Very one dimensional organic conductors – Less is more

J. S. B, M. Almeida, L.L. Lumata, P. Kuhns, A. Reyes, D. Graf, R. Henriques, L. Prettner (Green), J. Wright, and S. Brown

First, some news from the Magnet Lab in Tallahassee and

Los Alamos

2

Objective25 T central field

28 MW dc power (2 supplies)4 ports at mid-plane of 45° each

Vertical or horizontal field2 Sets of inner coil

25 T SPLIT RESISTIVE MAGNET

Jack Toth Project Leader

Now Working!Please consider coming to us for magnetooptics studies!

Steve McGill - femptosecondDmitry Smirnov – visible/ramanJason Li - FTIR

Instrumentation:

4 x scattering cone (line of sight)

aligned with cell vs. 45°4 tapered access ports

each: 11.4° x 45°

11.4°

~ 1m

Dewar32mmbore

~25T

Optics in the Split-Florida Helix 25 T

Visible/Fast optics IR & THz cw optics

Amplified Ti:Sapphire (2.5 mJ, 150 fs, 1 KHz) OPA, Streak camera, VIS and NIR detectorsAr+, He-Ne, He-Cd, and dye lasers for cw

Activities:

Preparing implementation of inelastic light scattering experiments

0.75m McPherson spectrometer

Custom optical cryostat being purchasedSelecting window materials

Bruker 66 FTIR spectrometer (roving cell-to-cell)Sub-THz tunable sources: BWO (Backward wave oscillators), Mid-IR CO2 laser (11 μm)

Mid-IR and Far-IR detectors

Near future:

Fiber-free techniques expand possibilities for UV spectroscopy, polarization-resolved, & time-resolved experiments

Transfer of existing techniques + Split-Helix = new capabilities:

TriVista High-resolution spectrometer

FTIR in Voigt geometry

IR luminescence

New High Magnetic Field Record97.4 tesla confirmed via magneto quantum

oscillations in poly-crystalline copper

*World Record magnetic field intensity for a Non-Destructive Pulsed Magnet

*

97.4 tesla

Very one dimensional organic conductors – Less is more

Per2[M(mnt)2] (M = Au, Pt, Co):Charge Density Wave

Spin-PeierlsMetal

Agenda:Some History

Part I: P = 0 (SP-CDW coupling) Part II: P ≠ 0 (Low Temp Metal and SC)

J. S. B, M. Almeida, L.L. Lumata, P. Kuhns, A. Reyes, D. Graf, R. Henriques, L. Prettner (Green), J. Wright, and S. Brown

Supported by NSF DMR-0602859 & 1005293 (JSB), by FCT (Portugal) PTDC/FIS/113500/2009 (MA), by NSF DMR-0804625 (SEB), and performed at the National High Magnetic Field Lab (supported by NSF DMR-0654118, by the State of Florida, and the DOE).

Quasi-one-dimensional organic conductor Perylene2[M(mnt)2]

Canadell et al., Eur. Phys. B 42, R453(2004).

(mnt =maleonitriledithiolate)

a = 16.612 Å ; ta = 2 meVb = 4.1891 Å : tb = 150 meVc = 26.583 Å; tc = 0 meV

“L. Alcácer Salts”: Mol. Cryst. Liq. Cryst. 120, 221(1985)

M

SP

CDW

2b

4b

b

CDW

Dimerization - spin Peierls when S = ½

p 1/4 filled band - conductor

d ½ filled band - insulator

Tetramerization - Peierls (CDW)

Main Result:

A CDW forms on the Perylene Chains

A Spin Peierls state forms on the M(mnt)2 chains with S ≠ 0.

The two transitions are coincident.

Why? Tetramer Dimer

In case you want to sleep through the history, here is the message:

Nature, 173, 168(1954).

Q1D metal

Ln(s)

1/T x 103

Ni

Cu

Pd

Q1D metal

M–I & spin

Transition

s /s R

T

c p 10

-4/m

ole

T (K)T (K)

Magnetic Transition

M-I Transition

lQ1D metal

M–I & spin

Transition

S =½ Dimer

formation

Dimerization of spin 1/2 d-electron chain.

Q1D metal

M–I & spin

Transition

S =½ Dimer

formation

PeryleneTetramer

Q1D metal

M–I & spin

Transition

DimerFormation

PeryleneTetramer

CDWM = Au

Collective CDW Transport: M = Au

Q1D metal

M–I & spin

Transition

Dimerformation

PeryleneTetramer

CDWM = AuM = Pt

Collective CDW Transport: M = Pt

Q1D metal

M–I & spin

Transition

Dimerformation

PeryleneTetramer

CDWM = AuM = Pt

CDW &SP

coupling

Q1D metal

M–I & spin

Transition

Dimerformation

PeryleneTetramer

CDWM = AuM = Pt

CDW &Pt chaincoupling

Spin Peierls!

Identification of magnetic transition as Spin-Peierls associated with the Pt Spin ½ chains (consistent with XRD).

Per2[Au(mnt)2]

Q1D metal

M–I & spin

Transition

Dimerformation

PeryleneTetramer

CDWM = AuM = Pt

CDW &Pt chaincoupling

Spin Peierls!

B dep. of CDW

Pt

Au

Q1D metal

M–I & spin

Transition

Dimerformation

PeryleneTetramer

CDWM = AuM = Pt

CDW &Pt chaincoupling

Spin Peierls!

B dep. of CDW

Pt too!

Per2[Pt(mnt)2]: Spin-Peierls + CDW system also shows similar B dependence.

Q1D metal

M–I & spin

Transition

Dimerformation

PeryleneTetramer

CDWM = AuM = Pt

CDW &Pt chaincoupling

Spin Peierls!

B dep. of CDW

Pt too!

Eq. 1

Eq. 2

Q1D metal

M–I & spin

Transition

DimerformationPeryleneTetramer

CDWM = AuM = Pt

CDW &Pt chaincoupling

Spin Peierls!

B dep. of CDW

Pt too!

CDW-SP coupling

B // chains

B chains

CDW induces

SP

B influences CDW-SP coupling

Graf et al., Phys. Rev. B 69, 125113 (2004)

High field phase diagram for

Per2[Au(mnt)2]

Q1D metal

M–I & spin

Transition

Dimerformation

PeryleneTetramer

CDWM = AuM = Pt

CDW &Pt chaincoupling

Spin Peierls!

B dep. of CDW

(Bcrit~ 40T)

Pt ?

CDW-SP coupling

Finally, our group did something!

Graf et al., Phys. Rev. Lett. 93, 076406 (2004).

Q1D metal

M–I & spin

Transition

Dimerformation

PeryleneTetramer

CDWM = AuM = Pt

CDW &Pt chaincoupling

Spin Peierls!

B dep. of CDW

(Bcrit~ 40T)

Pt ? (Bcrit~ 20T)

CDW-SP coupling

Field induced CDW?Second high field, high resistance phase?

Per2[Pt(mnt)2]

• Large difference in the nature of the T-B phase

diagrams determined from transport studies at high

fields indicates the possible role of SP chains in the

suppression of the CDW state.

How can we independently monitor the field

dependence of the Spin Peierls chain to see what it is

doing?

~ 10 KM = Au

M = Pt

Proton (1H) NMR – Strongly influenced by Pt spin state.

two-chain

CDWElectrical conductivity probes the perylene stacks.

CDWSPProtons on the perylene are the links to the Pt(mnt)2 anions.

SPThe localized spin ½ electron at the Pt(mnt)2

site gives rise to the spin-Peierls behavior.

Strategy: Study the 1H and 195Pt NMR signals with field and temperature, and compare it with the transport data.

p1H

195Pt

T-Dep

B-Dep

1H spectra change

dramatically at SP transition.

Multiple spectral lines: paramagneticSingle spectral line: spin singlet (SP)

E. L. Green et al., PRB (Rapid), in press.

T-B Phase Diagram: CDW – TransportSP – 1H NMR

E. L. Green et al., PRB (Rapid), in press.

Per2[Pt(mnt)2]

SP Boundary Follows CDW Boundary to First Critical Field region ~ 20 T. Strong coupling.

1H NMR results for

The larger picture:Phase diagram for both S=0 and S = ½ cases

Second moment analysis of high field spectra indicate that SP spin singlet state is breaking down and system is becoming spin polarized. Torque magnetization corroborates this process.

CDW

Spin

cha

in m

omen

t

B (T)

B (T)

Part I summary (P = 0)

• There are several unsolved questions:1) What is the mechanism for the coupling of the

SP and CDW chains/order parameters? (only one (?) theory has treated it)

2) Who drives who? Is the CDW necessary for the SP to form? (Mostly based on interpretation of experimental results.)

3) What is the origin of the “FISDW” high field phase? (Several theories and speculations)

1) Theory: Dimerization induced by the RKKY interaction, J. C. Xavier, R. G. Pereira, E. Miranda, I. Affleck, Physical Review Letters, 90, 247204 (2003).

Model: One dimensional S=1/2 Kondo model with L sites.

is the conduction electron spin operator.Kondo coupling J > 0

Dimerization of the S=1/2 spin system at ¼ filling is determined from the order parameter:

Results of theory:Relevant to Per2[Pt(mnt)2]1D suppresses SDWSmall energy scale consistent with suppression by field. Opens a charge gap as well (i.e. like CDW) at ¼ filling.RKKY drives the dimerized spin + charge gap (“SP+CDW”) transition.

Dimerization induced by the RKKY interaction, J. C. Xavier, R. G. Pereira, E. Miranda, I. Affleck, Physical Review Letters, 90, 247204 (2003).

Need a two chain theory where S and s are on different chains.

2) Who drives who?CDW and SP form at same Tsp-cdw

CDW driven:1) CDW can form in absence of spin chain.2) Coulomb interactions when CDW forms may drive

dimerization in SP chains. 3) NMR & transport: SP order parameter seems to

develop fully slightly later that CDW does.

SP driven:4) Xavier et al. – RKKY5) SP seems to “pull down” CDW transition: For M =

Au, Tcdw = 12 K; for M = Pt, Tsp-cdw = 8 K.

R. McDonald, PPHMF & private communication.

3) What is the origin of the “FISDW” high field phase?

• Nesting (after restoration of metallic phase) – but only weakly orbital• Lebed(JETP): (“Gorkov-Lebed”) - TFICDW ~ 0.1 K , but THF ~ 4 K• Lebed(PRL): Zeeman splitting of 4 bands where original CDW nesting condition is restored – but why in M=Pt but not M=Au – higher fields?• Restoration of non-magnetic CDW system when SP is spin polarized – however, SP and CDW order parameters appear to be attractive, not repulsive.

Part 2 (P ≠ 0) The Metal

Pressure dependence in Per2[M(mnt)2] is non-trivial.

Can’t detect this at low T by Fermiology due to CDW formation at higher temperatures.

Canadell et al., Eur. Phys. B 42, R453(2004).

Try to get rid of CDW with Pressure

Counterion dimerisation effects in the two-chain compound (Per)2[Co(mnt)2]: structure and anomalous pressure dependence of the electrical transport propertiesM. Almeida, V. Gama, I. C. Santos, D. Graf and J. S. B., CrystEngComm, 2009, 11, 1103–1108

This anomalous behaviour can be understood as a consequence of a change of the perylene molecule overlap due to a transverse sliding of molecules along alternated directions of their planes imposed by the dimerised anion stacks.

P (kbar)

TMI & TR

Log(

R/R 0)

1/T

P

TAu

Pt

Evolution of superconductivity from a charge density wave ground state in pressurized (Per)2[Au(mnt)2]D. Graf , J.S. B., M. Almeida, J.C. Dias, S. Uji, T. Terashima and M. Kimata, Euro Physics Letters 85 27009/1-5(2009).

Metallic at 5.3 Kbar – slow cooled!

Bakrim and Bourbonnais, Supeconductivity close to the charge-density-wave instability, Euro Phys. Lett. 90, 27001(2010).

Q1D metal

Superconductivity

Superconductivity close to the charge-density-wave instability H. Bakrim and C. Bourbonnais, Euro Physics Letters 90, 27001(1-6)(2010).

D. Graf, J. S. Brooks, E. S. Choi, M. Almeida, R. T. Henriques, J. C. Dias, and S. Uji, Geometrical and orbital effects in a quasi-one-dimensional conductor, Physical Review B 80, 155104 (1-5)(2009).

Per2[Au(mnt)2]5 kbar

Complex

AMRO

Q1D metal

Superconductivity

Angular dependent resistance

oscillations

D. Graf, J. S. Brooks, E. S. Choi, M. Almeida, R. T. Henriques, J. C. Dias, and S. Uji, Quantum interference in the quasi-one-dimensional organic conductor (Per)2Au(mnt)2 Phys. Rev. B 75, 245101/4(2007).

Quantum Interference Orbits.

(Per)2[Au(mnt)2]

Q1D metal

Superconductivity

Angular dependent resistance

oscillations

Quantum Interference

Orbits

SummaryQ1D metal

M–I & spin

Transition

Dimerformation

PeryleneTetramer

CDWM = AuM = Pt

CDW &Pt chaincoupling

Spin Peierls!

B dep. of CDW(Bcrit~ 40T)

Pt ? (Bcrit~ 20T)

CDW-SP coupling

Field induced CDW?

Superconductivity

Angular dependent resistance oscillations

Quantum Interference Orbits

This two-chain highly one dimensional conductor comes in magnetic and non-magnetic flavors – Provides a huge variety of physical states and properties. – Surely there are many more surprises to come as theoretical and experimental methods advance.

Immediate theoretical questions:SP-CDW coupling in a two-chain system.Step 1: B = 0.Step 2: B large.

Chaikin: (TMTSF)2ClO4 = Quantum GravityJSB: Per2[M(mnt)2] = Dark Energy

Thanks to Serguei, Natasha, and Pierre!

M

SP-CDW

q

c B

a

Per2[Pt(mnt)2]

very one dimensional organic conductors – Less is more

J. S. Brooks1* and M. Almeida2*

1NHMFL/Physics, 1800 E. Paul Dirac Dr., Tallahassee FL, 32310 USA2Instituto Tecnológico e Nuclear / CFMCUL, Estrada Nacional no 10, P-2686-953 Sacavém, Portugal

In this talk, we present a summary of recent work under “extreme conditions”, meaning high fields, low temperatures, and high pressure where organic conductors in the class (Per)2[M(mnt)2] do some pretty amazing things. Here M can be a spin = 0 (Au, Cu, Co), or a spin = 1/2 (Pt, Pd, Ni, Fe) metal ion. The work to be described, done by my group and collaborators, follows on nearly 30 years of previous, beautiful work by the Lisbon group and their collaborators that has been summarized in a relatively complete paper by Almeida and Henriques. Our more recent work has focused so far on the (Per)2[Au(mnt)2] S=0 , (Per)2[Pt(mnt)2] S=1/2 , and also (Per)2[Co(mnt)2] . In this presentation, for (Per)2[Au(mnt)2] and (Per)2[Pt(mnt)2], we will review the effects of high magnetic field on the charge density (CDW) and spin-Peierls (SP) ground states, the effects of pressure on these ground states, and the appearance of quantum interference, “magic angle effects”, and superconductivity (see also theory by Bakrim and Bourbonnais ) in (Per)2[Au(mnt)2] when the CDW is removed at high pressure. We will also review the unusual increase in the CDW transition temperature with pressure in (Per)2[Co(mnt)2]. The final topic in the presentation will focus on our most recent work involving 195Pt and 1H NMR in (Per)2[Pt(mnt)2] where we have tracked the spin-Peierls behavior of the [Pt(mnt)2] chains with field and temperature and have compared our results with previous electrical transport and magnetization studies of the CDW phase diagram under high magnetic fields. We will discuss these results in light of theoretical work that considers the interaction of itinerant conduction electrons and localized moments in quasi-one-dimensional systems. The overarching purpose of this presentation is to attract both the experimental and theoretical community to consider further work on these amazing systems that are clearly as rich in physical phenomena as the BEDT-TTF , TMTSF, and TMTTF materials.

*Supported by NSF DMR-0602859 & 1005293 (JSB), by FCT (Portugal) PTDC/FIS/113500/2009 (MA), by NSF DMR-0804625 (SEB), and performed at the National High Magnetic Field Lab (supported by NSF DMR-0654118, by the State of Florida, and the DOE).