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James C. Davis
James Gilbert White Distinguished Professor in the Physical Science
We undertake a wide range of experimental low-temperature research into the fundamental macroscopic quantum physics of superconductors, superfluids, supersolids, heavy-fermions, topological insulators and superconductors, and spin liquids, as well as developing new techniques for visualization and measurement of complex quantum matter.
Superfluid Josephson Effects
Superfluid 3He Josephson junctions use nano-aperture arrays fabricated at Cornell Nanofabrication Center. Using these devices, we discovered Josephson oscillations in superfluid 3He (Nature 388, 449 (1997)), the current-phase relationship of a superfluid Josephson junction (Science 278, 1435-1438 (1997)), -states within Josephson junction of a topological p-wave superfluid weak link (Nature 392, 687-690 (1998), Nature 396, 554-557 (1998)) and the first superfluid DC-SQUID (Nature 412, 55 (2001)).
These projects were in collaboration with Prof. R. Packard of U.C. Berkeley.
Solid and ‘Supersolid’ 4He
A possible supersolid phase has been reported at high pressure in solid 4He. We have recently developed the first SQUID-based torsional oscillator system for supersolid studies. Using this new approach, we found evidence for a ‘superglass’ state in solid 4He (Science 324, 632 (2009)) and were able to identify a unified relationship between rotational, relaxational, and shear dynamics of this quantum solid (Science 332, 821, (2011)). At present we are exploring the limits of DC mass flow through the putative ‘supersolid’ state of 4He.
These projects are in collaboration with Dr. A.V. Balatsky of LANL, New Mexico, USA, and Dr. M. Yamashita of Kyoto University, Japan.
Copper-based High Temperature Superconductivity
In 1999, we introduced spectroscopic imaging STM for visualization of electronic structure in complex electronic matter. We have used this approach extensively for studies of copper-based high temperature superconductors. We imaged electronic bound-states at individual impurity atoms (Science 285, 88 (1999)) including non-magnetic Zn impurity atoms on in Bi2Sr2CaCu2O8+d, Nature 403, 746 (2000) and magnetic Ni impurity atoms in Bi2Sr2CaCu2O8+ (Nature 411, 920 (2001)). We discovered the granular electronic structure of cuprates in underdoped Bi2Sr2CaCu2O8+d (Nature 413, 282 (2001), Nature 415, 412 (2002)). We also discovered the famous electronic density waves in underdoped cuprates (Science 266, 455 (2002), Nature 430, 1001 (2004), Science 314, 1914 (2006)), and intra unit cell symmetry breaking that generates and electronic nematic state (Science 315, 1380 (2007), Nature 466, 374 (2010), Science 333, 426 (2011)).
We introduced the quasiparticle interference imaging for STM determination of momentum-space electronic structure in complex electronic materials (Science 297, 1148 (2002), Nature 422, 520 (2003)) and used these techniques to determine effects of dopant atom and the approach of Mott insulator state (Science 309, 1048 (2005), Nature 454, 1072 (2008)). We studied the microscopic pairing mechanism via the iinterplay of electron-lattice interactions and superconductivity in Bi2Sr2CaCu2O8+ (Nature 442, 546 (2006)), we found the spectroscopic fingerprint of phase incoherent d-wave superconductivity (Science 325, 1099 (2009)) and we identified the hidden critical point underpinning high-Tc superconductivity phase diagram (Science 344, 612 (2014)).
In 2016, we developed nanometer resolution scanned Josephson tunneling microscopy (SJTM) to image Cooper-pair tunneling from a d-wave superconducting STM tip to the Cooper-pair condensate of underdoped Bi2Sr2CaCu2O8. The resulting images of the Cooper-pair condensate show clear pair density modulations oriented along the Cu-O bond directions. Fourier analysis reveals the direct signature of a Cooper-pair density wave (PDW) at wavevectors QP≈(0.25,0)2π/a0;(0,0.25)2π/a0. In theory, the PDW state is akin to the famous Fulde-Feller-Larkin-Ovchinnikov FFLO state of spatially modulated superconductivity, but generated by strong correlations instead of high magnetic fields. Since the original theoretical proposals in 1964, no FFLO (or PDW) state has previously been observed. Nature 532, 343 (2016)
The Bi2Sr2CaCu2O8+d project is in collaboration with Prof. S. Uchida of Tokyo University and Dr. H Eisaki of AIST Tsukuba, Japan, the Ca2-xNaxCuO2Cl2 project is in collaboration with Prof. H. Takagi of Tokyo University and RIKEN, Japan. Theoretical collaborations are with Prof. D.-H. Lee of UC Berkeley, and Profs. E.-A. Kim and M. Lawler of Cornell University.
Iron-Based High Temperature Superconductivity
In 2009, we introduced spectroscopic imaging STM and quasiparticle interference imaging for visualization of electronic structure in iron-based superconductors. We used this approach to discover the nematic electronic phase in iron-based superconductors (Science 327, 181 (2010)), the impact of individual dopant atoms and of high energy radiation damage (Nature Physics 9, 220 (2013), Science Advances 1, 1500033, (2015)), and the superconducting electronic structure (Science 336, 563 (2012)) and magnetically mediated pairing mechanism of iron-based superconductivity (Nature Physics 11, 117 (2015)).
The iron-based high-Tc superconductivity project is in collaboration with Prof. P. Canfield of Ames National Lab., Dr. H. Eisaki of AIST, Tsukuba, Japan, and Prof. A. Mackenzie of St. Andrews University, Scotland. Theoretical collaborations are with Profs. E.-A. Kim and M. Lawler of Cornell University.
Topological Quantum Matter
Topological insulators and topological superfluids (3HeA, 3HeB) are well known states of matter. Topological superconductors are proposed to exist but no definitive proof has so far emerged – although SrRuO-214 is widely believed to be a time-reversal violating odd-parity superconductor. We pursue a program of studies of topological insulator surface states and searches for topological superconductivity. In the field of ferromagnetic topological insulators (FM TI) where a formally equivalent topological order should exist, by introducing the Dirac-mass 'gapmap' technique, i.e. simultaneously visualizing the mass gap Δ(r) and the ferromagnetic dopant atoms at the atomic-scale, we discovered intense nanoscale disorder in the Dirac-mass and demonstrated that this is directly related to fluctuations in the magnetic-dopant atom density n(r) (Proc. Nat. Acad. Sci. 112, 1316 (2015)).
The SrRuO-214 project is in collaboration with Prof. A. Mackenzie of St. Andrews University & Max Planck Inst. Dresden. The CrBiSeTe FM TI project is in collaboration with Dr. Genda Gu at Brookhaven Nat. Lab.
Heavy Fermion Superconductivity & Quantum Criticality
Heavy fermions are composite quantum objects made by quantum superposition of free electrons and fixed magnetic-spins. The result is an exotic fluid of electronic particles that are free to move through a material but have effective mass thousands of times that of a free electron; they have eluded understanding for almost half a century. In 2010, Davis achieving the first visualization of heavy fermions (Nature 465, 570 (2010)), followed by the discovery the electronic structure of heavy fermion superconductivity (Nature Physics 9, 468 (2013)), and the magnetically mediated pairing mechanism of heavy fermion superconductivity (Proc. Nat. Acad. Sci. 111, 11663 (2014)).
The URu2Si2 project is in collaboration with Prof. G. Luke, McMaster University, Canada. The CeCoIn5 project is in collaboration with Dr. C. Petrovic of Brookhaven National Lab., and Prof. A.P. Mackenzie of St. Andrews University
In 2015, we launched the first study of spin liquids in our group. These are quantum magnets in which formation of classical magnetic states, e.g. ferromagnetism, is impossible. By introducing novel techniques for magnetic fluid flow studies, we recently discovered that the magnetic fluid in the canonical pyrochlore materials is a supercooled spin liquid – an unprecedented quantum magnetic state (Proc. Nat. Acad. Sci. 112, 8549 (2015)).
The pyrochlore spin liquid project is in collaboration with Prof. G. Luke, McMaster University, Canada.
Dr. Mohammad Hamidian (Harvard University) Dr. Jinho Lee (Seoul National University, Korea), Dr. Chung Koo Kim & Dr. Kazuhiro Fujita & Dr. Inhee Lee (Brookhaven Nat. Lab., NY), Dr. Andrej Mesaros (Cornell University)
Dr. Stephen D. Edkins, Dr. Peter O. Sprau, Dr. Anna Eyal.
Andrey Kostin, Azar Eyvazov, Rahul Sharma, Ritika Dusad, Yi Xue Chong
Quantum oscillations between two weakly coupled reservoirs of superfluid 3He S.V. Pereverzev, A. Loshak, S. Backhaus, J.C. Davis and R.E. Packard, Nature 388, 449 (1997).
Direct measurement of the current-phase relationship of a superfluid 3He weak link, Backhaus S., Pereverzev S.V., Davis J.C., and Packard R.E., Science 278, 1435-1438 (1997).
Discovery of a metastable -state in superfluid 3He weak link, S. Backhaus, R. Simmonds, S. Pereverzev, A. Loshak, J.C. Davis R.E. Packard Nature 392, 687-690 (1998).
Observation of Third Sound in Superfluid 3He A.M. R Schechter, R.W. Simmonds, R.E. Packard, and J.C. Davis, Nature 396, 554-557 (1998).
Josephson effect and a p-state in superfluid 3He, S. Backhaus, R. W. Simmonds, A. Loshak, J. C. Davis & R. E. Packard, Nature 397, 485 (1999)
Quasi-Particle Scattering Resonances in Bi2Sr2CaCu2O8+d, E.W. Hudson, S. H. Pan, A. K. Gupta, K-W Ng, and J.C. Davis, Science 285, 88 (1999)
Imaging the Effects of Individual Zinc Impurity Atoms on Superconductivity in Bi2Sr2CaCu2O8+d, S.H. Pan, E.W. Hudson, K.M. Lang, H. Eisaki, S. Uchida, and J.C. Davis, Nature 403, 746 (2000)
Interplay of magnetism and high-Tc superconductivity at individual magnetic impurity atoms in Bi2Sr2CaCu2O8+ Hudson, E.W., Lang. K, Madhavan, V., Pan, S.H., Eisaki, H., Uchida, S. & Davis, J.C. Nature 411 920 (2001).
Quantum Interference of Superfluid 3He, R. W. Simmonds, A. Marchenkov, J. C. Davis and R.E. Packard, Nature 412 55 (2001).
Microscopic electronic inhomogeneity in the high-temperature superconductor Bi2Sr2CaCu2O8+d S. H. Pan, J. O’Neil, R.L. Badzey, H. Ding, J. R. Englebrecht, Z. Wang, H. Esiaki, S. Uchida, A. Gupta. K-W Ng, E. W. Hudson K.M. Lang and J. C. Davis, Nature 413 282 (2001).
Imaging the granular structure of high-Tc superconductivity in underdoped Bi2Sr2CaCu2O8+d, K. M. Lang, V. Madhavan, J. Hoffman, E.W. Hudson, H. Eisaki, S. Uchida, and J.C. Davis, Nature 415, 412 (2002).
A four unit cell periodic pattern of quasiparticle states surrounding vortex cores in Bi2Sr2CaCu2O8+d J. E. Hoffman, E.W. Hudson, K. Lang, V. Madhavan, H. Eisaki, S. Uchida, and J.C. Davis, Science 266,455 (2002).
- Imaging Quasiparticle Interference in Bi2Sr2CaCu2O8+d” J. Hoffman, K. McElroy, D-H Lee, K.M. Lang, H Eisaki, S. Uchida, and J. C. Davis, Science 297, 1148 (2002).
Relating atomic scale electronic phenomena to wave-like quasiparticle states in superconducting Bi2Sr2CaCu2O8+d K. McElroy, R. W. Simmonds, J. E. Hoffman, D.-H. Lee, J. Orenstein, H. Eisaki, S. Uchida & J.C. Davis., Nature 422, 520 (2003).
A ‘checkerboard’ electronic crystal state in Lightly Hole-Doped Ca2-xNaxCuO2Cl2 T. Hanaguri, C. Lupien, Y. Kohsaka, D.-H. Lee,M. Takano, H. Takagi, & J. C. Davis. Nature 430, 1001 (2004).
Atomic-scale Sources and Mechanism of Nanoscale Electronic Disorder in Bi2Sr2CaCu2O8+. K. McElroy, Jinho Lee, J. Slezak, D.-H. Lee, H. Eisaki, S. Uchida, J.C. Davis. Science 309, 1048 (2005).
Interplay of electron-lattice interactions and superconductivity in Bi2Sr2CaCu2O8+, Jinho Lee, K. Fujita, K. McElroy, J.A. Slezak, M. Wang, Y. Aiura, H. Bando, M. Ishikado,T. Masui, J. -X. Zhu, A. V. Balatsky, H. Eisaki, S. Uchida,andJ. C. Davis, Nature 442, 546 (2006).
The Ground State of Pseudogap in Cuprates: La1.875Ba0.125CuO4, T. Valla, A. V. Fedorov, J. C. Davis , Jinho Lee, and G. D. Gu, Science 314, 1914 (2006).
An intrinsic bond-centered electronic glass with disperse unidirectional domains in underdoped cuprates, Y. Kohsaka, C. Taylor, A. Schmidt, K. Fujita, C. Lupien, T. Hanguri, H. Eisaki, S. Uchida, H. Takagi and J. C. Davis, Science 315, 1380 (2007).
How Cooper pairs vanish approaching the Mott insulator in Bi2Sr2CaCu2O8+dY. Kohsaka, C. Taylor, P. Wahl, A. Schmidt, Jhinhwan Lee, K. Fujita, J. Alldredge, Jinho Lee, K. McElroy, H. Eisaki, S. Uchida, D.-H. Lee, & J.C. Davis, Nature 454, 1072 (2008).
Evidence for a ‘Superglass’ State in Solid 4He, B. Hunt, E. Pratt, V. Gadagkar, M. Yamashita, A. V. Balatsky & J.C. Davis, Science 324, 632 (2009).
Spectroscopic Fingerprint of Phase Incoherent d-Wave Superconductivity in the Cuprate Pseudogap State, Jhinhwan Lee, K. Fujita, C.K. Kim, A. Schmidt, H. Eisaki, S. Uchida, & J.C. Davis, Science 325, 1099 (2009).
Nematic Electronic Structure in the ‘Parent’ State of Iron-based Superconductor Ca(Fe1-xCox)2As2, T.-M. Chuang, M.P. Allan, J.Lee, Ni Ni, S. Bud’ko, G. Boebinger, P.C. Canfield& J.C. Davis, Science 327, 181 (2010).
Imaging the Fano Lattice to Hidden Order transition in URu2Si2, A.R. Schmidt, Mohammad H. Hamidian, P. Wahl, F. Meier, A.V. Balatsky, T.J. Williams, G.M. Luke and J.C. Davis, Nature 465, 570 (2010).
Intra-unit-cell Electronic Nematicity of the High-Tc Cuprate Pseudogap States, M. J. Lawler, K. Fujita, Jhinhwan Lee, A.R. Schmidt, Y. Kohsaka, Chung Koo Kim, H. Eisaki, S. Uchida, J.C. Davis, J.P. Sethna, and Eun-Ah Kim, Nature 466, 374 (2010).
Interplay of Rotational, Relaxational, and Shear Dynamics in Solid 4He, E.J. Pratt, B. Hunt, V. Gadagkar, M. Yamashita, M. J. Graf, A. V. Balatsky and J.C. Davis, Science 332 821, (2011).
Topological Defects Coupling Smectic Modulation to Intra-Unit–Cell Nematicity in Cuprates A. Mesaros, K. Fujita, H. Eisaki, S.I. Uchida, J.C. Seamus Davis, Subir Sachdev, Jan Zaanen, M.J. Lawler and Eun-Ah Kim, Science 333, 426 (2011).
Anisotropic Energy-Gaps of Iron-based Superconductivity from Intra-band Quasiparticle Interference in LiFeAs M. P. Allan, A. W. Rost, A. P. Mackenzie, Yang Xie, J. C. Davis, K. Kihou, H. Eisaki, and T.-M. Chuang, Science 336, 563, (2012).
Simultaneous Transitions in Cuprate Momentum-Space Topology and Electronic Symmetry Breaking. K. Fujita, C.K. Kim, Inhee Lee, Jinho Lee, M. H. Hamidian, I. Firmo, H. Eisaki, S. Uchida, M.J. Lawler, E.-A. Kim, and J.C. Davis. Science 344, 612 (2014).
Detection of a Cooper-Pair Density Wave in Bi2Sr2CaCu2O8+x, M. Hamidian et al, Nature 532, 343 (2016)