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.

-(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

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”

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

I.

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

)

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

T = 1.5 K: peak in 1/T1 occurs at B1.

B1Bth

B//c, field (frequency) dependent data.

Metallic pulses

“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

Bth

B1

Bth B1

Works because FISDW is primarily orbital.

Rotation data at 30 T.

Bth B1 B* BRE

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).

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.

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

H-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 -(BETS)2FeCl4 – B. Zhou

• Lisbon: constant-acceleration spectrometer and a 25 mCi 57Co source in a Rh matrix– J. C. Waerenborgh

<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.

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:

Experimental and computed hyperfine field Bhf and derived H-d field.

Waerenborgh et al.arXiv:0909.1096

(PRB-submitted)

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.

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.

-(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.

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.

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.

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.

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:

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.

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?

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!