Davor Pavuna, EPF de Lausanne - W2agz.com

Student Guide to RT-Superconductivity :Physics & Nano-EngineeringDavor PavunaInstitute of Physics of Complex Matter

SC History, Teaching & Our StrugglesHigher-Tc MATERIALS:Direct ARPES on Thin High-Tc Films:Heteroepitaxy &The Role of StrainOUR CONVICTIONS:Beyond High-Tc

To All of You :My Profound Gratitude

Pierre-Gilles de GennesNevil Mott

Introductory Superconductivity Textbook (1992):

SuperconductivityTheoretical predictions ofresistivity of metals at low TKamerlingh Onnes, 1911

Critical temperature of superconductorsT c < 30 Kconventional superconductors

Sir Nevil Mott

Hg-2223 cuprate2000

Alex Müller & Georg Bednorz, 1986:

Paul Chu & M.K. Wu, YBCO‘123’, 1987

"Improved Low Contact Resitance to Superconducting YBaCuO Ceramics"Nature 328, p.603, (1987)"Electronic Properties And Critical Current Densities Of (YBCO) 1-x Ag xSolid State Comm. 68, no.6, p. 535, (1988)Compounds",

Direct ARPES on Thin High-Tc Films:Heteroepitaxy &The Role of Strain

Helmuth Berger (EPDL):Single Crystals Growth>30’000 samples since 1970 !

Photoelectron intensitydopingARPES on cleaved cupratesEDC on cleaved Bi-2212X-rays, UVhe -LensesAnalyzerMCPT c (K)576290627556SampleA k,DOSI(k, ) ~ f() A(k, )0.2 0Binding energy (eV)

Batlogg & Varma, Physics World 2000

Lev Gor’kov, 1987 : phase separationJim Phillips/ Jacques Friedel:(1987) : Pseudogap… Erice, Santa Fe, SPIE meetings …Stripes (1996)

EPFL 1989: ARPES onCleaved BSCCO-2212 Crystals&Deliberately Induced Disorderby2.5 MeV electron bombardment

PRL 1999

T cor T* [K]Tallon’s generic diagram…short-range AF fluctuating magnetic order500400300T NT*200100T c00.0 0.1 0.2 0.3hole concentration, pstatic "spin" glasslong-range AF static magnetic order"normal" metal

T c[K]Tallon: QP lifetime...1.51.0NS150100-1200 -600 0E [meV](0,)(,)I p/I b0.5T c500.00(,0)10SCI p/I b5T c00.0 0.1 0.2 0.3hole concentration, p-1200 -600 0E [meV]

Ivan Bozovic and Davor PavunaCorrelated Electron Materials:Physics & Nano-EngineeringI – VI(SPIE,1994 – 2005)

Laser ablation -> Film -->ARPESX-rays, UVLensesAnalyzerhe -MCPSampleA k,DOSI(k, ) ~ f() A(k, )

Why ARPES on FILMS ?Physics Heteroepitaxy :Control E(k) … and the (LATTICE) STRAIN !Control ‘building blocks’ + functionality

Swiss outpost in Wisconsin: laser ablation facilityfor high-temperature superconductors growth

Film OptimizationModify one of theparametersFilm growthon differentsubstratesVariousStructural studies:XRD, (EXAFS) ...Comparisonwith resultsonsingle crystals:upgradesResistivityand susceptibilityUnderstandingofsuperconductivityCan ground state be altered byinduced strainor by doping?NOPhotoemission with CMA:Is Fermi edge robust?YESARPESstudies

Resistivity, a.u.NBCO-123 Epitaxial Films on STONBCO R(T)very smooth, almostoutgrowth free surfaces,crystal coherence ≈0.8 mM. Abrecht et.al.,Journal of AppliedPhysics 91 (3), 1187 (2002)130.502 89 91 931080 130 180 230 280Temperature, K

2001: As grown epitaxial films ofhigh-Tc superconductors exhibita clear Fermi edge(No cleaving)Fermi edge

La 2-x Sr x CuO 4 Under StrainRelaxedIn-plane compressive strain(SrLaAlO 4 )In-plane tensile strain(SrLaGaO 4 , SrTiO 3 )

Compressive

ResistivityResistivityTensile Strain : Resistivity233LO199LO1.2 10 5 0 50 100 150 200 250 3001401 10 58 10 41201006 10 44 10 42 10 480604020100755025000 10 20 3000 50 100 150 200 250 300T [K]T [K]Huge tensile strainc-axis: 13.10 ÅTensile strain (partially relaxed)c-axis: 13.18 Å(Bulk c-axis: 13.23 Å)

Reconstructed Fermi SurfaceFilm under tensile strainRelaxed filmk z a / k z a / k y a / k x a / k y a / k x a / Cloetta et al. PRB 74, 014519(2006)

Direct ARPES on Strained HTSC FilmsAn illustration of reconstructed FS for overdoped (x= 0.2) LSCO-214films undercompressive strain and tensile strain .Tc is enhancedTc is diminished

ab(m cm) ab(m cm)disorderdopingCompressive strain in LSCO actsOPPOSITE to the deliberatelyinduced disorder :0.4T c (K)62728290 Compressive Strain01T c (K)5675849062a)00b)100 200Temperature (K)300

Schematic Electronic Phase Diagram

LSCO-214 is like a Napoleon Cake

Reminder:I. Bozovic:Soft La-O coordinateS. Uchida:Role of Apical OxygenDisorder

Resistivity (10 -6 ∙cm )LSCO Films: Transport properties60010080Resistivity of anLSCO film on LSAOsubstrate.It shows T c= 51.5 K,the record for LSCOin any form.400200604020050 51 52 53 54 5500 50 100 150 200 250 300Temperature (K)Bozovic et al. Phys. Rev. Lett. 89, 107001 (2002)

Laser ablation (EPFL)Scienta (EPFL)

H. Raffy et al.Bi-2001 films:T* is enormous !Can we enhanceT cto ≈50Kbyoptimized growth ?

ARPES on LSCO-214 films and on cleaved crystals – agree !Compressive strain: FS changes from hole-like to electron-likeT c is enhanced by compressive strain for all dopingsit correlates with apical oxygen & c-axis.Tensile strain: Dispersion along the c-axis becomes important.Superconductivity diminishes under huge tensile strain.The ‘’Napoleon-Cake’’ lattice importantWork on Bi-2201 and LBCO in progress

Beyond High-Tc Superconductivity

Hg-2223 cuprate2000

300 KOur Challenge2050

Some RTSC Candidates:Hydrogen under 400GPaALL MBE (or PLD) Heterostructures:Li-doped Berillium HydrideInterface Superconductivity (AgO-STO)…

500 KColossal Superconductivity2100

George Bernard Shaw:… all progress is due to theman who is non-reasonable !

… there are many unknownresearchers worldwideall the time trying to makea RT-superconductor !?!