pseudo-gap observed at martensite transition in a ni2mnga … · 2019. 1. 16. · 2 mnga single...
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Pseudo-gap Observed at MartensiteTransition 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 02467USA2Los Alamos National Laboratory, Los Alamos, NM 87545 USA3Temple University, Physics Department, Philadelphia, PA 19122,USA4 Universitat de Barcelona, Departament d’Estructura i Constituentsde la Matèria, Facultat de Física, Diagonal 647, E-08028 Barcelona,Catalonia, Spain
Work sponsored by: Dept. of Energy and Boston College
Back Scatter Laue, T = 293K
Low Energy ElectronDiffraction (LEED)at T=293 K
Ni2MnGa (100)CubicFm-3ma = 5.825 Ang.Vol = 192.34 Ang.3Ni (0.25,0.25,0.25)Mn (0.5,0.5,0.5)Ga (0, 0, 0)
Ni2MnGa Single Crystal
Curie Transition:
TC
MT
PMTN-Gr
Heat Capacity at H=0 [T]:
TC Ferromagnetic Transition
Dilatometry
MT197 K
PMT214 K
MT is field independent
FCC to Monoclinic at MT
Lee, et al., Phys. Rev. B 66 (2002).
Fermi Surface Map
Temperature Dependent UV-Spectroscopy (hν=21.21eV)
Temperature Dependent UV-Spectroscopy (hν=21.21eV)
a-U(001) surface
surface normale-
analyzer
(100) plane
f
q
ARPES - chooseazimuthal q to specify k-vector to probe, and thenvary polar f to collectDOS at various kII andobserve dispersion ofbands along k-vector
!
kII
=2m
eE
kinetic
2
h
"sin#
!
Ekinetic = h" # e$#Ebinding
[100]
kX
kY
kZ
Z [001]
[010]
Brillouinzoneorientation
ARPES: AngleResolvedPhotoemissionSpectroscopy
ARPES-295 K
ARPES-219 K
Contour heightcolor key
ARPES-219 K
ARPES-173 K
Contour heightcolor key
-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5
Eb [eV]
Energy Dispersion Curves:
normal incidence normal incidence
ARPES at (pi,0) for u-doped Bi2212,90K Pseudo-gap state, 30K-SC state.
Norman et al., Adv. in Physics, 54 (2005)
Evidence of pseudo-gaps in other materials:
T-dependent photoemission ofKMo6O17 (purple-bronze) RT to 45 K.
Valbuena, et al., J. Phys. Chem. Solids 67 (2006)
(b)
ARPES at (pi,0) for u-doped Bi2212,90K Pseudo-gap state, 30K-SC state.
Norman et al., Adv. in Physics, 54 (2005)
Evidence of pseudo-gap in Bi2212:
Ni2MnGa data
Evidence of pseudo-gap in KMo6O17 (Purple-bronze):
T-dependent photoemission ofKMo6O17 (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 inARPES) while perfect nesting occurs at the MT (no dispersion inARPES).
3. The pre-martensite transition is a failed attempt to transition to a lowerenergy state.
4. Our temperature dependent and ARPES measurements appear toconfirm 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?