Angle Resolved Photoemission studies of the Charge Density Wave in RTe 3

Transcription

1 Angle Resolved Photoemission studies of the Charge Density Wave in RTe 3 (R = Y, La, Ce ) Véronique Brouet,,3 Laboratoire de physique des solides d Orsay (France) W.L. Yang,3, X.J. Zhou,3, Z. Hussain 3, Z.X. Shen,3 Advanced Light Source, Lawrence Berkeley National Laboratory (USA) 3 Stanford Synchrotron Radiation Laboratory, Stanford University (USA) N. Ru, K.Y. Shin and I.R. Fisher Stanford University (USA)

2 Angle Resolved Photoemission studies of the Charge Density Wave in RTe 3 (R = Y, La, Ce ) - RTe and RTe 3 structure - RTe 3 electronic structure determined by ARPES - Location and magnitude of the CDW gap along the Fermi Surface - Residual metallic pockets due to imperfect nesting

3 RTe and RTe 3 structure R/Te slab almost insulating Te (s p 4 ) square plane with electrons per Te

4 Transport anisotropy RTe 3 LaTe Crystal growth from binary melt? (in plane) (m? -cm) T (K)? (perp) (m? -cm) N. Ru, I.R. Fisher? c /? a ~ RRR ~ 5-

5 Charge density wave detected by transmission electron microscopy (3 K) SmTe 3, - Satellites pour q =.4??/a E. DiMasi, M.C. Aronson, J.F. Mansfield, B. Foran and S. Lee, Phys. Rev. B 5, 456 (95)

6 RTe 3 electronic structure

7 Square Te plane in CeTe 3 Electronic structure in a plane p x p y t t // Energy (ev) Tight-binding model Momentum k x Energy (=Ef for RTe3) kx (*pi/a)

8 More realistic FS calculation Fermi Surface in YTe 3 (S. Dugdale, Bristol university) «Bilayer splitting» Te p z orbital

9 CeTe 3 Fermi Surface h?=55ev K A para ky (pi/a units) - - kx (pi/a units) Spectral weight integrated between E f and E f - mev First observation (in SmTe 3 ) : Gweon et al. Physical Review Letters 8, 886 (998) 3

10 Folding of CeTe 3 Fermi Surface Ce Te ky (pi/a units) Ce/Te slab Te planes - - kx (pi/a units) 3 c b a - The low intensity of the folded Fermi Surface reflects the D character of the compound -

11 Location of the CDW gaps

12 Gap opening on the best nested parts of the Fermi Surface (I) K y =.63 ky (pi/a units) kx (?/a) K y = kx (?/a) - - kx (pi/a units) 3 K y =.7 Gap (mev) kx(?/a) K y = Ky (pi/a units) kx(?/a)

13 ky (pi/a units) Gap opening on the best nested parts of the Fermi Surface (II) kx (pi/a units) Gap (mev) 4 3 Square Outer Ky (pi/a units).8...4

14 The gap opens on parts of the Fermi Surface exhibiting the best nesting ky (pi/a units) Q Ky q N - - kx (pi/a units) Kx 3 Gap (mev) 4 3 Square Outer Q=.4?/a corresponds to the satellites seen by TEM Ky (pi/a units)

15 YTe 3 Fermi Surface h?=35ev K A para. 3 The gap is found along ky.

16 Evolution of the CDW properties as a function of rare earth Gap measured by ARPES 4 CeTe3 LaTe3 Gap (mev) 35 3 DyTe3 GdTe3 YTe3 5 TbTe Lattice parameter 4.45 N(E f ) increases with the lattice parameter, which probably stabilizes the CDW. This supports the description as a nesting driven CDW (also DiMasi et al. PRB 95).

17 Imperfect nesting : residual metallic pockets in CeTe 3

18 Fermi Surface Imperfect nesting Shadow band Q good nesting = gap opening Energie Q Moment bad nesting = metallic pockets Energie Q Moment Residual metallicity The size of the metallic pockets can be deduced for example from de Haas van Alphen oscillations.

19 Oscillations in magnetization of LaTe 3 N. Ru, I.R. Fisher, A. McKenzie

20 Fermi Surface Imperfect nesting Shadow band Q good nesting = gap opening Energie Q Moment bad nesting = metallic pockets Energie Q Moment Residual metallicity The size of the metallic pockets can be deduced for example from de Haas van Alphen oscillations.

21 Folded and shadow bands Binding energy (ev) kx (?/a) Binding energy (ev) ?/a - kx Shadow band (CDW) Binding Energy (ev) Binding energy (ev) - -4?/a - kx Folded bands (3D structure)

22 Crossing of CDW shadow bands in metallic parts of the CDW.. YTe Kx Kx

23 Determination of metallic pockets Ky (pi/a units)..5 ky (pi/a units).5 Kx (pi/a units) - - kx (pi/a units) 3 The Fermi surface seems to be made out of «arcs», but a closed contour is expected.

24 Determination of metallic pockets.5 Energy(eV) Ky (pi/a units).5 Energy(eV) Energy (ev) Kx (pi/a units) px py folded px folded py CDW shadow px CDW shadow py Energy(eV) Energy (ev) Kx (?/a units).4

25 Determination of metallic pockets.5 Energy(eV) Ky (pi/a units).5 Energy (ev) Energy(eV) Kx (pi/a units) px py folded px folded py CDW shadow px CDW shadow py Energy (ev) Energy(eV) Kx (?/a units).4

26 Determination of metallic pockets.5 Energy(eV) Ky (pi/a units).5 Energy (ev) Energy(eV) Kx (pi/a units) px py folded px folded py CDW shadow px CDW shadow py Energy (ev) Energy(eV) Kx (?/a units).4

27 Determination of metallic pockets.5 Energy(eV) ky (pi/a units).5 Energy (ev) Energy(eV) kx (pi/a units) px py folded px folded py CDW shadow px CDW shadow py Energy (ev) Energy(eV) Kx (?/a units).4.4

28 Metallic pockets.5.5 ky (pi/a units)..5 Ky (pi/a units)..5.5 kx (pi/a units).5 Kx (pi/a units) ARPES allows to get the details of the Fermi Surface pockets V. Brouet et al., PRL (4)

29 Conclusion - ARPES gives support for the charge density wave in CeTe 3 to be described as a nesting driven Fermi Surface instability. - The detailed topology of the residual Fermi surface has been obtained. - RTe 3 might be an interesting example of D Fermi liquid to study further.