SLIDE 1
External-fields induced novel phenomena in Mott insulator Ca 2 RuO 4 - - PowerPoint PPT Presentation
External-fields induced novel phenomena in Mott insulator Ca 2 RuO 4 - - PowerPoint PPT Presentation
External-fields induced novel phenomena in Mott insulator Ca 2 RuO 4 Fumihiko NAKAMURA ADSM, Hiroshima University . Pressure induced Superconductivity . E induced Ins.-Metal transition >> Collaborators << >>
SLIDE 2
SLIDE 3
POSSIBLE NEW STATES
Ⅰ. Quantum Critical natures in the vicinity of magnetic ordered state
from P. L. Alireza, G.G.Lonzerich
3D system
SLIDE 4
How about “2D system” ?
0.1 0.2 0.3 100 200 300
Td
La
2-xSr xCuO 4
S.C.
Antiferro Insulator
Orthorhombic
Tetragonal
TEMPERATURE (K) x : Sr concentration
2D system FM
?
Theoretical prediction
- nly
Hatatani and Moriya, JPSJ, 64 (1995) 3434
“Ca2RuO4” was a candidate. 2D system AFM
SLIDE 5
Rich variety of pressure phase diagram
from Mott insulator to Q2D FM metal
F.Nakamura, PRB65 (2002)220402, JPSJ (2007).
Mott transition
Mixed phase (Ins./Metal) AF
A type B type
Mott Ins. itinerant FM Q2D Metal
0.1 1 10 0.1 1 10 100 1000
Temperature (K) Pressure (GPa)
Quantum critical nature Q2D Metal
100 200 300 10
- 6
10
- 5
10
- 4
10
- 3
10
- 2
10
- 1
ab c
3.0 GPa 2.0 GPa 2.0 GPa Ca2RuO4 8.0 GPa 3.0 GPa (mcm) Temperature (K)
SLIDE 6
Y.Yamauchi, et al., Physica C (2010).
Itinerant and Anisotropic FM in Ca2RuO4
Generalized Rhodes-Wohlfarth Plot
the scale for itinerant FM
0.1 0.2 0.3 10 20 30 40
TC / T0 peffMrem ZrZn1.9 Sr2CaRu2O7 Ca2RuO4 (1 ~ 2GPa)
peffMrem TC / T0
MnSi Ni3Al ZrZn2 Sc3In CeF2 Au4V CrB12
0.1 0.15 5 10
(GPa) 2 1.9 1.8 1.2 1.5 1
localize (up to 1) itinerant 0HA 1.04T 0.049T 0.14T Co Fe Ni
4 8 12 0.5 1.0
0H || a 0H || c
/
H (T)
0.2 0.4 0.6
0H || c 0H || b 0H || a
1.8GPa 2 K
Ca2RuO4 M (B/Ru-ion)
0HA ~ 9.5T
Strongly anisotropic FM due to Spin-orbit coupling
SLIDE 7
To explore superconductivity in a Mott ins. Ca2RuO4
AF
A type B type
Mott Ins.
anisotropic itinerant FM
Q2D Metal
S C ? Our project started in 1999. >>> One decade after 250m
Over 10GPa: Very hard work !!
- Alireza. Rev.Sci.Ins.74, 4728 (2003).
Resistance ac susceptibility 0.1 1 10 0.1 1 10 100 1000
Temperature (K) Pressure (GPa)
SLIDE 8
Resistance (2-terminal) ac susceptibility
- P. L. Alireza, et al., Journal of Physics: Condensed Matter 22 (2010) 052202.
arXiv:0912.1513 [cond-mat.supr-con]
We found pressure induced SC at ~10 GPa
SLIDE 9
From Mott insulator to “ SC ” via itinerant FM
- P. L. Alireza, et al., Journal of Physics: Condensed Matter 22 (2010) 052202.
arXiv:0912.1513 [cond-mat.supr-con]
Tc ~ 0.4 K at P ~14 GPa
SLIDE 10
- 1. How about relation between FM and SC ?
- 2. How about difference in SC between
SRO and CRO ? ( p or s-wave SC ? )
- 3. Ru214 is 2D Fermi liquid metal
but what is difference ? Quantum oscillation data is required.
New SC phase in pressurised CRO
Pressurisation above ~8 GPa turns CRO from FM metal to SC (Tc ~ 0.4 K and ~14 GPa).
SLIDE 11
Ⅱ. “Electric-field” induced Mott transition “Electric field” has higher potential than P
Reported breakdown in Mott insulator
Eth (kV/cm) Egap (eV) La2-xSrxNiO4
1)
1~10 0.26 Sr2CuO3
2)
1~3 SrCuO2
2) 0.3~1
(TTeC1TTF)-TCNQ 3)
0.3~1.2
Ca2RuO4 ? 0.2 / 0.05 (@RT)
1) M.Imada, Rev.Mod.Phys. 70 4 (1998). 2) Y.Taguchi., PRB. 62 11 (1999). 3) Y. Iwasa ., APL. 39, 10441 (1989).
εgap
2
E th = e2ε0 a We expect “Eth ~3kV/cm” @RT for Ca2RuO4 based on Zener breakdown model.
SLIDE 12
Breakdown in 4d Mott insulator Ca2RuO4
- ccurs at “Surprisingly weak Eth~40V/cm”
Zener Breakdown No ! Why is Eth ~ 40V/cm so weak in Ca2RuO4 ?
0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8
Current (A) Voltage (V)
40V/cm 50V/cm
Ca2RuO4 Ca2RuO4 E // c 295K E // ab 295K
0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 Current (A) Voltage (V)
Avalanche Breakdown ?
SLIDE 13
Metal-Insulator transition in Ca2RuO4 accompanied by structural change
Mott Insulator
d
Sr2RuO4
U/W
La2CuO4
～
Ca2RuO4
Band Ru Ca/Sr O
dxy dxz dyz
O2 O1
(Ru-O2 < Ru-O1)
Insulator ( S-Pbca flatted )
dxy dxz dyz
O2 O1
(Ru-O1 <Ru-O2 )
Metal ( L-Pbca )
Filling
- 1. Substitution ( (Sr/Ca)2RuO4 )
- 2. Heating (temperature )
3.Pressure 4.Electric field
SLIDE 14
The breakdown accompanied by structural transition from S- to L-Pbca
44 45 46 Ca2RuO 4 (006)
67V/cm 42V/cm 40V/cm 20V/cm 0 V/cm 2 (degree) Intensity (arb. units)
Breakdown in CRO is “Bulk transition”. Avalanche Breakdown NO !
20 40 60 0.0 0.2 0.4
25 50 75 100
E // c 295K
Ca2RuO 4
I (A) E (V/cm) S-Pbca L-Pbca Volume fraction (%)
L-Pbca S-Pbca E // c 295K Ca2RuO4 (Metal) (Ins.) L-Pbca S-Pbca E // c 295K Ca2RuO4 (Metal)
1 1 .9 1 2 .0 1 2 .1 1 2 .2 1 2 .3 1 2 .4 Lattice parameter c (Å)
(Insulator)
SLIDE 15
Summary
Dielectric Breakdown in Mott insulator Ca2RuO4 occurs at “Superisingly weak Eth~40V/cm” accompanying with structural transition
c axis: 11.9 Å (insulator) → 12.3 Å (metal) DB in CRO → Bulk transition
- 3. Avalanche Breakdown
- 2. Joule heating
- 1. Zener Breakdown
No No No
What is the possible mechanism for weak Eth ?
SLIDE 16
How about possible mechanism for Dielectric breakdown in Ca2RuO4 ?
Change of the internal charge distribution. Enough amount of charge for the metalisation is internally stored in the apical oxygen (O2) of CRO, and then it can be poured into the RuO2 plane
- nly by quite weak field of Eth~40V/cm.
Insulator ( S-Pbca ) Metal ( L-Pbca )
Eth~ 40V/cm
O2 O1 O2 O1
SLIDE 17
current sweep We observed NDR !
(Negative Differential Resistance)
YES NO
0.0 0.5 1.0 1.5 0.0 0.1 0.2 0.3 I (A) V (V)
Other possible mechanism
Insulator bulk Metal
nonequilibrium e.g. filamentary
Structural change
20 40 60 0.0 0.2 0.4
25 50 75 100
E // c 295K
Ca2RuO4
I (A) E (V/cm) S-Pbca L-Pbca Volume fraction (%)
L-Pbca S-Pbca E // c 295K
Ca2RuO4
(Metal) (Ins.)
L-Pbca S-Pbca E // c 295K
Ca2RuO4
(Metal) (Ins.)
1 1 .9 1 2 .0 1 2 .1 1 2 .2 1 2 .3 1 2 .4 Lattice parameter c (Å)