Bogoliubov quasiparticle in high-Tcsuperconductors observed by

angle-resolved photoemission spectroscopy

Takashi TakahashiDept. Physics, Tohoku University

Bogoliubov quasiparticle in high-Tcsuperconductors observed by

angle-resolved photoemission spectroscopy

Takashi TakahashiDept. Physics, Tohoku University

Superconductivity

Discovery

Tc =4 KKamerlingh Onnes (1911)

Hg

Electric current

Meissner effect

Eternal current Superconducting wire

Ultra-fast computer

Linear motor car

Progress of superconductivity

Discovery

Tc =4 K

Hg

Kamerlingh Onnes (1911)

Our living world

Tc = 23K

Tc = 4K

High-Tc superconductor

Bednorz & Muller (1986)● ●Nobel Prize (1987)

Revolution !

Tc > 150 K

Fulleren & MgB2

Bednorz & Muller (1986)● ●Nobel Prize (1987)

Revolution !

Tc > 150 K

C60 MgB2

Fulleren & MgB2

Bednorz & Muller (1986)● ●Nobel Prize (1987)

Tc > 150 K

C60 MgB2BCS theory

B C S theory

Nobel Prize (1972)

Cooper pair

Bogoliubov quasiparticles (BQPs)

Bogoliubov transformation

J. Phys. USSR 11 (1947) 23Nuovo Cimento 7 (1958) 794

How to observe BQPs ?How to observe BQPs ?

How to observe BQPs ?

Each QP has a characteristic energy In sold : Energy dispersion

(Energy as a function of momentum)

Band dispersion of BQPs

Formation of Bogoliubov quasiparticle band

How to measure the band dispersion of BQPs ?

ARPESAngle-resolved photoemission spectroscopy

Angle-Resolved Photoemission Spectroscopy (ARPES)

External Photoelectric EffectEinstein (1905) Band Mapping

ARPES apparatus at Tohoku University

Energy resolution = 1.3 meV !

Momentum resolution = 0.01 A-1 !

Ultrahigh-resolution PES spectra of Au

What to measure to observe BQPs?

Bednorz & Muller (1986)● ●Nobel Prize (1987)

Revolution !

Tc > 150 K

Bi2Sr2Ca2Cu3O10 (Bi2223)

CuO

Tc=110 K

CuO2 plane

Super current

High-resolution ARPES spectra of Bi2223PRL 90 (2003) 217001

kF

Electron branch of BQP band

Fermi surface

kF

A

B

ARPES spectra of Bi2223 divided by FD function

Hole branch of BQP band

Evidence for BQP band in Bi2223FD-divided ARPES intensity plot near EF

BQP picture is qualitatively established. How abut the coherence factors ?

Full branch of BQP band

Coherence factors |uk|2 and |vk|2

Comparison of BQP dispersion and coherence factors between “experiment” and “theory”

BCS theory is quantitatively verified.

Excellent quantitative agreement !

Bogoliubov quasiparticles do exist !

ARPES confirms it 50 yrs after the proposal !

BCS theory is a universal concept in describing superconductivity for low and high-Tc

superconductors

BCS theory + Bogoliubov quasiparticle

BCS theory + Bogoliubov quasiparticle

GREAT !!

Superconductivity

Discovery

Tc =4 K

Hg

Kamerlingh Onnes (1911)

Electric current

Superconductivity

Discovery

Tc =4 K

Hg

Kamerlingh Onnes (1911)

Electric current

Application

Superconductivity

Discovery

Tc =4 K

Hg

Kamerlingh Onnes (1911)

Electric current

Application

Variety of new hgh-Tc superconductor

Discovery

Tc =4 KKamerlingh Onnes (1911)

Bednorz & Muller (1986)

Cuprate superconductors

Hg● ●

Nobel Prize (1987)

Revolution !

Tc > 150 K

C60MgB2

SuperconductivityDiscovery

Tc = 4 K Tc > 120 K

High-Tc superconductors

Hg

Electric current

Kamerlingh Onnes (1911) Bednorz & Muller (1986)● ●

ApplicationNobel Prize (1987)

Application of high-Tc superconductors

Bednorz & Muller (1986)● ●

Nobel Prize (1987)

BCS theory + Bogoliubov quasiparticle

Comparison of coherent peak between Bi2212 and V3Si

Bogoliubov quasiparticle in high-Tc superconductors observed by angle-resolved photoemission spectroscopyBogoliubov quasiparticle in high-Tc superconductors observed by angle-resolved photoemission spectroscopySuperconductivityProgress of superconductivityHigh-Tc superconductorFulleren & MgB2Fulleren & MgB2B C S theoryBogoliubov quasiparticles (BQPs)How to observe BQPs ?How to observe BQPs ?Formation of Bogoliubov quasiparticle bandHow to measure the band dispersion of BQPs ?Angle-Resolved Photoemission Spectroscopy (ARPES)ARPES apparatus at Tohoku UniversityWhat to measure to observe BQPs?Bi2Sr2Ca2Cu3O10 (Bi2223)High-resolution ARPES spectra of Bi2223ARPES spectra of Bi2223 divided by FD functionEvidence for BQP band in Bi2223Coherence factors |uk|2 and |vk|2Comparison of BQP dispersion and coherence factors between “experiment” and “theory”Bogoliubov quasiparticles do exist !GreatGreatSuperconductivitySuperconductivitySuperconductivityVariety of new hgh-Tc superconductorSuperconductivityApplication of high-Tc superconductorsBCS theory + Bogoliubov quasiparticleComparison of coherent peak between Bi2212 and V3Si