Vertical stacking of heterostructures that combine layered materials offer new ways of combining interesting properties of dissimilar electronic materials. Over the past few years we have been integrating graphene with complex-oxide heterostructures, specifically, the LaAlO /SrTiO system. Furthermore, conducting nanostructures can be written under graphene, producing interesting interactions between the two systems. Here we report Coulomb drag measurements between single-layer graphene and a conductive LaAlO /SrTiO interface. Fabry-Perot oscillations are observed in both graphene and drag signal in graphene, which indicate the local doping in graphene by conductive atomic force microscope(c-AFM) lithography. While the drag resistance is greatly enhanced in SrTiO in the superconducting region, the drag in graphene remain unchanged. We also observed key differences between longitudinal drag and hall drag in both graphene and SrTiO .

1. 2020 APS March Meeting, Denver, CO
We gratefully acknowledge support from:
NSF DMR-1104191 (JL, CBE),
AFOSR FA9550-12-1-0057 (JL, CBE)
ONR N00014-15-1-2847.
Qing Guo1,3
1University of Pittsburgh
2University of Wisconsin-Madison
3Pittsburgh Quantum Institute
Jianan Li1,3, Lu chen1,3, Mengchen Huang 1,3, Jen-Feng Hsu
1, Hyungwoo Lee 2, Chang-Beom Eom 2, Brian D’Urso 1,
Patrick Irvin 1,3, and Jeremy Levy 1,3.
Coulomb drag between graphene and
LaAlO3/SrTiO3 heterostructures
R51: Graphene: bilayers, imaging transport and
electronic properties, adatoms.

2. Coulomb drag background
Anomalous low-temperature Coulomb drag
Nature Communications vol5, 5824 (2014)
Nature vol488, 481–484 (2012)
Perfect Coulomb drag
• Two closely spaced but electrically
isolated conductors
• Powerful technique to study electron
correlations
Nature Physics vol13,746–750 (2017)
Exciton condensate in graphene
Phys. Rev. Lett. 119, 056802
Frictional Magneto-Coulomb Drag in Graphene
Science Vol. 316, Issue 5821 (2007)

3. LaAlO3/SrTiO3 Interface
• Electrical tuning of major properties
in solid state
– Metal insulator transition
Science 313, 1942 (2006)
– Superconducting
Science 317, 1196 (2007)
– Ferromagnetic
Nat. Comm. 5 5019 (2014)
– Ferroelectric
PRL 116, 257601 (2016)
– Spin-orbit
Shalom et al, PRL 104, 126802 (2010)
Caviglia et al, PRL 104, 126803 (2010)
– …
Critical Thickness ~4uc
Science 313, 1942 (2006)
Metal-Insulator Transition
Science 313, 1942 (2006)
LaAlO3
SrTiO3
2DEG

4. LaAlO3/SrTiO3 Nanostructure Anatomy
Ti/Au interface
contact
Vtip
Vtip>0 writes
+ + + + +
+
+ +
+ +
+ ++
+ + + + +
protons
-
- - - - -
electrons
≥ 2 nm
barrier
1.2 nm
Vtip<0 erases
• LaAlO3/SrTiO3 heterostructure
– 3.4 unit cells LaAlO3
– Grown on TiO2 terminated SrTiO3
• Conductive-AFM Lithography
– Surface protonation
C-AFM Lithography

5. Integrate graphene with LaAlO3/SrTiO3
• Quantum hall effect
• High mobility

6. Writing nanostructure on Graphene/ LaAlO3/SrTiO3
PFM set up
design
• Write nanowire on
LaAlO3/SrTiO3 interface
across graphene region
• Conductance jump
• Nanowire can be imaged by
piezoelectric force
microscopy
PFM Phase image

7. Coulomb drag device and leakage test
Leakage test
Schematic device on AFM image
Side view shows the c-AFM
lithography process
𝑉𝐺𝑆

8. • Current running in SrTiO3, drag resistance measured in graphene
Drag resistance is graphene and STO
• Current running in graphene, drag resistance measured in SrTiO3

9. Drag signal in superconducting region
• Varying driving current in graphene, drag resistance measured in STO
• Drag signal is greatly enhanced in superconducting region

10. Drag in graphene(device 2)
• Run current in
SrTiO3, Measure
drag voltage in
graphene• Drag signal has
different pattern under
low and high
magnetic field

11. Kwant simulation
Parameters:
Hopping energy: -2.8 eV
Lattice constant: 2.46Å

12. Kwant simulation
• Tight binding model
• Conducting in low magnetic field
and high magnetic field
• Assumption: momentum
transferred from STO carriers to
graphene carries through one
collision

13. Drag in Hall and Longitudinal Direction
• Run current in SrTiO3, Measure
drag voltage in graphene
• Magneto drag is more obvious
in small magnetic field, while
transverse drag is more
obvious at higher magnetic
field

14. Drag in Hall and Longitudinal Direction
• Varying driving current
in graphene, Measure
drag resistance in
SrTiO3 .
• The hall drag resistance
is almost symmetric
under magnetic field
while hall drag
resistance is
antisymmetric under
magnetic field
𝑅 𝑆𝐺
𝑥𝑦
𝑅 𝑆𝐺
𝑥𝑥

15. • Conducting region can be created via conductive
AFM lithography techniques and imaged by
Piezoelectric Force Microscopy
• In the high-magnetic-field regime, drag resistance
is observed to be magnetically tunable
• Drag signal is greatly enhanced in STO
superconducting region.
Summary
We gratefully acknowledge support from:
• NSF DMR-1104191 (JL, CBE),
• AFOSR FA9550-12-1-0057 (JL, CBE)
• ONR N00014-15-1-2847.

16. B48.00011 Superconductivity at the LaAlO3/SrTiO3 1D
Zigzag Nanowires
B48.00012 Frictional drag between two LaAlO3/SrTiO3
superconducting nanowires
J65.00009 Engineered Chirality of One-Dimensional
Nanowires
L48.00002 Capillary waves on ferroelastic domain walls
as a pairing mechanism in strontium titanate
L62.00009 Development of single-electron and single-
electron-pair sources in LaAlO3/SrTiO3 nanostructures
L64.00002 Cryogenic Piezoforce Microscopy of
Sketched LaAlO3/SrTiO3 Nanostructures
L64.00003 Dependence of LaAlO3/SrTiO3 Electron
Pairing Strength on Crystallographic Orientation
L64.00004 Transport properties of non-reciprocal 1D
quantum channels at the LaAlO3/SrTiO3 interface
L64.00005 Nanoscale control of the metal-insulator
transition in free-standing LaAlO3/SrTiO3 membranes
L64.00006 Influence of Temperature on LaAlO3/SrTiO3
Nanowire Lifetimes Under Ambient Conditions
L64.00007 Surface Acoustic Wave Generation and
Detection on LaAlO3/SrTiO3
L64.00008 Creating nano-scale “vias” in LaAlO3/SrTiO3
for integration of nanostructures
M62.00004 Giant Thermopower in Quasi-One-
Dimensional LaAlO3/SrTiO3 Quantum Wires
M62.00005 Effects of writing parameters on electron
transport in sketched single-electron transistors
R51.00011 Frictional drag between graphene and
LaAlO3/SrTiO3 heterostructures
U51.00006 THz spectroscopy of graphene and graphene
nanoribbons using LaAlO3/SrTiO3 nanoscale junctions
X48.00003 Uniaxial strain effect on superconductivity in
1D and 2D LaAlO3/SrTiO3 channels