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J.C. Seamus Davis
James Gilbert White Distinguished Professor Emeritus
Davis Group research concentrates upon the fundamental physics of electronic, magnetic, atomic and space-time quantum matter. A specialty is development of innovative instrumentation to allow direct visualization (or perception) of characteristic quantum many-body phenomena at atomic scale
Davis Group operates three suites of ultra-low vibration laboratories, one in Clark Hall at Cornell University (US), the second at Kane Building at University College Cork (IE) and a third is at Beecroft Building at Oxford University (UK). The overall objective is to exploit the distinct capabilities and facilities at all laboratories to maximize scientific efficiency.
Ours is as single research group conducting scientifically harmonized studies with complementary scientific instruments at all three locations. Other key components of our program are at the Max Planck Graduate Center for Quantum Materials in Dresden.
- Laboratory of Atomic and Solid State Physics (LASSP)
- Cornell Center for Materials Research (CCMR)
- Kavli Institute at Cornell for NanoScale Science
We recently introduced nanometer resolution Scanned Josephson Tunneling Microscopy (SJTM), a technique allowing imaging of Cooper-pair tunneling from a superconducting STM tip to the Cooper-pair condensate of a superconductor. The SJTM operates at millikelvin temperatures and sequentially forms an array of 65,500 nanoscale Josephson junctions, whose Josephson critical current Ic is then measured to form the condensate image (Nature 532, 343 (2016)). For the first time in superconductivity research, one can visualize the Cooper-pair condensate itself.
SJTM is a very promising new approach to research into all kinds of heterogeneous superconductivity. Projects of immediate research interest include:
Magnetic Monopole Fluids
Magnetic monopoles are hypothetical elementary particles exhibiting quantized magnetic charge m0 and quantized magnetic flux. A classic proposal for detecting such magnetic charges is to measure the quantized jump in magnetic flux threading the loop of a superconducting quantum interference device (SQUID) when a monopole passes through it. Naturally, with the theoretical discovery that a fluid of emergent magnetic charges should exist in several lanthanide-pyrochlore magnetic insulators including Dy2Ti2O7, this SQUID technique was proposed for their direct detection (Castelnovo et al Nature 451, 42 (2008)). Experimentally, this has proven extremely challenging because of the high number density, and generation-recombination (GR) fluctuations, of the monopole plasma. Recently, however, theoretical advances by Prof. S. Blundell of Oxford University have allowed the spectral density of spin-noise due to GR fluctuations of magnetic charge pairs to be determined.
In 2018 we developed a high-sensitivity, SQUID based spin-noise spectrometer, and measured the frequency and temperature dependence of spin-noise spectral density for Dy2Ti2O7 samples. Virtually all the elements predicted for a magnetic monopole fluid, including the existence of intense magnetization noise and its characteristic frequency and temperature dependence, are detected.
High precision measurement of the spin-noise spectrum is an innovative approach to magnetic quantum fluids. It opens a wide variety of new research avenues including the following projects of immediate interest:
Magnetic Topological Insulators
Surface states of topological insulators (TIs) are expected to exhibit many valuable new electronic phenomena when a 'mass gap' is opened in their Dirac spectrum by ferromagnetism (FM). Such ferromagnetic topological insulators (FMTI) should exhibit phenomena including the Quantum Anomalous Hall Effect (QAHE), the Jackiw-Rebbi Solitons (JRS), and Emergent Axionic Electrodynamics. The QAHE has indeed been observed but, mysteriously, iti is only detected at mK temperatures.
To explore the intriguing physics of FMTI, we recently developed the first visualization technique for the Dirac mass of FMTI surface states. We found that the Dirac mass m(r) is extremely disordered and correlates with the local density of the magnetic dopant atoms generating FM state. This chaotic Dirac-mass landscape m(r) poses far more questions on FMTI than it answers.
Topological Kondo Insulators
In a crystal with a sub-lattice of localized f-electron states, the Kondo effect generates a heavy-fermion band structure. At high temperatures, a conventional (light) electronic band coexists with localized f-electron states on each magnetic atom. At lower temperatures, hybridization between this light band and the f-electron states results in opening a hybridization gap, and its splitting into two new very flat bands with greatly enhanced density-of-electronic-states N(E) within just a few meV of EF. We developed a dilution-refrigerator-based mK SISTM instrument for mapping simultaneously the r-space and k-space electronic structure of heavy-fermion systems at temperatures down to 20 mK. Demonstration of the feasibility of this approach for visualizing heavy-fermion formation, and measuring heavy-fermion band-structures, launched the field of STM studies of heavy fermions (Nature 465, 570 (2010)).
Research Plans: The capability to image heavy fermions opens exciting new avenues for research into strongly entangled electronic quantum matter.
Cu/Fe HT Superconductors
Novel ‘electronic liquid crystal’ phases have long been predicted for correlated electronic materials, especially those where the intense correlations generate the highest temperature superconductivity. By using direct atomic-scale visualization we have discovered several of these phases including the smectic (DW) state in CuHTS (Science 295, 466 (2002); Nature 430 , 1001 (2004) ; Science 315, 1380 (2007)); the nematic phase in CuHTS (Nature 466, 374 (2010); Science 333, 426 (2011)); the famous nematic phase of FeHTS (Science 327, 181 (2010); Science 357, 75 (2017)) the Cooper-Pair Density Wave (PDW) state in CuHTS (Nature 532, 343 (2016)).
Having established the existence of these broken-symmetry electronic liquid crystal states, the challenge now is to understand their relationship to the HTS.
Viscous Electron Fluids
There is now widespread interest in whether some electron fluids exhibit viscosity. Key evidence for this phenomenon comes from studied of ultra-pure dellafossite crystals (A.P. Mackenzie Rep. Prog. Phys. 80 032501 (2017 )).
A profound challenge for this field is to detect turbulence of an electronic fluid. No phenomena have ever been observed for any electron fluid. Thus, exploratory studies to visualize viscous phenomena in an electron fluid are of great interest
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).
Atomic-scale 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).
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).
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).