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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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**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**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”**I.**(Osada et al. - first high field phase diagram, Bth, B1, B2)**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?**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.**Metallic pulses**B//c, field (frequency) dependent data. T = 1.5 K: peak in 1/T1 occurs at B1. Bth B1**“Simultaneous”**Resistance and 1/T1 measurements. Sub-phase boundary clearly shows a change in the nesting condition.**“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**Rotation data at 30 T.**BRE Bth B1 B***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).**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**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.**“**’’ Hp-d ~ 4 T. S=5/2 spectrum produces a Schottky CP below TN.**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**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.**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:**Experimental and computed hyperfine field Bhf and derived**Hp-d field. Waerenborgh et al. arXiv:0909.1096 (PRB-submitted)**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.**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**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.**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!)**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).**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.**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**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?**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?**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.

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