Rami Dana -Research statement

Rami Dana - Research statement Research Background General: I have a complete experience in the design, purchase, assembly, testing and operation of experimental systems, versatile lab experience from UHV to cryogenics to fabrication to measurement techniques and data analysis. My interest lies in the broad field of condense matter, specifically, a record in surface science and characterization. M.sc: My M.sc thesis describes the fractal nature of islands in submonolayer near coverage of  = 0.5. The islands where formed by ripening and coalescence after starting from a random distribution of the atoms and heating the substrate [1]. In my work I compare between scanning tunneling microscope (STM) experimental results of silicon island on si(111) 7x7 and Monte Carlo simulations on a new Conservative Ising Model with Kawasaki dynamics[2] and curvature effect. See left image - bottom. PhD: My PhD thesis has two parts; STM realization of finite-size misfit in homoepitaxy [3] and a dual-tip STM (DTSTM) for the characterization of mesoscopic transport on surfaces [4]. The finite-size misfit was used to explain the shape transition of homoepitaxial silicon islands above the percolation threshold as predicted by the Linear Chain Model (LCM) [5]. See left image - top. The motivation to characterize surface transport on the mesoscale was in the heart of a new approach for a dual-tip STM. The design was based on the mechanically controllable break-junction (MCBJ) with two electron- beam induced deposition nano-tips. See center image. PostDoc projects: a) Single donors near Silicon surfaces as candidates for quantum qubits. b) Search for Majorana Fermions in Topological Insulators (TI) - Superconductors (SC) heterostructures. One interesting result is the realization of p(E) [6] theory in SIS junction between SC Nb tip [7] and proximity induced SC on the surface of the TI Bi2Se3 [8]. See right image - top. Current work - For the last two years I was working with a dilution refrigerator equipped with a single/dual tip mK-STM [9] and 13.5 T magnetic fields. I was looking for Majorana Fermions in condense matter physics by using normal Tungsten or SC Nb tips on the TI Bi2Se3 or the SC TI Cu0.2Bi2Se3. My recent results are evidence for the effect of vortexes on the sub-gap spectrum of Cu0.2Bi2Se3. Here I found the appearance of a zero-bias conductance peak at the vortex core (and edge) when the SC gap is closed [10]. See right image - bottom.

Virtual pivot Vertical spring Horizontal spring

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Left: Top – model [5] & Bottom - transition from compact (green) to ramified (purple) to linear chains (pink) both in experiment and simulation. Center: Top - DTSTM model to measure trans-conductance current [11], center new design for a MCBJ-DTSTM with virtual pivot & Bottom - two induced deposition tips on both sides of the DTSTM. Right: Top - P(E) applied to proximity induced SIS junction, center - STM image of Cu0.2Bi2Se3 & Bottom – ZBCP at the center (left), center and edge (right) of a vortex when the SC gap is closed.

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Main fields of interest Topological Insulators - Predicted in 2007 [12] and experimentally evident since 2008 [13] TIs are a subject to much theoretical and experimental work. Their possible host for Majorana Fermions in condenses matter as hetero-structures with SC or as topological SC (TSC, for example Cu0.2Bi2Se3) and the better understanding of their properties are in the heart of the motivation. I have already worked with the following samples and established collaborations with groups that make and can supply it. Bi2Se3 (Yong P. Chen, Purdue) as TI and TSC by growing Nb islands or inducing SC with Nb tips. CuxBi2Se3 as TSC, both as grown by the Bridgman method (Yong P. Chen, Purdue) or by electro-chemically intercalating Cu (self-made). NbxBi2Se3 (Hor, Yew San, MST) as TSC. Exploring the fine sub-gap structure in these samples, and identifies set-ups as candidates to host Majorana fermions. See left image. Quantum transport – Exploring quantum- dots, quantum point contact, Kondo effect, Coulomb blocked and more, specifically, SC quantum dot in S-QD-TSC junctions. I have preliminary results showing the effect of coupling between a SC tip and SC quantum dot on the sub-gap structure. See center image. Superconductivity - SC in different materials, specifically in TSC, the nature and use of SC tips and induced SC (also by SC islands) to form Josephson junctions in STM. Using of microwave response to characterize the carriers in these junctions. See right image. Surface science techniques – From characterization to manipulation to fabrication to the development of new tools, specifically, multi-probe SPM. I already designed a dual-tip version for low-temperature STM Trans-conductance on surfaces - Because a double-tip STM can probe the all-important single-particle Green function of a sample, it has the potential of becoming an extremely useful new tool in surface analysis. That was concluded by, Niu, Chang and Shih in their "Duble-tip scanning tunneling microscope for surface analysis" PRL paper from 1995 [11]. Niu et. al. had identified key experimental parameters for such measurements and described some basic applications of a double-tip STM: (1) probing the k-resolved band structure of surface states, as well as the shape of Bloch functions; (2) measuring scattering phase shifts or amplitude of surface defects; (3) observing transition from ballistic to diffusive transport to localization; and (4) measuring inelastic mean free paths. Research plane The lab - Build STM lab, preferably mK or 4.2 K, with sample preparation and characterization chambers including sputtering, e-beam evaporation, LEED and AUGER. I have all the blue print for that. Funds - apply for research grants based on the main fields of interest above. The emphasis will be on the new contribution that dual-tip STM can made, a challenge not fully encountered. Collaboration - Collaboration is needed in order to start from the relevant theory, prepare the best samples, use one or

Left – sub-gap spectrum taken on Cu0.2Bi2Se3 with Nb tip with 0.2 T magnetic field along different lines (top: fine structure, center: energy splitting, bottom: ZBCP). Center – Nb islands on Cu0.2Bi2Se3 dragged by the STM tip as seen by the before (top) and after (bottom) images. The spectrum along the blue and green lines in the top image showing a change in sub-gap structure probably due to coupling. Right– Microwave response at different AC voltages showing Cooper pairs as carriers in NB tip–Nb junction (top: data, center: simulation for 2e, bottom: simulation for e).

more characterization techniques to collect as much data as possible and analyze the to put it in the right context. Collaboration start at your department but can be expended to other department and institutions. Physicist, material scientists, chemists, clean room personal (MBE) and computer scientists can all be a part of an STM project. Innovation - To be at the front of your research field, it is not enough to reproduce. You need to come with new ideas, design new apparatus and “re-search” for new physical phenomena. Teaching - In order to have a highly functional lab, you need to start by training your own people. Teaching at the campus in general is an opportunity to have your effect on young student, a platform to introduce your field of interest and the best way to rethink, renew and simply learn. Students - The students are the hurt of your operation. I intend to have students from diverse backgrounds to address the different needs of STM lab. Some of the work involves; Theory, cad design, instrumentation and LabView, system assembly, UHV and cryogenic techniques, measurements and data analysis. Starting from small projects for undergraduates like; building electronic devices, designing UHV components, preparing samples or writing software. On to graduate students that can take over a project of exploring specific quantum transport phenomenon, characterizing a specific sample or developing new SPM technique. And, postdocs that can oversee system modification projects new sample preparations, theory and data analysis. STM is as challenging and interesting experimental technique as it gets and only the highest standards will result in a productive lab. It is a demanding environment that takes time, persistent, attention to details, resilience, expertise, knowledge, hard work, innovation and above all love for science. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Z. Olami, Y. Manassen, N. R. Rao and R. Dana, Fractalization of silicon islands at coverage close to 0.5 monolayers, Surf. Sci 520: 35, 2002 K. Kawasaki, In Phase Transition and Critical Phenomena, ed. By C. Domb, M. C. Green (Academic Press, New York 1972), Vol. 2, p. 443 R. Dana and Y. Manassen, Mesoscopic mismatch as a driving force for modified morphology above percolation, EuroPhys. Lett. 79: 16001, 2007 Rami Dana, Irina Kiruschev, Phong Dinh Tran, Pascal Doppelt, Yishay Manassen, Towards a Dual-Tip STM Application in Mesoscopic Electron Transport, Israel Journal of Chemistry 48: 87-97, 2008 J. Tersoff, R.M. Tromp, Phys. Rev. Lett. 70 (1993) 2782 G.-L. Ingold and H. Grabert, Phys. Rev. B 50 (1994) 39S Anita Roychowdhury, M. A. Gubrud, R. Dana, J. R. Anderson, C. J. Lobb, F. C. Wellstood, and M. Dreyer, A 30 mK, 13.5 T scanning tunneling microscope with two independent tips, Rev. Sci. Inst. 85, 043706 2014 Rami Dana et. al., SIS junction between Nb tip and proximity-induced superconductivity on the surface of Bi2Se3, to be submitted A. Roychowdhury, R. Dana, M. Dreyer, J. R. Anderson, C. J. Lobb and F. C. Wellstood, Plasma etching of superconducting Niobium tips for scanning tunneling microscopy, J. Appl. Phys. 116, 014308 (2014) Rami Dana et. al., Simultaneous ZBCP and gap closing on the surface of Cu0.2Bi2Se3 with 0.2T, to be submitted Q. Niu, M. C. Chang and C. K. shih, Phys. Rev. B, 51 (1995) 5502 L. Fu and C. L. Kane, Phys. Rev. B 76, 045302 2007 D. Hsieh, D. Qian, L. Wray, Y.Q. Xia, Y.S. Hor, R.J. Cava, M.Z. Hasan, Nature 452 (7190), 970-974