Giacomo Prando Research threads 1. Magnetism in flatland 2....
Transcript of Giacomo Prando Research threads 1. Magnetism in flatland 2....
Giacomo Prando
Research threads
1. Magnetism in flatland
2. Iridium oxides – thin films
3. Many-body localization and Floquet time-crystals (“Incontri del martedì”, 27.11.2018)
4. Orbital-selectivity in iron-based pnictides
13.09.2018 – Pavia, “Congresso interno di Dipartimento”
Giacomo Prando
Research threads
1. Magnetism in flatland
2. Iridium oxides – thin films
3. Many-body localization and Floquet time-crystals (“Incontri del martedì”, 27.11.2018)
4. Orbital-selectivity in iron-based pnictides
13.09.2018 – Pavia, “Congresso interno di Dipartimento”
In the beginning was graphene
Nat. Mater. 6 183 (2007)
A truly two-dimensional material with exceptional mechanical and electronic properties
“Relativistic” condensed matter physics
+ Massive bunch of novel physical phenomena
Prospects for two-dimensional electronics
Mind the gap, please – TM dichalcogenides
Versatile materials complementing graphene
Mechanical exfoliation in
atomic trilayers is possible
Scalable devices based on Lego-like architectures (vdW heterostructures)
Chem. Rev. 113 3766 (2013); Nature 499 419 (2013); Nat. Rev. Mater. 2 17033 (2017)
Superconductivity in flatland
Gate-induced superconductivity in atomically thin layers of MoS2
Nat. Nanotech. 11 339 (2016)
Ising superconductivity in atomically thin layers of NbSe2
Nat. Phys. 12 139+144 (2015)
Magnetism in flatland Cr2Ge2Te6 , Nature 546 265 (2017)
CrI3 , Nature 546 270 (2017)
Magnetism – really in “flatland”?
CrI3
I
Cr
3 μB
+ Samples are not atomically-thin + Samples are on substrates + Ising-like anisotropy for magnetic moments ...Mermin-Wagner theorem is safe.
“Flatland” or not – interesting physics
Electrical control of magnetism in CrI3
Nat. Nanotech. 13 544+549 (2018); Nat. Mater. 17 406 (2018)
“Flatland” or not – scalable spintronic devices
M
M
Ins
Tunnelling magnetoresistance
Magnetic tunnel junction
Science 360 1214+1218 (2018)
Nat. Mater. 11 372 (2012)
“Flatland” or not – scalable spintronic devices
M
M
Ins
Tunnelling magnetoresistance
Magnetic tunnel junction
Science 360 1214+1218 (2018)
Nat. Mater. 11 372 (2012)
Sizeable ferromagnetic signal from VSe2 monolayers
+ Strong magnetism (15 μB per V)
+ The effect persists at room temperature
+ VSe2 is non-magnetic in the bulk
Nat. Nanotech. 13 289 (2018)
TM dichalcogenides – Ferromagnetism in VSe2
Experimental tools – spin-polarized muons
Sample: Se[50nm]/VSe2[ML]/MoS2[substrate]
Conventional-NMR signal: proportional to nuclear magnetization. Inconvenient
Muon spin rotation with positive muons
Contemp. Phys. 40 175 (1999)
Experimental tools – spin-polarized muons
Paul Scherrer Institute, Switzerland
After muon implantation in the sample:
Quantum sensor of local magnetism.
No need of external magnetic fields.
Journ. Phys. C 20 3187 (1987); Contemp. Phys. 40 175 (1999)
Experimental tools – spin-polarized muons
Journ. Phys. C 20 3187 (1987); Contemp. Phys. 40 175 (1999)
Experimental tools – spin-polarized muons
Space- and time-resolved detection of positrons: Information on local magnetism
Journ. Phys. C 20 3187 (1987); Contemp. Phys. 40 175 (1999)
Experimental tools – spin-polarized muons
Low-energy positive muons
Unique spectrometer – tuning of muons’ kinetic energy possible
Control over implantation depth over tens of nm.
Optimal conditions for probing magnetism in nanostructures.
VSe2
Unpublished experimental results (July 2018) – spin-polarized muons
Sample: Se[50nm]/VSe2[ML]/MoS2[substrate] (black dots)
Temperature dependence: reminiscent of strong magnetic signal
Reference sample: Se[50nm]/MoS2[substrate] (pink squares)
The same behaviour is observed without VSe2
Experimental results (July 2018) – open questions
+ Signal loss due to muonium (μ+e-)
+ Muon spin rotation needs large samples (2 cm): are we dealing with a homogeneous device?
+ Nominally-identical substrates result in different properties:
any insight leading to better control in the growth?
New measurements at Leibniz-IFW in Dresden by means of different experimental tools
Work in progress!
Nat. Nanotech. 13 289 (2018)
Giacomo Prando
Research threads
1. Magnetism in flatland
2. Iridium oxides – thin films
3. Many-body localization and Floquet time-crystals (“Incontri del martedì”, 27.11.2018)
4. Orbital-selectivity in iron-based pnictides
13.09.2018 – Pavia, “Congresso interno di Dipartimento”
3d electrons – cuprates
Hubbard model
Crossover from antiferromagnetic insulator to Fermi liquid
Phys. Rev. Lett. 101 076402 (2008); Nature 464 183 (2010)
5d electrons – iridates
“Spin-orbital Mottness”
Phys. Rev. Lett. 101 076402 (2008) Phys. Rev. Lett. 108 177003 (2012)
Spin and orbital degrees of freedom are entangled
Sizeable coupling between
lattice and magnetism
5d electrons – iridates
Phys. Rev. Lett. 102 017205 (2009); Journ. Phys. Cond. Matt. 25 422202 (2013); Ann. Rev. CMP 7 195 (2016)
Structural strain-induced modifications in PLD-grown heterostructures (PoliMi) Both static and dynamic (piezo) strain
RIXS: spectrum of magnetic excitations (PoliMi)
PRIN – iridate thin films
Phys. Rev. B 92 024405 (2015); Phys. Rev. B 95 115111 (2017)
Basic magnetic properties: low-energy muons (UniPv)
PRIN – iridate thin films
Phys. Rev. B 92 024419 (2015)
Magnetic anisotropy: (anti)ferromagnetic resonance (UniPv)
PRIN – iridate thin films
Phys. Rev. B 94 024412 (2016)