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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.
-(BEDT-TTF)2TlHg(SCN)4 first material measured at the NHMFL. 20 T at 50 mK*.
• Some major Chernokolovka physics advances:– FS reconstruction in -(ET)2MHg(SCN)4
– AMRO and its interpretationDue to: Kartsovnik, Kovalev, Shibaeva, Rozenberg, Schegolev, Kushch,
Laukhin, Pesotskii, Yakovenko, et al.
*Brooks,…Kartsovnick M V, Schegolev A I, et al. 1996 Physica B 216 380
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Selected Paradigm Materials
(TMTSF)2ClO4
-(BEDT-TSeF)2FeCl4
S = 5/2
Per2[Au(mnt)2]CDW + Pressure: AMRO & SC
Per2[Pt(mnt)2] (S = ½)Spin Peierls + CDW + FieldPhase diagram:NMR & Transport
FISDW phase diagram:NMR vs. Transport
Mysterious MI-AF transition:Mössbauer studies
-(BETS)2FexGa1-xCl4-yBry
“alloy studies”
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(Osada et al. - first high field phase diagram, Bth, B1, B2)
I.
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Chung 2000
McKernan 1995
Uji 1997
77SeNMR?
Lumata 2008
Is High field T-B phase diagram of (TMTSF)2ClO4 time dependent?
Yu 1990
T(K
)
H(T)
Naughton1988
H(T)
T(K
)
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L. Lumata – simultaneous 77Se NMR and magnetotransport in (TMTSF)2ClO4.
Two modes:1) Fixed angle, change frequency/field
2) Rotation () in b-c plane, fix frequency, change Bperp = Bcos()
a
c
b
B
Measure: Spectrum, 1/T1, and enhancement factor
“Metallic pulse”: 12 W @ 1 ns pulse width
“SDW pulse”: 12 W @ 500 to 50 ns pulse width
V. Mitrovic,Takigawa et al.
*
0.21 mm dia. NMR coil
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T = 1.5 K: peak in 1/T1 occurs at B1.
B1Bth
B//c, field (frequency) dependent data.
Metallic pulses
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“Simultaneous”Resistance and 1/T1 measurements.
Sub-phase boundary clearly shows a change in the nesting condition.
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“Simultaneous”Resistance ,1/T1, and enhancement factor vs. rotation at 14 T.
Takahashi et al.
Bth
B1
Bth
B1
Bth B1
Works because FISDW is primarily orbital.
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Rotation data at 30 T.
Bth B1 B* BRE
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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.
Q1
L. L. Lumata: Phys. Rev. B 78, 020407(R)(2008). J. Physics: Conf. Series 132, 012014(2008).
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57Fe Mossbauer in -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
II.
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Interplay of and d electron spins is a complex problem.
M: Akutsu et al. Kobayashi et al.
Uji Global Phase Diagram:Tuning internal field HJ from 0 to 32 T with X:-(BETS)2FexGax-1Cl4
Bsf via Sasaki et al.Tokumoto et al.
Some-d phenomena in -(BETS)2FeCl4
EPR – Rutel, Oshima, et al.
H//c
Also, magnetoresistance, etc.
TMI-AF = 8.3 K
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H-d ~ 4 T. S=5/2 spectrum produces a Schottky CP below TN.
“
’’
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Strategy: look at the Fe3+ sites directly using Mössbauer spectroscopy
• Lisbon: 99% 57Fe enriched TEAFeCl4 – S. Rabaça
• Tokyo: Electrochemical crystallization of -(BETS)2FeCl4 – B. Zhou
• Lisbon: constant-acceleration spectrometer and a 25 mCi 57Co source in a Rh matrix– J. C. Waerenborgh
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<Bhf> ~ 0
57Fe Mossbauer in -BETS2FeCl4
<Bhf> 0
<Bhf>1 &<Bhf>2
<Bhf>1 &<Bhf>2
Single<Bhf>
Below TMI, we find two sextets corresponding to Ms = 5/2 with slightly different Bhf values. The sextets merge below 3 K.
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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 H-d:
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Experimental and computed hyperfine field Bhf and derived H-d field.
Waerenborgh et al.arXiv:0909.1096
(PRB-submitted)
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Main results of Mössbauer measurements:1. Paramagnetic state above TMI
2. Abrupt onset of Bhf below TMI.
3. Also paramagnetic below TMI, but now H-d is finite.
4. Bhf 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 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 -spin system does.
A probe of the spin dynamics, field-dependent Cp, and Mössbauer studies would be useful. Also: Theory.
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A brief look at -(BETS)2FexGa1-xCl4-yBry
Results from SdH:
Disorder for x 0,1 and/or y 0,4 (TD)
Effective mass (F) correlated with M-X bond length?
Radical change in FS for -(BETS)2FeCl2Br2
TD ~ 0.5 K TD ~ 3.5 K
III.
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-(BETS)2GaBr4 -(BETS)2FeCl2Br2
F = 948 T; TD = 0.55 KF = 4616 T
F = 80 to 120 TF = 260 T; TD = 3.5 K
Different FS No negative MR.
E. Steven et al., ISCOM Physica B, to be published.
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Recent Progress in the Per2[M(mnt)2] compounds
“Lebed’ resonance” and orbital signatures in AMRO studies Per2[Au(mnt)2]
Pressure induced CDW-to-SC transition in Per2[Au(mnt)2]
195Pt NMR study of SP and CDW behavior in Per2[Pt(mnt)2] in high fields.
(work still in progress!)
IV.
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EPL 85 No 2 (January 2009) 27009
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, 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).
IVa.
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CDW?High Field
(> 18 T)&
High Pressure (~ 5 bar)
reveal FS topologyOrbital: QI type
oscillations.
Geometrical:a-c plane
commensurate effects.
Per2[Au(mnt)2]
IVb.
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Orbital effects: Magnetic field dependentTwo families due to two extremal area planes in the Fermi Surface
Geometrical effects: Magnetic field independentRelated to crystallographic directions where the transfer integral paths are strongest. Next step: Lebed magic angle effects? Metal, NFL, Nernst, etc.
Main Results:
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Interaction of Peierls and Spin Peierls transitions in Per2[Pt(mnt)2]
TCDW/TCDW(0) ~ -(BB/kBTCDW(0))2
TSP/TSP(0) ~ -044(BB/kBTSP(0))2 - 02(BB/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?
IVc.
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Graf et al., PRL.
A.G. Lebed and Si Wu, PRL 99, 026402 (2007)
T(K)
Pt
Breaking the Peierls and Spin Peierls states in Per2[Pt(mnt)2] with high magnetic field.
Strategy: follow the 195Pt NMR signal with field and temperature, and compare it with the transport data. But, could the
Pt chains be involved?
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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.
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Cпасибо!