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Interlayer tunneling spectroscopy of NbSe 3 and graphite at high magnetic fields

Interlayer tunneling spectroscopy of NbSe 3 and graphite at high magnetic fields. Yu.I. Latyshev Institute of Raduio-Engineering and Electronics RAS, Mokhovaya 11-7, Moscow 125009 In collaboration with А. P . О rlov , A.Yu . Latyshev IREE RAS, Moscow

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Interlayer tunneling spectroscopy of NbSe 3 and graphite at high magnetic fields

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  1. Interlayer tunneling spectroscopy of NbSe3 and graphite at high magnetic fields Yu.I. Latyshev Institute of Raduio-Engineering and Electronics RAS, Mokhovaya 11-7, Moscow 125009 In collaboration with А.P. Оrlov, A.Yu. Latyshev IREE RAS, Moscow A.A. Sinchenko Moscow Eng. Physical Institute А.V. IrzhakMoscow Inst. of Steel and Alloys P. Monceau, Th. Fournier Neel Institute, Grenoble, France J.Marcus D. Vignolles LNCMP, Toulouse, France

  2. OUTLINE • Introduction to interlayer tunneling in layered superconductors and charge density wave materials. • CDW gap spectroscopy at high magnetic field in NbSe3. • Graphite. Nanostractures fabrication with focused ion beam. • Pseudogap. • Interlayer tunneling spectroscopy of Landau levels. • Behaviour in high magnetic fields. • Conclusions.

  3. Interlayer tunneling in layered HTS and CDW materials

  4. Layered crystalline structure σ║/σ┴=103-104 NbSe3 Sample configuration L L L s

  5. Bi-2212. Gap/pseudogap spectroscopy Yu.I. Latyshev et al.ISS Conf. 1999, Physica C, 2001; V.M. Krasnov et al. PRL, 2000, 2001

  6. Spectroscopy of CDW gap and intragap states.NbSe3 4.2К 170К Yu.I. Latyshev, P. Monceau, S. Brazovskii, A.P. Orlov, Th. Fournier, PRL 2005, 2006

  7. 1. CDW gap spectroscopy in high magnetic fields

  8. Anomalously high magnetoresistance in NbSe3 . Orbital effect on partly gapped CDW state. Magnetic field destroys ungapped pockets C.A. Balseiro and L.M. Falicov 1984, 1985 L.P. Gor’kov and A.G. Lebed 1984 R.V. Coleman et al. PRL 1985 Magnetic field improves nesting condition and thus can increase CDW gap Q Q 2K 2K F F A. Bjelis, D. Zanchi, G. Montambeaux PR B 1996, cond-mat /1999 also have shown the possibility to increase Tp by magnetic field. H=0 H perfe c t im perfe c t

  9. Zeeman splitting effect on CDW ordering In a zero field the CDW state is degenerated with respect to spin up ­ ­ ¯ ¯ and spin down configurations. Magnet i c field releases s degeneration due to Zeeman splitting. As a result Q ­ ­ CDW vector in creases with field while Q decreases ¯ ¯ Q > Q > Q ­ ­ ¯ ¯ 0 Therefore a CDW state with a fixed Q tends to be destroyed with field. 0 One can expect the interplay between orbital and Pauli effects at high fields of the scale 2BH ~ kTp. . For NbSe3 with Tp =60K that requires experiments at fields ~50T

  10. Experiments at pulsed magnetic field (see also p. 29 at poster session) LNCMP, Toulouse High speed acquisition system

  11. Field-induced gap. 3D picture. T=65 K

  12. Induced CDW gap above Peierls transition temperature H=35T H=0

  13. Field induceed CDW state Phase diagram. Interplay of orbital and Pauli effects. Non-monotonic behaviour of Tp(H) is defined by interplay between orbital and Pauli effects on CDW pairing. Orbital effect is realized in improving of nesting condition and, thus, in increase of  and Tp, while Zeeman splitting tends to destroy CDW pairing. Experimental crossover field corresponds to H  30T,2BH0 kTp That is consistent with calculatons of Zanchi, Bjelis, Montambeau PRB 1996 for the case of moderate imperfection parameter (valid for NbSe3) BH0 / (2Tp)  0.1 or For Tp = 61 K that corresponds to H0 30T

  14. 2. Interlayer tunneling spectroscopy of graphite

  15. Questions: • Is there interlayer correlation? • Is that possible to observe Dirac fermion features by interlayer tunneling technique? • Which is the inter-graphene behaviour in high magnetic fields?

  16. Fabrication of nanostructures

  17. FIB microetching method Yu.I. Latyshev, T. Yamashita, et al. Phys. Rev. Lett., 82 (1999) 5345. S.-J. Kim, Yu.I.Latyshev, T. Yamashita, Supercond. Sci. Technol. 12 (1999) 729. FIB machine Seiko Instruments Corp. SMI-9000(SP) Ga+ ions 15-30 kV Beam current : 8pA – 50 nA Minimal beam diameter: 10nm

  18. Stacked structures fabricated from layered materials by FIB methods NbSe3 single crystals are thin whiskers with a thickness of 1-3 m, a width of 20 m and a length of about 1 mm Figure 2. (a-c) Stages of the double sided FIB processing technique for fabrication of the stacked structure; (d) SEM image of the structure. The structure sizes are 1 x 1 x 0.02 - 0.3 Yu. I. Latyshev et al. Supercond.Sci.Techn. 2007

  19. Pseudogap in graphite

  20. Interlayer tunneling in graphite mesas At 300K   0.2  cm, //  50  cm,  /// ~ 4000 At 4.2K  /// ~ 30 000 Mesa sizes; 1m x 1m x 0.02-0.03 We found an evidence of pseudogap formation in graphite below T0 =30K. Vpg  10-15 mV Vpg  3.5 kT0 !? Yu.I.Latyshev, A.P.Orlov, A.Yu. Latyshev,Th. Fournier, J. Marcus and P. Monceau 2007

  21. Observation of Dirac fermions in graphite previous experiments

  22. ARPES on graphite S.Y. Zhou et al. Nature Physics, 2006

  23. Landau quantization in graphite from STMG.Li and E.Andrei, Nature Phys. 07 Graphene spectrum E(k) =  vF(h/2) k Landau quantization E(n)= sgn n [2e (h/2) VF2|n|B]1/2 E(n)  (nB)1/2 Bilayer graphene E(n)= sgn n hc[|n|(|n|+1)]2 c = eB/m* Fit: vF= 1.07 108 cm/s as for graphene and for graphite data from ARPES For linear E(H) dependence m* = 0.028 m0

  24. Landau quantization in graphite from magneto-transmission experiment M. Orlita et al. Phys. Rev. Lett. 2008 selection rule: n = 1,

  25. Interlayer tunneling our experiments

  26. Landau quantization in graphite (Interlayer tunneling Yu.I.L, A.P. Orlov, D. Viqnolles 07 0.41 0.47 0.54 0.61 0.69 0.77 0.87 0.97 1.08 1.20 1.34 1.49 1.65 1.82 2.02 2.23 2.46 2.70 2.92 6 6 G #1 N30 G #3 N 20 Spectra are well reproducible, peak position does not dependent on N We found Landau quantization from interlayer tunneling transitions -1<->1, -2<->2 consistent with STM and magneto-transmission data аnother selection rule: |n| = 0 valid for coherent tunnеling

  27. Comparison of the 1st level energy for two samples V  H1/2 typical for Dirac fermions

  28. Comparison with STM and magneto transmission data Transitions -1<->1, -2<->2, -3<->3 observed are consistent with STM and magneto-transmission data. VF = 108 cm/s, En(nH)1/2

  29. Effects in strong magnetic fields

  30. Graphite at strong fieldsYu.I.L., A.P.Orlov, D. Vignolles, P. Monceau 07 Observation H. Ochimizu et al., Phys. Rev. B46, 1986 (1992). Explanation was related with the CDW formation along the field axis D. Yoshioka and H. Fukuyama, J. Phys. Soc. Jpn. 50, 725 (1981). We attempted to find CDW gap above 30 T Effect nearly disappeared for 20 graphene layers

  31. Pseudogap at graphite at high fieldsYu.L., A.P. Orlov, D. Vignolles, P. Monceau 06-07 Pseudogap appears above 20T, Vpg  150 mV Remarkable features: (1) increase of tunnel conductivity with field (2) field induced PG ???

  32. Field dependence of pseudogap value No essential field dependence above 25 T We consider that the big value of the field induced pseudogap is an indication of some collective excitations in graphene at high fields

  33. CONCLUSIONS • FIB technique has been adapted for fabrication mesa type structures on various nanomaterials as HTS materials, CDW layered materials and graphite. • We found the effect of CDW gap induction by high magnetic field above Peierls transition temperature. We also found non-monotonic dependence of Tp(H) which is interpreted as the interplay between orbital and Pauli effects on CDW ordering. • We found interlayer correllative gap in graphite below 25K with energy of 10-15 mV. • Using interlayer tunnelingwe identified in graphite Landau levels typical for Dirac fermions in graphene. • We found field induced pseudogap in graphite. The high value of the pseudogap, 150 mV, points out to its possible origin related with collective excitations in graphene.

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