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Some Igor Schegolev and Chernokolovka Recollections:

Some Igor Schegolev and Chernokolovka Recollections:. Igor visited Gor’kov at the NHMFL in the early 90’s: Learned about “Igor” software. a -(BEDT-TTF) 2 TlHg(SCN) 4 first material measured at the NHMFL. 20 T at 50 mK*. Some major Chernokolovka physics advances:

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Some Igor Schegolev and Chernokolovka Recollections:

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  1. Some Igor Schegolev and Chernokolovka Recollections: • Igor visited Gor’kov at the NHMFL in the early 90’s: Learned about “Igor” software. a-(BEDT-TTF)2TlHg(SCN)4 first material measured at the NHMFL. 20 T at 50 mK*. • Some major Chernokolovka physics advances: • FS reconstruction in a-(ET)2MHg(SCN)4 • AMRO and its interpretation Due to: Kartsovnik, Kovalev, Shibaeva, Rozenberg, Schegolev, Kushch, Laukhin, Pesotskii, Yakovenko, et al. *Brooks,…Kartsovnick M V, Schegolev A I, et al. 1996 Physica B216 380

  2. Selected Paradigm Materials Per2[Au(mnt)2] CDW + Pressure: AMRO & SC Per2[Pt(mnt)2] (S = ½) Spin Peierls + CDW + Field Phase diagram: NMR & Transport l-(BEDT-TSeF)2FeCl4 S = 5/2 (TMTSF)2ClO4 FISDW phase diagram: NMR vs. Transport Mysterious MI-AF transition: Mössbauer studies k-(BETS)2FexGa1-xCl4-yBry “alloy studies”

  3. I. (Osada et al. - first high field phase diagram, Bth, B1, B2)

  4. Is High field T-B phase diagram of (TMTSF)2ClO4 time dependent? Naughton1988 Yu 1990 McKernan 1995 T(K) T(K) H(T) H(T) Uji 1997 Lumata 2008 Chung 2000 77Se NMR?

  5. L. Lumata – simultaneous 77Se NMR and magnetotransport in (TMTSF)2ClO4. c 0.21 mm dia. NMR coil B q a b Two modes: 1) Fixed angle, change frequency/field 2) Rotation (q) in b-c plane, fix frequency, change Bperp = Bcos(q) Measure: Spectrum, 1/T1, and enhancement factor h * “Metallic pulse”: 12 W @ 1 ns pulse width “SDW pulse”: 12 W @ 500 to 50 ns pulse width V. Mitrovic, Takigawa et al.

  6. Metallic pulses B//c, field (frequency) dependent data. T = 1.5 K: peak in 1/T1 occurs at B1. Bth B1

  7. “Simultaneous” Resistance and 1/T1 measurements. Sub-phase boundary clearly shows a change in the nesting condition.

  8. “Simultaneous” Resistance ,1/T1, and enhancement factor vs. rotation at 14 T. Takahashi et al. Bth B1 Works because FISDW is primarily orbital. B1 B1 Bth Bth

  9. Rotation data at 30 T. BRE Bth B1 B*

  10. Q1 Main results: 1/T1 does not peak at the resistive Metal-FISDW transition, but inside the FISDW phase. (Hebel-Slichter like? Theory needed.) “Primitive model”, McKernan et al. SSC 145, 385(2008) appears relevant at “Bre”. Sub-phases clearly seen in NMR. Improved nesting model for all phase transitions needed. L. L. Lumata: Phys. Rev. B 78, 020407(R)(2008). J. Physics: Conf. Series 132, 012014(2008).

  11. II. 57Fe Mossbauer in l-BETS2FeCl4 Ga: no magnetic order, superconductivity Fe: AF magnetic order, M-I transition Conventional wisdom: d-electron (Fe3+, S = 5/2) states drive the AF-MI transition

  12. Some p-d phenomena in l-(BETS)2FeCl4 H//c M: Akutsu et al. c: Kobayashi et al. EPR – Rutel, Oshima, et al. Uji Global Phase Diagram: Tuning internal field HJ from 0 to 32 T with X: l-(BETS)2FexGax-1Cl4 Bsf via t: Sasaki et al. Tokumoto et al. TMI-AF= 8.3 K Also, magnetoresistance, etc. Interplay of p and d electron spins is a complex problem.

  13. “ ’’ Hp-d ~ 4 T. S=5/2 spectrum produces a Schottky CP below TN.

  14. Strategy: look at the Fe3+ sites directly using Mössbauer spectroscopy • Lisbon: 99% 57Fe enriched TEAFeCl4 • S. Rabaça • Tokyo: Electrochemical crystallization of l-(BETS)2FeCl4 • B. Zhou • Lisbon: constant-acceleration spectrometer and a 25 mCi 57Co source in a Rh matrix • J. C. Waerenborgh

  15. 57Fe Mossbauer in l-BETS2FeCl4 <Bhf>1 & <Bhf>2 <Bhf> ~ 0 <Bhf>  0 Single <Bhf> <Bhf>1 & <Bhf>2 Below TMI, we find two sextets corresponding to Ms =  5/2 with slightly different Bhf values. The sextets merge below 3 K.

  16. Assume the Fe3+ spin is in the presence of finite Hp-d and that the relaxation is relatively fast. The hyperfine field is: Assume spin wave theory (with linear dispersion for AF order) describes the T-dependence of Hp-d:

  17. Experimental and computed hyperfine field Bhf and derived Hp-d field. Waerenborgh et al. arXiv:0909.1096 (PRB-submitted)

  18. Main results of Mössbauer measurements: • Paramagnetic state above TMI • Abrupt onset of Bhf below TMI. • Also paramagnetic below TMI, but now Hp-d is finite. • Bhf is temperature dependent, predicts that Hp-d is also temperature dependent, and reasonably described by AF spin-wave theory. • Two Fe sites with different Bhf values, with intensity ratio 2:1. Merge below 3 K. Q vector change? Mössbauer and CP appear to agree that Fe3+ spins do not have long range AF order below TMI, even though the p-spin system does. A probe of the spin dynamics, field-dependent Cp, and Mössbauer studies would be useful. Also: Theory.

  19. III. TD ~ 0.5 K TD ~ 3.5 K A brief look at k-(BETS)2FexGa1-xCl4-yBry Results from SdH: Disorder for x  0,1 and/or y  0,4 (TD) Effective mass (Fa) correlated with M-X bond length? Radical change in FS for k-(BETS)2FeCl2Br2

  20. k-(BETS)2GaBr4 k-(BETS)2FeCl2Br2 FN1 = 80 to 120 T FN2 = 260 T; TD = 3.5 K Fa = 948 T; TD = 0.55 K Fb = 4616 T Different FS No negative MR. E. Steven et al., ISCOM Physica B, to be published.

  21. IV. Recent Progress in the Per2[M(mnt)2] compounds Pressure induced CDW-to-SC transition in Per2[Au(mnt)2] “Lebed’ resonance” and orbital signatures in AMRO studies Per2[Au(mnt)2] 195Pt NMR study of SP and CDW behavior in Per2[Pt(mnt)2] in high fields. (work still in progress!)

  22. Slow cooling rate under pressure is very important! IVa. EPL85 No 2 (January 2009) 27009 CDW-SC Proximity: ???????????????????? J. Merino and R. H. McKenzie, Superconductivity Mediated by Charge Fluctuations in Layered Molecular Crystals, PRL 87, 237002(2001). SDW-SC: T. Vuletic et al., Coexistence of superconductivity and spin density wave orderings in the organic superconductor (TMTSF)2PF6, Eur. Phys. J. B 25, 319 (2002).

  23. IVb. Per2[Au(mnt)2] CDW? High Field (> 18 T) & High Pressure (~ 5 bar) reveal FS topology Orbital: QI type oscillations. Geometrical: a-c plane commensurate effects.

  24. Main Results: Geometrical effects: Magnetic field independent Related to crystallographic directions where the transfer integral paths are strongest. Next step: Lebed magic angle effects? Metal, NFL, Nernst, etc. Orbital effects: Magnetic field dependent Two families due to two extremal area planes in the Fermi Surface

  25. Interaction of Peierls and Spin Peierls transitions in Per2[Pt(mnt)2] IVc. DTCDW/TCDW(0) ~ -g(mBB/kBTCDW(0))2 DTSP/TSP(0) ~ -0.44(mBB/kBTSP(0))2 - 0.2(mBB/kBTSP(0))4 How and when does magnetic field break the Peierls (1/4 filled) and Spin Peierls (1/2 filled) ground states in the parallel chain system?

  26. A.G. Lebed and Si Wu, PRL 99, 026402 (2007) Pt T(K) Breaking the Peierls and Spin Peierls states in Per2[Pt(mnt)2] with high magnetic field. Graf et al., PRL. Strategy: follow the 195Pt NMR signal with field and temperature, and compare it with the transport data. But, could the Pt chains be involved?

  27. Pt T(K) Main Result So Far: The NMR signal vanishes when the CDW-Metal Phase Boundary Is Approached. Possible that SP is not broken until the CDW phase boundary is reached.

  28. Cпасибо!

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