1. NMR study of 133Cs in a new quasi-one-dimensional conducting platinate
Ian Leatherbury
Undergraduate student,
University of South Alabama, Department of Physics, Mobile, Alabama
COLLABORATORS:
J. A. Alexander and A. A. Gapud
Department of Physics, University of South Alabama
A. P. Weber, L. Pham, and R. E. Sykora
Department of Chemistry, University of South Alabama
A. P. Reyes and P. Kuhns
National High Magnetic Field Laboratory
FUNDING:
National Science Foundation (NSF) – Research at Undergraduate Institutions
NHMFL: DoE, NSF, State of Florida

2. Overview TCP: new quasi-one-dimensional platinate Method: NMR on 133Cs
Intro: platinates – KCP
Structure from room-temperature x-ray diffractometry
Anomalous R(T) not seen in KCP
Method: NMR on 133Cs
Quadrupole splitting: verify Cs in structure, align sample
T1 versus temperature
Key Findings, preliminary results
Verified Cs structure
Anomalous peak in T1(T)
Conclusion, further work
(Quick overview, don’t take too long, but still give a good idea what your talk is all about.)

3. Platinates: KCP Quasi-one-dimensional (Q1D) conductors
Parallel Pt chains
Peierls transition
Structural change leads to new gap between valence and conduction bands
Metal to insulator transition
K2[Pt(CN)4]Br H2O (KCP)
Well known
Pt chain ringed by 4 CN
Adjacent Pt planes rotated 45o
Pt-Pt spacing:
Longitudinal – along chain: Å
Transverse – between chains: Å
4 H2O rings each Pt-CN plane
K, Br separate Pt-CN-H2O chains.
Peierls transition temperature not observed (above room temperature?): already semiconducting
DC R(T): increases with lower temperature T
From: Toombs, Physics Reports 40, No. 3(1978)181.

4. New Q1D platinate: TCP Cs4[Pt(CN)4](CF3SO3)2
Structure from room-temp XRD
Like TCP, Pt chain ringed by 4 CN and adjacent Pt planes rotated 45o
Pt-Pt spacing (room temp):
Longitudinal: Å (5% longer)
Transverse: Å (38% farther)
Cs instead of H2O
Triflates instead of K, Br Pt CN

5. New Q1D platinate: TCP Cs4[Pt(CN)4](CF3SO3)2 DC transport measurements
R(T): anomalous peak below 200 K
NMR: Preliminaries:
Objective: T1 vs. T
Unlike KCP, could not find Pt !
Used 133Cs instead

6. 133Cs NMR: Toward T1: symmetry
I = 7/2: Nuclear quadrupole moment Q: interaction with local electric field gradient (EFG)
Spin states are perturbed
Resonance frequency νo split into 2xI frequencies νm = νo + mνQ ,
m = 0, 1, … (I-1/2)
Splitting depends on local symmetry of 133Cs
Expect: four νm spectra:
Each Pt/CN plane: 4 Cs w/ same local symmetry
Dependence on angle θ between applied field and crystal symmetry axis: A C’ C A’ A’
Each plane: 2 equivalent symmetry sites, A and A’ shifted 90o : two spectra
Adjacent plane: same sites but shifted 45o: C and C’: two spectra C’ C A

7. 133Cs NMR: Toward T1: symmetry
Data:
four quadrupole spectra
versus orientation θ

8. 133Cs NMR: Toward T1: symmetry
Modeling using Labview
Check consistency with
with sample data:
Find sample orientation
To match data, sample angle θ = 3.17 deg 8

9. 133Cs NMR: T1 vs. T: data Fixed field and orientation
Above 150 K: T1 ~ 200 s
KCP: ~ 10-3 sec!
Below 110 K: T1 ~ 103 sec
KCP: ~ 102 sec, 4.2 K
Anomalous “peak”
KCP: monotonic increase with cooling
Centered around 121 K
T1 down to < 30 sec
121 K 9

10. 133Cs NMR: T1 vs. T: fitting Power law No peak, monotonic
T < 120K: gap Δ
~ exp( - Δ/ kT ); Δ/k~265K
Normally valid at lower T
Few points (long T1!)
Critical fluctuations
(T – Tc)-β
T > 120K: Critical fluctuations and power law 10

11. Summary: Not at all like KCP…
TCP: new platinate, anomalous R(T < 200K)
NMR on 133Cs
Confirmed the configuration of Cs in TCP, via angular dependence of quadrupole spectra
T1 vs. T: anomalous “peak” at ~ 120 K, precipitous increase below 120
Best fit: combination of critical fluctuations and energy gap
Structural transition? Doing cryogenic XRD…