ias 0911 pal seminars slides a

8/4/2019 IAS 0911 PAL Seminars Slides A

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physics and the phenomenology of

HiTc superconductors.

Patrick Lee

MIT

Based on lectures given at MIT with T. Senthil. Ithank Senthil for the use of some of his material.


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1. Strong correlation physics: interaction betweene ec rons om na es e r ne c energy. o nsu a or

and its doping. HiTc as an example. (Early sections in Lee,, , , ,

Physics, 71,012501(2008))

. .

Thermodynamic measurements: specific heat, spin susceptibility.

, , - .

thermo-power, thermal conductivity.

.

AC conductivity, optical, microwave and IR, time domain spectroscopy.

NMR

ARPES

Tunneling and STM.

. ome eory an a scuss on o pseu o-gap p ys cs.


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Corner sharing octahedrals.

-

3d

eg dz2, dx2-y2 z2

t2g dxy,dyz,dzx

Octahedral

C O l l l d l


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CuO plane: strongly-correlated electron

One hole per site: should be a metal according to band theory.

Mott insulator.

Hopping matrix element tin a tight binding model

Undoped CuOUndoped CuO22plane:plane:

nvo v ng u or a .

Hubbard model:ott nsu ator ue toott nsu ator ue to

ee-- -- ee-- interactioninteraction

Virtual ho in inducesVirtual ho in induces

Add on site repulsion Uto represent screened

AF exchange J=4tAF exchange J=4t22/U/U.

Mott insulator if U>>4t


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.should be a conductor in the absence of strong disorder.

The surprise is that it becomes a superconductor!

Undoped CuOUndoped CuO22plane:plane: CuOCuO22plane with doped holes:plane with doped holes:ott nsu ator ue toott nsu ator ue to

ee-- -- ee-- interactioninteraction

Virtual ho in inducesVirtual ho in induces

LaLa3+3+ SrSr2+2+: La: La22--xxSrSrxxCuOCuO44

AF exchange J=4tAF exchange J=4t22/U/U


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Mott insulator

Charge transfer insulator.

Electron picture Hole picture

Ogata and Fukuyama, Rep. Progress in Physics, 71, 036501 (2008)


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By fitting the spin wave dispersionmeasure y neutron scatter ng. a soneeds a small ring exchange term.)

.

Spin flip breaks 6 bonds,

arges nown amongtransition metal oxide, except

for the Cu-O chain compound

.

where J=220meV.


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Doping a charge transfer insulator: The Zhang-Rice singlet

Due to AF exchangebetween Cu and O, the

sin let s mmetric orbitalgains a large energy, oforder 6 eV. This singlet

effective hopping t givenby:

S mmetric orbital -centered on Cu.


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What is unique about the cuprates?

Pure CuO2 plane Single band Hubbard model, or its strong, - .

opeholes t

t 1) low dimension

= Com etition: i jnn

large J= 135 meVt favors delocalization of electrons

avors or er ng o oca ze sp ns3) quantum spin S =1/2 (NNN hopping t may explain asymmetry

Between electron and hole doping )


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-

1. Well defined quasi-particles exist provided 1/


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ARPES An le Resolved

Photoemission Spectroscopy)

ias 0911 pal seminars slides a

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