Scanning tunneling measurements of single layers of superconducting 2H-TaSe 2 crystals

Transcription

1 Scanning tunneling measurements of single layers of superconducting 2H-TaSe 2 crystals Jose Augusto Galvis XV JORNADA DE JÓVENES CIENTÍFICOS DEL INSTITUTO DE CIENCIA DE MATERIALES NICOLÁS CABRERA Low Temperature Laboratory, Department of Condensed Matter Physics Faculty of Science, Universidad Autónoma de Madrid, Spain

2 OUTLINE 1. INTRODUCTON TaSe 2 system 2. EXPERIMENTAL TECHNIQUES 3 He/ 4 He Dilution cryostat and STM description Vector magnetic field solenoid Overview experimental setup 3. RESULTS 2

3 Superconductivity in Low dimensional systems 2D systems INTRODUCTION Layered superconductors High Tc cuprates Weakly coupled CuO 2 layers Electrons moving within copper oxide layers Dichalcogenides family The layers are weakly bonded by van der waals forces Growth of single layers Electrons moving into individuals layers with low charge Transfer Ultrathin films superconductors Study of localization phenomena 3

4 TaSe 2 The crystal structure is strongly 2-dimensional with adjacent layers bonded with weak van der Waals forces 4H RESULTS Hexagonal structure Prism Trigonal structure Antiprism 2H 1T 2H 1T Superconducting transition T C = 150 mk No superconducting transition Poorly studied in the superconducting phase Very low charge Transfer between the two different layers. Low-Dimensional Systems

5 3a 0 X 3a 0 CDW STRONG CDW MODULATION RESULTS 2H structure T CDW =122K Prism High charge density 1T structure 13a 0 X 13a 0 CDW Medium charge density Low charge density Antiprism T CDW =473K 5

6 3 He/ 4 He Dilution cryostat and STM EXPERIMENTAL TECHNIQUES THE STM IS ATTACHED AND THERMALIZED WITH THE MIXING CHAMBER 6

7 3 He/ 4 He Dilution cryostat and STM EXPERIMENTAL TECHNIQUES Sample Maximum displacement: 7

8 3 He/ 4 He Dilution cryostat and STM EXPERIMENTAL TECHNIQUES The sample holder is set on a moving part, which can be moved from the outside of cryostat through piano wire attached to a precision screw. Sample holder Rotating the precision screw the sample holder moves. Skate Piano wire 8

9 EXPERIMENTAL TECHNIQUES 3He/4He Dilution cryostat and STM 9

10 Vector magnetic field solenoid and experimental setup EXPERIMENTAL TECHNIQUES VECTOR MAGNETIC FIELD SOLENOID The STM is located just in the geometrical center of the coils. 0 5 TESLA IN Z DIRECTION 0 1,2 TESLA IN THE X Y PLANE 10

11 Vector magnetic field solenoid and experimental setup EXPERIMENTAL TECHNIQUES 11

12 RESULTS RESULTS IN TaSe 2 12

13 Transport measurements RESULTS 1.0 R (T)/R(300K) T CDW (arb. units) mt Temperature (K) mt Temperature (mk) 13

14 The atomic arrangements 2H Structure 3a 0 X 3a 0 CDW RESULTS 2H Prism 1T Structure Se Ta 13a 0 X 13a 0 CDW 1T Antiprism 14

15 2H TaSe 2 single layers 2.6nm 1T 2.5nm RESULTS Single-layer 2H-TaSe 2 thickness 2H 0nm 2H 0nm 1T 19 nm 67 nm 1.0 nm 1.0 nm 1.0 nm 1.0 nm 2H 1T 2H 1T 5.1 nm nm nm nm 1.0 nm 1.0 nm nm -1 nm nm Inter-layer spacing c = 6.35Å 15

16 Phenomenology in the different structures T = 150 mk RESULTS Topographic characterization Spectroscopic characterization 16

17 Modulation of the zero bias peak RESULTS Topographic image Tunneling conductance curves taken on top of neighboring Se atoms CDW structure Spectroscopic image ZBP modulation structure The zero bias peak is modulated by a charge density wave, and coexists with a V shaped gap feature. 17

18 Critical temperature RESULTS Temperature dependence of the zero bias peak in 2H single-layer Temperature dependence of the superconducting gap in 2H multi-layer Normalized tunneling conductance K 950 mk 900 mk 850 mk 800 mk 700 mk 600 mk 500 mk 400 mk 300 mk 180 mk 70 mk Bias voltage (mv) The zero bias peak in the single layer and the superconducting gap in the multi layer disappears at the same temperature. 18

19 In plane magnetic field dependence B=0T nm Normalized tunneling conductance B=0.1T B=0.3T 0.2 nm 0 nm 0.2 nm 0 nm The peak significantly broadens At the edges of the Se atom, the peak splits Zeeman splitting nm Bias voltage (mv) 19

20 Conclusions RESULTS TaSe 2 Single layers. Highly anomalous tunneling conductance features with a Zero bias conductance peak which evidences localized states at the Fermi energy. The zero bias peak is modulated by a charge density wave. Anomalous low dimensional superconductivity in single layers. Establishment of zero energy resonant bound states extended over whole single layer within a charge ordered state. 20

21 Thanks for your attention 21