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.