Highlights on Some Experimental Progress of FeSe
Xingjiang ZHOU
2014/10/08
Bulk FeSe Superconductor
F.-C. Hsu et al., PNAS
105 (2008) 14262;
S. Medvedev et al.,
Nat. Mater. 8 (2009) 630.
N. Katayama et al.,
J. Phys. Soc. Jpn. 79 (2010)113702.
 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
8-Layer
2-Layer
C. L. Song et al.,
Phys. Rev. B 84 (2011) 020503(R).
~30-Layer
C. L. Song et al.,
Science 332 (2011) 1410.
 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.
FeSe Films Grown on SrTiO3 (001)
Single-layer, Tc
~ 80 K?
Double-layer, semiconducting
20.1meV
9.5meV
Q. Y. Wang et al., Chinese Phys. Lett. 29 (2012) 037402.
 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.
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~65K
in Single-Layer FeSe/SrTiO3 Film
Tc~65 K
2D/kTc=6~7
S. L. He et al.,
Nature Materials 12, 605
(2013).
 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.
Layer-Dependent Electronic Structure
in FeSe/SrTiO3 Films
S. Y. Tan et al., Nature Materials 12, 634 (2013).
 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 A
R. 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.
Replica Bands and Electron-Phonon Coupling in
Single-layer FeSe/SrTiO3 Film
J. J. Lee et al., arXiv: 1312.2633.
 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
Resistivity
Magnetism
W. H. Zhanget al., Chinese Physics Letters 31 (2014) 017401.
Both transport and magnetic measurements indicate single-layer
FeSe/SrTiO3 is superconducting although the Tc is not as high as
that from ARPES.
arXiv: 1406.3435.
Schematic of 4 point probe (4PP） transport measurement setup.
J. F. Ge et al., arXiv: 1406.3435.
Temperature and external magnetic field dependence of
electrical transport property of a single-layer film of FeSe
11T
3K
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.