All Publications

  • Phase-Selective Synthesis of Rhombohedral WS2 Multilayers by Confined-Space Hybrid Metal-Organic Chemical Vapor Deposition. Nano letters Zhang, Z., Hocking, M., Peng, Z., Pendharkar, M., Courtney, E. D., Hu, J., Kastner, M. A., Goldhaber-Gordon, D., Heinz, T. F., Mannix, A. J. 2024

    Abstract

    Rhombohedral polytype transition metal dichalcogenide (TMDC) multilayers exhibit non-centrosymmetric interlayer stacking, which yields intriguing properties such as ferroelectricity, a large second-order susceptibility coefficient χ(2), giant valley coherence, and a bulk photovoltaic effect. These properties have spurred significant interest in developing phase-selective growth methods for multilayer rhombohedral TMDC films. Here, we report a confined-space, hybrid metal-organic chemical vapor deposition method that preferentially grows 3R-WS2 multilayer films with thickness up to 130 nm. We confirm the 3R stacking structure via polarization-resolved second-harmonic generation characterization and the 3-fold symmetry revealed by anisotropic H2O2 etching. The multilayer 3R WS2 shows a dendritic morphology, which is indicative of diffusion-limited growth. Multilayer regions with large, stepped terraces enable layer-resolved evaluation of the optical properties of 3R-WS2 via Raman, photoluminescence, and differential reflectance spectroscopy. These measurements confirm the interfacial quality and suggest ferroelectric modification of the exciton energies.

    View details for DOI 10.1021/acs.nanolett.4c02766

    View details for PubMedID 39373237

  • Deterministic fabrication of graphene hexagonal boron nitride moire superlattices. Proceedings of the National Academy of Sciences of the United States of America Kamat, R. V., Sharpe, A. L., Pendharkar, M., Hu, J., Tran, S. J., Zaborski, G. J., Hocking, M., Finney, J., Watanabe, K., Taniguchi, T., Kastner, M. A., Mannix, A. J., Heinz, T., Goldhaber-Gordon, D. 2024; 121 (40): e2410993121

    Abstract

    The electronic properties of moire heterostructures depend sensitively on the relative orientation between layers of the stack. For example, near-magic-angle twisted bilayer graphene (TBG) commonly shows superconductivity, yet a TBG sample with one of the graphene layers rotationally aligned to a hexagonal Boron Nitride (hBN) cladding layer provided experimental observation of orbital ferromagnetism. To create samples with aligned graphene/hBN, researchers often align edges of exfoliated flakes that appear straight in optical micrographs. However, graphene or hBN can cleave along either zig-zag or armchair lattice directions, introducing a [Formula: see text] ambiguity in the relative orientation of two flakes. By characterizing the crystal lattice orientation of exfoliated flakes prior to stacking using Raman and second-harmonic generation for graphene and hBN, respectively, we unambiguously align monolayer graphene to hBN at a near-[Formula: see text], not [Formula: see text], relative twist angle. We confirm this alignment by torsional force microscopy of the graphene/hBN moire on an open-face stack, and then by cryogenic transport measurements, after full encapsulation with a second, nonaligned hBN layer. This work demonstrates a key step toward systematically exploring the effects of the relative twist angle between dissimilar materials within moire heterostructures.

    View details for DOI 10.1073/pnas.2410993121

    View details for PubMedID 39331413

  • Quantitative determination of twist angle and strain in Van der Waals moiré superlattices APPLIED PHYSICS LETTERS Tran, S. J., Uslu, J., Pendharkar, M., Finney, J., Sharpe, A. L., Hocking, M., Bittner, N. J., Watanabe, K., Taniguchi, T., Kastner, M. A., Mannix, A. J., Goldhaber-Gordon, D. 2024; 125 (11)

    View details for DOI 10.1063/5.0223777

    View details for Web of Science ID 001313187100002

  • Thermal relaxation of strain and twist in ferroelectric hexagonal boron nitride moiré interfaces JOURNAL OF APPLIED PHYSICS Hocking, M., Henzinger, C. E., Tran, S. J., Pendharkar, M., Bittner, N. J., Watanabe, K., Taniguchi, T., Goldhaber-Gordon, D., Mannix, A. J. 2024; 136 (2)

    View details for DOI 10.1063/5.0210112

    View details for Web of Science ID 001272420800003

  • Torsional force microscopy of van der Waals moirés and atomic lattices. Proceedings of the National Academy of Sciences of the United States of America Pendharkar, M., Tran, S. J., Zaborski, G., Finney, J., Sharpe, A. L., Kamat, R. V., Kalantre, S. S., Hocking, M., Bittner, N. J., Watanabe, K., Taniguchi, T., Pittenger, B., Newcomb, C. J., Kastner, M. A., Mannix, A. J., Goldhaber-Gordon, D. 2024; 121 (10): e2314083121

    Abstract

    In a stack of atomically thin van der Waals layers, introducing interlayer twist creates a moiré superlattice whose period is a function of twist angle. Changes in that twist angle of even hundredths of a degree can dramatically transform the system's electronic properties. Setting a precise and uniform twist angle for a stack remains difficult; hence, determining that twist angle and mapping its spatial variation is very important. Techniques have emerged to do this by imaging the moiré, but most of these require sophisticated infrastructure, time-consuming sample preparation beyond stack synthesis, or both. In this work, we show that torsional force microscopy (TFM), a scanning probe technique sensitive to dynamic friction, can reveal surface and shallow subsurface structure of van der Waals stacks on multiple length scales: the moirés formed between bi-layers of graphene and between graphene and hexagonal boron nitride (hBN) and also the atomic crystal lattices of graphene and hBN. In TFM, torsional motion of an Atomic Force Microscope (AFM) cantilever is monitored as it is actively driven at a torsional resonance while a feedback loop maintains contact at a set force with the sample surface. TFM works at room temperature in air, with no need for an electrical bias between the tip and the sample, making it applicable to a wide array of samples. It should enable determination of precise structural information including twist angles and strain in moiré superlattices and crystallographic orientation of van der Waals flakes to support predictable moiré heterostructure fabrication.

    View details for DOI 10.1073/pnas.2314083121

    View details for PubMedID 38427599

  • Tuning the band topology of GdSb by epitaxial strain APL MATERIALS Inbar, H. S., Ho, D. Q., Chatterjee, S., Engel, A. N., Khalid, S., Dempsey, C. P., Pendharkar, M., Chang, Y., Nishihaya, S., Fedorov, A. V., Lu, D., Hashimoto, M., Read, D., Janotti, A., Palmstrom, C. J. 2023; 11 (11)

    View details for DOI 10.1063/5.0155218

    View details for Web of Science ID 001123168300001

  • Role of a capping layer on the crystalline structure of Sn thin films grown at cryogenic temperatures on InSb substrates. Nanotechnology Chen, A. H., Dempsey, C., Pendharkar, M., Sharma, A., Zhang, B., Tan, S., Bellon, L., Frolov, S. M., Palmstrøm, C. J., Bellet-Amalric, E., Hocevar, M. 2023

    Abstract

    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 Dong, J. T., Inbar, H. S., Pendharkar, M., van Schijndel, T. J., Young, E. C., Dempsey, C. P., Palmstrom, C. J. 2023; 41 (5)

    View details for DOI 10.1116/6.0002960

    View details for Web of Science ID 001045985800002

  • Gate-tunable superconducting diode effect in a three-terminal Josephson device. Nature communications Gupta, M., Graziano, G. V., Pendharkar, M., Dong, J. T., Dempsey, C. P., Palmstrom, C., Pribiag, V. S. 2023; 14 (1): 3078

    Abstract

    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 Dong, J. T., Inbar, H. S., Pendharkar, M., van Schijndel, T. J., Young, E. C., Dempsey, C. P., Palmstrom, C. J. 2023; 41 (3)

    View details for DOI 10.1116/6.0002606

    View details for Web of Science ID 000984104900001

  • Epitaxial growth, magnetoresistance, and electronic band structure of GdSb magnetic semimetal films PHYSICAL REVIEW MATERIALS Inbar, H. S., Ho, D. Q., Chatterjee, S., Pendharkar, M., Engel, A. N., Dong, J. T., Khalid, S., Chang, Y., Guo, T., Fedorov, A., Lu, D., Hashimoto, M., Read, D., Janotti, A., Palmstrom, C. J. 2022; 6 (12)

    View details for DOI 10.1103/PhysRevMaterials.6.L121201

    View details for Web of Science ID 000898121500003

  • Selective control of conductance modes in multi-terminal Josephson junctions. Nature communications Graziano, G. V., Gupta, M., Pendharkar, M., Dong, J. T., Dempsey, C. P., Palmstrøm, C., Pribiag, V. S. 2022; 13 (1): 5933

    Abstract

    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 SCIENCE ADVANCES Wang, J., Schrade, C., Levajac, V., van Driel, D., Li, K., Gazibegovic, S., Badawy, G., Veld, R., Lee, J., Pendharkar, M., Dempsey, C. P., Palmstrom, C. J., Bakkers, E. M., Fu, L., Kouwenhoven, L. P., Shen, J. 2022; 8 (16): eabm9896

    Abstract

    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 Op Het Veld, R. M., Xu, D., Schaller, V., Verheijen, M. A., Peters, S. E., Jung, J., Tong, C., Wang, Q., de Moor, M. A., Hesselmann, B., Vermeulen, K., Bommer, J. S., Lee, J., Sarikov, A., Pendharkar, M., Marzegalli, A., Koelling, S., Kouwenhoven, L. P., Miglio, L., Palmstrom, C. J., Zhang, H., Bakkers, E. M. 2021; 4 (1)

    View details for DOI 10.1038/s42005-021-00578-4

    View details for Web of Science ID 000632398000001

  • Mechanism for embedded in-plane self-assembled nanowire formation PHYSICAL REVIEW MATERIALS Wilson, N. S., Kraemer, S., Pennachio, D. J., Callahan, P., Pendharkar, M., Palmstrom, C. J. 2020; 4 (6)

    View details for DOI 10.1103/PhysRevMaterials.4.066003

    View details for Web of Science ID 000540668400002

  • In-plane selective area InSb-Al nanowire quantum networks COMMUNICATIONS PHYSICS Veld, R., Xu, D., Schaller, V., Verheijen, M. A., Peters, S. E., Jung, J., Tong, C., Wang, Q., de Moor, M. A., Hesselmann, B., Vermeulen, K., Bommer, J. S., Lee, J., Sarikov, A., Pendharkar, M., Marzegalli, A., Koelling, S., Kouwenhoven, L. P., Miglio, L., Palmstrom, C. J., Zhang, H., Bakkers, E. M. 2020; 3 (1)

    View details for DOI 10.1038/s42005-020-0324-4

    View details for Web of Science ID 000521832000001

  • Transport studies in a gate-tunable three-terminal Josephson junction PHYSICAL REVIEW B Graziano, G., Lee, J., Pendharkar, M., Palmstrom, C., Pribiag, V. S. 2020; 101 (5)

    View details for DOI 10.1103/PhysRevB.101.054510

    View details for Web of Science ID 000515608100004

  • 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 Lee, J., Choi, S., Pendharkar, M., Pennachio, D. J., Markman, B., Seas, M., Koelling, S., Verheijen, M. A., Casparis, L., Petersson, K. D., Petkovic, I., Schaller, V., Rodwell, M. W., Marcus, C. M., Krogstrup, P., Kouwenhoven, L. P., Bakkers, E. M., Palmstrom, C. J. 2019; 3 (8)

    View details for DOI 10.1103/PhysRevMaterials.3.084606

    View details for Web of Science ID 000482589300003

  • Contribution of top barrier materials to high mobility in near-surface InAs quantum wells grown on GaSb(001) PHYSICAL REVIEW MATERIALS Lee, J., Shojaei, B., Pendharkar, M., Feldman, M., Mukherjee, K., Palmstrom, C. J. 2019; 3 (1)

    View details for DOI 10.1103/PhysRevMaterials.3.014603

    View details for Web of Science ID 000455689900003

  • Parity transitions in the superconducting ground state of hybrid InSb-Al Coulomb islands NATURE COMMUNICATIONS Shen, J., Heedt, S., Borsoi, F., van Heck, B., Gazibegovic, S., Veld, R., Car, D., Logan, J. A., Pendharkar, M., Ramakers, S. J., Wang, G., Xu, D., Bouman, D., Geresdi, A., Palmstrom, C. J., Bakkers, E. M., Kouwenhoven, L. P. 2018; 9: 4801

    Abstract

    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 de Moor, M. A., Bommer, J. S., Xu, D., Winkler, G. W., Antipov, A. E., Bargerbos, A., Wang, G., van Loo, N., Veld, R., Gazibegovic, S., Car, D., Logan, J. A., Pendharkar, M., Lee, J., Bakkers, E. M., Palmstrom, C. J., Lutchyn, R. M., Kouwenhoven, L. P., Zhang, H. 2018; 20

    View details for DOI 10.1088/1367-2630/aae61d

    View details for Web of Science ID 000448991200008

  • Interface formation of epitaxial MgO/Co2MnSi(001) structures: Elemental segregation and oxygen migration JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS McFadden, A., Wilson, N., Brown-Heft, T., Pennachio, D., Pendharkar, M., Logan, J. A., Palmstrom, C. J. 2017; 444: 383-389

    View details for DOI 10.1016/j.jmmm.2017.08.027

    View details for Web of Science ID 000413147400060

  • Ultrawide thermal free-carrier tuning of dielectric antennas coupled to epsilon-near-zero substrates NATURE COMMUNICATIONS Iyer, P. P., Pendharkar, M., Palmstrom, C. J., Schuller, J. A. 2017; 8: 472

    Abstract

    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 Iyer, P. P., Pendharkar, M., Schuller, J. A. 2016; 4 (10): 1582-1588

    View details for DOI 10.1002/adom.201600297

    View details for Web of Science ID 000386356900018

https://orcid.org/0000-0003-1857-6131