Pseudo-gap Observed at Martensite
Transition in a Ni2MnGa Single Crystal
C. P. Opeil1, J. C. Lashley2, R. K. Schulze2, B. Mihaila2, J. L. Smith2,
L. Hults2, P. Riseborough3, L. Mañosa4 and A. Planes4
1Boston
College, Physics Department, Chestnut Hill, MA 02467
USA
2Los Alamos National Laboratory, Los Alamos, NM 87545 USA
3Temple University, Physics Department, Philadelphia, PA 19122,
USA
4 Universitat de Barcelona, Departament d’Estructura i Constituents
de la Matèria, Facultat de Física, Diagonal 647, E-08028 Barcelona,
Catalonia, Spain
Work sponsored by: Dept. of Energy and Boston College
Ni2MnGa Single Crystal
Low Energy Electron
Diffraction (LEED)
at T=293 K
Back Scatter Laue, T = 293K
Ni2 M nGa (100)
Cubic
Fm-3m
a = 5.825 Ang.
Vol = 192.34 Ang.3
Ni (0.25,0.25,0.25)
M n (0.5,0.5,0.5)
Ga (0, 0, 0)
Curie Transition:
Heat Capacity at H=0 [T]:
PMT
MT
TC
TC Ferromagnetic Transition
N-Gr
Dilatometry
MT
197 K
MT is field independent
Fermi Surface Map
PMT
214 K
FCC to Monoclinic at MT
Lee, et al., Phys. Rev. B 66 (2002).
Temperature Dependent UV-Spectroscopy (hν=21.21eV)
Temperature Dependent UV-Spectroscopy (hν=21.21eV)
ARPES: Angle
Resolved
Photoemission
Spectroscopy
e-
Ekinetic = h" # e$ # Ebinding
!
Brillouin
zone
orientation
!
[100]
kX
kII =
kZ
Z
ARPES - choose
analyzer
2meEkinetic
2
h
azimuthal q to specify kvector to probe, and then
vary polar f to collect
DOS at various kII and
observe dispersion of
bands along k-vector
surface normal
f
a-U(001) surface
" sin#
q
[001]
kY
[010]
(100) plane
ARPES-295 K
Contour height
color key
ARPES-219 K
ARPES-219 K
Contour height
color key
ARPES-173 K
Energy Dispersion Curves:
normal incidence
normal incidence
-2.5
-2.0
-1.5 -1.0
-0.5
Eb [eV]
0.0
0.5
Evidence of pseudo-gaps in other materials:
(b)
ARPES at (pi,0) for u-doped Bi2212,
90K Pseudo-gap state, 30K-SC state.
Norman et al., Adv. in Physics, 54 (2005)
T-dependent photoemission of
KMo6O17 (purple-bronze) RT to 45 K.
Valbuena, et al., J. Phys. Chem. Solids 67 (2006)
Evidence of pseudo-gap in Bi2212:
ARPES at (pi,0) for u-doped Bi2212,
90K Pseudo-gap state, 30K-SC state.
Norman et al., Adv. in Physics, 54 (2005)
Ni2MnGa data
Evidence of pseudo-gap in KMo6O17 (Purple-bronze):
T-dependent photoemission of
KMo6O17 (purple-bronze) RT to 45 K.
Valbuena, et al., J. Phys. Chem. Solids 67 (2006)
Ni2MnGa data
Summary:
1. The martensite, Ni2MnGa, exhibits a “pseudo-gap” behavior at B.E. =
0.3 eV as T --> TMT.
2. Pseudo-gap at PMT appears to be imperfect nesting (dispersion in
ARPES) while perfect nesting occurs at the MT (no dispersion in
ARPES).
3. The pre-martensite transition is a failed attempt to transition to a lower
energy state.
4. Our temperature dependent and ARPES measurements appear to
confirm Lee’s hypothesis concerning FS nesting. {Lee et al., Phys.
Rev. B 66 (2002)}.
5. Are pseudo-gaps just a generic feature of metals/alloys?