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?