Research
activities:
Superconductivity: My high-dissipation group studies properties of superconductors and
nanostructures, looking at phenomena such as quantized flux vortices, phase coherence
in superconducting microbridges, localization and
metal-insulator transitions. The experimental facilities include a
comprehensive thin-film fabrication laboratory and facilities for measurements
at sub-Kelvin temperatures, high magnetic fields (the highest in the state),
and extreme power densities (the highest in the world for any superconductor). A more comprehensive list of our laboratory
facilities can be found at facilities.html. In the area of dissipation in superconductors, this is one of the
leading groups in the world and has discovered several new effects in the past
few years. Currently our group includes graduate students Daniel Arcos and Peng Yang (Ph.D. candidates), and Wu Cheng and Bill
Campbell (M.S. candidates), and undergraduate research assistant Kenneth
Grasser. My local collaborations include Professors Jim Knight and Boris Ivlev on theoretical topics in condensed matter physics,
and outside collaborations include research groups in Japan, Korea, Germany,
Switzerland, and various institutions within the United States.
A superconducting state is formed when electrons in a
metal form pairs and condense into a single macroscopic quantum state. Several
peculiar properties can arise from the formation of the superconducting state
such as electrical conduction without resistance, perfect diamagnetism, and the
quantization of magnetic flux into elementary fluxons.
The properties of perfect conduction and diamagnetism hold only for low
currents and fields, and at higher current densities a superconductor becomes
resistive and can dissipate energy intensely. A large current drastically
modifies the superconducting state by dephasing the
macroscopic wavefunction, the so-called pair-breaking
effect. Our group was the first to demonstrate current induced pair-breaking in
a high-temperature superconductor and, very recently, in the newly discovered
magnesium di-boride superconductor.
In the motion of magnetic flux vortices in
superconductors, a new class of dynamic phases was discovered which result from
a non-equilibrium quasiparticle distribution
function. Other recent work includes the confirmation that the
superconductivity in the YBaCuO high-temperature
superconductor is underlain by finite normal conduction in the zero-temperature
limit (prior to this work the controversy over this quantity ranged from zero
to infinity).
Besides the fundamental work, we are involved in
several projects funded by Lockheed-Martin Energy Systems that investigate the
practical applications of superconductors. The basic research is funded by the
U.S. Department of Energy. A more technical description of my research can be found at research.html.
The research program is designed
to give the student a well-rounded and diversified experience in
interdisciplinary areas---helpful for success in today's professional
scientific environment. The training emphasizes gaining a clear understanding
of research problems and tackling them independently, while developing the
requisite skills along the way, including effective technical communication.
Musical Acoustics: My other significant interest is in
exploring the working of human hearing and neural processing of sounds,
especially as it pertains to the HiFi reproduction of
musical recordings. The website http://www.physics.sc.edu/kunchur/p155.htm for my musical
acoustics course will provide you with some background in these activities.
Suppressed flux motion in magnesium diboride films, D. H. Arcos and M. N. Kunchur, Phys. Rev. B (in press) 2005. pdf file
Current-Induced Pair Breaking in
Magnesium Diboride, M. N. Kunchur,
Topical Review published in the J. Phys.: Condens. Matter 16, R1183-R1204
(2004). pdf
file
Energy relaxation at a
hot-electron instability, J. M. Knight and M. N. Kunchur, submitted
to Phys. Rev. B (2004). pdf
file
The pair-breaking critical current density of magnesium diboride, M. N. Kunchur, Sung-Ik Lee, and W. N. Kang, Phys Rev. B 68, 064516 (2003). pdf file
Critical flux pinning and enhanced upper-critical-field in magnesium diboride films, M. N. Kunchur, C. Wu, B. I. Ivlev, Sung-Ik Lee, and W. N. Kang, Phys. Rev. B 68, 100503 (2003). pdf file ps file
Mixed-state transport
characteristics of magnesium diboride films, M.
N. Kunchur, C. Wu, D. H. Arcos, G. Saracila, E.-M. Choi, K. H. P. Kim, W. N. Kang,
S.-I. Lee, Braz. J. Phys. 33, 705 (2003). pdf
file ps file
Unstable flux flow due to heated electrons in Y-Ba-Cu-O films, M. N. Kunchur, Phys. Rev. Lett. 89, 137005 (2002). pdf file
Hot-Electron Instability in Superconductors, M. N. Kunchur and J. M. Knight, Mod. Phys. Lett. B 17, 549 (2003). pdf file
Shear fragmentation of unstable flux flow, M. N. Kunchur, B.I. Ivlev, and J. M. Knight, Phys. Rev. B 66, 60505 (2002). pdf file
Steps in the negative-differential-conductivity regime of a superconductor, M. N. Kunchur, B.I. Ivlev, and J. M. Knight, Phys. Rev. Lett. 87, 177001 (2001). pdf file
Van Hove singularities and vortex motion in superconductors, B.I. Ivlev, M. N. Kunchur and S. Mejia Rosales, Phys. Rev. B 64, 024508 (2001). pdf file
Metallic
normal state of YBa2Cu3O7 , M. N.Kunchur, B. I. Ivlev, D. K.
Christen, and J. M. Phillips, Phys. Rev. Lett. 84, 5204 (2000). pdf file
Cherenkov resonances in vortex dissipation in superconductors, B.I. Ivlev, S. Mejia Rosales, and M. N. Kunchur, Phys. Rev. B 60, 12419 (1999). pdf file
Hysteretic Internal Fields and Critical Currents in Polycrystalline Superconductors, M. N. Kunchur and T. R. Askew, J. Appl. Phys. 84, 6763 (1998).pdf file GZipped PS file
Decomposition of the Hall effect in the mixed state of superconductors, M. N. Kunchur, D. K. Christen, and B. I. Ivlev, Physica C 307, 241 (1998).pdf file
High frequency effects in superconductors from short duration dc pulses, M. N. Kunchur, D. K. Christen, and J. M. Phillips, pg. 180 in "Advances in Superconductivity and its Applications to Microwaves", Eds. G. P. Srivasatava and R. P. Tandon, Allied Publishers Ltd., New Delhi (1998).pdf file ps file
The files below
are large and are best saved before viewing.
Hall effect in YBa2Cu3O7 in the limit of free flux flow, M. N. Kunchur, D. K. Christen, C. E. Klabunde, and J. M. Phillips, Phys. Rev. Lett. 72, 2259 (1994).pdf file
Pair-breaking effect of high current densities on the superconducting transition on YBa2Cu3O7 , M. N.Kunchur, D. K. Christen, C. E. Klabunde, and J. M. Phillips, Phys. Rev. Lett. 72, 752 (1994).pdf file
Observation of free flux flow at high dissipation levels in YBa2Cu3O7 epitaxial films, M. N. Kunchur, D. K. Christen, and J. M. Phillips, Phys. Rev. Lett 70, 998 (1993). pdf file
Exploring the dissipative regime of superconductors for practical current-lead applications, M. N. Kunchur, D. K. Christen, C. E. Klabunde, and K. Salama, Appl. Phys. Lett. 67, 848 (1995).pdf file
Novel transport behavior found in the dissipative
regime of superconductors, M. N.
Kunchur, Mod. Phys. Lett. B. 9,
399 (1995). (Hard copy can be sent by mail upon requrest.)
Transport Behavior in Superconductors at Extreme Dissipation Levels, M. N. Kunchur, D. K. Christen, and B. I. Ivlev, pg. 135 in "Advances in Superconductivity: New Materials, Critical Currents and Devices", Eds. R. Pinto, S. K. Malik, A. K. Grover, and P. Ayyub, New Age International Ltd. Publishers, New Delhi (1997).pdf file
Critical fields and critical currents of superconducting discs in transverse magnetic fields, M.N. Kunchur and S.J. Poon, Phys. Rev. B 43, 2916 (1991).pdf file
Superposition of decaying flux distributions: A memory effect from flux creep, M.N. Kunchur, S.J. Poon, and M.A. Subramanian, Phys. Rev. B 41, 4089 (1990).pdf file
Absence of Superconductivity in Metallic Granular Aluminum, M. Kunchur, P. Lindenfeld, W. L. Mclean, and J. S. Brooks, Phys. Rev. Lett. 59, 1232 (1987).pdf file
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