proves that nonadiabatic effects due to the electronphonon coupling are timereversal symmetry breaking interactions for the vibrational field in systems with noncollinear magnetism and large spinorbit coupling. Since in these systems the deformation potential matrix elements are necessarily complex, a nonzero synthetic gauge field (Berry curvature) arises in the dynamic equations of the ionic motion. As a result, phonon modes are elliptically polarized in the nonadiabatic framework and intrinsic vibrational angular momenta occur even for nondegenerate modes and without external probes. These results are validated by performing fully relativistic abinitio calculations on two insulating platinum clusters and a metallic manganese compound, with noncollinear magnetism.In both cases, nonadiabatic vibrational modes carry sizeable angular momenta comparable to the orbital electronic ones in itinerant ferromagnets
Vortex confinés dans des nanostructures de Pb/Si(111) étudiés par microscopie à effet tunnel by
Lise SerrierGarcia(
)
1 edition published in 2014 in French and held by 1 WorldCat member library worldwide
In type II superconductors, the applied magnetic field penetrates the material in quanta of flux called vortices, vortices of superconducting currents circulating around a normal core. In the work of this thesis, we show how the confinement of a system to a scale comparable to the nanometric coherent length substantially modifies its superconducting properties.This study is carried out in nanostructures of lead deposited insitu on a silicon (111) substrate, then studied by scanning tunneling spectroscopy, under UHV, at 300 mK, and under magnetic field. In extremely confinement (lateral size D<<10 ?), systems create Giant vortices, quantum objects predicted 45 years ago. In the weakly confinement (D~10 ?), vortices may be pinned, then are organized in the triangular Abrikosov lattice, finally interpenetrate in surface superconductivity with the increasing magnetic field. Crystalline superconducting Pb islands are here connected by a disordered nonsuperconducting wetting layer of Pb. In the vicinity of each superconducting island, the wetting layer acquires specific tunnelling characteristics which reflect the interplay between the proximity induced superconductivity and the inherent electron correlations of this ultimate diffusive twodimensional metal. Spatial evolution of the tunnel spectra are simulated by combining the Usadel equations and the theory of dynamic Coulomb blockade. With reducing the distance between the islands, the proximity effect around each overlaps and forms a Josephson junction. Thanks to the tunneling spectroscopy, number, position, the spectrum and the form of Josephson vortex cores are studied in detail for a large variety of junctions
1 edition published in 2014 in French and held by 1 WorldCat member library worldwide
In type II superconductors, the applied magnetic field penetrates the material in quanta of flux called vortices, vortices of superconducting currents circulating around a normal core. In the work of this thesis, we show how the confinement of a system to a scale comparable to the nanometric coherent length substantially modifies its superconducting properties.This study is carried out in nanostructures of lead deposited insitu on a silicon (111) substrate, then studied by scanning tunneling spectroscopy, under UHV, at 300 mK, and under magnetic field. In extremely confinement (lateral size D<<10 ?), systems create Giant vortices, quantum objects predicted 45 years ago. In the weakly confinement (D~10 ?), vortices may be pinned, then are organized in the triangular Abrikosov lattice, finally interpenetrate in surface superconductivity with the increasing magnetic field. Crystalline superconducting Pb islands are here connected by a disordered nonsuperconducting wetting layer of Pb. In the vicinity of each superconducting island, the wetting layer acquires specific tunnelling characteristics which reflect the interplay between the proximity induced superconductivity and the inherent electron correlations of this ultimate diffusive twodimensional metal. Spatial evolution of the tunnel spectra are simulated by combining the Usadel equations and the theory of dynamic Coulomb blockade. With reducing the distance between the islands, the proximity effect around each overlaps and forms a Josephson junction. Thanks to the tunneling spectroscopy, number, position, the spectrum and the form of Josephson vortex cores are studied in detail for a large variety of junctions
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