High-Tc Superconductor Surface State

104/18/23

Group member: 陈玉琴、郭亚光、贾晓萌、刘俊义、刘晓雪　彭星星、王建力、王鹏捷★、喻佳兵

★:Group Leader & Speaker

Foreword2

Contents

I. General Concept

II. Crystal Structure

III. Pseudogap in High-Tc Superconductor

IV. Vortex in High-Tc Superconductor

V. Local Electronic Modulations Observed by STM

VI. Summary

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Contents

I. General Concept

II. Crystal Structure

III. Pseudogap in High-Tc Superconductor

IV. Vortex in High-Tc Superconductor

V. Local Electronic Modulations Observed by STM

VI. Summary

4

General Concept　 Disappearance of Resistance (H.K.Onnes,Commun.Phys.Lab.12,120(1911)

　 Meissner Effect (Meissner, W, Naturwissenschaften 21 (44): 787–88.(1933)

　 BCS Theory (Physical Review 97 (6): 1724–1725.)

Two electrons with opposite spin and momentum combine a Cooper pair, the coherence length is about 10-4cm which can be unimpeded form current.

　 Energy gap

In order to break a pair, one has to change energies of all other pairs. This means there is an energy gap for single-particle excitation, unlike in the normal metal.

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2B )/1(13.52k cc TTT

General Concept　 Critical Field/Temperature/Current

　 McMillan Limit (PRB. 16,643(1977))

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])(1[ 20

Cc T

THH

KTC 40~])62.01(

)1(04.1exp[2.1

Scanning Tunneling Spectrum

7Rev. Mod. Phys. 79, 353 (2007)

Contents

I. General Concept

II. Crystal Structure

III. Pseudogap in High-Tc Superconductor

IV. Vortex in High-Tc Superconductor

V. Local Electronic Modulations Observed by STM

VI. Summary

8

Contents

I. General Concept

II. Crystal Structure

III. Pseudogap in High-Tc Superconductor

IV. Vortex in High-Tc Superconductor

V. Local Electronic Modulations Observed by STM

VI. Summary

9

Crystal Structure

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Fig.(a) Bi2Sr2CaCu2O8

Fig.(b) YBa2Cu3O6 Fig.(c) Schematics of the dx2−y2 superconducting gap in the unit-cell coordinate system.

Rev. Mod. Phys. 79, 353 (2007)

STM Topography and Spectroscopy of a cleaved Bi2Sr2CaCu2O8 thin film

11Rev. Mod. Phys. 79, 353 (2007)

Contents

I. General Concept

II. Crystal Structure

III. Pseudogap in High-Tc Superconductor

IV. Vortex in High-Tc Superconductor

V. Local Electronic Modulations Observed by STM

VI. Summary

12

Contents

I. General Concept

II. Crystal Structure

III. Pseudogap in High-Tc Superconductor

IV. Vortex in High-Tc Superconductor

V. Local Electronic Modulations Observed by STM

VI. Summary

13

From Conventional SC to High-Tc SC

14Rev. Mod. Phys. 79, 353 (2007)

Pseudogap on different SC Materials

15Rev. Mod. Phys. 79, 353 (2007)

Conflicts from Y123 &Nd123

16Rev. Mod. Phys. 79, 353 (2007)

Two Scenarios of the Mechanism

1. The scenario of preformed pairs.(Fig. (a)) 2. The scenario of a non-superconducting related pseudogap. (Fig. (b))

17Rev. Mod. Phys. 79, 353 (2007)

Recently Research

18Nature Physics 9, 442–446 (2013)

02 June 2013

Contents

I. General Concept

II. Crystal Structure

III. Pseudogap in High-Tc Superconductor

IV. Vortex in High-Tc Superconductor

V. Local Electronic Modulations Observed by STM

VI. Summary

19

Contents

I. General Concept

II. Crystal Structure

III. Pseudogap in High-Tc Superconductor

IV. Vortex in High-Tc Superconductor

V. Local Electronic Modulations Observed by STM

VI. Summary

20

Vortex in High-Tc Superconductor

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Vortex Measurement

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Illustration of the vortex-lattice imaging by STM: (a) Local SIN junction with typical BCS s-wave characteristics when the tip is between vortices. (b) Local NIN junction with a constant conductance for a dirty BCS superconductor when the tip is positioned over a vortex core.

Rev. Mod. Phys. 79, 353 (2007)

Difference between 2 kind of SCConventional Superconductor High-Tc Superconductor

23Left: Phys. Rev. Lett. 62, 214 (1989) Right: Rev. Mod. Phys. 79, 353 (2007)

Difference between 2 kind of SC

Conventional Superconductor High-Tc Superconductor

24Left: Phys. Rev. Lett. 62, 214 (1989) Right: Rev. Mod. Phys. 79, 353 (2007)

Contents

I. General Concept

II. Crystal Structure

III. Pseudogap in High-Tc Superconductor

IV. Vortex in High-Tc Superconductor

V. Local Electronic Modulations Observed by STM

VI. Summary

25

Contents

I. General Concept

II. Crystal Structure

III. Pseudogap in High-Tc Superconductor

IV. Vortex in High-Tc Superconductor

V. Local Electronic Modulations Observed by STM

VI. Summary

26

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Two different types of spatial variations have been seen by STS:

•Large but irregular spatial variations of the gap, with typical lengths scales of the order of 3–10 nm, in samples which are not specially treated for homogeneity;

•Weaker but spatially periodic LDOS modulations with a wavelength of about 1.6–2 nm.

Local Electronic Modulations

The Experiment about Periodic Modulations

1.The first indication of the presence of such periodic spatial modulations was the observation that around the center of a vortex there is a modulation of the LDOS.

2. Subsequently, Howald, Eisaki, Kaneko, Greven,and Kapitulnik 2003 found that charge modulations were also present in the absence of a magnetic field.

They reported that the structure appeared at an energy around 25 meV and that the superperiod did not disperse with energy.

3. Hoffman, McElroy, et al. 2002 reported similar zero-field electronic modulations, but in contrast to Howald, Eisaki, Kaneko, Greven, and Kapitulnik

2003 they found that these modulations disperse with energy,energy. They successfully interpreted their findings in terms of quasiparticle interference due to scattering from impurities and other inhomogeneities.

4.More recently Vershinin, Misra, Ono, et al. 2004 observed electronic modulations in the pseudogap phase above T.

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Quasiparticle Interference Oscillations In the Superconducting State

Rev. Mod. Phys. 79, 353 (2007)

Quasiparticle Interference Oscillations In the Superconducting State

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Representation of the quasiparticle energy along the Fermi surface. qA and qB are two possible vectors connecting quasiparticle states with identical energies, giving rise to interference patterns.

Science 279, 353 (2007)

Recently Research

31Nature 462, 335-338 (2009)

Recently Research

32Nature 462, 335-338 (2009)

Contents

I. General Concept

II. Crystal Structure

III. Pseudogap in High-Tc Superconductor

IV. Vortex in High-Tc Superconductor

V. Local Electronic Modulations Observed by STM

VI. Summary

33

Contents

I. General Concept

II. Crystal Structure

III. Pseudogap in High-Tc Superconductor

IV. Vortex in High-Tc Superconductor

V. Local Electronic Modulations Observed by STM

VI. Summary

34

Summary

I. General Concept

II. Crystal Structure

III. Pseudogap in High-Tc Superconductor

IV. Vortex in High-Tc Superconductor

V. Local Electronic Modulations Observed by STM

VI. Summary

35