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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 high temperature superconductors, manganese oxide based colossal magneto-resistance materials, and ruthenium oxide based metamagnets,

(ii) studies of superfluid Quantum Nanofluidics,

(iii) exploration of possible Bosonic Supersolid Phases both in electronic systems and in 4He and,

(iv) studies of mechanical force sensitivity limits and gravity at the nanoscale.

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Atomic Scale Wavefunction Imaging of Complex Electronic Matter

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 recently discovered ¡®Checkerboard¡¯ ordered Vortex-core states¹, Local quantum states at individual impurity atoms², Nanoscale disorder the superconducting electronic structure³ Quantum interference of cuprate quasiparticles⁴ ¡®Checkerboard¡¯ Charge Ordered state at very low doping⁵, the Effects of Individual Dopant Atoms on high temperature superconductivity⁶, Effects of Atomic Scale Electron-lattice interactions on high temperature superconductivity⁷, Structure of the pseudogap ground-state in cuprate superconductors - La_2-xBa_xCuO₄ (x=1/8) by ARPES and STM⁸, 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+¥ä⁹. Future work will involve temperature and field dependent studies of all these phenomena, as well as studies of similar properties in other high-Tc 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

Since, one is essentially imaging the modulus of the electronic wavefunctions. SI-STM can 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.

This work is supported by NSF and in collaboration with NHMFL.

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. A supersolid phase has also been reported at high pressure in solid 4He. We are developing new techniques to explore both of these stimulating possibilities.

References

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