TY - JOUR AB - Superconductor/semiconductor hybrid devices have attracted increasing interest in the past years. Superconducting electronics aims to complement semiconductor technology, while hybrid architectures are at the forefront of new ideas such as topological superconductivity and protected qubits. In this work, we engineer the induced superconductivity in two-dimensional germanium hole gas by varying the distance between the quantum well and the aluminum. We demonstrate a hard superconducting gap and realize an electrically and flux tunable superconducting diode using a superconducting quantum interference device (SQUID). This allows to tune the current phase relation (CPR), to a regime where single Cooper pair tunneling is suppressed, creating a sin(2y) CPR. Shapiro experiments complement this interpretation and the microwave drive allows to create a diode with ≈ 100% efficiency. The reported results open up the path towards integration of spin qubit devices, microwave resonators and (protected) superconducting qubits on the same silicon technology compatible platform. AU - Valentini, Marco AU - Sagi, Oliver AU - Baghumyan, Levon AU - de Gijsel, Thijs AU - Jung, Jason AU - Calcaterra, Stefano AU - Ballabio, Andrea AU - Aguilera Servin, Juan L AU - Aggarwal, Kushagra AU - Janik, Marian AU - Adletzberger, Thomas AU - Seoane Souto, Rubén AU - Leijnse, Martin AU - Danon, Jeroen AU - Schrade, Constantin AU - Bakkers, Erik AU - Chrastina, Daniel AU - Isella, Giovanni AU - Katsaros, Georgios ID - 14793 JF - Nature Communications TI - Parity-conserving Cooper-pair transport and ideal superconducting diode in planar germanium VL - 15 ER - TY - GEN AB - Superconductor/semiconductor hybrid devices have attracted increasing interest in the past years. Superconducting electronics aims to complement semiconductor technology, while hybrid architectures are at the forefront of new ideas such as topological superconductivity and protected qubits. In this work, we engineer the induced superconductivity in two-dimensional germanium hole gas by varying the distance between the quantum well and the aluminum. We demonstrate a hard superconducting gap and realize an electrically and flux tunable superconducting diode using a superconducting quantum interference device (SQUID). This allows to tune the current phase relation (CPR), to a regime where single Cooper pair tunneling is suppressed, creating a $ \sin \left( 2 \varphi \right)$ CPR. Shapiro experiments complement this interpretation and the microwave drive allows to create a diode with $ \approx 100 \%$ efficiency. The reported results open up the path towards monolithic integration of spin qubit devices, microwave resonators and (protected) superconducting qubits on a silicon technology compatible platform. AU - Valentini, Marco AU - Sagi, Oliver AU - Baghumyan, Levon AU - Gijsel, Thijs de AU - Jung, Jason AU - Calcaterra, Stefano AU - Ballabio, Andrea AU - Servin, Juan Aguilera AU - Aggarwal, Kushagra AU - Janik, Marian AU - Adletzberger, Thomas AU - Souto, Rubén Seoane AU - Leijnse, Martin AU - Danon, Jeroen AU - Schrade, Constantin AU - Bakkers, Erik AU - Chrastina, Daniel AU - Isella, Giovanni AU - Katsaros, Georgios ID - 13312 KW - Mesoscale and Nanoscale Physics T2 - arXiv TI - Radio frequency driven superconducting diode and parity conserving Cooper pair transport in a two-dimensional germanium hole gas ER - TY - THES AB - Semiconductor-superconductor hybrid systems are the harbour of many intriguing mesoscopic phenomena. This material combination leads to spatial variations of the superconducting properties, which gives rise to Andreev bound states (ABSs). Some of these states might exhibit remarkable properties that render them highly desirable for topological quantum computing. The most prominent and hunted of such states are Majorana zero modes (MZMs), quasiparticles equals to their own quasiparticles that they follow non-abelian statistics. In this thesis, we first introduce the general framework of such hybrid systems and, then, we unveil a series of mesoscopic phenomena that we discovered. Firstly, we show tunneling spectroscopy experiments on full-shell nanowires (NWs) showing that unwanted quantum-dot states coupled to superconductors (Yu-Shiba-Rusinov states) can mimic MZMs signatures. Then, we introduce a novel protocol which allowed the integration of tunneling spectroscopy with Coulomb spectroscopy within the same device. Employing this approach on both full-shell NWs and partial-shell NWs, we demonstrated that longitudinally confined states reveal charge transport phenomenology similar to the one expected for MZMs. These findings shed light on the intricate interplay between superconductivity and quantum confinement, which brought us to explore another material platform, i.e. a two-dimensional Germanium hole gas. After developing a robust way to induce superconductivity in such system, we showed how to engineer the proximity effect and we revealed a superconducting hard gap. Finally, we created a superconducting radio frequency driven ideal diode and a generator of non-sinusoidal current-phase relations. Our results open the path for the exploration of protected superconducting qubits and more complex hybrid devices in planar Germanium, like Kitaev chains and hybrid qubit devices. AU - Valentini, Marco ID - 13286 SN - 2663 - 337X TI - Mesoscopic phenomena in hybrid semiconductor-superconductor nanodevices : From full-shell nanowires to two-dimensional hole gas in germanium ER - TY - JOUR AB - Hybrid semiconductor–superconductor devices hold great promise for realizing topological quantum computing with Majorana zero modes1,2,3,4,5. However, multiple claims of Majorana detection, based on either tunnelling6,7,8,9,10 or Coulomb blockade (CB) spectroscopy11,12, remain disputed. Here we devise an experimental protocol that allows us to perform both types of measurement on the same hybrid island by adjusting its charging energy via tunable junctions to the normal leads. This method reduces ambiguities of Majorana detections by checking the consistency between CB spectroscopy and zero-bias peaks in non-blockaded transport. Specifically, we observe junction-dependent, even–odd modulated, single-electron CB peaks in InAs/Al hybrid nanowires without concomitant low-bias peaks in tunnelling spectroscopy. We provide a theoretical interpretation of the experimental observations in terms of low-energy, longitudinally confined island states rather than overlapping Majorana modes. Our results highlight the importance of combined measurements on the same device for the identification of topological Majorana zero modes. AU - Valentini, Marco AU - Borovkov, Maksim AU - Prada, Elsa AU - Martí-Sánchez, Sara AU - Botifoll, Marc AU - Hofmann, Andrea C AU - Arbiol, Jordi AU - Aguado, Ramón AU - San-Jose, Pablo AU - Katsaros, Georgios ID - 12118 IS - 7940 JF - Nature KW - Multidisciplinary SN - 0028-0836 TI - Majorana-like Coulomb spectroscopy in the absence of zero-bias peaks VL - 612 ER - TY - DATA AB - This .zip File contains the transport data, the codes for the data analysis, the microscopy analysis and the codes for the theoretical simulations for "Majorana-like Coulomb spectroscopy in the absence of zero bias peaks" by M. Valentini, et. al. The transport data are saved with hdf5 file format. The files can be open with the log browser of Labber. AU - Valentini, Marco AU - San-Jose, Pablo AU - Arbiol, Jordi AU - Marti-Sanchez, Sara AU - Botifoll, Marc ID - 12522 TI - Data for "Majorana-like Coulomb spectroscopy in the absence of zero bias peaks" ER - TY - JOUR AB - A semiconducting nanowire fully wrapped by a superconducting shell has been proposed as a platform for obtaining Majorana modes at small magnetic fields. In this study, we demonstrate that the appearance of subgap states in such structures is actually governed by the junction region in tunneling spectroscopy measurements and not the full-shell nanowire itself. Short tunneling regions never show subgap states, whereas longer junctions always do. This can be understood in terms of quantum dots forming in the junction and hosting Andreev levels in the Yu-Shiba-Rusinov regime. The intricate magnetic field dependence of the Andreev levels, through both the Zeeman and Little-Parks effects, may result in robust zero-bias peaks—features that could be easily misinterpreted as originating from Majorana zero modes but are unrelated to topological superconductivity. AU - Valentini, Marco AU - Peñaranda, Fernando AU - Hofmann, Andrea C AU - Brauns, Matthias AU - Hauschild, Robert AU - Krogstrup, Peter AU - San-Jose, Pablo AU - Prada, Elsa AU - Aguado, Ramón AU - Katsaros, Georgios ID - 8910 IS - 6550 JF - Science SN - 00368075 TI - Nontopological zero-bias peaks in full-shell nanowires induced by flux-tunable Andreev states VL - 373 ER - TY - DATA AB - This .zip File contains the transport data for "Non-topological zero bias peaks in full-shell nanowires induced by flux tunable Andreev states" by M. Valentini, et. al. The measurements were done using Labber Software and the data is stored in the hdf5 file format. Instructions of how to read the data are in "Notebook_Valentini.pdf". AU - Valentini, Marco ID - 9389 TI - Research data for "Non-topological zero bias peaks in full-shell nanowires induced by flux tunable Andreev states" ER -