• Theoretical Condensed-Matter Physics
• Theoretical Elementary Particle Physics
• Astrophysics and General Relativity
• Experimental Elementary Particle Physics
• Accelerator Physics
• Experimental Condensed-Matter Physics
• Biological Physics
• Multidisciplinary Research
• Major Research Facilities
• Resources for Researchers

B.Sc., 1983, National University of Ireland, Cork. Ph.D., 1989, University of California, Berkeley. Research Assistant, University of California, Berkeley, 1984-1989. Postdoctoral Research Associate, University of California, Berkeley, 1990-1993. Assistant Professor, Physics, University of California, Berkeley, 1993-1997 . Faculty Physicist, L. Berkeley National Laboratory, 1998-2002 . Associate Professor, Physics, University of California, Berkeley, 1998-2000. Professor, Physics, University of California, Berkeley, 2001-2002 . Professor, Physics, Cornell University, 2003- present. Senior Physicist, Brookhaven National Laboratory, 2006-present. SUPA Distinguished Research Professor, St. Andrews University, Scotland, 2007-present. Visiting Professor, University of British Columbia, Vancouver, CA, 2009. Director of the Department of Energy EFRC - Center for Emergent Superconductivity, 2009-present. NSF National Young Investigator Award, 1994. Packard Fellow in Science and Engineering, 1994. Alfred P. Sloan Research Fellow, 1996. Miller Research Professor, 2000. Outstanding Performance Award, L. Berkeley National Laboratory, 2001. Ehrenfest Lecturer, University of Leiden, Holland, 2002. Fellow of the Institute of Physics, 2002. Fellow of the American Physical Society, 2005. Fritz London Memorial Prize, 2005. Pagels Lecturer at the Aspen Center for Physics (2008). Loeb Lecturer in Physics, Harvard University (2008). Einstein Lecturer, Weizmann Institute, Israel (2009). H. Kamerling-Onnes Prize, 2009.

Research Areas
Our research interests are in the application of experimental techniques of high precision low temperature physics to questions of fundamental significance. At present, these include (i) Spectroscopic Imaging STM studies of atomic scale electronic phenomena in transition metal oxides including the copper oxide high temperature superconductors, manganese oxide colossal magneto-resistance materials, and ruthenium oxide based quantum nematic metamagnets, (ii) exploration of possible Bosonic Supersolid Phases both in electronic systems and in Solid ⁴He, (iii) Spectroscopic Imaging STM studies of atomic scale electronic phenomena in f-electron Heavy Fermion systems, and (iv) studies of mechanical Force Sensitivity Limits and Gravity at the Nanoscale.

Current Research

Atomic Scale Wavefunction Imaging in Exotic Superconductors and Magnetic Materials

Our unique scanning tunneling spectroscopic imaging technology, achieving atomic-resolution ‘wavefunction imaging’ down to 15 mK in fields up to 9 Tesla, is used to study high temperature superconductivity and other highly correlated electronic systems such as manganites and ruthenates.

In the cuprates, we have discovered ‘Checkerboard’ ordered Vortex-core states [1], Local quantum states at individual impurity atoms [2], Nanoscale disorder the superconducting electronic structure [3] Quantum interference of cuprate quasiparticles [4] ‘Checkerboard’ Charge Ordered state at very low doping [5], the Effects of Individual Dopant Atoms on high temperature superconductivity [6], Effects of Atomic Scale Electron-lattice interactions on high temperature superconductivity[7], Structure of the pseudogap ground-state in cuprate superconductors - La_2-xBa_xCuO₄ (x=1/8) by ARPES and STM [8],  and introduced atomic resolution tunneling-asymmetry imaging to reveal an intrinsic Cu-O-Cu bond-centered electronic glass with disperse 4a₀-wide unidirectional domains in underdoped Ca_1.88Na_0.12CuO₂Cl₂ and Bi₂Sr₂Dy_0.2Ca_0.8Cu₂O_8+δ – observation of Electronic ‘Stripes’ in Cuprates [9]. Future work will involve temperature and field dependent studies of all these phenomena, as well as studies of similar properties in other high-T_c superconductors and other highly correlated electron systems.

The Bi₂Sr₂CaCu₂O_8+d project is in collaboration with Prof. S. Uchida of Tokyo University and Dr. H Eisaki of AIST Tsukuba, Japan, the Ca_2-xNa_xCuO₂Cl₂ project is in collaboration with Prof. H. Takagi of Tokyo University and Dr. T. Hanaguri of RIKEN, Tokyo, Japan, the Sr₃Ru₂O₇ project is in collaboration with Prof. A. Mackenzie and Dr. F. Baumberger of St. Andrews University, Scotland, and the La_2-xBa_xCuO₄ project is in collaboration with Dr. Genda Gu and colleagues at Brookhaven National Laboratory.

Development of a 20-Tesla Spectroscopic Imaging STM for Nanoscale Studies of Complex Electronic/Magnetic Materials
Since, one is essentially imaging the modulus of the electronic wavefunctions. SI-STM can therefore become a key tool for development and study of advanced magnetic/electronic materials, because it reveals directly the impact on atomic-scale electronic structure of processing, dopant profiles, crystalline disorder, and electronic/magnetic phase transitions due to external fields.
However, these powerful SI-STM techniques have only been available in moderate magnetic fields. A 20 Tesla SI-STM would allow these techniques to be applied to nanoscale studies of complex electronic/magnetic materials in very high fields. And, as recommended by the National Academy, it is a strategic goal of the National High Magnetic Field Lab (NHMF) in Tallahassee, to introduce these capabilities. We are proceeding with a development program with several parallel objectives: (i) design, fabrication, installation, development and testing of the world’s first 20T-SI-STM system, (ii) high-magnetic-field SI-STM research into correlated electron system physics as discussed below and, (iii) transfer of the prototyped technology to NHMFL in Tallahassee via collaborative construction of a duplicate 20T-SI-STM system there.

Josephson Effects in Superfluid Helium
We have developed device-quality superfluid ³He Josephson junctions by using nanoaperture arrays fabricated at Cornell Nanofabrication Center. Using these devices, we have made a series of discoveries including; Superfluid Josephson oscillations [10], p-states in ³He Josephson junctions [11], and superfluid quantum interference [12]. The quantum interference was observed in the first superfluid quantum interference device (DC-SQUID) which is an ultra-sensitive quantum gyroscope. These projects were in collaboration with Prof. R. Packard of U.C. Berkeley.

Force Sensitivity Limits and Gravity at the Nanoscale
We are studying the ultimate limits of force and position sensing with nano-mechanical systems and SQUID-based classical accelerometers at very low temperatures - with a view to developing new force sensing tests for fundamental physics. Of immediate interest is a type of Cavendish Experiment which is designed to detect gravity at micron scale distances and departures from Newton’s Law of Universal Gravitation into the nanometer range.

Bosonic Supersolids both in Solid ⁴He and in Correlated Electron Systems
The possibility of an electronic supersolid underpinning superconductivity in the cuprates was recently revealed by some of our work [1,5,9]. A supersolid phase has also been reported at high pressure in solid ⁴He. We have recently develop the first SQUID-based tensional oscillator system and used it to study the dynamics of supersolid ⁴He [13].

1.   J. Hoffman et al, Science 297, 1148 (2002).
2.   E. Hudson et al,  Science 285, 88 (1999); S. Pan et al,  Nature 403, 746 (2000); E.W. Hudson et al,  Nature 411, 920 (2001).
3.   S. H. Pan et al,  Nature 413, 282 (2001), K. M. Lang et al, Nature 415, 412 (2002).
4.   J. Hoffman et al, Science 266, 455 (2002); K. McElroy et al, Nature 422, 520 (2003).
5.   T. Hanaguri et al, Nature 430, 1001 (2004)
6.   K. McElroy et al Science 309, 1048 (2005).
7.   Jinho Lee et al Nature 442, 546 (2006).
8.   T. Valla et al, Science 314, 1914, ( 2006).
9.   Y. Kohsaka et al Science 315 , 1380 (2007); Y. Kohsaka et al Nature 454, 1072 (2008).
10.  S.V. Pereverzev et al, Nature 388, 449 (1997).
11.  S. Backhaus et al,  Science 278, 1435 (1997); S. Backhaus, et al, Nature 392, 687 (1998).
12.  R. W. Simmonds et al, Nature 412, 55 (2001).
13.  B. Hunt et al, Science 324, 632 (2009).

Post-docs
Dr. Kazuhiro Fujita, Dr. Tien-Ming Chuang, Dr. Sourin Mukhopadhyay, Dr. Benjamin Hunt, Dr. Andy Schmidt

Visiting Scientists
Milan Allan, Dr. Tien-Ming Chuang

Graduate Students
Ethan Pratt, Chung Koo Kim, Mohammad Hamidian, Vikram Gadagkar and Yang Xie

Spotlight

Jalina Keeling is an undergraduate student with the Itai Cohen Group on Complex Matter Physics (who is at Cornell as part of the NSF's Research Experiences for Undergraduates program). She is conducting experiments similar to the epitaxial growth of crystals, but using polymer beads. She uses a confocal microscope to scan a sample of these beads from bottom to top. Her research seeks to answer the questions "What structures form? How do we tune the concentration of polymers to change ...
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