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)