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Pengcheng Dai's group works at the University of Tennessee in Knoxville (UTK) in the Physics Department on condensed matter physics.
Experimental condensed matter physics uses neutrons as probes to study strongly correlated electron systems. The microscopic origin of high-transition temperature (Tc) superconductivity, magnetism and electron-lattice coupling in high-Tc superconductors. Magnetism and lattice effects in colossal magnetoresistance (CMR) manganese oxides. Quantum criticality in Ru-based oxide materials and other transitional metal oxides. Our work is supported by the National Science Foundation and the Department of Energy.
Updates:
[May 28th, 2008] Understanding superconductivity has been a long term goal of the condensed matter physicists. The recent discovery of superconductivity in Fe-based oxypnictides has reinvigorated the field of high-Tc superconductivity. On May 28 issue of advance on line publication, our group reports the discovery of static antiferromagnetic order in the parent compound of the nonsuperconducting LOFeAs, and showed that the static order disappears when the system is doped to induce superconductivity. This phenomenon is very reminiscent of that the copper oxide superconductors, a class of high-Tc superconducting materials that were discovered in 1986, but its superconductivity mechanism is still elusive in spite of more than 20 years of work. With another class of material that exhibits high-Tc superconductivity, condensed matter physicists can finally compare and contrast these two classes of materials and ask what are the key ingredients for high-Tc superconductivity. In the present paper published by Nature advance online publication, doi: 10.1038/nature07057 , we find the magnetism aspect of the new superconductors to have remarkably similar to those of cuprates. Of course, more work has to be done to sort out the detailed comparison of these two classes of superconductors. For more information, see UT press release ; NIST press release ; and Physics department story .
[Apr 9th, 2008] On Chancellor's honor night, April 9th, both the PI and graduate student Songxue Chi have been recognized for research work on strongly correlated electron materials. The PI won the "Research and Creative Achievement" award while Songxue was recognized as having "Extraordinary Professional Promise". See Research and Creative Achievement and Extraordinary Professional Promise
[Apr 7th, 2008] In a new paper recently posted on cond-mat, we report the discovery of static antiferromagnetic order in the parent compound of the newly discovered FeAs based superconductor LaOFeAs, and the static AF order disappears when the system becomes superconducting. This work is lead by postdoc Clarina dela Cruz in collaboration with NIST/AMES scientists (Drs. Q. Huang, J. W. Lynn, J. Zarestsky) and Prof. Nanlin Wang's group at the institute of Physics, Chinese Academy of Sciences. See: arXiv: 0804.0795
[Mar 25th, 2008] A new paper from the group lead by Songxue Chi describing a detailed neutron scattering experiment and theory to determine the crystal electric field levles on PrOsAs has been published in Phys. Rev. B 77, 094428 (2008) .
[Mar 25th, 2008] A new paper from the group lead by Songxue Chi describing a detailed neutron scattering experiment and theory to determine the crystal electric field levles on PrOsAs has been published in Phys. Rev. B 77, 094428 (2008) .
[Dec 18th, 2007] A new paper from the group lead by Shiliang Li describing a detailed neutron scattering experiment on spin excitations of an underdoped superconducting YBa2Cu3O6.45 (Tc=48 K) has been published in Phys. Rev. B 77, 014523 (2008) . We find that the low-temperature spin excitations in YBCO family of compounds change dramatically when the system is tuned across the metal-to-insulator crossover. Our results suggest that the spin resonance and spin gap in YBCO might be a consequence of metallic ground state superconductors.
[Dec 13th, 2007] Understanding the mechanism of high-Tc superconductivity in doped copper oxides remains one of the most daunting problems in condensed matter physics. Perhaps the most debated current issue in the field of high-Tc superconductivity is the microscopic origin of the superconducting 'glue' that binds electrons into superconducting pairs. While the interaction that pairs the electrons to form the superconducting state is mediated by lattice vibrations (phonons) in traditional superconductors, the leading contenders in the case of high-Tc superconductors are lattice vibrations (phonons) and spin excitations, with the additional possibility of pairing without mediators. Using scanning tunneling microscopy, our collaborators in Boston College and us report spatially resolved, reproducible spectroscopy of the electron-doped superconductor PLCCO that reveal a collective mode in the material's electronic excitations at ~10.5 meV [See Nature 450, 1058-1061 (2007).]. This is consistent with magnetic neutron resonance observed earlier on the same sample by our group and inconsistent with oxygen optical phonon modes [see Nature 442, 59 (2006) and update July 2006]. Our results thus suggest an electronic origin of the mode — and possibly the superconducting 'glue' — consistent with the involvement of spin-excitations rather than phonons.
[Oct 11th, 2007] A new paper discussing the Fermi-surface evolution as a function of annealing in electron-doped cuprates has just appeared in PRL. This is a collaborative work between our group and the group of Hong Ding at Boston College. See See PRL 99, 157002 (2007).
[Sep 21st, 2007] A new paper from the group on the evolution of quantum spin excitations through field-induced superconducting-normal state phase transition has just been published in PNAS. See PNAS 104, 15259 (2007).
[Jul 5th, 2007] A new paper with Jun Zhao as the leading author describing the observation of the neutron resonance in electron-doped Nd1.85Ce0.15CuO4 has now been published in Phys. Rev. Lett. This paper follows the group's discovery of the mode last year in electron-doped Pr0.88LaCe0.12CuO4, thus proving the mode is a general feature of optimally electron-doped materials. See Phys. Rev. Lett. 99, 017001 (2007) for more details.
[Jul 4th, 2007] A new review article lead by group's long time collaborator Prof. Jiandi Zhang of FIU has just been published in J. Phys.: Condens. Matt. This paper summarizes the our collaborative efforts to understand spin excitations in Colossal magnetoresistance manganites. See J. Phys. Condens. Matter 19, 315204 (2007). for more details.
[Jun 20th, 2007] A new paper lead by graduate student Songxue Chi on spin-lattice coupling in layered CMR manganite Pr0.5Ca1.5MnO4 has just been published by PNAS. This is a part of Songxue's Ph. D thesis, which is to focus on layered manganites and filled skutterudite PrOs4As12. see: PNAS 104, 11796-11801 (2007).
[Apr 23rd, 2007] Congratulations to Stephen Wilson for winning the Fowler-Marion Outstanding Graduate Student Award at the physics department's annunal honor's day. This award recognizes a senior graduate student for his outstanding Ph. D thesis work and citizenship.
[Apr 7th, 2007] A paper describing spin wave excitations of CMR manganites La1-xCaxMnO3 (x=0.25, 0.3) throughout Brillouin zone has been published in PRB. This work completes the group's efforts over the past 9 years to study spin excitations in three-dimensional CMR materials. For more details see PRB 75, 144407 (2007).
[Mar 30th, 2007] Congratulations to graduate student Stephen Wilson, who has successfully defended his Ph. D thesis on March 30th. Stephen will work with Bob Birgeneau at UC-Berkeley and LBL from June 1, 2007.
[Jan 17th, 2007] A new paper entitled " Microscopic annealing process and its impact on superconductivity in T'-structure electron-doped copper oxides" from the group lead by former student Hye Jung Kang has been published as an article in Nature Materials. See Nature Materials 6, 224-229 (2007) for article and for News and Views by Hidenori Takagi.
[Nov 20th, 2006] Congratulations to graduate student Stephen Wilson for winning the 2006-2007 GMAG (Topical Group on Magnetism and its applications) Student Dissertation Award. Stephen will give an invited talk at APS March meeting in Denver, receive a $500 prize and up to an additional $250 in travel expenses to attend the meeting.
[Oct 31st, 2006] A new short review article to celebrate 20 years since the discovery of high-transition temperature superconductors, written in Chinese by PI and postdoc Shiliang Li, was published in Physics, a Chinese popular phyiscs monthly journal. See Wuli 35, 837 (2006) .
[Aug 28th, 2006] A new paper entitled "Evolution of the low-energy spin dynamics in electron-doped high-transition temperature superconductor Pr0.88LaCe0.12CuO4" by Wilson et al has been published in PRB. For a reprint, see: Phys. Rev. B 74, 144514 (2006) .
[Aug 11th, 2006] A new paper entitled "Magnetic energy change available to superconducting condensation in optimally doped YBa2Cu3O6.95" by Hyungje Woo, Pengcheng Dai, S. M. Hayden, H. A. Mook, T. Dahm, D. J. Scalapino, T. G. Perring, and F. Dogan has been accepted by journal Nature Physics and will appear shortly. For complete paper, click here.
[Jul 5th, 2006] A new paper from the group on discovery of the magnetic resonance in electron-doped high-Tc superconductor with graduate student Stephen Wilson as the lead author just appeared in journal Nature; See: Nature 442, 59 (2006) . For press releases from NIST and UT see: NIST press release and UT press release .
[Jul 3rd, 2006] The PI's, Pengcheng Dai's, promotion to the rank of Professor of Physics and Astronomy at The University of Tennessee has been approved by the Board of Trustees and will become effective on August 1, 2006.
[Jun 22nd, 2006] A new paper on spontaneous spin-lattice coupling in CuFeO2 by Feng Ye, a close collaborator of the group, had just appeared in PRB as a Rapid Communication. See F. Ye et al., Phys. Rev. B 73, 220404(R) (2006).
[May 1st, 2006] Our group's collaboration paper with Prof. Brian Maple's group at UCSD on electronic and magnetic properties of PrOs4As12 just appeared in the inaugural article by Maple et al. in Proceedings of the National Academy of Sciences (PNAS). See:PNAS 103, 6783-6789 (2006).
[Apr 28th, 2006] Graduate student Jun Zhao won the Paul H. Stelson Fellowship in Physics for Professonal promise in Physics hornor's day.
[Apr 24th, 2006] A new paper on spin excitations of PrLaCeCuO4 from the group with graduate student Stephen Wilson as the lead author just appeared in PRL. See: Phys. Rev. Lett. 96, 157001 (2006).
[Jan 30th, 2006] A new paper on CMR manganite from the group just appeared in PRL. See: Phys. Rev. Lett. 96, 047204 (2006).
[Jan 27th, 2006] New graduate student Chad Bircher joined group after passing his qualifying exam.
[Aug 10th, 2005] New student Jun Zhao joined our group.
[Aug 5th, 2005] New website is developed by Serena Dai and Alice Gu.
[Jul 20th, 2005] Pengcheng has given a talk at UCSB: Microscopic Evidence for a Magnetic Quantum Critical Point in Electron Doped Superconductivity .
[Jun 1st, 2005] Electronically competing phases and their magnetic field dependence in electron-doped nonsuperconducting and superconducting Pr0.88 LaCe0.12 CuO4± delta is published in Phys. Rev. B 71, 214512 (2005).
[May, 2005] Hyejung Kang was awarded her Ph. D and now is working at NIST.
[Mar 1st, 2005] Electronic inhomogeneity and competing phases in electron-doped superconducting Pr0.88 La Ce0.12 Cu O4- delta is published in Phys. Rev. B 71, 100502 (2005).
[Feb 11th, 2005] Quantum Critical Scaling and origin of Non-Fermi-Liquid behavior in Sc1-xUxPd3 is published in Phys. Rev. Lett. 94, 056402 (2005).
