Unconventional superconductivity

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Unconventional superconductivity Some of my
favorite topics
M. Sigrist
ETH Zurich
Outline
Sr2RuO4 - order parameter symmetry and
consequences chirality,
spin-orbit coupling, inhomogeneous
3K-phase T-violating superconductivity flux
dynamics
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Sr2RuO4 - Analog of 3He
Tc 1.5 K
Y. Maeno, G. Bednorz et al. 1994
Sr2RuO4
Sr
Quasi-2D strongly correlated Fermi liquid
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Symmetry of the superconducting state
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Two-component order parametern
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Sr2RuO4 a two-component superconductor
Spin triplet superconducting phase
Analog to A-phase of superfluid 3He
orbital angular momentum
chiral p-wave state
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Mixed state - Vortex lattice
Standard vortex lattice
Triangular Abrikosov vortex lattice
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Non-resonant ultrasound absorption
Single-component order parameter
only coupling to longitudinal sound modes
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Chiral pairing
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Topology of the gap function
ky
ei?
?
kx
Phase winding around the Fermi surface
? changes by 2???or -2?
broken parity and time reversal symmetry
chirality
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Gapless Chiral Edge States
Andreev bound states - a link to the IQHE
surface
SC
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Edge states in tunneling
Surface state are observable in tunneling Surface
density of state
Honerkamp, Matsumoto MS Yamashiro, Tanaka et al.
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Time reversal symmetry breaking phase
and
Cooper pairs with an angular momentum or chirality
magnetic moment !?
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Spontaneous magnetism
Zero-field muon spin relaxation
Muon spin depolarized by random Internal field
Magnetism generated by superconductivity (0.1 -
1 Gauss)
Luke, Uemura et al.
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Sr2RuO4 Inhomogeneous 3 Kelvin -phase
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3-Kelvin phase
Sr2RuO4 with excess Ru-metal inclusions
Onset of inhomogeneous superconductivity close to
3 K 3-Kelvin phase
resistivity
Ru-metal Tc 0.5 K
?m-size Ru-inclusions
Nucleation of superconductivity on the
interface between Ru and Sr2RuO4?
Maeno et al
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3-Kelvin phase - nucleation at the interface
Monien MS
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Capillary and frustration effect
Lowest energy with same phase Josephson coupling
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Upper critical field Hc2
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Upper critical field Hc2
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Remarks
Sr2RuO4
Two-component order parameter
complex phenomenology
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Fractional vortices and the dynamics of flux
lines
with D. Agterberg
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Superconductors with multi-component order
parameters
Multiple phase transitions
Broken time reversal symmetry
Heavy Fermion SC U1-xThxBe13, UPt3 ,
Maple et al. (2002)
Fisher et al. (1989)
Ott et al. (1985)
Chiral superconducting phase
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Domain walls
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Topological defects
two degenerate phases
domains and domain walls
Order parameter
??
??
kxiky
kx-iky
x
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Domain wall defects - Bloch line
two-component order parameter
sphere
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Structure of domain wall vortex
Ueda, Rice MS
relative phase
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Stability of fractional vortices
decay of conventional vortex
??
??
??
stable
stable
stable
stable
metastable
R
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Domain walls as vortex sheet
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Domain wall as a vortex sheet
vortex trapped on domain wall
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Vortex sheet barrier and flux dynamics
Fractional vortices strongly pinned on domain wall
Depinning requires recombination
maximal fractional vortex density
finite barrier height
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Experimental situation
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Unusual flux creep behavior
Kim-Anderson
with
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Vortex sheet barrier and flux dynamics
Fractional vortices strongly pinned on domain wall
Depinning requires recombination
maximal fractional vortex density
finite barrier height
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Noisy hysteresis in UPt3
Low-temperature phase with more than one component
Superconducting double transition
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Noise due to moveable barriers
Bean profile with domain walls
several avalanches
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Are domain walls really important ?
Field cooling yields single-domain phase ! ?
Zero-field cooling (ZFC)
vanishing flux creep
Field-cooling (FC)
ordinary flux creep
no domains no effect
Dumont Mota
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Remarks
Multi-component order parameters allow for
fractional vortices which can be stabilized on
domain walls in degenerate phases
Domain walls appear as intrinsic pinning
structures for vortices
Modified vortex dynamics due to domain walls
Additional flux pinning without change of
critical depinning current