Fishing Bosons in the depths of Fermi Sea Giorgio Benedek Università di Milano- Bicocca http://www2.mater.unimib.it/utenti /benedek/ Pavia, 6 March 2014 from a collaboration with: J. Peter Toennies Marco Bernasconi Davide Campi Pedro M. Echenique Evgueni V. Chulkov Irina Sklydneva Klaus-Peter Bohnen Rolf Heid Vasse Chis
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Fishing Bosons in the depths of Fermi Sea Giorgio Benedek Università di Milano-Bicocca Pavia, 6 March 2014.
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Fishing Bosons in the depths of Fermi Sea
Giorgio BenedekUniversità di Milano-Bicoccahttp://www2.mater.unimib.it/utenti/benedek/
Pavia, 6 March 2014
from a collaboration with:J. Peter ToenniesMarco BernasconiDavide CampiPedro M. EcheniqueEvgueni V. ChulkovIrina SklydnevaKlaus-Peter BohnenRolf HeidVasse Chis
Otto Stern (Sohrau 1888 – Berkeley 1969) Nobel Laureate 1943
Otto Stern, O.R. Frisch, I. Estermann (Hamburg, 1929-1933).
He
NaCl(001)
[meV]
542.4
][Å
2[Å]
1iEk
),(2
),(
nma
kkk ifz
GG K
Kk
a
Supersonic nozzle beam sources
J. P. Toennies: HUGO (MPI-SF, Goettingen)
Angular distributions
Diffraction
Inelastic processes: - inelastic bound state resonances - kinematical focussing
iffiiz
f
ff
)(
EGEnk
dΩdE
d
kFF
)Δ(Im|)(1|
12
v i-EE
EGvif
QQ
QQ uu
0
)0()0()Δ(
*
Manson and Celli (1971)
GB (GF formulation, 1973)
displacements of the SURFACE atoms (layer index = 0)
Surface phonons 2: from one monolayer…
…to a slab of Nz layers
Rayleighwave
Longitudinalresonance
U. Harten, J.P. Toennies and Ch. Wöll (1983-85)
Time-of-Flight spectra
Questions: 1) Why the longitudinal resonance is so soft?
2)Why is it observed at all?3)Why is it found in ALL metals?
The bones and the skin!
Bibi Giorgio, Vittorio & Peter
V. Chis, B. Hellsing, G. Benedek, M. Bernasconi, E. V. Chulkov, and J. P. Toennies“Large Surface Charge-density Oscillations Induced by Subsurface Phonon Resonances”Phys. Rev. Letters, 101, 206102 (2008)
for a 5 or 7 ML film on a rigid substratePb/Cu(111)
Surface charge density oscillations of the topmost modes at Q = 0
5 ML Pb/rigid substrate
Almost identical SCDO’s for two completely different modes:
just as found in HAS experiments!
HAS perceives underground phonons (5 layers deep) via e-p interaction !
),()( tnA,tV rr
'''
( ) ( )( ) ( , ; )n n'
n, nnnn n
f if n i A g
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K QK K Q Q
r rr K K + Q
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i
f
ff
)(
EnVEnk
dΩdE
dQ QK QK )(),()](1[
212
HAS scattering intensities
the non-diagonal elements of the electron density matrix act as effective inelastic
scattering potential
electron-phonon interaction matrix
02 2
0
( , )( , )
1 (4 / ) ( , )e Q
QQ
Qelectronic susceptibility
v vvFff
EENEfdΩdE
dQ QQ )()()(
)1(2
)()(2
1)()();,( 32
' ' QQQK QKK rrQKK IENifg Fn n n'nnn
mode-selected e-p coupling lambda
a slowly varying function
HAS from metal surfaces and thin films can measure the mode-selected electron-phonon coupling constants !
T. Zhang, P. Cheng, W.-J. Li, Y.-J. Sun, G. Wang, X.-G. Zhu, K. He, L. Wang, X. Ma, X. Chen, Y. Wang, Y. Liu, H.-Q. Lin, J.F. J ia, and Q.-K. Xue, Nature Physics 6, 104-108 (2010).
S. Qin, J. Kim, Q. Niu, and C.-K. Shih, Science 324,1314 (2009).
Persistent SC in Pb/Si(111)
16 ML down to 1 !
Theory predicts also the drop of
total and Tc below 4 ML !
Superconductivity in Pb/Si(111) ultra-thin films
1
The interface mode is the culprit for SC!
Acoustic Surface Plasmons (ASP) observed by HAS in Cu(111)!
ASP
ASP0
Band structure of graphene
Dirac massless fermions
Dirac massive fermions
Graphene / Ru(0001)0
HAS: Daniel Farias (Madrid)
DIRAC?
|2/1|
1
KK UTm
m
m
KTK 2
)( 2
mm
4222)( cmcppE
mKcqKp 2/),(
32,
c
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hcmm PP Planck lattice
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)(21910
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m
m
mm
eV1.04
)(2
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r
mm
am
hrV eh
eh at r = aback to solid
r
hc
m
mrV
PG
Δ)(
Conclusions:
HAS can measure deep sub-surface phonons in metal films: a complete
spectroscopy (not accessible to other probes such as EELS)
HAS can directly measure the mode-selected electron-phonon coupling
in metals: a fundamental information
a) for the theory of 2D superconductivity
b) for the theory of IETS (STS) intensities
c) for understanding phonon-assisted surface reactions, etc.
C.S. Jayanthi, H. Bilz, W. Kress and G. Benedek, Phys. Rev. Letters 59, 795 (1987) (after an idea of Phil Allen for the superconducting phonon anomalies
of Nb)
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Density-Functional Perturbation Theory vs. Multipole expansion