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

Selected Paradigm Materials (TMTSF) 2 ClO 4 -(BEDT-TSeF) 2 FeCl 4 S = 5/2 Per 2 [Au(mnt) 2 ] CDW + Pressure: AMRO & SC Per 2 [Pt(mnt) 2 ] (S = ½) Spin Peierls + CDW + Field Phase diagram: NMR & Transport FISDW phase diagram: NMR vs. Transport Mysterious MI-AF transition: Mössbauer studies  -(BETS) 2 Fe x Ga 1-x Cl 4-y Br y “alloy studies”

(Osada et al. - first high field phase diagram, B th, B 1, B 2 ) I.

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

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

T = 1.5 K: peak in 1/T 1 occurs at B 1. B1B1 B th B//c, field (frequency) dependent data. Metallic pulses

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

“Simultaneous” Resistance,1/T 1, and enhancement factor vs. rotation at 14 T. Takahashi et al. B th B1B1 B1B1 B1B1 Works because FISDW is primarily orbital.

Rotation data at 30 T. B th B1B1 B* B RE

Main results: 1/T 1 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 “B re ”. Sub-phases clearly seen in NMR. Improved nesting model for all phase transitions needed. Q1Q1 L. L. Lumata: Phys. Rev. B 78, (R)(2008). J. Physics: Conf. Series 132, (2008).

57 Fe Mossbauer in -BETS 2 FeCl 4 Ga: no magnetic order, superconductivity Fe: AF magnetic order, M-I transition Conventional wisdom: d-electron (Fe 3+, S = 5/2) states drive the AF-MI transition II.

Interplay of  and d electron spins is a complex problem. M: Akutsu et al.  Kobayashi et al. Uji Global Phase Diagram: Tuning internal field H J from 0 to 32 T with X: -(BETS) 2 Fe x Ga x-1 Cl 4 B sf via  Sasaki et al. Tokumoto et al. Some  -d phenomena in -(BETS) 2 FeCl 4 EPR – Rutel, Oshima, et al. H//c Also, magnetoresistance, etc. T MI-AF = 8.3 K

H  -d ~ 4 T. S=5/2 spectrum produces a Schottky C P below T N. “ ’’

Strategy: look at the Fe 3+ sites directly using Mössbauer spectroscopy Lisbon: 99% 57 Fe enriched TEAFeCl 4 –S. Rabaça Tokyo: Electrochemical crystallization of -(BETS) 2 FeCl 4 –B. Zhou Lisbon: constant-acceleration spectrometer and a 25 mCi 57 Co source in a Rh matrix –J. C. Waerenborgh

~ 0 57 Fe Mossbauer in -BETS 2 FeCl 4  0 1 & 2 1 & 2 Single Below T MI, we find two sextets corresponding to M s =  5/2 with slightly different B hf values. The sextets merge below 3 K.

Assume the Fe 3+ spin is in the presence of finite H p-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 H  -d :

Experimental and computed hyperfine field B hf and derived H  -d field. Waerenborgh et al. arXiv: (PRB-submitted)

Main results of Mössbauer measurements: 1.Paramagnetic state above T MI 2.Abrupt onset of B hf below T MI. 3.Also paramagnetic below T MI, but now H  -d is finite. 4.B hf is temperature dependent, predicts that H  -d is also temperature dependent, and reasonably described by AF spin-wave theory. 5.Two Fe sites with different B hf values, with intensity ratio 2:1. Merge below 3 K. Q vector change? Mössbauer and C P appear to agree that Fe 3+ spins do not have long range AF order below T MI, even though the  -spin system does. A probe of the spin dynamics, field-dependent C p, and Mössbauer studies would be useful. Also: Theory.

A brief look at  -(BETS) 2 Fe x Ga 1-x Cl 4-y Br y Results from SdH: Disorder for x  0,1 and/or y  0,4 (T D ) Effective mass (F  ) correlated with M-X bond length? Radical change in FS for  -(BETS) 2 FeCl 2 Br 2 T D ~ 0.5 KT D ~ 3.5 K III.

 -(BETS) 2 GaBr 4  -(BETS) 2 FeCl 2 Br 2 F  = 948 T; T D = 0.55 K F  = 4616 T F  = 80 to 120 T F  = 260 T; T D = 3.5 K Different FS No negative MR. E. Steven et al., ISCOM Physica B, to be published.

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

EPL 85 No 2 (January 2009) Slow cooling rate under pressure is very important! CDW-SC Proximity: ???????????????????? J. Merino and R. H. McKenzie, Superconductivity Mediated by Charge Fluctuations in Layered Molecular Crystals, PRL 87, (2001). SDW-SC: T. Vuletic et al., Coexistence of superconductivity and spin density wave orderings in the organic superconductor (TMTSF) 2 PF 6, Eur. Phys. J. B 25, 319 (2002). IVa.

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

Orbital effects: Magnetic field dependent Two families due to two extremal area planes in the Fermi Surface 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. Main Results:

Interaction of Peierls and Spin Peierls transitions in Per 2 [Pt(mnt) 2 ]  T CDW /T CDW (0) ~ -  (  B B/k B T CDW (0)) 2  T SP /T SP (0) ~ -0  44(  B B/k B T SP (0))  2(  B B/k B T SP (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? IVc.

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

T(K) Pt 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.

Cпасибо!