Condensed Matter

Enhancement of the Upper Critical Field in Disordered Transition Metal Dichalcogenide Monolayers

Stefan Ilic
Wednesday, June 13, 2018 - 2:30pm to 3:30pm

We calculate the effect of impurities on the superconducting phase diagram of transition metal dichalcogenide monolayers in the presence of an in-plane magnetic field. Because of strong intrinsic spin-orbit coupling, the upper critical field greatly surpasses the Pauli limit at low temperatures. We find that it is insensitive to intravalley scattering and, ultimately, limited by intervalley scattering.


Supercurrent in the quantum Hall regime

Gleb Finkelstein
Thursday, November 9, 2017 - 4:00pm

One of the promising routes towards creating novel topological states and excitations is to combine superconductivity and quantum Hall (QH) effect. However, signatures of superconductivity in the QH regime remain scarce, and a superconducting current through a QH weak link has so far eluded experimental observation. By utilizing high mobility graphene/boron nitride heterostructures we demonstrate the existence of a novel type of supercurrent-carrying states in a QH regime at magnetic fields as high as 2 Tesla. At low magnetic fields, devices demonstrate the Fraunhoffer pattern and Fabri-...

The Hall Effects Edwin Hall Never Imagined

Xiaofeng Jin
Thursday, September 14, 2017 - 4:30pm

The anomalous Hall Effect (AHE) is one of the oldest and most prominent transport phenomena in magnetic materials. However, the microscopic mechanism of the AHE has remained unresolved for more than a century because its rich phenomenology defies standard classification, prompting conflicting claims of the dominant processes. We differentiate these processes through temperature--‐dependent measurements on epitaxial Fe, Ni, Co, and NixCu1--‐x  Films of varying thickness [1],  [2]. The results allow an unambiguous identification of both intrinsic and extrinsic mechanisms of the anomalous...

Quantum Entanglement and the Geometry of Spacetime

Matthew Headrick
Monday, February 13, 2017 - 4:30pm to 6:00pm

Recent developments in the study of quantum gravity have revealed a surprising and beautiful connection between quantum entanglement and the geometry of spacetime. This discovery offers a new perspective on old puzzles concerning black holes, and may lead to a profoundly new way of thinking about the emergence of spacetime from fundamental quantum-mechanical building blocks. I will describe these developments, explaining along the way the necessary background in quantum gravity and quantum information theory.

Quantum Control of Spins in Silicon

Mark Eriksson
Monday, April 3, 2017 - 4:30pm to 5:30pm

One of the remarkable features of spins in the solid state is the enormous range of time-scales over which coherent manipulation is possible. If one considers gate-controlled manipulation of nuclear spins at one extreme, and strongly-interacting multi-electron qubits at the other extreme, coherent control of spins in semiconductors has been demonstrated with over 9 orders of magnitude variation in the manipulation time. Remarkably, confining three electrons in two neighboring quantum dots enables all electrical control and measurement of spin dynamics on time scales less...

Electromechanics: A New Quantum Technology

Konrad Lehnert
Monday, March 27, 2017 - 4:30pm to 5:30pm

Devices that combined electricity with moving parts were crucial to the very earliest electronic communications. Today, electromechanical structures are ubiquitous yet under-appreciated signal processing elements. These devices exploit the relative slowness of sound compared to light to create compact filter and clock elements. Moreover they convert force and acceleration signals into more easily processed electrical signals. Can these humble, apparently classical, objects exhibit genuinely quantum behavior? Indeed, by strongly coupling the vibrations of a...

From Conjectures to Paradigms: the Evolving Influence of Field Theory and Topology in Condensed Matter

Rajiv Singh
Monday, February 27, 2017 - 4:30pm to 5:30pm

The 2016 Nobel Prize in Physics to Kosterlitz, Thouless and Haldane honors a new set of ideas and theoretical formalism that has gradually become the mainstay of modern condensed matter thinking. Quantum Field Theory, Topology and the Renormalization Group, lie at the heart of present day theory of condensed matter. The Kosterlitz-Thouless theory of phase transitions and Haldane's conjecture on the spin dependence of spectrum of spin-chains were two of the most influential works in bringing these ideas together. These along with the Thouless-Kohmoto-Nightingale-Den Nijs-(TKNN) work on...

New Topological Phases and Effects in Solids

Joel Moore
Monday, January 30, 2017 - 4:30pm to 5:30pm

Much of condensed matter physics is concerned with understanding how different kinds of order emerge from interactions between a large number of simple constituents. In ordered phases such as crystals, magnets, and superfluids, the order is understood through "symmetry breaking": in a crystal, for example, the continuous symmetries of space under rotations and translations are not reflected in the ground state. A major discovery of the 1980s was that electrons confined to two dimensions and in a strong magnetic field exhibit a completely different, topological type of...

Condensed Matter and Materials Theory (CMMT)

  • By Aude Marjolin
  • 7 September 2016

CMMT supports theoretical and computational materials research in the topical areas represented in DMR's core or individual investigator programs, which include: Condensed Matter Physics (CMP), Biomaterials (BMAT), Ceramics (CER), Electronic and Photonic Materials (EPM), Metals and Metallic Nanostructures (MMN), Polymers (POL), and Solid State and Materials Chemistry (SSMC). The program supports fundamental research that advances the conceptual understanding of hard and soft materials, and materials-related phenomena; the development of associated analytical, computational, and data-centric techniques; as well as predictive materials-specific theory, simulation, and modeling for materials research.

Department of Physics and Astronomy, University of Pittsburgh
Ph.D., Physics, University of Pittsburgh, 2011

Owing to the recent development of material growth methods including the pulsed laser deposition (PLD) and molecular beam epitaxy (MBE), atomically sharp interfaces between materials become available. At these interfaces, the electron-electron interaction is greatly enhanced, leading to novel phases including metal-insulator transition,  superconductivity, magnetism and spin-orbit interaction.

A notable example is the (001) LaAlO3/SrTiO3 (LAO/STO) interface, where a polar discontinuity drives electronic interface reconstruction and leads to a 2D electron liquid (2DEL) at the interface. The interface conductivity is critically dependent on the LAO thickness. Below a critical thickness 4 unit cell the interface is insulating, otherwise the interface is conducting.

Since the discovery of the 2DEL in 2004[1], intense interests have been casted on this area.  Up to now, the knowledge on this interface is growing rapidly, and so do the debates. The 2DEL is gate tunable, with a critical LAO thickness dependence[2]. The interface is superconducting, an inherent property of STO[3, 4]. More interestingly, it has a similar superconducting phase diagram as the high-Tc superconductor. Although both LAO and STO are non-magnetic, the interface is magnetic[5, 6].  More interestingly, magnetism and superconductivity can co-exist[7-9]. Owing to the inversion symmetric breaking, the interface has strong tunable spin-orbit interaction[10, 11]. Provided all these interesting phases, we invented the conductive-AFM lithography method that allows us to fabricate nanostructures on demand, effectively programing all these properties into nanoscale. Indeed, it is fun to watch all these properties interplay at nanoscale.

  1. A. Ohtomo, and H. Y. Hwang, Nature 427, 423 (2004).
  2. S. Thiel et al., Science 313, 1942 (2006).
  3. N. Reyren et al., Science 317, 1196 (2007).
  4. A. D. Caviglia et al., Nature 456, 624 (2008).
  5. A. Brinkman et al., Nat Mater 6, 493 (2007).
  6. Ariando et al., Nature communications 2, 188 (2011).
  7. J. A. Bert et al., Nat Phys 7, 767 (2011).
  8. D. A. Dikin et al., Physical Review Letters 107 (2011).
  9. L. Li et al., Nat Phys advance on (2011).
  10. A. D. Caviglia et al., Physical Review Letters 104, 126803 (2010).
  11. M. Ben Shalom et al., Physical Review Letters 104, 126802 (2010).
Selected Publications: 
  • "Electron pairing without superconductivity," Guanglei Cheng, Michelle Tomczyk, Shicheng Lu, Josh P. Veazey, Mengchen Huang, Patrick Irvin, Sangwoo Ryu, Hyungwoo Lee, Chang-Beom, Eom, C. Steve Hellberg, Jeremy Levy, Nature 521,196 (2015)
  • "Writing and Low-Temperature Characterization of Oxide Nanostructures," Akash Levy, Feng Bi, Mengchen Huang, Shicheng Lu, Michelle Tomczyk, Guanglei Cheng, Patrick Irvin, Jeremy Levy, J. Vis. Exp. 89, e51886 (2014)
  • "Anomalous Transport in Sketched Oxide Nanostructures," Guanglei Cheng, Josh Veazey, Patrick Irvin, Cheng Cen, Daniel Bogorin, Feng Bi, Mengchen Huang, Chung-Wung Bark, Sangwoo Ryu, Kwang-Hwan Cho, Chang-Beom Eom and Jeremy Levy, Physcial Review X, 3, 011021 (2013)
Most Cited Publications
  1. "Sketched oxide single-electron transistor," Cheng, G., Siles, P.F., Bi, F., Cen, C., Bogorin, D.F., Bark, C.W, Folkman, C.M., et al,  Nature Nanotechnology 6, no. 6 (2011)
  2. "Electron pairing without superconductivity," Cheng, G., Tomczyk, M., Lu, S., Veazey, J.P., Huang, M., Irvin, P., Ryu, S., et al, Nature 521, no. 7551 (2015)
  3. "Anomalous high mobility in LaAlO3/SrTiO3 nanowires," Irvin, P., Veazy, J.P., Cheng, G., Lu, S., Bark, C.W., Ryu, S., Eom, C.B., Levy, J., Nano Letters 13, no. 2 (2013) 
  4. "Anomalous transport in sketched nanostructures at the LaAlO3/SrTiO3 interface," Cheng, G., Veazy, J.P., Irvin, P., Cen, C., Bogorin, D.F., Bi, F., Huang, M., et al, Physical Review X 3, no. 1 (2013)
  5. "Tunable electron-electron interactions in LaAlO3/SrTiO3 nanostructures," Cheng, G., Tomczyk, M., Tacla, A.B., Lee, H., Lu, S., Veazey, J.P., Huang, M., Irvin, P., Ryu, S., Eom, C.-B., Daley, A., Pekker, D., Levy, J. (2016) Physical Review X, 6 (4), art. no. 041042.
Recent Publications
  1. "Towards Oxide Electronics: a Roadmap," Coll M., Fontcuberta J., Althammer M., Bibes M., Boschker H., Calleja A., Cheng G., Cuoco M., Dittmann R., Dkhil B., El Baggari I., Fanciulli M., Fina I., Fortunato E., Frontera C., Fujita S., Garcia V., Goennenwein S.T.B., Granqvist C.-G., Grollier J., Gross R., Hagfeldt A., Herranz G., Hono K., Houwman E., Huijben M., Kalaboukhov A., Keeble D.J., Koster G., Kourkoutis L.F., Levy J., Lira-Cantu M., MacManus-Driscoll J.L., Mannhart J., Martins R., Menzel S., Mikolajick T., Napari M., Nguyen M.D., Niklasson G., Paillard C., Panigrahi S., Rijnders G., Sánchez F., Sanchis P., Sanna S., Schlom D.G., Schroeder U., Shen K.M., Siemon A., Spreitzer M., Sukegawa H., Tamayo R., van den Brink J., Pryds N., Granozio F.M. Applied Surface Science Vol. 482, 1-93 (2019).
  2. "Quantized Ballistic Transport of Electrons and Electron Pairs in LaAlO3/SrTiO3Nanowires." Anil Annadi, Guanglei Cheng, Hyungwoo Lee, Jung-Woo Lee, Shicheng Lu, Anthony Tylan-Tyler, Megan Briggeman, Michelle Tomczyk, Mengchen Huang, David Pekker, Chang-Beom Eom, Patrick Irvin, and Jeremy Levy. Nano Letters 18 (7), 4473-4481 (2018).
  3. "Graphene-Complex-Oxide Nanoscale Device Concepts." Giriraj Jnawali, Hyungwoo Lee, Jung-Woo Lee, Mengchen Huang, Jen-Feng Hsu, Feng Bi, Rongpu Zhou, Guanglei Cheng, Brian D’Urso, Patrick Irvin, Chang-Beom Eom, and Jeremy Levy. ACS Nano 2018 12 (6), 6128-6136
  4. "One-Dimensional Nature of Superconductivity at the LaAlO3/SrTiO3 Interface." Yun-Yi Pai, Hyungwoo Lee, Jung-Woo Lee, Anil Annadi, Guanglei Cheng, Shicheng Lu, Michelle Tomczyk, Mengchen Huang, Chang-Beom Eom, Patrick Irvin, and Jeremy Levy. Phys. Rev. Lett. 120, 147001 (2018)
  5. "Shubnikov–de Haas–like Quantum Oscillations in Artificial One-Dimensional 
    LaAlO3/SrTiO3 Electron Channels." Guanglei Cheng, Anil Annadi, Shicheng Lu, Hyungwoo Lee, Jung-Woo Lee, Mengchen Huang, Chang-Beom Eom, Patrick Irvin, and Jeremy Levy. Phys. Rev. Lett. 120, 076801 (2018)