1. Very one dimensional organic conductors – Less is more J. S. B, M. Almeida, L.L. Lumata, P. Kuhns, A. Reyes, D. Graf, R. Henriques, L. Prettner (Green), J. Wright, and S. Brown First, some news from the Magnet Lab in Tallahassee and Los Alamos

2. 2 Objective 25 T central field 28 MW dc power (2 supplies) 4 ports at mid-plane of 45° each Vertical or horizontal field 2 Sets of inner coil 25 T SPLIT RESISTIVE MAGNET Jack Toth Project Leader Now Working! Please consider coming to us for magnetooptics studies! Steve McGill - femptosecond Dmitry Smirnov – visible/raman Jason Li - FTIR

3. Instrumentation: 4 x scattering cone (line of sight) aligned with cell vs. 45° 4 tapered access ports each: 11.4° x 45° 11.4° ~ 1m Dewar 32mm bore ~25T Optics in the Split-Florida Helix 25 T Visible/Fast optics IR & THz cw optics Amplified Ti:Sapphire (2.5 mJ, 150 fs, 1 KHz) OPA, Streak camera, VIS and NIR detectors Ar +, He-Ne, He-Cd, and dye lasers for cw Activities: Preparing implementation of inelastic light scattering experiments 0.75m McPherson spectrometer Custom optical cryostat being purchased Selecting window materials Bruker 66 FTIR spectrometer (roving cell-to-cell) Sub-THz tunable sources: BWO (Backward wave oscillators), Mid-IR CO 2 laser (11 μm) Mid-IR and Far-IR detectors Near future: Fiber-free techniques expand possibilities for UV spectroscopy, polarization-resolved, & time- resolved experiments Transfer of existing techniques + Split-Helix = new capabilities: TriVista High-resolution spectrometer FTIR in Voigt geometry IR luminescence

4. New High Magnetic Field Record 97.4 tesla confirmed via magneto quantum oscillations in poly-crystalline copper *World Record magnetic field intensity for a Non-Destructive Pulsed Magnet * 97.4 tesla

5. Very one dimensional organic conductors – Less is more Per 2 [M(mnt) 2 ] (M = Au, Pt, Co): Charge Density Wave Spin-Peierls Metal Agenda: Some History Part I: P = 0 (SP-CDW coupling) Part II: P ≠ 0 (Low Temp Metal and SC) J. S. B, M. Almeida, L.L. Lumata, P. Kuhns, A. Reyes, D. Graf, R. Henriques, L. Prettner (Green), J. Wright, and S. Brown Supported by NSF DMR-0602859 & 1005293 (JSB), by FCT (Portugal) PTDC/FIS/113500/2009 (MA), by NSF DMR-0804625 (SEB), and performed at the National High Magnetic Field Lab (supported by NSF DMR-0654118, by the State of Florida, and the DOE).

6. Quasi-one-dimensional organic conductor Perylene 2 [M(mnt) 2 ] Canadell et al., Eur. Phys. B 42, R453(2004). (mnt =maleonitriledithiolate) a = 16.612 Å ; t a = 2 meV b = 4.1891 Å : t b = 150 meV c = 26.583 Å; t c = 0 meV “L. Alcácer Salts”: Mol. Cryst. Liq. Cryst. 120, 221(1985)

7. M SP CDW 2b 4b b CDW Dimerization - spin Peierls when S = ½  1/4 filled band - conductor d ½ filled band - insulator Tetramerization - Peierls (CDW) Main Result: A CDW forms on the Perylene Chains A Spin Peierls state forms on the M(mnt) 2 chains with S ≠ 0. The two transitions are coincident. Why? TetramerDimer In case you want to sleep through the history, here is the message:

8. Nature, 173, 168(1954).

9. Q1D metal Ln(  ) 1/T x 10 3 Ni Cu Pd

10. Q1D metal M–I & spin Transition  /  RT  p 10 -4 /mole T (K) Magnetic Transition M-I Transition

11. l Q1D metal M–I & spin Transition S =½ Dimer formation Dimerization of spin 1/2 d-electron chain.

12. Q1D metal M–I & spin Transition S =½ Dimer formation Perylene Tetramer

13. Q1D metal M–I & spin Transition Dimer Formation Perylene Tetramer CDW M = Au Collective CDW Transport: M = Au

14. Q1D metal M–I & spin Transition Dimer formation Perylene Tetramer CDW M = Au M = Pt Collective CDW Transport: M = Pt

15. Q1D metal M–I & spin Transition Dimer formation Perylene Tetramer CDW M = Au M = Pt CDW & SP coupling

16. Q1D metal M–I & spin Transition Dimer formation Perylene Tetramer CDW M = Au M = Pt CDW & Pt chain coupling Spin Peierls! Identification of magnetic transition as Spin-Peierls associated with the Pt Spin ½ chains (consistent with XRD).

17. Per 2 [Au(mnt) 2 ] Q1D metal M–I & spin Transition Dimer formation Perylene Tetramer CDW M = Au M = Pt CDW & Pt chain coupling Spin Peierls! B dep. of CDW

18. Pt Au Q1D metal M–I & spin Transition Dimer formation Perylene Tetramer CDW M = Au M = Pt CDW & Pt chain coupling Spin Peierls! B dep. of CDW Pt too! Per 2 [Pt(mnt) 2 ]: Spin-Peierls + CDW system also shows similar B dependence.

19. Q1D metal M–I & spin Transition Dimer formation Perylene Tetramer CDW M = Au M = Pt CDW & Pt chain coupling Spin Peierls! B dep. of CDW Pt too! Eq. 1 Eq. 2

20. Q1D metal M–I & spin Transition Dimer formation Perylene Tetramer CDW M = Au M = Pt CDW & Pt chain coupling Spin Peierls! B dep. of CDW Pt too! CDW-SP coupling B // chains B  chains CDW induces SP B influences CDW-SP coupling

21. Graf et al., Phys. Rev. B 69, 125113 (2004) High field phase diagram for Per 2 [Au(mnt) 2 ] Q1D metal M–I & spin Transition Dimer formation Perylene Tetramer CDW M = Au M = Pt CDW & Pt chain coupling Spin Peierls! B dep. of CDW (B crit ~ 40T) Pt ? CDW-SP coupling Finally, our group did something!

22. Graf et al., Phys. Rev. Lett. 93, 076406 (2004). Q1D metal M–I & spin Transition Dimer formation Perylene Tetramer CDW M = Au M = Pt CDW & Pt chain coupling Spin Peierls! B dep. of CDW (B crit ~ 40T) Pt ? (B crit ~ 20T) CDW-SP coupling Field induced CDW? Second high field, high resistance phase? Per 2 [Pt(mnt) 2 ]

23. Large difference in the nature of the T-B phase diagrams determined from transport studies at high fields indicates the possible role of SP chains in the suppression of the CDW state. How can we independently monitor the field dependence of the Spin Peierls chain to see what it is doing? ~ 10 K M = Au M = Pt

24. Proton ( 1 H) NMR – Strongly influenced by Pt spin state. two-chain

25. CDW Electrical conductivity probes the perylene stacks. CDW  SP Protons on the perylene are the links to the Pt(mnt) 2 anions. SP The localized spin ½ electron at the Pt(mnt) 2 site gives rise to the spin- Peierls behavior. Strategy: Study the 1 H and 195 Pt NMR signals with field and temperature, and compare it with the transport data.  1H1H 195 Pt

26. T-Dep B-Dep 1 H spectra change dramatically at SP transition. Multiple spectral lines: paramagnetic Single spectral line: spin singlet (SP) E. L. Green et al., PRB (Rapid), in press.

27. T-B Phase Diagram: CDW – Transport SP – 1 H NMR E. L. Green et al., PRB (Rapid), in press. Per 2 [Pt(mnt) 2 ] SP Boundary Follows CDW Boundary to First Critical Field region ~ 20 T. Strong coupling. 1 H NMR results for

28. The larger picture: Phase diagram for both S=0 and S = ½ cases Second moment analysis of high field spectra indicate that SP spin singlet state is breaking down and system is becoming spin polarized. Torque magnetization corroborates this process. CDW Spin chain moment B (T)

29. Part I summary (P = 0) There are several unsolved questions: 1)What is the mechanism for the coupling of the SP and CDW chains/order parameters? (only one (?) theory has treated it) 2)Who drives who? Is the CDW necessary for the SP to form? (Mostly based on interpretation of experimental results.) 3)What is the origin of the “FISDW” high field phase? (Several theories and speculations)

30. 1)Theory: Dimerization induced by the RKKY interaction, J. C. Xavier, R. G. Pereira, E. Miranda, I. Affleck, Physical Review Letters, 90, 247204 (2003). Model: One dimensional S=1/2 Kondo model with L sites. is the conduction electron spin operator. Kondo coupling J > 0 Dimerization of the S=1/2 spin system at ¼ filling is determined from the order parameter:

31. Results of theory: Relevant to Per 2 [Pt(mnt) 2 ]  1D suppresses SDW  Small energy scale consistent with suppression by field.  Opens a charge gap as well (i.e. like CDW) at ¼ filling.  RKKY drives the dimerized spin + charge gap (“SP+CDW”) transition. Dimerization induced by the RKKY interaction, J. C. Xavier, R. G. Pereira, E. Miranda, I. Affleck, Physical Review Letters, 90, 247204 (2003). Need a two chain theory where S and s are on different chains.

32. 2) Who drives who? CDW and SP form at same T sp-cdw CDW driven: 1)CDW can form in absence of spin chain. 2)Coulomb interactions when CDW forms may drive dimerization in SP chains. 3)NMR & transport: SP order parameter seems to develop fully slightly later that CDW does. SP driven: 1)Xavier et al. – RKKY 2)SP seems to “pull down” CDW transition: For M = Au, T cdw = 12 K; for M = Pt, T sp-cdw = 8 K.

33. R. McDonald, PPHMF & private communication. 3) What is the origin of the “FISDW” high field phase? Nesting (after restoration of metallic phase) – but only weakly orbital Lebed(JETP): (“Gorkov-Lebed”) - T FICDW ~ 0.1 K, but T HF ~ 4 K Lebed(PRL): Zeeman splitting of 4 bands where original CDW nesting condition is restored – but why in M=Pt but not M=Au – higher fields? Restoration of non-magnetic CDW system when SP is spin polarized – however, SP and CDW order parameters appear to be attractive, not repulsive.

34. Part 2 (P ≠ 0) The Metal Pressure dependence in Per 2 [M(mnt) 2 ] is non-trivial. Can’t detect this at low T by Fermiology due to CDW formation at higher temperatures. Canadell et al., Eur. Phys. B 42, R453(2004). Try to get rid of CDW with Pressure

35. Counterion dimerisation effects in the two-chain compound (Per) 2 [Co(mnt) 2 ]: structure and anomalous pressure dependence of the electrical transport properties M. Almeida, V. Gama, I. C. Santos, D. Graf and J. S. B., CrystEngComm, 2009, 11, 1103–1108 This anomalous behaviour can be understood as a consequence of a change of the perylene molecule overlap due to a transverse sliding of molecules along alternated directions of their planes imposed by the dimerised anion stacks. P (kbar)

36. T MI & T R Log(R/R 0 ) 1/T P T Au Pt

37. Evolution of superconductivity from a charge density wave ground state in pressurized (Per) 2 [Au(mnt) 2 ] D. Graf, J.S. B., M. Almeida, J.C. Dias, S. Uji, T. Terashima and M. Kimata, Euro Physics Letters 85 27009/1-5(2009). Metallic at 5.3 Kbar – slow cooled! Bakrim and Bourbonnais, Supeconductivity close to the charge-density-wave instability, Euro Phys. Lett. 90, 27001(2010). Q1D metal Supercon ductivity

38. Superconductivity close to the charge-density-wave instability H. Bakrim and C. Bourbonnais, Euro Physics Letters 90, 27001(1-6)(2010).

39. D. Graf, J. S. Brooks, E. S. Choi, M. Almeida, R. T. Henriques, J. C. Dias, and S. Uji, Geometrical and orbital effects in a quasi-one-dimensional conductor, Physical Review B 80, 155104 (1-5)(2009). Per 2 [Au(mnt) 2 ] 5 kbar Complex AMRO Q1D metal Supercon ductivity Angular dependent resistance oscillations

40. D. Graf, J. S. Brooks, E. S. Choi, M. Almeida, R. T. Henriques, J. C. Dias, and S. Uji, Quantum interference in the quasi-one-dimensional organic conductor (Per) 2 Au(mnt) 2 Phys. Rev. B 75, 245101/4(2007). Quantum Interference Orbits. (Per) 2 [Au(mnt) 2 ] Q1D metal Supercon ductivity Angular dependent resistance oscillations Quantum Interference Orbits

41. Summary Q1D metal M–I & spin Transition Dimer formation Perylene Tetramer CDW M = Au M = Pt CDW & Pt chain coupling Spin Peierls! B dep. of CDW (B crit ~ 40T) Pt ? (B crit ~ 20T) CDW-SP coupling Field induced CDW? Superconductivity Angular dependent resistance oscillations Quantum Interference Orbits This two-chain highly one dimensional conductor comes in magnetic and non-magnetic flavors – Provides a huge variety of physical states and properties. – Surely there are many more surprises to come as theoretical and experimental methods advance. Immediate theoretical questions: SP-CDW coupling in a two-chain system. Step 1: B = 0. Step 2: B large. Chaikin: (TMTSF) 2 ClO 4 = Quantum Gravity JSB: Per 2 [M(mnt) 2 ] = Dark Energy

42. Thanks to Serguei, Natasha, and Pierre!

44. M SP- CDW  c B a Per 2 [Pt(mnt) 2 ]

45. very one dimensional organic conductors – Less is more J. S. Brooks 1* and M. Almeida 2* 1 NHMFL/Physics, 1800 E. Paul Dirac Dr., Tallahassee FL, 32310 USA 2 Instituto Tecnológico e Nuclear / CFMCUL, Estrada Nacional n o 10, P-2686-953 Sacavém, Portugal In this talk, we present a summary of recent work under “extreme conditions”, meaning high fields, low temperatures, and high pressure where organic conductors in the class (Per) 2 [M(mnt) 2 ] do some pretty amazing things. Here M can be a spin = 0 (Au, Cu, Co), or a spin = 1/2 (Pt, Pd, Ni, Fe) metal ion. The work to be described, done by my group and collaborators, follows on nearly 30 years of previous, beautiful work by the Lisbon group and their collaborators that has been summarized in a relatively complete paper by Almeida and Henriques. Our more recent work has focused so far on the (Per) 2 [Au(mnt) 2 ] S=0, (Per) 2 [Pt(mnt) 2 ] S=1/2, and also (Per) 2 [Co(mnt) 2 ]. In this presentation, for (Per) 2 [Au(mnt) 2 ] and (Per) 2 [Pt(mnt) 2 ], we will review the effects of high magnetic field on the charge density (CDW) and spin-Peierls (SP) ground states, the effects of pressure on these ground states, and the appearance of quantum interference, “magic angle effects”, and superconductivity (see also theory by Bakrim and Bourbonnais ) in (Per) 2 [Au(mnt) 2 ] when the CDW is removed at high pressure. We will also review the unusual increase in the CDW transition temperature with pressure in (Per) 2 [Co(mnt) 2 ]. The final topic in the presentation will focus on our most recent work involving 195 Pt and 1 H NMR in (Per) 2 [Pt(mnt) 2 ] where we have tracked the spin- Peierls behavior of the [Pt(mnt) 2 ] chains with field and temperature and have compared our results with previous electrical transport and magnetization studies of the CDW phase diagram under high magnetic fields. We will discuss these results in light of theoretical work that considers the interaction of itinerant conduction electrons and localized moments in quasi-one-dimensional systems. The overarching purpose of this presentation is to attract both the experimental and theoretical community to consider further work on these amazing systems that are clearly as rich in physical phenomena as the BEDT-TTF, TMTSF, and TMTTF materials. *Supported by NSF DMR-0602859 & 1005293 (JSB), by FCT (Portugal) PTDC/FIS/113500/2009 (MA), by NSF DMR-0804625 (SEB), and performed at the National High Magnetic Field Lab (supported by NSF DMR-0654118, by the State of Florida, and the DOE).