Highlights on Some Experimental Progress of FeSe

Xingjiang ZHOU

2014/10/08

S. Medvedev et al., Nat. Mater. 8 (2009) 630.

N. Katayama et al.,J. Phys. Soc. Jpn. 79 (2010)113702.

F.-C. Hsu et al., PNAS 105 (2008) 14262;

Bulk FeSe Superconductor

Simple crystal structure; In FeSe, Tc can be enhanced from 8.5K to 36.7K at high

pressure;

In Fe(SexTe1-x), Tc can reach 14.5K.

FeSe Films Grown on Graphene

Single-layer FeSe/Graphene is non superconducting above 2.2K; Tc increases with the number of layers in FeSe/Graphene films, reaching 8K for 8 layers with a superconducting gap of 2.1 meV; V-shaped STS curve in the superconducting state indicating a node in the gap function.

C. L. Song et al., Phys. Rev. B 84 (2011) 020503(R).

C. L. Song et al., Science 332 (2011) 1410.

8-Layer 2-Layer ~30-Layer

FeSe Films Grown on SrTiO3 (001)

Single-layer FeSe/SrTiO3 film shows a STS peak at ~20 meV, corresponding to an estimated Tc~80 K if it is superconducting;

Double-layer FeSe/SrTiO3 film is semiconducting.

20.1meV

9.5meV

Single-layer,Tc ~ 80 K? Double-layer, semiconducting

Q. Y. Wang et al., Chinese Phys. Lett. 29 (2012) 037402.

Distinct Electronic Structure of Superconducting FeSe/SrTiO3 Films

Cut 1 Cut 2

D. F. Liu et al., Nature Communications 3 (2012) 931.

Distinct electronic structure: no Fermi surface near G, only electron-like Fermi surface near M.

Phase Diagram and Indication of Tc~65Kin Single-Layer FeSe/SrTiO3 Film

2 /D kTc=6~7

S. L. He et al., Nature Materials 12, 605

(2013).

Tc~65 K

There are two phases present in single-layer FeSe/SrTiO3 film with different electronic structure (N phase and S phase); By annealing in vacuum, N phase can transform into S phase;

Indication of Tc~65 K observed.

S. Y. Tan et al., Nature Materials 12, 634 (2013).

Layer-Dependent Electronic Structure in FeSe/SrTiO3 Films

For two-layer or multiple layer FeSe/SrTiO3 films, it is reported that SDW state is formed; The SDW temperature decreases with increasing number of FeSe layers.

Substrate Strain-Dependent Electronic Structure and Superconductivity of Single-layer FeSe Film

FeSeBR: SL-FeSe/Nb:BaTiO3/KTaO3 heterostructures, relaxed;

a=3.76 A

FeSeBU: SL-FeSe/Nb:BaTiO3/KTaO3 heterostructures, unrelaxed;

a=3.99 A

FeSeSX: SL FeSe/Nb:SrTiO3/KTaO3 heterostructures;

a=3.99 A

FeSeS: FeSe/Nb:SrTiO3 ;

a=3.906 AR. Peng et al., Nature Communications 5 (2014) 5044.

The lattice constant changes from 3.76 A to 3.99 A, Tc shows little change near (70+_5)K;The superconductivity is not sensitive to strain of the substrate.

J. J. Lee et al., arXiv: 1312.2633.

Replica Bands and Electron-Phonon Coupling in Single-layer FeSe/SrTiO3 Film

Replica bands are observed with a separation of ~100 meV; It is proposed this is due to electron coupling with STO phonon.

Transport and Magnetic Measurements on Single-Layer FeSe/SrTiO3 Films

W. H. Zhanget al., Chinese Physics Letters 31 (2014) 017401.

Resistivity Magnetism

Both transport and magnetic measurements indicate single-layerFeSe/SrTiO3 is superconducting although the Tc is not as high asthat from ARPES.

arXiv: 1406.3435.

Schematic of 4 point probe (4PP ） transport measurement setup.

J. F. Ge et al., arXiv: 1406.3435.

11T3K

Temperature and external magnetic field dependence of electrical transport property of a single-layer film of FeSe

J. F. Ge et al., arXiv: 1406.3435.

4PP transport measurement on Bi2212 crystal (Tc~90K) with measurement configurations of C1423 (a) and C1234 (b), respectively.

J. F. Ge et al., arXiv: 1406.3435.

Temperature dependence of electrical transport property of another FeSe/STO sample measured with the 100-μm-tip-separation 4PP fixed at one measuring location while temperature was increasing.

J. F. Ge et al., arXiv: 1406.3435.