David Goldhaber-Gordon, Postdoctoral Faculty Sponsor
Role of a capping layer on the crystalline structure of Sn thin films grown at cryogenic temperatures on InSb substrates.
Metal deposition with cryogenic cooling is a common technique in the condensed matter community for producing ultra-thin epitaxial superconducting layers on semiconductors. However, a significant challenge arises when these films return to room temperature, as they tend to undergo dewetting. This issue can be mitigated by capping the films with an amorphous layer. In this study, we investigate the influence of different in-situ fabricated caps on the structural characteristics of Sn thin films deposited at 80 K on InSb substrates. Regardless of the type of capping, we consistently observe that the films remain smooth upon returning to room temperature and exhibit epitaxy on InSb in the cubic Sn (α-Sn) phase. Notably, we identify a correlation between alumina capping using an electron beam evaporator and an increased presence of tetragonal Sn (β-Sn) grains. This suggests that heating from the alumina source may induce a partial phase transition in the Sn layer. The existence of the β-Sn phase induces superconducting behavior of the films by percolation effect. This study highlights the potential for tailoring the structural properties of cryogenic Sn thin films through in-situ capping. This development opens avenues for precise control in the production of superconducting Sn films, facilitating their integration into quantum computing platforms.
View details for DOI 10.1088/1361-6528/ad079e
View details for PubMedID 37890472
- Electronic structure of InSb (001), (110), and (111)B surfaces (vol 41, 032808, 2023) JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 2023; 41 (5)
Gate-tunable superconducting diode effect in a three-terminal Josephson device.
2023; 14 (1): 3078
The phenomenon of non-reciprocal critical current in a Josephson device, termed the Josephson diode effect, has garnered much recent interest. Realization of the diode effect requires inversion symmetry breaking, typically obtained by spin-orbit interactions. Here we report observation of the Josephson diode effect in a three-terminal Josephson device based upon an InAs quantum well two-dimensional electron gas proximitized by an epitaxial aluminum superconducting layer. We demonstrate that the diode efficiency in our devices can be tuned by a small out-of-plane magnetic field or by electrostatic gating. We show that the Josephson diode effect in these devices is a consequence of the artificial realization of a current-phase relation that contains higher harmonics. We also show nonlinear DC intermodulation and simultaneous two-signal rectification, enabled by the multi-terminal nature of the devices. Furthermore, we show that the diode effect is an inherent property of multi-terminal Josephson devices, establishing an immediately scalable approach by which potential applications of the Josephson diode effect can be realized, agnostic to the underlying material platform. These Josephson devices may also serve as gate-tunable building blocks in designing topologically protected qubits.
View details for DOI 10.1038/s41467-023-38856-0
View details for PubMedID 37248246
- Electronic structure of InSb (001), (110), and (111)B surfaces JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 2023; 41 (3)
- Epitaxial growth, magnetoresistance, and electronic band structure of GdSb magnetic semimetal films PHYSICAL REVIEW MATERIALS 2022; 6 (12)
Selective control of conductance modes in multi-terminal Josephson junctions.
2022; 13 (1): 5933
The Andreev bound state spectra of multi-terminal Josephson junctions form an artificial band structure, which is predicted to host tunable topological phases under certain conditions. However, the number of conductance modes between the terminals of a multi-terminal Josephson junction must be few in order for this spectrum to be experimentally accessible. In this work, we employ a quantum point contact geometry in three-terminal Josephson devices to demonstrate independent control of conductance modes between each pair of terminals and access to the single-mode regime coexistent with the presence of superconducting coupling. These results establish a full platform on which to realize tunable Andreev bound state spectra in multi-terminal Josephson junctions.
View details for DOI 10.1038/s41467-022-33682-2
View details for PubMedID 36209199
Supercurrent parity meter in a nanowire Cooper pair transistor
2022; 8 (16): eabm9896
We study a Cooper pair transistor realized by two Josephson weak links that enclose a superconducting island in an InSb-Al hybrid nanowire. When the nanowire is subject to a magnetic field, isolated subgap levels arise in the superconducting island and, because of the Coulomb blockade, mediate a supercurrent by coherent cotunneling of Cooper pairs. We show that the supercurrent resulting from such cotunneling events exhibits, for low to moderate magnetic fields, a phase offset that discriminates even and odd charge ground states on the superconducting island. Notably, this phase offset persists when a subgap state approaches zero energy and, based on theoretical considerations, permits parity measurements of subgap states by supercurrent interferometry. Such supercurrent parity measurements could, in a series of experiments, provide an alternative approach for manipulating and protecting quantum information stored in the isolated subgap levels of superconducting islands.
View details for DOI 10.1126/sciadv.abm9896
View details for Web of Science ID 000786214100033
View details for PubMedID 35452283
View details for PubMedCentralID PMC9032955
- In-plane selective area InSb-Al nanowire quantum networks (vol 3, 59, 2020) COMMUNICATIONS PHYSICS 2021; 4 (1)
- Mechanism for embedded in-plane self-assembled nanowire formation PHYSICAL REVIEW MATERIALS 2020; 4 (6)
- In-plane selective area InSb-Al nanowire quantum networks COMMUNICATIONS PHYSICS 2020; 3 (1)
- Transport studies in a gate-tunable three-terminal Josephson junction PHYSICAL REVIEW B 2020; 101 (5)
- Selective-area chemical beam epitaxy of in-plane InAs one-dimensional channels grown on InP(001), InP(111)B, and InP(011) surfaces PHYSICAL REVIEW MATERIALS 2019; 3 (8)
- Contribution of top barrier materials to high mobility in near-surface InAs quantum wells grown on GaSb(001) PHYSICAL REVIEW MATERIALS 2019; 3 (1)
Parity transitions in the superconducting ground state of hybrid InSb-Al Coulomb islands
2018; 9: 4801
The number of electrons in small metallic or semiconducting islands is quantised. When tunnelling is enabled via opaque barriers this number can change by an integer. In superconductors the addition is in units of two electron charges (2e), reflecting that the Cooper pair condensate must have an even parity. This ground state (GS) is foundational for all superconducting qubit devices. Here, we study a hybrid superconducting-semiconducting island and find three typical GS evolutions in a parallel magnetic field: a robust 2e-periodic even-parity GS, a transition to a 2e-periodic odd-parity GS, and a transition from a 2e- to a 1e-periodic GS. The 2e-periodic odd-parity GS persistent in gate-voltage occurs when a spin-resolved subgap state crosses zero energy. For our 1e-periodic GSs we explicitly show the origin being a single zero-energy state gapped from the continuum, i.e., compatible with an Andreev bound states stabilized at zero energy or the presence of Majorana zero modes.
View details for DOI 10.1038/s41467-018-07279-7
View details for Web of Science ID 000450161100001
View details for PubMedID 30442935
View details for PubMedCentralID PMC6237907
- Electric field tunable superconductor-semiconductor coupling in Majorana nanowires NEW JOURNAL OF PHYSICS 2018; 20
- Interface formation of epitaxial MgO/Co2MnSi(001) structures: Elemental segregation and oxygen migration JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 2017; 444: 383-389
Ultrawide thermal free-carrier tuning of dielectric antennas coupled to epsilon-near-zero substrates
2017; 8: 472
The principal challenge for achieving reconfigurable optical antennas and metasurfaces is the need to generate continuous and large tunability of subwavelength, low-Q resonators. We demonstrate continuous and steady-state refractive index tuning at mid-infrared wavelengths using temperature-dependent control over the low-loss plasma frequency in III-V semiconductors. In doped InSb we demonstrate nearly two-fold increase in the electron effective mass leading to a positive refractive index shift (Δn > 1.5) that is an order of magnitude greater than conventional thermo-optic effects. In undoped films we demonstrate more than 10-fold change in the thermal free-carrier concentration producing a near-unity negative refractive index shift. Exploiting both effects within a single resonator system-intrinsic InSb wires on a heavily doped (epsilon-near-zero) InSb substrate-we demonstrate dynamically steady-state tunable Mie resonances. The observed line-width resonance shifts (Δλ > 1.7 μm) suggest new avenues for highly tunable and steady-state mid-infrared semiconductor antennas.Achieving large tunability of subwavelength resonators is a central challenge in nanophotonics. Here the authors demonstrate refractive index tuning at mid-infrared wavelengths using temperature-dependent control over the low loss plasma frequency in III-V semiconductors.
View details for DOI 10.1038/s41467-017-00615-3
View details for Web of Science ID 000409997500006
View details for PubMedID 28883391
View details for PubMedCentralID PMC5589832
- Electrically Reconfigurable Metasurfaces Using Heterojunction Resonators ADVANCED OPTICAL MATERIALS 2016; 4 (10): 1582-1588