Coherent Light-Matter Interactions in Monolayer Transition-Metal Dichalcogenides (eBook)

Edbert Jarvis Sie (Autor)

eBook Download: PDF

2017 | 1st ed. 2018
XVII, 129 Seiten
Springer International Publishing (Verlag)
978-3-319-69554-9 (ISBN)

Infos

This thesis presents optical methods to split the energy levels of electronic valleys in transition-metal dichalcogenides (TMDs) by means of coherent light-matter interactions. The electronic valleys found in monolayer TMDs such as MoS2, WS2, and WSe2 are among the many novel properties exhibited by semiconductors when thinned down to a few atomic layers, and have have been proposed as a new way to carry information in next generation devices (so-called valleytronics). These valleys are, however, normally locked in the same energy level, which limits their potential use for applications. The author describes experiments performed with a pump-probe technique using transient absorption spectroscopy on MoS2 and WS2. It is demonstrated that hybridizing the electronic valleys with light allows one to optically tune their energy levels in a controllable valley-selective manner. In particular, by using off-resonance circularly polarized light at small detuning, one can tune the energy level of one valley through the optical Stark effect. Also presented within are observations, at larger detuning, of a separate contribution from the so-called Bloch--Siegert effect, a delicate phenomenon that has eluded direct observation in solids. The two effects obey opposite selection rules, enabling one to separate the two effects at two different valleys.

Edbert Jarvis Sie was awarded a PhD in physics by Massachusetts Institute of Technology in 2017. He is now a postdoctoral research fellow at Stanford University.

Inhalt

Supervisor´s Foreword 6
Preface 8
Parts of this Thesis Have Been Published in the Following Journal Articles 10
Acknowledgments 11
Contents 14
Chapter 1: Introduction 17
1.1 Monolayer Transition Metal Dichalcogenides (TMDs) 18
1.1.1 Electronic Band Structure 18
1.1.2 Optical Selection Rules 21
1.1.3 Excitons 23
1.2 Time-Resolved Spectroscopy 24
1.2.1 Coherent Light-Matter Interactions 25
1.2.2 Quasi-equilibrium Dynamics 25
References 26
Chapter 2: Time-Resolved Absorption Spectroscopy 28
2.1 Experimental Setup 29
2.1.1 Overview 29
2.1.2 Laser Amplifier 29
2.1.3 Optical Parametric Amplifier 31
2.1.4 White Light Continuum 32
2.2 Data Analysis 35
2.2.1 Kramers-Kronig Analysis 36
2.2.2 Maxwell´s Equations for Monolayer Sample 37
References 40
Chapter 3: Intervalley Biexcitons in Monolayer MoS2 41
3.1 Intervalley Biexcitons 42
3.2 Experimental Methods 43
3.3 Experimental Results and Discussions 44
3.3.1 Intravalley and Intervalley Scattering 45
3.3.2 Signature of Intervalley Biexcitons 46
3.4 Time-Resolved Cooling Process 47
3.5 Conclusions 49
References 49
Chapter 4: Valley-Selective Optical Stark Effect in Monolayer WS2 51
4.1 Optical Stark Effect 52
4.1.1 Semiclassical Description 54
4.1.2 Quantum-Mechanical Description 56
4.2 Experimental Methods 57
4.3 Observation of the Optical Stark Effect 58
4.4 Valley Selectivity 59
4.5 Fluence and Detuning Dependences 60
4.6 Proposal: Valley-Specific Floquet Topological Phase in TMDs 62
4.7 Supplementary 63
4.7.1 Time-Resolved Spectra 63
4.7.2 Polarization-Resolved Spectra 65
4.7.3 Obtaining Energy Shift 65
4.7.4 Comparison from Semiclassical Theory 69
References 69
Chapter 5: Intervalley Biexcitonic Optical Stark Effect in Monolayer WS2 72
5.1 Blue-Detuned Optical Stark Effect 73
5.2 Experimental Methods 74
5.3 Experimental Results and Data Analysis 74
5.4 Intervalley Biexcitonic Optical Stark Effect 77
5.4.1 Four-Level Jaynes-Cummings Model 79
5.5 Perspective: Zeeman-Type Optical Stark Effect 81
5.6 Supplementary 81
5.6.1 Coherent and Incoherent Optical Signals 81
5.6.2 Time-Trace Fitting Decomposition Analysis 83
5.6.3 Possible Effects Under Red-Detuned Pumping 85
5.6.4 Fitting Analysis 86
References 87
Chapter 6: Large, Valley-Exclusive Bloch-Siegert Shift in Monolayer WS2 90
6.1 Bloch-Siegert Shift 90
6.1.1 Semiclassical Description 92
6.1.2 Quantum-Mechanical Description 95
6.2 Experimental Methods 97
6.3 Observation of the Bloch-Siegert Shift 98
6.4 Fluence and Detuning Dependences 100
6.5 Valley-Exclusive Optical Stark Shift and Bloch-Siegert Shift 100
6.6 Conclusions 103
References 104
Chapter 7: Lennard-Jones-Like Potential of 2D Excitons in Monolayer WS2 106
7.1 Many-Body Interactions in 2D TMDs 107
7.2 Experimental Methods 108
7.3 Optical Signature of Many-Body Effects 108
7.3.1 Exciton Redshift-Blueshift Crossover 109
7.3.2 At Low Density: Plasma Contribution 111
7.3.3 At High Density: Exciton Contribution 112
7.4 Lennard-Jones-Like Potential as an Effective Model 112
7.5 Chronological Signature of Interactions in Time-Resolved Spectra 114
7.6 Summary 117
7.7 Supplementary 117
7.7.1 Microscopic Many-Body Computation 117
7.7.2 Exciton-Exciton Annihilation Effect 120
7.7.3 Heat Capacity and Estimated Temperature 121
References 125
Chapter 8: XUV-Based Time-Resolved ARPES 128
8.1 Building a High-Resolution XUV Light Source for TR-ARPES 128
8.1.1 Overview 128
8.1.2 XUV Light Source 130
8.1.3 XUV Monochromator 132
8.1.4 XUV Diagnostic Chamber 135
8.2 Measuring TMDs Using 30 eV XUV TR-ARPES 136
8.2.1 WSe2 Semiconductors 137
8.2.2 WTe2 Semimetal 139
References 141

Produkt-Details

• Erscheint lt. Verlag: 11.11.2017
• Reihe/Serie: Springer Theses
• Reihe/Serie: Springer Theses
• Zusatzinfo: XVII, 129 p. 83 illus., 82 illus. in color.
• Verlagsort: Cham
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Atom- / Kern- / Molekularphysik
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Theoretische Physik
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• Themenwelt: Technik ► Maschinenbau
• Schlagworte: angle-resolved absorption spectroscopy • Bloch-Siegert effect • coherent light-matter interactions • electronic valleys • optical Stark effect • time-resolved absorption spectroscopy • valleytronics • XUV spectroscopy
• ISBN-10: 3-319-69554-1 / 3319695541
• ISBN-13: 978-3-319-69554-9 / 9783319695549