Institute of High Pressure Physics

The research project Terahertz Sensor Based on Topological Materials in TEAM programme of the Foundation for Polish Science.

Amount awarded TEAM/2016-3/25: 3 498 988 PLN

• Project goal

The main objective of the project is creation in Poland at Institute of High Pressure Physics PAS (IHPP PAS) a TEAM of scientists that will explore high frequency (Terahertz) properties/physics and applications of topological insulators for terahertz sensors.

• Innovation of the project

To reach such devices the project propose the research on innovative HgCdTe and GaSb/InAs structures overcoming existing up today problems: i) having TI states preserved up to elevated temperatures (up to 300 K) ii) allowing fast electrical switching (on/off) of TI states iii) explore GaSb/InAs quantum TI structures that can be fabricated using a standard semiconductor processing.

• What is within it to be achieved / created - what applications can have the results of the project and in what areas of our daily lives these results may find use
  (eg research will help to generate new medicines, streamline industrial processes, etc.)

Despite the long time from its discovery, there exists still many important problems hindering real world applications of topological isolators. The main problems are: i) TI states are preserved only at cryogenic temperatures (below 10 K); ii) there are no structures/mechanisms allowing fast electrical switching (on/off) of TI states iii) until now most of the discoveries are made using HgTe/CdTe semiconductor materials that do not allow standard high temperature device processing. The general scientific objective of this project is to research on novel two-dimensional structures possessing topological insulator phase that overcomes these existing problems. These novel topological insulators will be obtained special arrangements of III-V or II-VI semiconductor quantum wells. We will search for the best TI semiconductor structures by growing different structures and by tuning the energy band structure with hydrostatic pressure. We will particularly focus on the investigation of hydrostatic pressure driven evolution of basic properties because it allows accelerate research on finding the best parameters (energy band structure, energy and momentum relaxation times, and photon absorption and emission coefficients) in different topological phases without use of very time and budget consuming repetitive growth of the multiple structures. We will use “optical” excitations in Terahertz frequencies range as the main experimental tool. The measurements of inter- and intra-Landau level transitions, lying in THz range, as well as THz photoconductivity will be used to probe the band structure evolution. Independently, research on new THz plasma oscillation/instabilities in different topological insulators phases will be explored as an independent important scientific objective of the project. Thanks to these research we want to answer the basic science questions about the universality of the physical model of 2D TI and about mechanisms of breaking of the topological protection. We want also to answer the question how specific TI states and Dirac fermions (linear dispersion) in TI may modify/influence the THz plasma wave oscillations and instabilities discovered recently in nanometer size 2D structures. Acquired answers for questions mentioned above will provide basis for realizing new high frequency devices based on topological materials. To reach such devices the project propose the research on innovative HgCdTe and GaSb/InAs structures overcoming existing up today problems: i) having TI states preserved up to elevated temperatures (up to 300 K) ii) allowing fast electrical switching (on/off) of TI states iii) explore GaSb/InAs quantum TI structures that can be fabricated using a standard semiconductor processing. Preliminary research that show importance, feasibility and methodology has already started in the frame of international French/Polish/Russian “LIA-TERAMIR” [47]. Feasibility of main project objectives is already documented by multiple high impact international journals publications of the project author [A1, A24]. LIA-TERAMIR will also serve for the present project as the main frame of international collaboration providing, via partners from France and Russia, a privileged access to unique material/samples technology and equipment. At the same time the project will allow to increase the research potential in Poland, at IHPP PAS, by building by world-class leaders, the TEAM having strong international collaborations and performing basic/applied physics research on TI structures (TERA-TEAM) in view of demonstration of innovative TI based high frequency devices as well as terahertz radiation sensors.

Below you can find an example of theoretical modelling of HgTe/CdHgTe quantum wells and pressure phase diagram for such structures.

Figure 1. Typical band structure of (001)-oriented HgTe QWs at zero temperature and different QW width: (a) BI phase, d< d_c, (b) Dirac cone, d = d_c, (c) TI phase d >d_c, (d) SM phase, d > d_SM. Electron-like E₁ subband is shown in blue, while red curves correspond to the heavy-hole subbands. Last panel (e) on the right side shows the pressure phase diagram for single HgTe QWs. The shaded region corresponds to the semimetal phase SM. Open grey region conforms to the TI states. Results for two temperatures 0K and 100K are presented.