- CMT seminar
Floquet states and optical conductivity of irradiated topological insulators
Recent technological progresses in mid-infrared lasers have established a new route for engineering of the electronic band structure. An interplay between the periodicity of lattice and time originated from the oscillating field extends the Hilbert space by inducing the so-called Floquet-Bloch states and enables one to modify the band structure (opening the gaps) and to engineer phase transitions at will by using photon-assisted processes. Fortunately, such light-induced states have been experimentally observed on the surface of irradiated topological insulators (TI), optical lattices, graphene etc. Many striking light-induced phenomena are also predicted or observed in this field: quantum Hall conductivity and also quantum anomalous Hall insulator on TIs, etc. However, experimental challenge is still heat production during irradiation of the system by the laser beam.
In this talk, I will present a short review on the Floquet theory including on- and off- resonant regimes, the gap opening and emergence of topological phases accompanied by anomalous edge states. Then I will focus on the special case of magnetically topological insulator thin film irradiated by circularly-polarized electromagnetic field in the off-resonant regime. Fascinating feature of distinct phases emerges in the phase diagram depending on the frequency and intensity of the light as well as the system parameters and also magnetic field. We also present the results of time-averaged optical conductivity of a driven two-dimensional TI at on-resonant regime. Depending on the type of considered occupation model and optical weights of Floquet states, optical conductivity is analysed by means of the time-averaged density of states and modified band structure.
Host: Götz S. Uhrig
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Location & approach
The campus of TU Dortmund University is located close to interstate junction Dortmund West, where the Sauerlandlinie A 45 (Frankfurt-Dortmund) crosses the Ruhrschnellweg B 1 / A 40. The best interstate exit to take from A 45 is “Dortmund-Eichlinghofen” (closer to South Campus), and from B 1 / A 40 “Dortmund-Dorstfeld” (closer to North Campus). Signs for the university are located at both exits. Also, there is a new exit before you pass over the B 1-bridge leading into Dortmund.
To get from North Campus to South Campus by car, there is the connection via Vogelpothsweg/Baroper Straße. We recommend you leave your car on one of the parking lots at North Campus and use the H-Bahn (suspended monorail system), which conveniently connects the two campuses.
TU Dortmund University has its own train station (“Dortmund Universität”). From there, suburban trains (S-Bahn) leave for Dortmund main station (“Dortmund Hauptbahnhof”) and Düsseldorf main station via the “Düsseldorf Airport Train Station” (take S-Bahn number 1, which leaves every 20 or 30 minutes). The university is easily reached from Bochum, Essen, Mülheim an der Ruhr and Duisburg.
You can also take the bus or subway train from Dortmund city to the university: From Dortmund main station, you can take any train bound for the Station “Stadtgarten”, usually lines U41, U45, U 47 and U49. At “Stadtgarten” you switch trains and get on line U42 towards “Hombruch”. Look out for the Station “An der Palmweide”. From the bus stop just across the road, busses bound for TU Dortmund University leave every ten minutes (445, 447 and 462). Another option is to take the subway routes U41, U45, U47 and U49 from Dortmund main station to the stop “Dortmund Kampstraße”. From there, take U43 or U44 to the stop “Dortmund Wittener Straße”. Switch to bus line 447 and get off at “Dortmund Universität S”.
The AirportExpress is a fast and convenient means of transport from Dortmund Airport (DTM) to Dortmund Central Station, taking you there in little more than 20 minutes. From Dortmund Central Station, you can continue to the university campus by interurban railway (S-Bahn). A larger range of international flight connections is offered at Düsseldorf Airport (DUS), which is about 60 kilometres away and can be directly reached by S-Bahn from the university station.
The H-Bahn is one of the hallmarks of TU Dortmund University. There are two stations on North Campus. One (“Dortmund Universität S”) is directly located at the suburban train stop, which connects the university directly with the city of Dortmund and the rest of the Ruhr Area. Also from this station, there are connections to the “Technologiepark” and (via South Campus) Eichlinghofen. The other station is located at the dining hall at North Campus and offers a direct connection to South Campus every five minutes.
The facilities of TU Dortmund University are spread over two campuses, the larger Campus North and the smaller Campus South. Additionally, some areas of the university are located in the adjacent “Technologiepark”.